Direct esterification of o-phosphoric acid
This application is a continuation of application Ser. No. 33,600 filed Dec. 16, 1987,now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention: 
     This invention relates to the direct esterification of o-phosphoric acid with fatty alcohols, alkoxylated fatty alcohols and alkylphenol alkoxylates in the presence of a water entraining agent and at least one inorganic or organic base. 
     2. Statement of Related Art: 
     According to D. Sasse in &#34;Houben-Weyl&#34;, Vol. 12, &#34;Organische Phosphorverbindungen (Organic Phosphorus Compounds)&#34;, Part 2, page 143, the esterification of o-phosphoric acid with hydroxy compounds involves the formation of di- or polyphosphoric acids which then undergo alcoholic cleavage. 
     From Hollemann-Wiberg, &#34;Lehrbuch der anorganischen Chemie&#34;, 83rd to 90th Edition, page 453, 1976, it is known for example that, at temperatures above 200° C, o-phosphoric acid is converted with intermolecular elimination of water into diphosphoric acid which, in turn, changes via even higher polyphosphoric acids into metapolyphosphoric acid at temperatures above 300° C with further elimination of water. 
     Since the primary reaction mainly takes place at temperatures of at least 170° C., olefin is split off from the ester formed in a secondary reaction. Due to the relatively high vapor pressure of the olefins, the reaction temperature falls during the esterification and no more ester is formed. 
     The olefin formation is presumably the reason why no literature can be found on the direct esterification of fatty alcohols with o-phosphoric acid alone without the further use of phosphorus-containing substances. 
     U.S. Pat. No. 4,350,645 describes an esterification process using o-phosphoric acid. However, the o-phosphoric acid is not used on its own, but is used together with phosphorus pentoxide. 
     According to K. Sasse (loc. cit.), the reaction of a fatty alcohol with o-phosphoric acid proceeds up to an equilibrium in which the concentration of the ester formed is substantially proportional to the square of the concentration of the phosphoric acid. The establishment of the equilibrium is relatively quick in the case of lower alcohols, but rapidly decreases with increasing chain length of the aliphatic radical. 
     DESCRIPTION OF THE INVENTION 
     Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term &#34;about&#34;. 
     An object of the present invention is to provide a process for the direct esterification of o-phosphoric acid with alcohols in which there is no need for the additional use of phosphorus-containing compounds. 
     Another object of the present invention is, where possible, to remove the unreacted alcohol from the reaction mixture by distillation without olefin formation. 
     More specifically, the present invention relates to a process for the production of phosphoric acid alkyl ester mixtures wherein from 1 to 5 mole equivalents of a saturated or unsaturated C 6  -C 18  fatty alcohol and preferably a linear or branched, C 8  -C 18  fatty alcohol, or an adduct thereof containing from 1 to 20, and preferably from 1 to 12, moles of ethylene oxide and/or propylene oxide, and/or an adduct of from 1 to 20 moles of ethylene oxide and/or propylene oxide with alkylphenols containing from 8 to 15 carbon atoms in the alkyl substituents, for example adducts of from 1 to 20 moles of ethylene oxide and/or propylene oxide with nonylphenol, are directly esterified with 1 mole equivalent of o-phosphoric acid in the presence of from 0.05 to 0.2 mole equivalent, based on the quantity of phosphorus atoms present in the reaction mixture, of a basic (i.e. alkaline) inorganic or organic compound or a mixture of such compounds and a water-entraining agent with removal of the water of reaction from the reaction system. 
     In the context of the invention, fatty alcohols include, inter alia, hexyl alcohol, 2-ethylhexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, isononyl alcohol, decyl alcohol, isodecyl alcohol, undecyl alcohol, dodecyl alcohol, tridecyl alcohol, isotridecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, hexadecyl alcohol, heptadecyl alcohol, octadecyl alcohol, oleyl alcohol, elaidyl alcohol, and isostearyl alcohol. 
     Amines and alkali metal hydroxides are preferably used as the basic inorganic or organic compound. It is particularly preferred to use amines without any additional functional groups and having molecular weights in the range of from 129 to 297, for example dimethyl cocosamine, or potassium or sodium hydroxide. 
     According to the invention, suitable water-entraining agents include, inter alia, C 1  -C 4  alkyl benzenes, e.g. toluene and xylene. 
     Another feature of the present invention is that the esterification is carried out at a temperature of at least 160° C., usually in the range of from 130° to 250° C., preferably 160°-200° C. 
     Another feature of the present invention is that unreacted fatty alcohols can be directly removed from the reaction mixture by vacuum distillation. 
     Phosphoric acid esters prepared in accordance with the invention may be converted by known methods into their alkali metal salts, ammonium salts and alkanolamine salts, e.g. C 1  -C 4  alkanolamine salts. Salts of this type are widely used as cleaning preparations, emulsifiers, antistatic agents and rustproofing agents or the like. One advantage of the process of the invention is that the condensation reaction is distinctly accelerated. In addition, relatively high yields of di- and trialkyl ester can be obtained which cannot be obtained using phosphorus pentoxide. In one embodiment of the invention, unreacted alcohol may be directly removed from the reaction mixture by distillation before neutralization without olefin formation. The products obtained are very light in color. 
     The invention will be illustrated but not limited by the following examples. 
    
    
     EXAMPLES 
     In each of the following examples of the invention, the terms &#34;monoalkyl ester&#34;, &#34;dialkyl ester&#34;, and &#34;trialkyl ester&#34; refer to esters of phosphoric acid wherein the alkyl group or groups correspond to the alkyl groups in the alcohols employed in the reaction. 
     EXAMPLE 1 
     198 g (1.5 moles) n-octanol (OH number 425), 23.7 g (0.1 mole) dimethyl cocosamine, 0.3 g hypophosphorous acid (50%) and 40 ml toluene were introduced into a stirring apparatus equipped with a water separator, reflux condenser and thermometer. 115.2 g (1.0 mole) phosphoric acid (85%) were added with stirring. The mixture was then heated until it boiled vigorously under reflux. During the separation of water which began at 130° C., the temperature rose to 182° C. After 6 h, a total of 42.6 g of water had been separated off and the reaction was terminated. 
     The toluene was removed by distillation in a vacuum of 20 mbar and at a final temperature of 110° C. 282.6 g of a colorless oily liquid were obtained as residue. 
     The composition of the residue was analyzed by multistage potentiometric titration and determination of the phosphorus and amine content: 
     34.0% monoalkyl ester 
     42.2% dialkyl ester 
     11.8% trialkyl ester 
     3.4% o-phosphoric acid 
     0.0% n-octanol 
     8.4% dimethyl cocosamine 
     Other additions according to the invention were carried out under the same conditions. 
     
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              Composition (%)                                             
Ex-                      o-phos-                                          
ample     Yield                                                           
              mono-                                                       
                  di-                                                     
                     tri-                                                 
                         phoric                                           
                             octa-                                        
                                 addi-                                    
No. Addition                                                              
          (g) ester                                                       
                  ester                                                   
                     ester                                                
                         acid                                             
                             nol tion                                     
__________________________________________________________________________
2   potassium                                                             
          261.6                                                           
              30.2                                                        
                  60.0                                                    
                     0.0 0.8 7.1 1.9                                      
    hydroxide                                                             
3   cocosamine                                                            
          265.2                                                           
              21.0                                                        
                  63.2                                                    
                     0.9 5.0 3.2 6.7                                      
4   tributyl                                                              
          275.5                                                           
              37.9                                                        
                  45.1                                                    
                     3.4 2.2 5.0 6.4                                      
    amine                                                                 
5   N-lauryl                                                              
          266.5                                                           
              31.1                                                        
                  40.8                                                    
                     13.1                                                 
                         5.2 5.3 4.5                                      
    diamino-                                                              
    propane                                                               
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     EXAMPLE 6 
     195 g (1.5 moles) 2-ethylhexanol, 23.7 g (0.1 mole) dimethyl cocosamine, 0.3 g hypophosphorous acid (50%) and 115.2 g (1.0 mole) phosphoric acid (85%) were reacted in the presence of 40 ml toluene in an apparatus equipped as described in Example 1. 
     The maximum temperature was 161° C. and 43.6 g water were separated off. Removal of the toluene left 270.1 g of a colorless oily residue which had the following composition: 
     45.3% monoalkyl ester 
     26.4% dialkyl ester 
     3.8% trialkyl ester 
     6.2% o-phosphoric acid 
     10.1% 2-ethyhexanol 
     8.2% dimethyl cocosamine 
     EXAMPLE 7 
     390 g (1.5 moles) tallow alcohol (OH number 315.8; iodine number 1), 23.7 g (0.1 mole) dimethyl cocosamine, 0.5 g hypophosphorous acid (50%) and 115.2 g (1.0 mole) phosphoric acid (85%) were reacted in the presence of 75 ml toluene in an apparatus equipped as described in Example 1. The quantity of water separated off with a maximum temperature of 189° C. was 45.3 g. Removal of the toluene left 487 g of a residue which solidified on cooling (iodine number 1.6). The following composition was calculated from the total analysis: 
     20.9% monoalkyl ester 
     42.1% dialkyl ester 
     18.1% trialkyl ester 
     4.9% o-phosphoric acid 
     7.5% tallow alcohol 
     1.6% tallow olefin 
     4.9% dimethyl cocosamine 
     EXAMPLE 8 
     282 g (1.5 moles) n-dodecanol (OH number 298), 23.7 g (0.1 mole) dimethyl cocosamine, 0.3 g hypophosphorous acid (50%) and 115.2 g (1.0 mole) o-phosphoric acid were reacted in the presence of 40 ml toluene in an apparatus of the type described in Example 1. The quantity of water separated off was 45.0 g with a maximum temperature of 198° C. Removal of the toluene left 375 g of a residue which solidified on cooling (iodine number 2.2). The composition was as follows: 
     28.0% monoalkyl ester 
     43.6% dialkyl ester 
     10.1% trialkyl ester 
     4.6% o-phosphoric acid 
     7.3% n-dodecanol 
     6.4% dimethyl cocosamine 
     EXAMPLE 9 
     273 g (0.75 mole) of a mixture of dodecyl and tetradecyl alcohol reacted with 4 moles ethylene oxide, 11.8 g (0.05 mole) dimethyl cocosamine, 0.3 g hypophosphorous acid (50%), 57.6 g (0.5 mole) o-phosphoric acid (85%) and 40 ml toluene were reacted in an apparatus of the type described in Example 1. After 23.8 g water had been separated off up to a maximum temperature of 200° C., the toluene was removed and 307 g of a colorless liquid having the following composition were obtained: 
     19.1% monoalkyl ester 
     52.3% dialkyl ester 
     16.5% trialkyl ester 
     0.6% o-phosphoric acid 
     7.8% free alcohol 
     3.7% dimethyl cocosamine 
     EXAMPLE 10 
     396 g (3.0 moles) n-octanol, 47.4 g (0.2 mole) dimethyl cocosamine, 115.2 g (1.0 mole) o-phosphoric acid (85%) and 50 ml toluene were esterified in the apparatus described in Example 1. The maximum temperature was 201° C. and the quantity of water separated off was 59.1 g. The residue obtained after removal of the toluene contained 38.9% unreacted n-octanol which was separated off substantially quantitatively by distillation under a vacuum of 20 mbar and at a sump temperature of 170° C. The distillate had an iodine number of 0.7. It may be concluded from this that no thermal decomposition of ester to olefins had taken place. The distillation residue of 332g had the following composition: 
     11.0% monoalkyl ester 
     57.6% dialkyl ester 
     17.6% trialkyl ester 
     0.6% o-phosphoric acid 
     0.2% n-octanol 
     13.0% dimethyl cocosamine 
     COMPARISON EXAMPLE 1 
     Example 1 was repeated except that no dimethyl cocosamine or other basic inorganic or organic compound in accordance with the invention was added. After a reaction time of 9.5 h, 41.2 g water were separated off for a maximum temperature of 178° C. The reaction temperature ultimately fell to 158° C. 
     Removal of the toluene left only 197.6 g of residue. The n-octene formed as secondary product during the reaction had also distilled off. The composition of the residue was as follows: 
     52.7% monoalkyl ester 
     38.0% dialkyl ester 
     7.3% trialkyl ester 
     1.0% o-phosphoric acid 
     1.0% n-octanol 
     COMPARISON EXAMPLE 2 
     Example 8 was repeated except that no dimethyl cocosamine or other basic compound in accordance with the invention was added. Removal of the toluene left a residue of 266.4 g while the quantity of distillate was 94.2 g. The residue had an iodine number of 60 while the distillate had an iodine number of 131. Accordingly, a content of approximately 32% n-dodecane was calculated for the residue.