Stabilized ferrous compound composition
This invention relates to a composition comprising a ferrous compound as a main component, and more specifically, to a novel composition having improved stability comprising a ferrous compound and at least one compound selected from (A) an erythorbic acid compound, (B) a hydroxycarboxylic acid compound and (C) an oxocarboxylic acid compound. 
     Ferrous compounds such as ferrous sulfate and ferrous chloride are used as raw materials for the production of deodorants, black iron oxide, mordants, sewage treating agents, medicines, leather-making chemicals, red iron oxide, etc. These iron compounds, whether as an aqueous solution or a crystal powder, are susceptible to oxidation by oxygen present in air or water. This leads to the trouble that within short periods of time, they are changed to ferric compounds and colored, or they are precipitated and consumed. 
     Attempts have been made to overcome this trouble. For example, Japanese Laid-Open Patent Publication No. 156539/1983 discloses the addition of L-ascorbic acid to an aqueous solution of a ferrous compound, and Japanese Laid-Open Patent No. 142856/1985 proposes the powderization of the aqeuous solution obtained by the method of the first-mentioned Japanese patent document by drying. These methods, however, have the defect that the stabilizers used are limited to expensive L-ascorbic acid, and the use of this stabilizer alone produces no sufficient stabilizing effect. 
     It is an object of this invention to remove these defects of the prior art. 
     Extensive investigations of the present inventors have now led to the discovery that ferrous compounds can be stabilized for a long period of time even in air by incorporating at least one compound selected from (A) erythorbic acid compounds, (B) hydroxycarboxylic acid compounds and (C) oxocarboxylic acid compounds in the ferrous compounds. 
     Thus, according to this invention, there is provided an iron compound composition comprising a ferrous compound and as a stabilizer at least one compound selected from the group consisting of (A) erythorbic acid compounds, (B) hydroxycarboxylic acid compounds and (C) oxocarboxylic acid compounds. 
     Specific examples of the ferrous compounds are ferrous sulfate (FeSO 4 ), ferrous chloride (FeCl 2 ) and ferrous nitrate [Fe(NO 3 ) 2  ]. Ferrous sulfate is most preferred in view of its cost and availability. When the ferrous compound is used in the form of an aqueous solution, the concentration of the ferrous compound may be selected as desired within a range of concentrations which enable the ferrous compound to dissolve in water. 
     The erythorbic acid compounds (A) are known as an antioxidant for foods, etc. It has however been found for the first time by the present inventors that the erythorbic acid compounds (A) produce a marked effect as a stabilizer for ferrous compounds which are very susceptible to oxidation The compounds (A) may include both erythorbic acid itself, and its salts such as sodium and potassium salts. 
     The hydroxycarboxylic acid compounds (B) are hydroxycarboxylic acids containing at least one hydroxyl group and at least one carboxyl group in the molecule, or salts of these acids. Specific examples include aliphatic or aromatic compounds preferably having 2 to 8 carbon atoms, such as lactic acid, hydroxyacetic acid, hydroxybutyric acid, malic acid, tartaric acid, glyceric acid, citric acid, alpha-methylmalic acid, beta-hydroxyglutaric acid, desoxalic acid, monoethyl tartrate, monoethyl citrate, gluconic acid, galactaric acid, glucronic acid, ketogluconic acid, salicylic acid, p-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, gallic acid and hydroxyphthalic acid, and salts of these acids such as sodium, potassium and ammonium salts. The aliphatic compounds and their salts are preferred. 
     The oxocarboxylic acid compounds (C) are oxocarboxylic acids containing at least one aldehyde or keto group and at least one carboxyl group in the molecule. Specific examples include compounds preferably having 2 to 8 carbon atoms, such as glyoxylic acid, malonaldehydic acid, succinaldehydic acid, pyruvic acid, 2-ketobutyric acid, 4-acetylbutyric acid, 2-ketoglutaric acid, 4-keto-n-valeric acid, acetoacetic acid, oxomalonic acid, oxaloacetic acid and acetonedicarboxylic acid, and their salts such as sodium, potassium and ammonium salts. 
     These compounds (A), (B) and (C) may be used in combinations. Particularly, the use of the compound (A) in combination with the compound (B) and/or the compound (C) gives a synergistic improving effect as compared with the use of them singly. The mixing proportions of these in such a case may be selected as desired. Usually, 1 to 99 mole% of the compound (A) is used in combination with 99 to 1 mole% of the compound (B) and/or the compound (C). Preferably, 10 to 90 mole% of the compound (A) is used in combination with 90 to 10 mole% of the compounds (B) and/or the compound (C). More preferably, 20 to 80 mole% of the compound (A) is used together with 80 to 20 mole% of the compound (B) and/or the compound (C). 
     The amount of the stabilizer may be selected depending upon the properties required of the final composition. Usually, it is at least 0.5% by weight, preferably 0.5 to 20% by weight, and more preferably 1 to 10% by weight, based on the iron content of the ferrous compound. If the amount is excessively small, the stabilizing effect is insufficient. Excessively large amounts are economically disadvantageous. 
     The iron compound-containing composition may be in the form of an aqueous solution or a powder so long as it comprises the ferrous compound and the particular stabilizer described. The composition as an aqueous solution can be obtained by mixing an aqueous solution containing the ferrous compound with a water-soluble stabilizer selected from the above-specified stabilizer compounds. The powdery composition may be obtained by drying the aforesaid aqueous solution in a customary manner. For example, the aqueous solution is spray-dried, or under reduced pressure, at a temperature of not more than 150° C., preferably not more than 100° C. Alternatively, it may be obtained by mechanically mixing the ferrous compound in the form of a crystal powder with a powdery stabilizer of the specified group or a solution or dispersion of the stabilizer in water or a solvent. Desirably, the mixing temperature in this method is adjusted to not more than 150° C., preferably not more than 100° C. If the mixing temperature is excessively high, the stabilizer may undergo decomposition, or water of crystallization may be liberated from the ferrous compound. Such troubles will reduce the productivity. 
     The present invention can increase the stability of ferrous compounds as compared with known techniques using ascorbic acid. Powders or aqueous solutions of ferrous compounds so stabilized, either as such or impregnated in various carriers, can be widely used as raw materials for deodorants, water treating agents, mordants, medicines, pigments, mold proofing agents, bactericides, oxygen absorbing agents, etc. 
    
    
     The following examples illustrate the present invention more specifically. 
     EXAMPLE 1 
     In each run, a predetermined amount of erythorbic acid was dissolved in an aqueous solution of ferrous sulfate having an iron concentration of 50 g/liter. One hundred milliliters of the aqueous solution was put in a 100 ml. beaker, and a glass plate was placed on the beaker. The beaker was left to stand, and the color of the aqueous solution and the time of formation of a precipitate were observed. The results are shown in Table 1. 
     It is seen from the results given in Table 1 that when no stabilizer was used (Run No. 1-1), a precipitate formed within a short period of time, and the stability of the iron compound was inferior, whereas when erythorbic acid was added, the iron compound remained stable over a long period of time. 
     
                                           TABLE 1                                 
__________________________________________________________________________
Erythorbic acid                                                           
         Propor-                                                          
         tion                                                             
    Concen-                                                               
         based                                                            
Run tration                                                               
         on Fe                                                            
              Changes with time (*)                                       
No. (g/l)                                                                 
         (%)  1st day                                                     
                    2nd day                                               
                         3rd day                                          
                               4th day                                    
                                   5th day                                
                                       6th day                            
                                            7th day                       
                                                8th day                   
                                                     9th                  
                                                         10th             
__________________________________________________________________________
                                                         day              
Control                                                                   
1-1 0    0    Yellow-                                                     
                    Precipi-                                              
              ish green                                                   
                    tated                                                 
              Turbid                                                      
Invention                                                                 
1-2 1    2    Pale  →                                              
                         →                                         
                               →                                   
                                   Green                                  
                                       →                           
                                            →                      
                                                →                  
                                                     →             
                                                         →         
              blue                                                        
              Trans-                                                      
                    →                                              
                         →                                         
                               →                                   
                                   →                               
                                       →                           
                                            →                      
                                                →                  
                                                     →             
                                                         →         
              parent                                                      
1-3 1.5  3    Pale  →                                              
                         →                                         
                               →                                   
                                   →                               
                                       →                           
                                            →                      
                                                →                  
                                                     →             
                                                         →         
              blue                                                        
              Trans-                                                      
                    →                                              
                         →                                         
                               →                                   
                                   →                               
                                       →                           
                                            →                      
                                                →                  
                                                     →             
                                                         →         
              parent                                                      
1-4 3    6    Pale  →                                              
                         →                                         
                               →                                   
                                   →                               
                                       →                           
                                            →                      
                                                →                  
                                                     →             
                                                         →         
              blue                                                        
              Trans-                                                      
                    →                                              
                         →                                         
                               →                                   
                                   →                               
                                       →                           
                                            →                      
                                                →                  
                                                     →             
                                                         →         
              parent                                                      
1-5 5    10   Pale  →                                              
                         →                                         
                               →                                   
                                   →                               
                                       →                           
                                            →                      
                                                →                  
                                                     →             
                                                         →         
              blue                                                        
              Trans-                                                      
                    →                                              
                         →                                         
                               →                                   
                                   →                               
                                       →                           
                                            →                      
                                                →                  
                                                     →             
                                                         →         
              parent                                                      
__________________________________________________________________________
Erythorbic acid                                                           
         Propor-                                                          
         tion                                                             
Concen-  based                                                            
              Changes with time (*)                                       
Run tration                                                               
         on Fe                                                            
              11th    13th                                                
                         14th                                             
No. (g/l)                                                                 
         (%)  day                                                         
                 12th day                                                 
                      day                                                 
                         day                                              
                            15th day                                      
                                 16th day                                 
                                      17th day                            
                                           18th day                       
                                                19th day                  
                                                     20th                 
                                                          21st            
__________________________________________________________________________
                                                          day             
Control                                                                   
1-1 0    0                                                                
Invention                                                                 
1-2 1    2    →                                                    
                 →                                                 
                      →                                            
                         →                                         
                            →                                      
                                 →                                 
                                      Yellow-                             
                                           →                       
                                                →                  
                                                     →             
                                                          Precipi-        
                                      ish green           tated           
              →                                                    
                 →                                                 
                      →                                            
                         →                                         
                            →                                      
                                 →                                 
                                      →                            
                                           →                       
                                                →                  
                                                     Turbid               
1-3 1.5  3    →                                                    
                 Green                                                    
                      →                                            
                         →                                         
                            →                                      
                                 →                                 
                                      →                            
                                           Yellow-                        
                                                →                  
                                                     →             
                                                          Blackish        
                                           ish green      yellow          
              →                                                    
                 →                                                 
                      →                                            
                         →                                         
                            →                                      
                                 →                                 
                                      →                            
                                           →                       
                                                →                  
                                                     →             
                                                          →        
1-4 3    6    →                                                    
                 Green                                                    
                      →                                            
                         →                                         
                            →                                      
                                 →                                 
                                      →                            
                                           Yellow-                        
                                                →                  
                                                     →             
                                                          Blackish        
                                           ish green      yellow          
              →                                                    
                 →                                                 
                      →                                            
                         →                                         
                            →                                      
                                 →                                 
                                      →                            
                                           →                       
                                                →                  
                                                     →             
                                                          →        
1-5 5    10   →                                                    
                 Green                                                    
                      →                                            
                         →                                         
                            →                                      
                                 →                                 
                                      →                            
                                           Yellow-                        
                                                →                  
                                                     →             
                                                          Blackish        
                                           ish green      yellow          
              →                                                    
                 →                                                 
                      →                                            
                         →                                         
                            →                                      
                                 →                                 
                                      →                            
                                           →                       
                                                →                  
                                                     →             
                                                          →        
__________________________________________________________________________
 (*) The upper rows indicate the changes in the colors of the aqueous     
 solutions, and the lower rows, the changes in the transparency of the    
 aqueous solution. The indication &#34;precipitated&#34; means that a precipitate 
 formed and further observation was stopped.                              
 
    
     EXAMPLE 2 
     Run No. 1-4 of Example 1 was repeated except that sodium erythorbate was used instead of erythorbic acid. The results obtained were substantially the same as those obtained in Run No. 1-4 of Example 1. 
     EXAMPLE 3 
     In each run, a predetermined amount of each of the hydroxycarboxylic acids indicated in Table 2 was used instead of erythorbic acid. The results are shown in Table 2. 
     The results shown in Table 2 demonstrate that the iron compound was stable over a long period of time also when the hydroxycarboxylic acids were incorporated. 
     
                                           TABLE 2                                 
__________________________________________________________________________
Sample                                                                    
        Concen-                                                           
Run Stabi-                                                                
        tration                                                           
             Changes with time (*)                                        
No. lizer                                                                 
        (g/l)                                                             
             1st day                                                      
                   2nd day                                                
                        3rd day                                           
                             4th day                                      
                                 5th day                                  
                                      6th day                             
                                           7th day                        
                                               8th day                    
                                                   9th day                
__________________________________________________________________________
Control                                                                   
3-1 None                                                                  
        0    Yellow-                                                      
                   Precipi-                                               
             ish green                                                    
                   tated                                                  
             Turbid                                                       
Invention                                                                 
3-2 Tar-                                                                  
        1    Yellow-                                                      
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           Yellow                         
                                               →                   
                                                   →               
    taric    ish green                                                    
    acid     Trans-                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             parent                                                       
3-3     2    Yellow                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             ish green                                                    
             Trans-                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             parent                                                       
3-4     3    Yellow                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             ish green                                                    
             Trans-                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             parent                                                       
3-5 Gluco-                                                                
        1    Yellow                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           Yellow                         
                                               →                   
                                                   →               
    nic      ish green                                                    
    acid     Trans-                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             parent                                                       
3-6     2    Yellow-                                                      
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             ish green                                                    
             Trans-                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             parent                                                       
3-7     3    Yellow-                                                      
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             ish green                                                    
             Trans-                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             parent                                                       
3-8 Citric                                                                
        1    Yellow-                                                      
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
    acid     ish green                                                    
             Trans-                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             parent                                                       
3-9     2    Yellow-                                                      
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             ish green                                                    
             Trans-                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             parent                                                       
 3-10                                                                     
    Maleic                                                                
        1    Green →                                               
                        →                                          
                             →                                     
                                 Yellow-                                  
                                      →                            
                                           Yellow                         
                                               →                   
                                                   Blackish               
    acid           →                                               
                        →                                          
                             →                                     
                                 ish green                                
                                      →                            
                                           →                       
                                               →                   
                                                   yellow                 
             Trans-                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             parent                                                       
 3-11   2    Green →                                               
                        →                                          
                             →                                     
                                 Yellow-                                  
                                      →                            
                                           Yellow                         
                                               →                   
                                                   →               
                   →                                               
                        →                                          
                             →                                     
                                 ish green                                
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             Trans-                                                       
                   →                                               
                        →                                          
                             →                                     
                                 →                                 
                                      →                            
                                           →                       
                                               →                   
                                                   →               
             parent                                                       
__________________________________________________________________________
Sample                                                                    
       Concen                                                             
Run                                                                       
   Stabi-                                                                 
       tration                                                            
            Changes with time (*)                                         
No.                                                                       
   lizer                                                                  
       (g/l)                                                              
            10th day                                                      
                 11th day                                                 
                      12th day                                            
                           13th day                                       
                                14th day                                  
                                     15th day                             
                                          16th day                        
                                               20th day                   
                                                    21st                  
__________________________________________________________________________
                                                    day                   
Control                                                                   
3-1                                                                       
   None                                                                   
       0                                                                  
Invention                                                                 
3-2                                                                       
   Tar-                                                                   
       1    →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     Orange                               
                                          →                        
                                               →                   
                                                    →              
   taric    →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    →              
   acid                                                                   
3-3    2    →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    Yellow                
            →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    →              
3-4    3    →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    Yellow                
            →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    →              
3-5                                                                       
   Gluco-                                                                 
       1    →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     Orange                               
                                          →                        
                                               →                   
                                                    →              
   nic      →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               Turbid                     
                                                    →              
   acid                                                                   
3-6    2    →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                Yellow                                    
                                     →                             
                                          →                        
                                               →                   
                                                    →              
            →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    →              
3-7    3    →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                Yellow                                    
                                     →                             
                                          →                        
                                               →                   
                                                    →              
            →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    →              
3-8                                                                       
   Citric                                                                 
       1    →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                Precipi-                                  
   acid                         tated                                     
            →                                                      
                 →                                                 
                      →                                            
                           Turbid                                         
3-9    2    →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    Blackish              
                                                    yellow                
            →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    →              
 3-10                                                                     
   Maleic                                                                 
       1    →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          Precipi-                        
   acid                                   tated                           
            →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                Turbid                                    
                                     →                             
 3-11  2    Blackish                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    →              
            yellow                                                        
            →                                                      
                 →                                                 
                      →                                            
                           →                                       
                                →                                  
                                     →                             
                                          →                        
                                               →                   
                                                    →              
__________________________________________________________________________
 (*) Same as the footnote to TABLE 1.                                     
 
    
     EXAMPLE 5 
     Example 1 was repeated except that each of the oxocarboxylic acids shown in Table 3 was used instead of erythorbic acid. The results are shown in Table 3. 
     The results shown in Table 3 demonstrate that when the oxocarboxylic acids were incorporated, the iron compound also remained stable over a long period of time. 
     
                                           TABLE 3                                 
__________________________________________________________________________
Sample                                                                    
         Concen-                                                          
Run Stabi-                                                                
         tration                                                          
              Changes with time (*)                                       
No. lizer                                                                 
         (g/l)                                                            
              1st day                                                     
                    2nd day                                               
                         3rd day                                          
                              4th day                                     
                                   5th day                                
                                        6th day                           
                                             7th day                      
                                                 8th day                  
                                                     9th                  
                                                          10th            
__________________________________________________________________________
                                                          day             
Control                                                                   
5-1 None 0    Yellow-                                                     
                    Precipi-                                              
              ish green                                                   
                    tated                                                 
              Turbid                                                      
Invention                                                                 
5-2 2-keto-                                                               
         1    Pale  →                                              
                         →                                         
                              →                                    
                                   Blackish                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
    glu-      brown                brown                                  
    taric     Trans-                                                      
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
    acid      parent                                                      
5-3      2    Pale  →                                              
                         →                                         
                              →                                    
                                   Light                                  
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
              brown                brown                                  
              Trans-                                                      
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
              parent                                                      
5-4      3    Pale  →                                              
                         →                                         
                              →                                    
                                   Light                                  
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
              brown                brown                                  
              Trans-                                                      
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
              parent                                                      
5-5 Pyruvic                                                               
         1    Pale  →                                              
                         →                                         
                              →                                    
                                   Blackish                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
    acid      yellow               yellow                                 
              Trans-                                                      
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          Turbid          
              parent                                                      
5-6      2    Pale  →                                              
                         →                                         
                              →                                    
                                   Blackish                               
                                        →                          
                                             →                     
                                                 →                 
                                                     Brown                
                                                          →        
              brown                yellow                                 
              Trans-                                                      
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
              parent                                                      
5-7      3    Pale  →                                              
                         →                                         
                              →                                    
                                   Blackish                               
                                        →                          
                                             →                     
                                                 →                 
                                                     Brown                
                                                          →        
              brown                yellow                                 
              Trans-                                                      
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
              parent                                                      
5-8 Gly- 1    Yellow-                                                     
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     Yellow               
                                                          →        
    oxylic    ish green                                                   
    acid      Trans-                                                      
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
              parent                                                      
5-9      2    Yellow-                                                     
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     Yellow               
                                                          →        
              ish green                                                   
              Trans-                                                      
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
              parent                                                      
5-10     3    Yellow-                                                     
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     Yellow               
                                                          →        
              ish green                                                   
              Trans-                                                      
                    →                                              
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                             →                     
                                                 →                 
                                                     →             
                                                          →        
              parent                                                      
__________________________________________________________________________
Sample                                                                    
         Concen-                                                          
              Changes with time (*)                                       
Run Stabi-                                                                
         tration                                                          
              11th    13th              17th                              
No. lizer                                                                 
         (g/l)                                                            
              day                                                         
                 12th day                                                 
                      day                                                 
                         14th day                                         
                              15th day                                    
                                   16th day                               
                                        day                               
                                           18th day                       
                                                19th day                  
                                                     20th                 
                                                          21st            
__________________________________________________________________________
                                                          day             
Control                                                                   
5-1 None 0                                                                
Invention                                                                 
5-2 2-keto-                                                               
         1    →                                                    
                 Precipi-                                                 
    glu-      →                                                    
                 tated                                                    
    taric                                                                 
    acid                                                                  
5-3      2    →                                                    
                 →                                                 
                      →                                            
                         Reddish                                          
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                Precipi-                  
                         brown                  tated                     
              →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   Turbid                                 
                                        →                          
                                           →                       
5-4      3    →                                                    
                 →                                                 
                      →                                            
                         Reddish                                          
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                Precipi-                  
                         brown                  tated                     
              →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
5-5 Pyruvic                                                               
         1    →                                                    
                 Precipi-                                                 
    acid      →                                                    
                 tated                                                    
5-6      2    →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                Light                     
                                                     →             
                                                          →        
                                                brown                     
              →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                →                  
                                                     →             
                                                          →        
5-7      3    →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                Light                     
                                                     →             
                                                          →        
                                                brown                     
              →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                →                  
                                                     →             
                                                          →        
5-8 Gly- 1    →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                Precipi-                  
    oxylic                                      tated                     
    acid      →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                           Turbid                         
5-9      2    →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                →                  
                                                     →             
                                                          →        
              →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                →                  
                                                     →             
                                                          →        
 5-10    3    →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                →                  
                                                     →             
                                                          →        
              →                                                    
                 →                                                 
                      →                                            
                         →                                         
                              →                                    
                                   →                               
                                        →                          
                                           →                       
                                                →                  
                                                     →             
                                                          →        
__________________________________________________________________________
 (*) Same as the footnote to TABLE 1.                                     
 
    
     EXAMPLE 6 
     In each run, each of the stabilizers indicated in Table 4 was dissolved in a concentration of 1 g/liter in an aqueous solution of ferrous sulfate having an iron concentration of 50 g/liter. One hundred milliliters of the aqueous solution was put in a 100 ml beaker, and a glass plate was put over it. The beaker was left to stand for 20 days, and the color of the aqueous solution and the formation of a precipitate were observed. 
     
                       TABLE 4                                                     
______________________________________                                    
Amount of the stabilizer added (mole %)                                   
Stabilizer                                                                
        Control          Invention                                        
______________________________________                                    
Erythorbic                                                                
        100      0       0     60    40  60   40                          
acid                                                                      
Gluconic                                                                  
        0        100     0     40    60   0    0                          
acid                                                                      
Glyoxylic                                                                 
        0        0       100    0     0  40   60                          
acid                                                                      
State after                                                               
        Precipitated     Yellowish green and                              
20-day                   transparent                                      
standing                                                                  
______________________________________                                    
 
    
     It is seen from the above results that when erythorbic acid, gluconic acid and glyoxylic acid were used jointly, the stability of the iron compound was much better than when they were used singly. 
     EXAMPLE 7 
     Ferrous sulfate (FeSO 4 .7H 2  O; 275 g) was dissolved in distilled water purged with nitrogen to prepare an aqueous solution (1000 ml). Five grams (9% based on Fe) of each of the stabilizers indicated in Table 5 was dissolved in the aqueous soution to prepare an aqueous solution containing ferrous sulfate and the stabilizer. The aqueous solution was spray-dried by a spray dryer (Model GA-31, made by Yamato Science Co., Ltd.) under the following conditions to form a powdery composition. 
     Amount of the aqueous solution passed: 35 ml/min. 
     Flow rate of drying air: 0.6 m 3  /min. 
     Inlet temperature: 120° C. 
     Ten grams of the powdery composition was taken into a glass Petri dish, and the dish was left to stand in a hot air oven at 80° C. Changes in the outer appearance of the composition with time were observed. Then, the composition was taken out and dissolved in water to prepare an aqueous solution. Changes in the appearance of the aqueous solution with time were also observed. The results are shown in Table 5. 
     For comparison, the same experiment as above was conducted without using any stabilizer or by using L-ascorbic acid as the stabilizer. The results are also shown in Table 5. 
     The results given in Table 5 demonstrate the higher stability of the iron compound stabilized by the stabilizer in accordance with this invention than that stabilized with L-ascorbic acid. 
     
                                           TABLE 5                                 
__________________________________________________________________________
             Changes in appearance                                        
                           Stability of the 40%                           
             with time     aqueous solution (*)                           
             Immediately   Immediately                                    
             after pre-                                                   
                    After  after pre-                                     
                                  After                                   
Run No.                                                                   
     Stabilizer                                                           
             paration                                                     
                    1.5 hours                                             
                           paration                                       
                                  1.5 hours                               
__________________________________________________________________________
Invention                                                                 
7-1  Erythorbic acid                                                      
             Pale brown                                                   
                    Brown  O      O                                       
7-2  Tartaric acid                                                        
             White  Pale yellow-                                          
                           O      O                                       
                    ish white                                             
7-3  Citric acid                                                          
             Pale brown                                                   
                    Pale brown                                            
                           O      O                                       
7-4  Gluconic acid                                                        
             Pale green                                                   
                    Pale yellow-                                          
                           O      O                                       
                    ish green                                             
7-5  Glyoxylic acid                                                       
             Pale bluish                                                  
                    Pale bluish                                           
                           O      O                                       
             white  white                                                 
Control                                                                   
7-6  None    Pale bluish                                                  
                    Brown  X      X                                       
             white                                                        
7-7  L-ascorbic acid                                                      
             Pale brown                                                   
                    Brown  O      X                                       
__________________________________________________________________________
 (*): Evaluated by O which shows that the solution was a uniform          
 transparent solution, and X which shows that a precipitate formed.       
 
    
     EXAMPLE 8 
     In each run, each of the stabilizers indicated in Table 6 was added in an amount of 9% based on Fe to 275 g of crystals of ferrous sulfate, and the mixture was worked up by a mortar to form a white powdery composition. 
     Ten grams of the powdery composition was taken into a glass Petri dish. The Petri dish was left to stand at 20° C. for 10 days in a desiccator kept at a humidity of 79%, and changes in the outside appearance of the powdery composition were observed. After this test, the powdery composition was taken out and dissolved in water to form a 40% aqueous solution. Changes in the appearance of the aqueous solution were also observed. The results are shown in Table 6. 
     For comparison, the above experiment was repeated without using the stabilizer. The results are also shown in Table 6. 
     It is seen from Table 6 that the composition of this invention has better stability. 
     
                                           TABLE 6                                 
__________________________________________________________________________
             Changes in appearance                                        
                             Stability of the 40%                         
             with time       aqueous solution (*)                         
             Immediately     Immediately                                  
             after prep-                                                  
                     After   after prep-                                  
                                    After                                 
Run No.                                                                   
     Stabilizer                                                           
             aration 1.5 hours                                            
                             aration                                      
                                    10 days                               
__________________________________________________________________________
Invention                                                                 
8-1  Erythorbic acid                                                      
             Bluish white                                                 
                     Bluish white                                         
                             O      O                                     
8-2  Tartaric acid                                                        
             Bluish white                                                 
                     Bluish white                                         
                             O      O                                     
8-3  40% aqueous                                                          
             Greenish white                                               
                     Greenish white                                       
                             O      O                                     
     gluconic acid                                                        
     solution                                                             
8-4  40% aqueous                                                          
             Greenish white                                               
                     Greenish white                                       
                             O      O                                     
     glyoxylic acid                                                       
     solution                                                             
Control                                                                   
8-5  None    Bluish white                                                 
                     Bluish white                                         
                             X      X                                     
__________________________________________________________________________
 (*): Same as the footnote to TABLE 5.                                    
 
    
     EXAMPLE 9 
     Ten grams of each of the powdery compositions obtained in Runs Nos. 8-2 to 8-4 of Example 8 was taken into a glass Petri dish. The Petri dish was left to stand in a hot air oven at 80° C., and changes in the appearance of the powdery composition with time were observed. After the test, the powdery composition was taken out and dissolved in water to prepare a 40% aqueous solution. Then, changes in the appearance of the aqueous solution with time were observed. The results are shown in Table 7. 
     For comparison, the same test was repeated except that no stabilizer was used. The results are also shown in Table 7. 
     The results shown in Table 7 demonstrate the superiority of the composition of this invention. 
     
                                           TABLE 7                                 
__________________________________________________________________________
            Changes in appearance                                         
                            Stability of the 40%                          
            with time       aqueous solution (*)                          
            Immediately     Immediately                                   
            after pre-                                                    
                    After   after pre-                                    
                                   After                                  
Run No.                                                                   
     Stabilizer                                                           
            paration                                                      
                    1.5 hours                                             
                            paration                                      
                                   1.5 hours                              
__________________________________________________________________________
Invention                                                                 
9-1  Tartaric acid                                                        
            Bluish white                                                  
                    Greenish white                                        
                            O      O                                      
9-2  40% aqueous                                                          
            Greenish white                                                
                    Greenish white                                        
                            O      O                                      
     gluconic acid                                                        
     solution                                                             
9-3  40% aqueous                                                          
            Greenish white                                                
                    Greenish white                                        
                            O      O                                      
     glyoxylic acid                                                       
     solution                                                             
Control                                                                   
9-4  None   Bluish white                                                  
                    Light brown                                           
                            X      X                                      
__________________________________________________________________________
 (*): Same as the footnote to TABLE 5.