Isocyanuric acid ester stabilizer
This invention relates to an isocyanuric acid derivative represented by the general formula ##STR3## wherein A represents ##STR4## R being an alkyl, cycloalkyl, aryl or aralkyl group having 1 to 8 carbon atoms; a process for preparing same; a stabilizer for organic compounds comprising same as active constituent; and a method for stabilizing an organic substance. The isocyanuric acid derivative represented by the general formula (I) is a novel compound not found in the literature but first synthesized by the present inventors. 
     As is well known, various organic substances including synthetic resins such as polyolefin, ABS resin, polystyrene, high-impact polystyrene, polyamide, polyacetal, and ethylene-propylene copolymer, natural and synthetic rubbers such as butadiene rubber, isoprene rubber, isoprene-isobutylene copolymer rubber, styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, and EPDM, and petroleum products such as lubricating oil and fuel oil are liable to degradation when exposed to the action of heat, light, or oxygen. It is also known that various stabilizers are incorporated in these organic substances to protect them from such degradation. The conventional stabilizers, however, have a defect of insufficient thermal stability and when exposed to elevated temperatures for a long time, the stabilizing effect becomes gradually decreased. 
     The present invention is an outcome of the extensive study directed to the development of a compound highly effective in protecting the above-mentioned organic substances from degradation. 
     The present isocyanuric acid derivative represented by the general formula (I) is prepared by the reaction of triglycidyl isocyanurate with a propionic acid derivative represented by the general formula ##STR5## wherein R is as defined above and exemplified by methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, hexyl, octyl, 2-ethylhexyl, cyclopentyl, cyclohexyl, cycloheptyl, 1-methylcyclohexyl, phenyl, benzyl, and methylbenzyl. The reaction is generally carried out in an organic solvent in the presence of a basic catalyst. 
     The organic solvents suitable for the reaction include aromatic hydrocarbons such as benzene, toluene, and xylenes; aliphatic hydrocarbons such as n-hexane, cyclohexane, and n-heptane; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate and butyl acetate; halohydrocarbons such as chloroform and carbon tetrachloride; and aprotic polar solvents such as dimethylformamide and dimethyl sulfoxide. Alcohols are unsuitable, because they react with the starting material, triglycidyl isocyanurate, forming by-products. 
     Suitable catalysts are tertiary amines such as triethylamine and tributylamine; quaternary ammonium salts such as trimethylbenzylammonium hydroxide and tetramethylammonium hydroxide; imidazoles represented by 2-ethyl-4-methylimidazole; and alkali metal alkoxides such as potassium methoxide and sodium methoxide. The reaction temperature is 30° to 200° C., preferably 50° to 150° C. The molar ratio between the starting materials, that is, triglycidyl isocyanurate and a propionic acid derivative, is from 1:2.5 to 1:3.5. After completion of the reaction, the reaction product is separated in a customary manner and purified by recrystallization, washing with a solvent, or other known means. 
     The isocyanuric acid derivative of the present invention is effective as a stabilizer for various organic substances including synthetic resins such as polyolefin (e.g. polyethylene or polypropylene), ABS resin, polystyrene, high-impact polystyrene, and polyamide; synthetic rubbers such as butadiene rubber, isoprene rubber, styrene-butadiene copolymer rubber and EPDM; and petroleum products such as lubricating oil and fuel oil. 
     Although variable depending upon the type of organic substance being stabilized, the amount of the present isocyanuric acid derivative to be added is generally in the range of from about 0.001 to about 5, preferably from about 0.01 to about 2, parts by weight for 100 parts by weight of the organic substance. The incorporation of the compound in an organic substance is performed in a customary manner. 
     Although effective by itself for the stabilization of organic substances, the present isocyanuric acid derivative can be used, if necessary, in combination with other additives. It exhibits a synergistically enhanced stabilizing effect especially when used in combination with peroxide-decomposing agents of the organosulfur type such as thiodipropionate esters (e.g. dilauryl 3,3&#39;-thiodipropionate, dimyristyl 3,3&#39;-thiodipropionate, and distearyl 3,3&#39;-thiodipropionate) represented by the general formula ##STR6## wherein R 1  represents an alkyl group having 12 to 20 carbon atoms, or pentaerythritol derivatives (e.g. pentaerythritol tetrakis(β-lauryl thiopropionate) and pentaerythritol tetrakis(β-stearyl thiopropionate)) represented by the general formula ##STR7## wherein R 2  represents an alkyl group having 4 to 20 carbon atoms. These peroxide-decomposing agents are used preferably in an amount of 0.1 to 10 times the weight of the isocyanuric acid derivative of this invention. The total amount of the isocyanuric acid derivative and the peroxide-decomposing agent used in stabilizing an organic substance is generally 0.01 to 5 parts by weight for 100 parts by weight of the organic substance. 
     The light stability of the organic substance containing the present isocyanuric acid derivative can be improved by the addition of ultraviolet absorbers or light stabilizers of the hindered amine type such as, for example, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone, 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-3-t-butyl-5-methylphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3,5-di-t-butylphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3,5-diamylphenyl)benzotriazole, [2,2&#39;-thiobis-(4-t-octylphenolate)]butylamine nickel salt, 2,2,6,6-tetramethyl-4-piperidinyl benzoate, bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, 2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-butylmalonate, 1-[2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionyloxy}ethyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-2,2,6,6-tetramethylpiperidine, and dimethyl succinate-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate. The color of the stabilized organic substance can be improved by the addition of phosphite antioxidants such as, for example, distearylpentaerythritol diphosphite, tris(2,4-di-t-butylphenyl)phosphite, tris(2-t-butyl-4-methylphenyl)phosphite, and bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, tetrakis(2,4-di-t-butylphenyl)-4,4&#39;-biphenylene diphosphite. In addition to the above, the following materials may be used depending on practical purposes: plasticizers, metal deactivating agents, metallic soaps, nucleating agents, lubricants, antistatics, flame retardants, pigments, fillers, petroleum additives (e.g. corrosion inhibitors, rust preventives, pour point depressants, defoamers, detergent dispersants, and extreme pressure additives), and metal chelating agents. 
     When used together with said other additives, these additives can be used as a mixture with the isocyanuric acid derivative of this invention. 
    
    
     The invention is further illustrated below with reference to Examples. 
     EXAMPLE 1 
     A mixture of 4.17 g (0.015 mole) of 3,5-di-t-butyl-4-hydroxyphenylpropionic acid, 1.49 g (0.005 mole) of triglycidyl isocyanurate, 0.1 g (0.001 mole) of triethylamine, and 40 g of toluene was heated at 110° to 112° C. for 14 hours to allow the reaction to proceed. The reaction mixture was kept at 80° C. and 50 Torr for 5 hours to recover the solvent and to obtain as the residue 5.6 g (99% yield) of a crude product, pale yellow in color. The crude product was recrystallized from 20 ml of methanol to yield 2.6 g of white powder of 1,3,5-tris{3-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-2-hydroxypropyl}isocyanuric acid having a melting point of 59°-62° C. (Compound I-1). 
     
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                C %     H %    N %                                        
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Elementary analysis:                                                      
Calculated for C.sub.63 H.sub.93 N.sub.3 O.sub.15                         
                  66.2      8.4    3.9                                    
Found             66.8      8.2    3.7                                    
Mass analysis:                                                            
Molecular ion peak:                                                       
                  1131                                                    
Fragment ion peak:                                                        
                   377                                                    
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     EXAMPLE 2 
     A mixture of 3.54 g (0.015 mole) of 3-methyl-4-hydroxy-5-t-butylphenylpropionic acid, 1.49 g (0.005 mole) of triglycidyl isocyanurate, 0.11 g (0.001 mole) of 2-ethyl-4-methylimidazole, and 40 g of xylene was heated at 130° to 135° C. for 10 hours to allow the reaction to proceed. The reaction mixture was washed with 100 ml of 1% dilute hydrochloric acid, then with 100 ml of water. The organic layer was kept at 80° C. and 50 Torr for 3 hours to remove the solvent, leaving behind 4.7 g (93% yield) of a yellow wax-like crude product. The crude product was recrystallized from 15 ml of methanol to yield 2.3 g of a white powder of 1,3,5-tris{3-[3-(3-t-butyl-5-metyl-4-hydroxyphenyl)propionyloxy]-2-hydroxypropyl}isocyanuric acid having a melting point of 31°-34° C. (Compound I-2). 
     
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                C %     H %    N %                                        
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Elementary analysis:                                                      
Calculated for C.sub.54 H.sub.75 N.sub.3 O.sub.15                         
                  64.0      7.8    4.3                                    
Found             64.5      7.5    4.2                                    
Mass analysis:                                                            
Molecular ion peak:                                                       
                  1005                                                    
Fragment ion peak:                                                        
                   335                                                    
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     EXAMPLES 3 TO 7 
     Various isocyanuric acid derivatives (Compounds I-3, I-4, I-5, I-6 and I-7) were prepared by repeating the procedure of Example 1, except that each of the 3-t-butyl-4-hydroxy-5-(R=substituent)phenylpropionic acids, shown in Table 1, was used in place of the 3,5-di-t-butyl-4-hydroxyphenylpropionic acid. The results obtained were as shown in Table 1. 
     
                                           TABLE 1                                 
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                   Product of formula I                                   
Example                                                                   
     Starting material                                                    
                   Compound                                               
                         R in Melting                                     
                                   Yield,                                 
                                       Elementary analysis                
No.  R in formula II                                                      
                   No.   formula I                                        
                              point, °C.                           
                                   %           C %                        
                                                  H %                     
                                                     N %                  
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3    CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.3                
                   I-3   Same as                                          
                              38-41                                       
                                   45  Found:  68.2                       
                                                  8.6                     
                                                     3.3                  
                         in for-       Calculated for                     
                                               68.1                       
                                                  8.7                     
                                                     3.5                  
                         mula II       C.sub.69 H.sub.105 N.sub.3         
                                       O.sub.15 :                         
      ##STR8##     I-4        Wax- like                                   
                                   32  Found: Calculated for C.sub.75     
                                       H.sub.117 N.sub.3 O.sub.15         
                                               69.6 69.3                  
                                                  8.8 9.1                 
                                                     3.0 3.2              
  5                                                                       
      ##STR9##     I-5        65-69                                       
                                   41  Found: Calculated for C.sub.72     
                                       H.sub.105 N.sub.3 O.sub.15         
                                               69.3 69.0                  
                                                  8.4 8.5                 
                                                     3.1 3.4              
  6                                                                       
      ##STR10##    I-6        68-73                                       
                                   38  Found: Calculated for C.sub.69     
                                       H.sub.81 N.sub.3 O.sub.15 :        
                                               69.7 69.5                  
                                                  6.6 6.9                 
                                                     3.2 3.5              
  7                                                                       
      ##STR11##    I-7        40-44                                       
                                   43  Found: Calculated for C.sub.75     
                                       H.sub.93 N.sub.3 O.sub.15 :        
                                               70.3 70.6                  
                                                  7.5 7.3                 
                                                     3.0 3.3              
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     Below are shown Examples of stabilization tests for organic substances. In Examples, the following compounds were used for comparison. 
     A0-1 2,6-Di-t-butyl-4-methylphenol 
     A0-2 n-Octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate 
     A0-3 Pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] 
     A0-4 1,3,5-Trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene 
     EXAMPLE 8 
     
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                    Parts by                                              
                    weight                                                
______________________________________                                    
Unstabilized polypropylene resin                                          
                      100                                                 
(Sumitomo Noblen FS-200)                                                  
Calcium stearate      0.1                                                 
Compound being tested (Table 2)                                           
                      0.2                                                 
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     The above ingredients were blended together in a mixer for 5 minutes and then milled in molten state on a roller mixing mill at 180° C. The milled mixture was molded in a hot press at 210° C. into a sheet of 1 mm in thickness. Test specimens, 40×40×1 mm, were prepared from the sheet and tested in a Geer oven at 150° C. for the time elapsed before 30% of the surface area of each specimen had become brittle. The results obtained were as shown in Table 2. 
     
                       TABLE 2                                                     
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        Test compound                                                     
                  30% Enbrittlement time, hour                            
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Run No. 1     I-1         1100                                            
(This   2     I-2         1080                                            
invention)                                                                
        3     I-3         980                                             
        4     I-4         890                                             
        5     I-5         920                                             
Compara-                                                                  
        1     A0-1 .sup.  ≦24                                      
tive    2     A0-2 .sup.  270                                             
Run No. 3     A0-4 .sup.  640                                             
        4     None        ≦20                                      
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     EXAMPLE 9 
     Stabilization tests were carried out under the same conditions as in Example 8, except that the following compounding recipe was used. The results obtained were as shown in Table 3. 
     
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                     Parts by                                             
                     weight                                               
______________________________________                                    
Unstabilized polypropylene resin                                          
                       100                                                
(Sumitomo Noblen FS-200)                                                  
Calcium stearate       0.1                                                
Test compound (Table 3)                                                   
                        0.05                                              
Dilauryl 3,3&#39;-thiodipropionate                                            
                       0.2                                                
(SYA0-1) or pentaerythritol tetrakis-                                     
(β-laurylthiopropionate) (SYA0-2)                                    
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                       TABLE 3                                                     
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                       30% Enbrittlement                                  
             Test     time, hour                                          
             compound SYA0-1   SYA0-2                                     
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Run No.     6      I-1        1550   1490                                 
(This invention)                                                          
            7      I-2        2870   2900                                 
            8      I-3        1060   1100                                 
            9      I-4        1090   1120                                 
            10     I-5        1210   1350                                 
            11     I-6        --     2050                                 
            12     I-7        --     1700                                 
Comparative 5      A0-1 .sup. ≦24                                  
                                     ≦24                           
Run No.     6      A0-2 .sup.  540    580                                 
            7      A0-4 .sup.  930    830                                 
            8      None       ≦20                                  
                                     ≦20                           
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     EXAMPLE 10 
     Using an unstabilized polybutadiene rubber containing no antioxidant (JSR BR-01 extracted with acetone to remove the antioxidant), the compounding ingredients of the recipes 1, 2 or 3, shown below, were milled on a roller mill. The resulting rubber was tested for stability against both heat and oxidation as well as discoloration upon heating. The results obtained were as shown in Tables 4 and 5. 
     The stability against heat and oxidation was evaluated by subjecting the rubber specimen to thermal aging in a Geer oven at 100° C., measuring the gel content (toluene insolubles) at 15-hour intervals, and determining the time elapsed before the gel content had reached 10% by weight (this time span is herein referred to as gel I.P.). The discoloration upon heating was evaluated by the color of the rubber specimen (recipe 1) after heating in a Geer oven at 100° C. for 15, 60, and 120 hours. The rubber compositions of recipes 2 and 3 were evaluated after heating for 30 hours. 
     RECIPE 1 
     
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                   Parts by weight                                        
______________________________________                                    
Unstabilized polybutadiene rubber                                         
                     100                                                  
Test compound (Table 4)                                                   
                      1                                                   
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     RECIPE 2 
     
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Unstabilized polybutadiene rubber                                         
                       100                                                
Ditridecyl 3,3&#39;-thiodipropionate                                          
                       0.25                                               
Test compound (Table 5)                                                   
                       0.75                                               
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     RECIPE 3 
     
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Unstabilized polybutadiene rubber                                         
                        100                                               
Pentaerythritol tetrakis(β-lauryl-thio-                              
                        0.25                                              
propionate)                                                               
Test compound (Table 5) 0.75                                              
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                                           TABLE 4                                 
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(Recipe 1)                                                                
           Test  Gel I.P.                                                 
                      Color of rubber after heating for                   
           compound                                                       
                 (hour)                                                   
                      0 hour                                              
                          15 hours                                        
                               60 hours                                   
                                      120 hours                           
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Run No.  13                                                               
           I-1   160  White                                               
                          White                                           
                               White  White                               
(This invention)                                                          
         14                                                               
           I-2   125  &#34;   &#34;    &#34;      &#34;                                   
         15                                                               
           I-3   100  &#34;   &#34;    &#34;      &#34;                                   
         16                                                               
           I-4   105  &#34;   &#34;    &#34;      &#34;                                   
         17                                                               
           I-5   100  &#34;   &#34;    &#34;      &#34;                                   
         18                                                               
           I-6    95  &#34;   &#34;    &#34;      Pale yellow                         
         19                                                               
           I-7    95  &#34;   &#34;    &#34;      &#34;                                   
Comparative                                                               
          9                                                               
           A0-1 .sup.                                                     
                  80  &#34;   White                                           
                               Yellow Yellow                              
Run No.  10                                                               
           A0-2 .sup.                                                     
                  35  &#34;   &#34;    &#34;      &#34;                                   
         11                                                               
           A0-3 .sup.                                                     
                  55  &#34;   &#34;    Pale yellow                                
                                      &#34;                                   
         12                                                               
           None   5   &#34;   Yellow                                          
                               Yellow &#34;                                   
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                                           TABLE 5                                 
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                 Recipe 2 Recipe 3                                        
           Test  Gel I.P. Gel I.P.                                        
           compound                                                       
                 (hour)                                                   
                      Color                                               
                          (hour)                                          
                               Color                                      
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Run No.  20                                                               
           I-1   180  White                                               
                          210  White                                      
(This invention)                                                          
         21                                                               
           I-2   180  &#34;   250  &#34;                                          
         22                                                               
           I-3   120  &#34;   185  &#34;                                          
         23                                                               
           I-4   130  &#34;   190  &#34;                                          
         24                                                               
           I-5   125  &#34;   160  &#34;                                          
         25                                                               
           I-6   120  &#34;   150  &#34;                                          
         26                                                               
           I-7   115  &#34;   155  &#34;                                          
Comparative                                                               
         13                                                               
           A0-1 .sup.                                                     
                  90  &#34;   100  Pale yellow                                
Run No.  14                                                               
           A0-2 .sup.                                                     
                  50  &#34;    80  White                                      
         15                                                               
           A0-3 .sup.                                                     
                  85  &#34;   100  &#34;                                          
         16                                                               
           No     5   Yellow                                              
                           5   Yellow                                     
           Additive                                                       
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