US3045037A - Process for making phosphorus ester lube oil additive - Google Patents

Description

United States Patent fifice 3,045,037 Patented Jlily 1:7, 19.62

' 3,045,037 PROCESS FOR MAKING PHOSPHORUS ESTER LUBE OIL ADDITIVE Luigi Benedetti, Corso Sempione 33, Milan, Italy No Drawing. Filed Oct. 28, 1960, Ser. No. 65,598 Claims priority, application Italy Nov. 7, 1959 1 Claim. (Cl. 260-461) and the formation of coatings and deposits on the engine parts. Among the more important lubricant additives may be noted anti-oxidation, anti-corrosion, anti-rust, anti-foam additives, thickening agents, additives to'improve the viscosity index, lubricity agents and detergents. Each type of additive gives rise to its own particular effect and so it is obvious that lubricating oils require the addition of suitable mixtures of such additives according to the characteristic features such oils must have.

The present invention relates more particularly to those additives that exercise an anti-oxidation, anti-corrosive and detergent action. The addition of anti-oxidation agents to the lubricants serves to prevent the formation during use, of oxidation products which are of an acid nature and therefore corrosive, and of resinous compounds more or less polymerised, and more or less soluble in oil, which give rise to oil-dregs or coatings adhering to the metal surfaces. The anti-oxidants of this type in use are generally various types of organic sulphur compounds, complex amines and other complex alkyl-aryl derivatives containing-two or three of the following elements: Cl, P, S, N, etc. These anti-oxidants for lubricants "are effective under heat.

The anti-corrosives serve in a special manner to reduce corrosion of the points due to acid products of the oxidation of the engine lubricants. They are therefore fellowworkerswith the anti-oxidation agents and it is reckoned that their effect becomes apparent through the action of the corrosive products with which they co-operate in the formation of a protective layer on the metal surfaces of the moving working parts. The recognised anti-corrosives are composed chiefly of organic thioderivatives of phosphorus, arsenic, antimony, bismuth, and certain sulphur olefines, etc. i

Detergents are employed in the preparation of modern lubricants for engines. They serve to avoid, in high temperature engines especially, the formation of gums which render liners sticky and glued, the'deposits of oil-dregs which end up by closing filters and oil piping, the formation of scaling which impairs the cooling of the pistons. Recognised detergents in general are composed of organic thiophosphates of Ba and Ca, of sulphur olefines and the corresponding alkaline earth soaps, of metal alkylthiophenolates, etc.

From all the above it is evident that in the three kinds of additive mentioned, the organic derivatives of thiophosphoric acid or organic thiophosphates are frequently used. One aim of the present invention is to produce an additive for lubricating'oils of the type of the organic derivatives of a thiophosphoric acid, possessing at the same time anti-oxidation and anti-corrosive characteristics, and, in addition, exercising a detergent action and giving to the lubricating oil a characteristic of preventing wear; these qualities making it particularly suitable to the modern engines with an Otto cycle (4-stroke engine working cycle) with a high compression ratio.

Another aim of the present invention is to produce an additive of such a nature that it can be mixed with the" normal dispersing elements for lubricating oils such as oil-soluble polyvalent metal salts of petroleum sulphuric acids or of sulphur alkyl phenols, in order to preparev lubricants suitable for the most diverserequirements, and which will bes'table, easily kept in good condition, and which, when dissolved in mineral lubricating oil will not show a tendency to develop sulphuretted hydrogen in normal working conditions of the present day internal combustion engines.

A still further object of the present invention is to make practicable a process of manufacturing such an additive for lubricating oils.

In more particular detail, the additive for lubricatingoils, according to the invention belonging to the group of thioderiv-atives of phosphorus, is characterised by the fact that it is a mixedneutral ester of dithiophosphoric acid and by the fact that the three groups which esterify the dithiophosphoric 'acid' are dilferent from 'each other and belong to diverse chemical groups, the first being an aliphatic radical, the second being an aromatic radical and the thirdbeing an alicyclic radical, these radicals being all linked directly to the phosphorus atom by means of atoms of O and S.

The process for the production of the mixed neutral esters of dithiophosphoric acid according to the invention is characterised by the fact that it consists in preparing, in the first stage, an alkyl alkyl-aryl dithiophosphoric acid, and, in the second stage, in reacting by means of heat the alkyl alkyl-aryl dithiophosphoric acid thus obtained with an unsaturated monocyclic or bicyclic terpene. According to a characteristic of the invention, the alkyl alkyl-aryl dithiophosphoric acid is prepared by heating two molecules of an aliphatic alcohol and two molecules of an alkylphenol with pentasulphide of ence of a suitable solvent.

According to another characteristic of the invention the dithiophosphoric alkyl alkyl-aryl acid is prepared by heating four molecules of an aliphatic alcohol with pentasulphide of phosphorus until the corresponding dithiophosphoric dialkyl acid is formed; subsequently its transesterification is carried out by adding two molecules of alkylphenol, heating and driving off by distillation the alcohol corresponding to the substituted'radical.

From all the above it is evident that the mixed neutral ester of dithiophosphoric acid according to the invention, derives from the dithiophosphoric acid which has the following structural formula:

HO HO P=S HS in which the hydrogen atoms are replaced by three different radicals indicated respectively by R, R" and R'" I R'o R"0P=s V RI/IS where R=primary secondary or tertiary alkyl radical, preferably with 2-12 atoms of carbon, R=the alkyl-aryl radical, in which the aryl radical is preferably a benzene one and'the alkyl radicals are formed by one or more chains of primary, secondary or carbon. I R"=the cycloaliphatic radical of terpene'typel A tertiary hydrocarbons, preferably with 2-12 atoms of phosphorus in the pres As is apparent, the three radicals are not only different from each other but they belong to different classes of compounds and, to speak exactly, there are present contemporaneously aliphatic, alicyclic and aromatic radicals, all linked directly to the atom of P by atoms of O and S. In this way, the characteristics of the aliphatic, alicyclic and aromatic derivatives containing P and S are summed up in a single individual chemical unit.

The alkyl alkyl-aryl dithiophosphoric acids preferred are those in which both the esterifying alkyl radical and the one linked to the aromatic nucleus contain 2-l2 atoms of carbon. The alkyl alkyl-aryl alcohols employed in the preparation are, in general, ethyl, n-propyl, isopropyl alcohols, all the butyl, amyl, hexyl and heptyl alcohols, various alcohols with 8-12 atoms of carbon obtained by reduction of the corresponding fat acids, and primary ramified hydroxy-alcohols derived from propylene and butylene dimers.

The alkylphenols are, on the other hand, characterised by an aryl group corresponding to a benzene nucleus, while the alkyl groups, which may be present to the number of one or more, are formed by chains of hydrocarbons with preferably 2-12 atoms of carbon. The most representative alkylphenols are the various isomeric isopropyland p-tert-butyl-phenols the octyl, nonyl and dodecyl phenols, and the corresponding higher homologues, that is, those products obtained in most cases of alkylation with olefines of the corresponding hydrocarbons.

Among the unsaturated terpenes, the bicyclic derivatives, in particular, are to be preferred, as they ofier a better capacity to react with the dithiophosphoric acid esters. Among these derivatives, the most important are, with the exception of monocyclodipentene, the various isomeric pinenes, the carenes, and the mixtures of natural origin which contain them in various degrees, such as the essences of turpentine from various sources (French, Greek, Portuguese, Spanish, German, American).

Those compounds are preferred especially in which the alcohol used is a secondary lower alcohol, the alkylphenol has a lateral chain not very long and variously ramified, and the terpene is a pinene contained in turpentine essence. When these requirements are met, a product soluble in oil is obtained, which otfers, in comparison with other compounds of the series, a greater anti-corrosive activity and anti-oxidation property, due to the higher content of phosphorus and sulphur.

The preparation which leads to the formation of the final neutral ester is of the type of reactions of addition and is conducted first of all by preparing the alkyl alkylaryl dithiophosphoric acid, and next in order, by bringing such acid into contact with a monoor bicyclic unsaturated terpene and heating.

As regards the preparation of the alkyl alkyl-aryl dithiophosphoric acid, it can be accomplished, as already said, in the following manner:

(1) The alkyl alkyl-aryl dithiophosphoric acid can be prepared by heating two molecules of one alcohol and two molecules of an alkylphenol with pentasulphide of phosphorus, preferably in the presence of a suitable solvent.

(2) The alkyl alkyl-aryl dithiophosphoric acid can be prepared by heating four molecules of an alcohol with pentasulphide of phosphorus up to the formation of the corresponding dialkyl dithiophosphoric acid; the subsequent transesterification is carried out by adding two molecules of an alkylphenol, heating and eliminating by distillation the alcohol corresponding to the substituted radical.

If the first process is used, during the heating of the alcohol, the pentasulphide of phosphorus and of the alkylphenol, the alcohol, which, especially if a primary one, has a very great reaction afiinity with the pentasulphide of phosphorus, is the first to react by forming a certain amount of the corresponding dialkyl dithiophosphoric acid. This subsequently reacts by transesterification with the alkylphenol giving rise to alkyl alkyl-aryl dithiophosphoric acid; a molecule of alcohol is freed which in its turn combines further with the pentasulphide of phosphorus, thus renewing the cycle. For this reason, since dialkyl dithiophosphoric acids are notably unstable at high temperatures, and on the other hand it has been observed that the instability is lower in the case of alkyl alkyl-aryl dithiophosphoric acids, the reaction is at first carried out at a temperature not too high and later the temperature is raised to reach the boiling temperature of the solution (112-115 C.) (or close to it, according to the concentration) and kept at this value until the P 5 is completely dissolved. Both stages of the reaction are conducted in an atmosphere of nitrogen. The final solution is filtered and, by working at a maximum temperature of C. and under a vacuum lower than 20 mm., the solvent is almost entirely eliminated. If this method is followed, products with uniform characteristics and an adequate degree of purity can be obtained with good yields.

Should the reaction be carried out from the beginning at a temperature of 1l2115 C., the characteristics of the product, particularly in respect of purity, tend to worsen or deteriorate.

If the second process is employed, the first phase of the reaction is represented by the formation of dialkyl dithiophosphoric acid by a stoichiometric reaction of an alcohol with P 8 The reaction is carried out according to the usual procedure characteristic of this kind of preparation. The reaction temperature, according to the type of alcohol, varies between 70 and 95 C. Into the same reaction vessel, Without any particular precautionary measures and immediately after the P 5 has been completely dissolved, the calculated amount of alkylphenol is added. Thereafter the temperature is raised to C. and the alcohol formed in the transesterification is distilled until the required stoichiometric amount is obtained. During this operation, as the reacting mass becomes more and more viscous, it is difficult to obtain an effective stirring of the mixture and phenomena of local overheating occur.

All these operations are carried out in a nitrogen atmosphere. The products thus obtained, although they possess, with satisfactory uniformity, the chemical and physical characteristics of the products obtained by the first process, are characterised by a lesser degree of purity and by a notably higher tendency to deterioration. The yields are slightly lower than those obtained by the first process.

It is therefore preferable, in most cases, to use the first process which, permits, above all, working at lower temperatures and therefore reduces to a minimum the decomposition and oxidation phenomena characteristic of the dithiophosphoric esters.

Once the alkyl alkyl-aryl dithiophosphoric acid has been prepared according to one of the two processes, the reaction of addition between this acid and an unsaturated terpene is then always carried out with an excess of terpene, which, as required, varies from 5 to 40%. This reaction is slightly exothermic, and it is convenient to add the terpene or the acid (according to which is considered more convenient) in successive small lots, taking care that the temperature does not exceed 35-40 C. Heating at 110-120 C. is then prolonged for 1-5 hours, according to the reacting substances; practically neutral products are thus obtained which, after further washing with a solution of 5% Na CO and with H 0, and evaporation of the excess terpene at 100 C. under a vacuum of 2050 mm., are ready for practical use.

The anti-oxidation, anti-corrosive and detergent properties of the products of the present invention were tested on a W1 Petter Laboratory engine. The results obtained consistently showed the high anti-corrosive and anti- Hereunder are given some examples of the preparation of the mixed neutral esters of dithiophosphoric acid according to the invention.

Example 1 (a) 2-ethylhexyl-octylphenyl-dithiophosphoric acid is prepared by dissolving in the cold 250 g. of octylphenol and 158 g. of 2-ethylhexyl alcohol in 900 ml. of toluene; to the solution thus obtained is added, as rapidly as possible, 135 g. of pentasulphide of phosphorus, the temperature being kept at or below 40 C. Nitrogen is then introduced on to the surface in order to exclude any contact with air. The mixture is heated with stirring at 95 C. for one hour, the temperature is increased to 115 C. and the heating is prolonged until complete homogeneity of the mass is obtained. It is cooled at approximately 30 C. and is filtered. The filtrate is evaporated under a vacuum of 100-150 mm. at a heating temperature gradually increasing from 60 to 100 C. .until the solvent is completely eliminated. 345 g. of product is obtained, which after titration with a solution of 0.1 N alcoholic potash in the presence of phenolphthalein, or else with an excess of 0.1 iodine, shows an average equivalent weight of 454. The yield therefore is 335.5 g. of 100% product.

(b) To the charge obtained by the previous preparation are added 144 g. of Portuguese turpentine essence, care being taken that the temperature does not go beyond 40 C It is heated and stirred at 150 for 2 hours. It is allowed to cool at 100 C. and the excess of turpentine essence is evaporated at 100 and under a vacuum of 20 mm. 426 g. of Z-ethylhexyl-ethylphenyl-bornyl-dithiophosphate is obtained which can be used as an additive.

On analysis, a sample contained 5.44% P, 9.97% S.

Example 2 (a) Iso-propyl-octylphenyl-dithiophosphoric acid is prepared by dissolving in the cold 600 g. of octylphenyl and 176 g. of isopropyl alcohol in 70 ml. of toluene. 324 g. of pentasulphide is rapidly added, the temperature being kept at or below 40 C. Nitrogen is introduced superficially and the mixture is heated while being agitated for 1 hour at 80 C., and afterwards at 115 C. until complete homogeneity of the load is obtained. It is cooled at approximately 30 C., filtered and the solvent is evaporated from the filtrate at first under a vacuum of 100-200 mm. with a temperature rising from 60 to 100 C., finally at 100 C. and 20 mm. up to the complete elimination of the solvent. 1109 g. are obtained of a product which, on

analysis, gives an average equivalent weight of 385. The I yield is 1026 g. of 100% iso-propyl-octyl-phenyl-dithio-V phosphoric acid.

(b) To the load obtained by the previous reaction are added 450 g. of essence of Greek turpentine, carebeing taken not to go beyond C.; thereafter it is heated for 3 hours at 150" c., and allowed to cool at 100 1276 g. of product are obtained which can be used directly as an additive. The

and under a vacuum of 20 mm.

analysis of a sample gave the following results: 6.61% P and 11.6% S.

- Example 3 n-Butyl-nonylphenyl-dithiophosphoric acid is prepared by dissolving in the cold 446 g. of nonylphenol and 150 g. of n-butanol in 1000 ml. of toluene, adding rapidly 25 g. of pentasulphide of phosphorus and heating the mixture at 110-115 C. up to complete homogeneity. It is allowed to cool, is filtered and from the filtrate the solvent is removed completely by evaporating at first under a vacuum of 150-180 mm. and re-heating gradually from 60 to 100 C., finally'under a vacuum of 20 mm. at

100 C. 738 g. of product are obtained with an average equivalent weight of 427. The yield is 671 g. of 100% n butyl-nonylphenol-dithiophosphoric acid. The product can be employed just as it is in condensations with terpenes.

Example 4 phenol are added to the product, without cooling. The

mixture thus obtained is stirred continuously and kept at 130 C. for half an hour.

' ing the temperature from 130 to 150 C., 250 ml. of methphoric acid suitable for use in the production of additives for lubricating oils belonging to mixed neutral esters of dithiophosphoric acid, comprisingthe steps ofheating four molecules of a saturated monohydric aliphatic alcohol with phosphorus pentasulfide to form the corresponding dialkyl-dithiophosphoric acid, and subsequently transesterifying by addition of two molecules of alkylphenol, heating and removal by distillation of the alcohol corresponding to the substituted radical.

References Cited in the file of this patent UNITED STATES PATENTS 2,506,310 Mikeska May 2, 1950 2,627,523 Hook et a1. Feb. 3, 1953 2,665,295 Augustine Jan. 5, 1954 2,689,258 McDermott Sept. 14, 1954 Thereafter, by gradually rais