US3361856A - Process for preparing hydroxy-substituted esters of phosphorodithioic acids - Google Patents

Description

United States Patent 3,361,856 PROCESS FOR PREPARING HYDROXY-SUB- STHTUTED ESTERS 0F PHOSPHORODI- TliHOIC ACIDS William M. Le Suer, Cleveland, Ohio, assignor to The Lubrizol Corporation, Wicklitie, Ohio, a corporation of Ohio N0 Drawing. Filed Dec. 13, 1963, Ser. No. 330,225 6 Claims. (Cl. 26t)978) This invention relates to the chemistry of organo phosphorus compounds and more particularly, to the chemistry of phosphorodithioic acids. Still more particularly it relates to a process whereby these acids are converted to neutral hydroxy-substituted triesters of phosphorodithioic acids.

The development of petroleum lubricating oils has been toward the use of more etficient refining methods to reduce the sludging tendency of such oils. These highly refined oils, however, have decreased resistance to oxidation and are more likely to form soluble acidic oxidation products which are corrosive, particularly under severe service conditions. Although generally superior to lightly refined oils they tend to form a varnish film on hot metal surfaces, such as the cylinder walls and pistons of an internal combustion engine, under very severe engine operating conditions.

This invention is a process for making products which can be formulated with highly refined petroleum fractions to give improved motor oils and gear lubricants. In such formulation, the products of this process serve both as corrosion inhibitors and also as extreme pressure agents. For example, the addition of a small proportion of the product of this process to a refined lubricating oil greatly reduces the tendency of such oil to corrode metal surfaces, especially those of copper-lead and silver-lead bearings. In addition, gear lubricants which are subjected to extreme pressure conditions are greatly improved by the addition of the products of this process so that they may better withstand the extreme pressures of the environments in which they are used.

In addition to the desirability of these products as corrosion inhibitors and as extreme pressure agents, they are particularly useful in lubricating formulations because of their compatibility with other known lubricant additives.

Furthermore, these products are useful as ore floatation agents and as metal finishing agents. They are also valuable as starting materials for the preparation of still other effective lubricant additives.

It is a principal object of the invention to provide a novel process for the preparation of certain lubricant additives and lubricant additive intermediates.

It is also an object of the invention to provide a convenient process for the preparation of neutral phosphorusand sulfur-containing compositions.

These and other objects are accomplished by the process which comprises reacting a salt of a phosph-orodithioic acid having the structural formula (RO) PSSH NR' wherein R is a hydrocarbon radical and R is selected from the class consisting of hydrogen and hydrocarbon radicals, with at least about an equivalent amount of an organic compound selected from the class consisting of epoxides and thioepoxides, in the presence of an acidic compound, which is weaker in acidity than the dialkyl phosphorodithioic acid which is used. The product of this reaction is a hydroxy-substituted triester of phosphorodithioic acid.

The hydrocarbon radicals of the above structure may be aliphatic or aromatic and are substantially hydrocarbon in character. Illustrative types of such radicals include alkyl, cycloalkyl, aryl, aralkyl, 'alkaryl, alkenyl, cycloalkenyl, etc.

The phosphorodithioic acids from which the hydroxysubstituted triesters can be derived are well known. They may be prepared by the reaction of phosphorus pentasultitle with a hydroxy compound which corresponds to the organic radical R. This reaction is illustrated by the action of phosphorus pentasulfide on ethyl alcohol to produce 0,0'-diethylphosphorodithioic acid. In similar fashion, aliphatic hydroxy compounds such as propyl, butyl, isobutyl, amyl, hexyl, cyclohexyl, n-octyl, iso-octyl, lauryl, etc., alcohols or aromatic hydroxy compounds such as phenol, alkylated phenols, naphthols, alkylated naphthols, and the like may be reacted with phosphorus pentasulfide to produce phosphorodithioic acids of utility as starting materials for the present invention.

The reaction of phosphorus pentasulfide with a mixture of alcohols or phenols (e.g., isobutanol and n-hexanol in 2:1 weight ratios) results in phosphorodithioic acids in which the two organic radicals are different. Such acids likewise are useful herein.

The substituted ammonias or amines useful for forming the phosphorodithioic acid salts of this invention may be aliphatic amines, aromatic amines, or cyclo-aliphatic amines. Amines having from 1 to about 15 aliphatic carbon atoms are preferred. Methyl amine, ethyl amine, n-propyl amine, isopropyl amine, n-butyl amine, isob-utyl amine, secondary butyl amine, tertiary butyl amine, n-arnyl amine, isoamyl amine, n-heptyl amine, n-hexyl amine, octyl amine, nonyl amine, decyl amine, hendecyl amine, dodecyl amine, tridecyl amine, tetra-decyl amine, pentadecyl 'amine, dimethyl amine, diethyl amine, di-npropyl amine, diisopropyl amine, dibutyl amine, diamyl amine, dihexyl amine, trimethyl amine, triethyl amine, benzyl amine, pyridine, morpholine, ethylene diamine, piperazine, cyclopentyl amine, and diethylene triamine are specific examples of useful amines.

When an ammonium phosphorodithioate is reacted with an epoxide in the presence of a weaker acid, said weaker acid has the function of combining with the liberated ammonia. For this purpose, it must be of lower acidity than the phosphorodithioic acid in order not to displace the phosphorodithioic acid from its ammonium salt before its reaction with the epoxide. Suitable acids, therefore, are those which have a pK value greater than that of the phosphorodithioic acid which is about 1. Examples of such acids are: aliphatic carboxylic acids such as, formic, acetic, propionic, butyric, s-uccinic, malic, ascorbic, .gl-utaric, etc.; aromatic carboxylic acids such as benzoic, toluic, etc.; weaker inorganic acids such as sulfurous, boric, nitrous, carbonic, etc.; and acidic gases such as CO H 8, S0 etc.

The ammonium salt or substituted-ammonium salt of a phosphorodithioic acid may be prepared by adding an equivalent amount of ammonia or a substituted ammonia to the acid, or a solution of the acid in an inert solvent, to obtain the neutral salt, as illustrated by the following equations:

Similarly, the ammonium salt or substituted ammonium salt of a phosphorodithioic acid may be prepared by the 3 reaction of the acid with the ammonium salt of a weaker acid than the phosphorodithioic acid. This may be represented by the following equations:

(RO PSSH+NH OOC CH The reaction of a phosphorodithioic acid with ammonia is exothermic and may be carried out at tempera tures within the range of from about 35 C. to the decomposition temperature of the salt, or about 200 C. It is the usual procedure to start passing ammonia into the acid at about 20 C.60 C. and to allow the temperature to rise to about 90l00 C., keeping the tem perature of the reaction at about 100 C. by controlling the rate of ammonia addition and by external cooling if necessary.

The reaction of a phosphorodithioic acid with the ammonium salt of a weaker acid is also exothermic and may be carried out at temperatures within the range of from about C. to the decomposition temperature of the salt, or about 200 C. It is usually carried out by adding a concentrated aqueous solution of the ammonium salt of the weaker acid to the phosphorodithioic acid at 20 C. to about 40 C. and keeping the temperature of the reaction below about 60 C. by controlling the rate of addition of ammonium salt and by external cooling if necessary.

Most of the ammonium and substituted ammonium phosphorodithioates are crystalline salts at room temperature. This property affords the distinct advantage of being able to purify the amine phosphorodithioates by recrystallization from a suitable solvent before further reaction and thus obtaining very pure hydroxy-substituted triesters.

As stated previously, the weaker acid, which is present during the reaction of the ammonium phosphorodithioate with an epoxide, has the function of removing the byproduct ammonia as it is formed. Thus, in order to combine with all of the ammonia formed, the amount of weaker acid to be used must be equivalent to the amount of ammonia in the phosphorodithioate salt. However, part or nearly all of the ammonia may be removed from the epoxide-ammonium phosphorodithioate reaction by passing an inert gas such as nitrogen through the reaction mixture during the epoxide addition. In such instances it is necessary to use only a relatively small amount of the weaker acid near the end of the reaction to scavenge the remaining ammonia which, in many instances, is otherwise difiicult to remove.

A particularly advantageous embodiment of this invention is effected by reacting a dialkyl phosphorodithioic acid with an equivalent amount of an ammonium salt of a weaker acid thus forming an ammonium phosphorodithioate and the free weaker acid. An epoxide is then introduced into the mixture forming the hydroxy-substituted trister of phosphorodithioic acid and regenerating the ammonium salt of the weaker acid which can then be separated and recycled for reaction with more of the phosphorodithioic acid.

The reaction of the ammonium and substituted ammonium phosphorodithioate salts with an epoxide is somewith exothermic, especially in the presence of a weaker acid. The temperature, however, is easily controlled by the rate of addition of the epoxide. Although it is not necessary, it is preferred to control the temperature of the reaction mixture so that it is reasonably constant throughout the course of the reaction. The temperature of the reaction may be as low as -60 C. or lower, and on the other hand, it may be as high as 200 C. or even higher. Generally, for reasons of economy, it is preferred to carry out the process at a sufiiciently high temperature that the ammonium salt of the phosphorodithioic acid is a liquid 4- rather than to react the epoxide with a solution of the ammonium salt at a lower temperature.

The organic epoxides and thioepoxides may be represented by the structural formula wherein R" is a hydrocarbon radical or hydrogen, X is sulfur or oxygen, and n is 1 or 0. Those epoxides and thioepoxides are preferred in which one of the carbon atoms attached to oxygen or sulfur is also attached to two hydrogen atoms. In other words, the preferred epoxides and thioepoxides are terminal epoxides. These have been given the name terminal epoxides and thioepoxides because they may be thought of as being derived in most instances, from a vinyl compound which has a terminal olefinic double bond.

The term epoxide is used hereafter in a broad sense to denote the epoxides and the thioepoxides.

Specific examples of suitable epoxides include ethylene oxide, propylene oxide, epichlorohydrin, l-butene oxide, butadiene monoxide, l-amylene oxide, styrene oxide, ethylene sulfide, propylene sulfide, etc.

The reaction appears to involve equimolar proportions of the ammonium or substituted ammonium salt of the phosphorodithioic acid and the epoxide. This reaction appears to be unique in that ammonia or an amine is liberated upon addition of an epoxide. Since ammonia and amines are basic compounds it would not be expected that they would be liberated from their salts by a neutral material such as propylene oxide. The identity of the products have not been established other than that they are known to be hydroxy-substituted triesters and so they are best described in terms of their method of preparation. The products are neutral, having a phosphorus to sulfur ratio of 1:2, and as indicated before, appear to result from the reaction of one mole each of ammonium or substituted ammonium phosphorodithioate and epoxide.

It is usually convenient to use an excessive amount of the organic epoxide so as to insure a maximum yield. in most instances the epoxide is sufficiently volatile that its removal from the reaction mixture, after the reaction is finished, is a simple operation. In some cases, it is sufficent merely to allow the excess epoxide to evaporate from the product at room temperature, or the product may be flushed with an inert gas such as nitrogen, or subjected to reduced pressure.

The process of the invention is illustrated further in detail by the following specific examples:

Example 1 Dissolved hydrogen sulfide is removed from 660 grams (2 moles) of 0,0'-di(2-methylpentyl-4) phosphorodithioic acid by heating at 30-35 C. for 0.5 hour at 30 mm. mercury pressure. An aqueous solution of 170 grams (2.2 moles) of ammonium acetate dissolved in 79 grams (4.4 moles) of water is added at 30-48 C. in 0.5 hour. The reaction is mildly exothermic resulting in a clear yellow-green solution having a neutralization number of 4.5 (basic to bromphenol blue), into which 128 grams (2.2 moles) of propylene oxide is introduced at 4048 C. in 0.75 hour with external cooling in an exothermic reaction. Stirring is continued for 0.5 hour at 48 C. and the reaction mixture is then allowed to separate into layers. The organic phase is stripped at 75 at mm. mercury pressure and is filtered, resulting in 762 grams of product. The product contains 17.14 percent sulfur, 8.21 percent phosphorus, less than 0.02 percent nitrogen, 5.3 percent OH and has a neutralization number of 5.80 acid to phenolphthalein.

Example 2 Dry nitrogen gas is passed through a solution of 1980 grams (6 moles) of 0,0-di-(2-methylpentyl-4)phosphorodithioic acid for 0.25 hour and then 102 grams (6 .hour. Stirring is continued for 1.5 hours with the addition of 121 grams (1.9 moles) of sulfur dioxide. The filtered product is found to contain 8.39 percent phosphorus, 17.03 percent sulfur, 0.24 percent nitrogen, and to have a neutralization number of 28 acid to phenolphthalein.

Example 3 Nitrogen gas is passed through 660 grams (2.0 moles) of 0,0'-di-(2-methylpentyl-4) phosphorodithioic acid for 15 minutes at 25 C., followed by the addition of 100 grams of water and 137 grams (2.2 moles) of 28% aqueous ammonium hydroxide which is added in 0.5 hour at 2150 C. Propylene oxide, 128 grams (2.2 moles) is added below the surface in 1 hour while 1.6 standard cubic feet (2.2 moles) of carbon dioxide is passed into the reaction mixture at 4050 C. with cooling. The mixture is stirred for an additional 0.5 hour at 45 -50 C. and is then allowed to separate into two layers. The organic layer is heated to 75 C. at 100mm. mercury and is then filtered to give 767 grams of product containing 8.07 percent phosphorus, 17.47 percent sulfur, 0.021 percent nitrogen, and having a neutralization number of 1 acid to phenolphthalein.

Example 4 Nitrogen gas is passed through 660 grams (2 moles) of 0,0"-di-(2-methylpentyl-4) phosphorodithioic acid for 15 minutes at 25 C., and then a solution of 139 grams (2.2 moles) of ammonium formate in 150 grams of water is added at 3050 C. in 0.5 hour. The reaction is mildly exothermic resulting in a solution to which is added 128 grams (2.2 moles) of propylene oxide at 4050 C. in 0.75 hour with external cooling. The reaction mixture is stirred for 0.5 hour to assure complete reaction, and is then allowed to stand for 0.5 hour to separate into two layers. The organic layer is heated to 70-75 C. at 100 mm. mercury pressure and filtered. The filtrate is the product.

Example 5 Nitrogen gas is passed through 660 grams (2 moles) of 0,0'-di-(2-methylpentyl-4) phosphorodithioic acid for 15 minutes at 25 C., and then a solution of 231 grams (2.2 moles) of ethylamine acetate in 250 grams of Water is added at 3045 C. in 0.5 hour. The reaction is mildly exothermic resulting in a reaction mixture to which is added 128 grams (2.2 moles) of propylene oxide at 40-- 50 C. in 0.75 hour with external cooling. The reaction mixture is stirred for 0.5 hour to assure complete reaction, and is then allowed to separate into two layers. The organic layer is heated to 7075 C. at 100 mm. mercury pressure and filtered. The filtrate is the product.

Example 6 Nitrogen gas is passed through 660 grams (2 moles) of 0,0'-di-(2-methylpentyl-4) phosphorodithioic acid for 15 minutes at 25 C., followed by the addition of a concentrated aqueous solution containing 231 grams (2.2 moles) of dimethylamine acetate in 0.5 hour at 21-50 C. Butylene oxide, 159 grams (2.2 moles) is added at 4050 C. in 1 hour with cooling. The reaction mixture is stirred for 0.5 hour to assure complete reaction, and is then allowed to separate into two layers. The organic layer is heated to 75 C. at 100 mm. mercury pressure and filtered. The filtrate is the product.

Example 7 Ammonia gas, 37 grams (2.2 moles) is passed into 708 grams (2.0 moles) of 0,0'-di-iso-octyl phosphorodithioic acid and 20 grams (1.1 moles) of water in 1 hour at 25 60 C. Ethylene oxide, 97 grams (2.2 moles) and carbon dioxide, 97 grams (2.2 moles) are introduced beneath the surface of the resulting salt in 2 hours at 5060 C. with cooling. The reaction mixture is stirred an additional 0.5 hour, and the mixture is cooled to 25 C. and filtered. The filtrate is the product.

Example 8 To 588 grams (2.0 moles) of 0,0'-di-cyclohexyl phosphorodithioic acid, 200 grams (2.2 moles) of ammonium propionate is added in 0.5 hour at 2150 C. The reaction is mildly exothermic resulting in a solution to which is added 159 grams (2.2 equivalents) of butylene oxide at 40-50 C. in 1 hour with external cooling. The reaction mixture is stirred for 0.5 hour to assure complete reaction and is then allowed to separate into two layers. The organic layer is heated to C. at 100 mm. mercury pressure and filtered. The filtrate is the product.

Example 9 Dry nitrogen gas is passed for 0.5 hour through a phosphorodithioic acid prepared by reacting 4 moles of a mixture of 65% isobutanol and 35% primary amyl alcohol with 1 mole of phosphorus pentasulfide. An aqueous solution of 340 grams of ammonium acetate (4.4 moles) dissolved in 158 grams (8.8 moles) of water is added to 1108 grams (4.0 moles) of this phosphorodithioic acid at 30-50 C. for 0.5 hour. Propylene oxide, 255 grams (4.4 moles) is added below the surface in 1 hour at 50 55 C. with cooling. The mixture is stirred for an additional 0.5 hour at 50 C. and is then allowed to separate into two layers. The organic layer is heated to 75 C. at 100 mm. mercury pressure and is then filtered. The filtrate is the product.

A useful derivative of the hydroxy-substituted triesters of phosphorodithioic acids is prepared by the reaction with an inorganic phosphorus reagent selected from the class consisting of phosphorus acids, phosphorus oxides, and phophorus halides. The preferred inorganic phosphorus reagent in the reaction with the hydroxy-substituted triesters of phosphorodithioic acids is phosphorus pentoxide. The products of this reaction are acidic materials which in themselves are useful.

These acidic materials may be further reacted with basic reacting metal oxides or with amines to make other useful products. These are described more fully in copencling application No. 130,270, filed Aug. 9, 1961, now US. 3,197,496.

What is claimed is:

1. In the process of preparing a hydroxy-substituted phosphorodithioic acid triester by reacting at a temperature below the decomposition temperature the ammonium salt of a phosphorodithioic acid having the structural formula (RO) PSSH-NR wherein R is a hydrocarbon radical and R hydrogen or hydrocarbon, with at least about an equivalent amount of an epoxide, whereby NR' is formed as a by-product; the improvement comprising conducting the reaction in the presence of an acidic compound of lesser acidity than the phosphorodithioic acid of the said salt, said acidic compound being present in the reaction mixture in an amount sufiicient to remove the NR remaining in the reaction mixture.

2. The improvement of claim 1 wherein the acidic compound has a pK greater than about 1.

3. The improvement of claim 1 wherein the acidic compound is an aliphatic carboxylic acid.

4. The improvement of claim 1 wherein the acidic compound is an aromatic carboxylic acid.

5. The improvement of claim 1 wherein the acidic compound is acetic acid.

6. In the process of preparing a hydroxy-substituted phosphorodithioic acid triester by reacting at a temperature below the decomposition temperature the ammonium salt of a phosphorodithioic acid having the structural formula (RO) PSSH-NH wherein R is alkyl, with an aliphatic epoxide whereby NH is formed as a by-product, the improvement comprising conducting the reaction in the presence of an acidic compound selected from the group consisting of carbon dioxide, sulfur dioxide and reaction mixture in an amount sufficient to remove the NH remaining in the reaction mixture.

References Cited UNlTED STATES PATENTS 3,284,548 11/1966 Wierber 260953 CHARLES B. PARKER, Primary Examiner.

boric acid, said acidic compound being present in the 10 A- H- SUITO, Assistant Examiner.

Claims (1)

1. IN THE PROCESS OF PREPARING A HYDROXY-SUBSTITUTED PHOSPHORODITHIOIC ACID TRIESTER BY REACTING AT A TEMPERATURE BELOW THE DECOMPOSITION TEMPERATURE THE AMMONIUM SALT OF A PHOSPHORODITHIOIC ACID HAVING THE STRUCTURAL FORMULA (RO)2PSSH$NR''3 WHEREIN R IS A HYDROCARBON RADICAL AND R'' HYDROGEN OR HYDROCARBON, WITH AT LEAST ABOUT AN EQUIVALENT AMOUNT OF AN EPOXIDE, WHEREBY NR''3 IS FORMED AS A BY-PRODUCT; THE IMPROVEMENT COMPRISING CONDUCTING THE REACTION IN THE PRESENCE OF AN ACIDIC COMPOUND OF LESSER ACIDITY THAN THE PHOSPHORODITHIOIC ACID OF THE SAID SALT, SAID ACIDIC COMPOUND BEING PRESENT IN THE REACTION MIXTURE IN AN AMOUNT SUFFICIENT TO REMOVE THE NR3 REMAINING IN THE REACTION MIXTURE.