United States Patent Office

Patented June 20, 1950 2,512,582 UNITED STATES2,512,582 PATENT OFFICE MIXED ALKYL BENZYL PHOSPHATES AND THEIR PRODUCTION Edwin P. Plueddemann, Woodbridge, N.J., as signor to Food Machinery and Chemical Cor poration, a corporation of Delaware . No Drawing. Application March 22, 1946, Serial No. 656,541 . 12 Claims. (C. 260 2 This invention relates to mixed alkyl benzyl the intermediate alkyl acid phosphates by the phosphates, and more particularly, to substan reaction of phosphorus pentoxide with about tially neutral tertiary alkyl benzyl-esters of phos ithree mols of the desired alcohol. phoric acid wherein the alkyl chain contains at product is, approximately an equimolarThe resultingmixture least, three and preferably at least four carbon 5 atoms. {of ... monoalkyl and dialkyl acid, phosphates. In the past trialkyl phosphates and tribenzyl these acid phosphates may be neutralized with phOSphates were generally prepared by the reac an alkaline material such as sodium hydroxide tion of trisilver phosphate with an appropriate 'or potassium hydroxide to give a thick paste of alkyl halide or a benzyl halide. Such reactions 10 , the alkali salts containing about 20 per cent have proven to have a number of industrial dis-, 'water. The acid, phosphates may also be dis advantages. I have tried to form benzyl phos Solved in a suitable solvent before neutralization phates by reacting alkali phosphates such as to give a more nobile mixture. A portion of the tripotassium phosphate, or dipotassium... acid Water may then be removed by simple distillation phosphate with benzyl chloride. Such attempts or as an azeotrope with the solvent employed. have been entirely unsuccessful. When such re An excess of a benzyl halide, advantageously actions were attempted, practically no reaction benzyl chloride, is then added and the mixture took place under mild conditions, and undermore warmed with stirring until precipitation of alkali vigorous conditions, the benzyl chloride either de chloride is substantially complete. A wide range composed or polymerized, thereby precluding the 20 of reaction conditions is possible, but in the pres Successful formation of tribenzyl phosphate. :ence of large quantities of water and at tempera In more recent times trialkyl phosphates have tures below about 120° C. the desired reaction been prepared more conveniently by the reaction proceeds slowly and the reaction time required is of phosphorus oxychloride with aliphatic alco -excessive... I have found that temperatures of 120 to 170. C. are especially well suited for the hols under carefully controlled conditions. Sev 25 reaction aithough even higher temperatures may eral of the trialkyl phosphates have been pre be used if desired. For example, the reaction pared. On a commercial Scale in this manner, may be completed at 180°. C., the reflux tempera Certain alcohols, however, such as the tertiary ture of benzyl chloride. ... aliphatic alcohols are unsuitable for the prepa Under all reaction conditions. I have observed ration of neutral esters by this method because 30 that benzyl chloride enters, into side reactions of the great sensitivity of the ester linkages to with water, solvent, or other materials with the decomposition in the presence of the hydrogen liberation of hydrogen chloride. The hydrogen chloride formed as one of the products of the chloride immediately liberates alkyl acid phos reaction. Benzyl alcohol, for this application, phates from their salts and thus interferes with more closely resembles the tertiary than the gri 35 the reaction of these salts with benzyl chloride. Inary aliphatic alcohols. Even under carefully At higher temperatures the liberated acid phos Controlled conditions the major products obtained phates decompose and are periananently lost to from the reaction of benzyl alcohol with phos the reaction. At lower... reaction temperatures phorus oxychloride are benzyl chloride and acid this decomposition is less serious and the lib phosphates. If one attempts to prepare mixed 40 erated acid may be neutralized by occasional alkyl benzyl phosphates by the reaction of alkyl additions of alkali in Small portions. I have chlorophosphates with benzyl alcohol, a large found, however, that it is possible to run the proportion of benzyl chloride and acid phosphates esterification reaction in the presence of an ex are formed and Only a poor yield of the neutral cess of alkali carbonate. The carbonate is essen mixed esters can be recovered, - v. 45 tially inert, to the alkylphosphates and to benzyl I have now discovered that neutral alkyl benzyl i. chloride, but will react, with acid materials as phosphates may be obtained in good yield, from they are liberated, thus maintaining a neutral or the reaction of a benzyl halide with the alkali slightly alkaline medium. In the presence of an salts of organic acid phosphates. This reaction excess of alkali carbonate I have found that sub may be effected at elevated temperatures by 50 stantially, no decomposition of organic phos warming the reactants together in the presence , phates in the reaction mixture results...even at of a suitable liquid solvent or diluent medium temperatures up to 180° C. A method is there such as an Organic Solvent. Or water or a com fore available for condensing benzyl-chloride with bination of the two. the alkyl-phosphate salts at a temperature at When preparing mixed alkyl benzyl phps. which a rapid reaction may be obtained. phates, I have found it advantageous to prepare Solvents may be employed to aid in bringing 2,512,582 4 3. gone substantially to completion in four to five the alkyl phosphate salts and benzyl chloride into hours. The observed difference in reactivity is contact. Choice of a solvent with an appropriate probably due to the lesser solubility of the lower boiling range also aids in controlling the reaction alkyl phosphate salts in the organic phase of the temperature. Preferred solvents for the reac reaction mixture, and to the greater... ease of tion are organic liquids boiling at a temperature hydrolysis of the lower alkyl phosphates in the above about 120° C. that are miscible with benzyl presence of water. chloride and that act at least as partial solvents At the end of the reaction period, the reaction for the alkyl phosphate salts. The solvent also mixture may be washed and the lights removed should be relatively unreactive with benzyl by distillation or the mixture may be filtered to chloride. Among such solvents are ketones, O remove alkali chloride and the organic fraction alcohols, and esters. Secondary and tertiary distilled directly from a Small excess of Solid base alcohols normally are more suitable than the to recover the mixed alkyl benzyl phosphates. primary alcohols. A particularly appropriate Normally the distillation is preferably carried solvent for the preparation of a given alkyl ben out at subatmospheric pressures. Due to the zyl phosphate is the trialkyl phosphate corre 5 mixed nature of the product and due to the sponding to the starting alkyl acid phosphate. tendency for radical interchange during pro For example, tributyl phosphate is an outstand longed heating, it is usually not practicable to ing reaction medium for the preparation of butyl fractionate the product to obtain pure separate benzyl phosphates from benzyl chloride and salts fractions of benzyl, dialkyl phosphate' and di of acid butyl phosphate. Any side reaction be 20 benzyl monoalkyl phosphate, but purified frac tween benzyl chloride and the solvent, in this tions can be obtained by exercising special Con case, serves only to produce more butyl benzyl trols and by distilling over a narrow temperature phosphates. An excess of benzyl chloride may range. Some tribenzyl phosphate is also formed also serve as solvent in the presence of a Small during the reaction and distillation, and may re quantity of water. The alkali phosphates are 25 main as a high boiling residue. Tribenzyl phos not readily soluble in benzyl chloride, but do phate itself generally decomposes, before it can come into enough contact for reaction, probably be distilled even under a good vacuum, but it by emulsification, in the presence of water. may readily be recovered if it is present in ap After a portion of the alkyl phosphate Salts have preciable quantities by recrystallization from the reacted, the esters formed serve as a sufficient 30 solvent and the water may be substantially re still residue after removal of more volatile mate moved while the reaction is completed. rials.The Substantially neutral or neutral high boil Various materials have been found to act ing mixture of alkyl monobenzyl, alkyl dibenzyl, catalytically in aiding the reaction of benzyl and tribenzyl phosphates and other complex ben chloride with alkyl phosphate salts. Among zyl phosphates obtained herein is included in these are iodides and other salts of mercury, the term mixed alkyl benzyl phosphates. Such copper, lead, and silver, as well as pyridine, mixtures have commercial value as a high boil trialkyl amines, and other organic amines and ing solvent or plasticizer. Material distillable bases. Fairly complete reaction may be obtained within a more narrow temperature range may even in the absence of these catalysts, but their 40 be separated if desired, but ordinarily no chem presence shortens the necessary reaction time ically pure compounds need be isolated. and increases the yield of alkylbenzyl phosphates The mixed alkyl benzyl phosphates of this in recovered. Catalysts for the desired condensa vention, particularly those containing from three tion also catalyze side reactions of benzyl chlo carbon atoms up in the alkyl chain and espe ride with resulting liberation of hydrogen chlo 45 cially those containing from four to eight carbon ride. In the absence of excess alkali carbonate atoms in the alkyl chain, have decided advan this increased rate of acid formation in the tages when compared to the most nearly analo presence of catalysts may actually result in a gous prior art compounds.

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