US2358305A - Lubricating composition - Google Patents

Description

Patented Sept. 19, 1944 LUBRICATING COMPOSITION Elmer W. Cook, New York, N, Y., and William D. Thomas, Jr., Stamford, Conn., asslgnors to American Cyanamid Company, New York, N. Y., a corporation Maine No Drawing. Application July 30, 1942,

Serial No. 452,888

10 Claims.

This invention relates to the stabilization of lubricating oils of the type known as crankcase oils: i. e. hydrocarbon oils of relatively low viscosity and pour-point such as are used in the crankcases of internal combustion engines. More particularly, the invention relates to those classes of crankcase oils for truck, bus, aeroplane, tractor and marine gasoline and Diesel engines that are known as heavy-duty" oils and which contain added chemicals that increase their eilective service life under severe operating conditions. A principal object of the invention resides in the provision of a crankcase lubricant of this type containing a new class of chemical compounds having both detergent and anti-oxidant properties, whereby the formation of hard sludge deposits is inhibited. A further object resides in the provision of a class of chemical compounds having adequate solubility in crankcase oils for use as detergents and antioxidants therein under all conditions arising from heavy duty service. A still further object resides in the provision oi a class of inhibitors for crankcase oils which are easily prepared from relatively cheap raw materials.

We have now discovered a new class of complex or mixed esters of dithiophosphoric acid which possess oil-solubility equal to or greater than the solubilities of the esters of dithiophosphoric acid with alcohols only, but which contain an organic carboxylic acid chemically combined with the dithiophosphoric acid radical. We have also .found that these complex esters will form oil-soluble salts with heavy metals, and that these heavy metal salts possess excellent detergent properties for the prevention of sludge deposits in the engine when added to crankcase oils in concentrations of 0.1- or more. i

The complex dithiophosphoric acid esters used in practising the invention are preferably prepared by heating together a mixture of one or more alcohols or phenols, one or more monocarboxylic acids, and P285, the heating being continued at suitable reaction temperatures of about 90120 C. and preferably with agitation until the evolution of H28 has ceased. In general, at least 2 moles of a monohydric alcohol or phenol should be present in the mixture for each mole of P285 while the remaining 2 molecular equivalents may be made up wholly of monocarboxylic acids or partially of monocarboxylic acid and partially of alcohol or phenol. When the H28 evolution is complete it will be found that the monocarboxylic acid is chemically combined in the dithiophosphoric acid ester, and that a heat-stable complex 'of definite molecular constitution is formed. We believe that this complex is analogous in structure to the acid esters prepared by heating 4 moles of a monohydric alcohol with one mole of Pass. It forms salts with equimolecular quantities of sodium, potassium, and other alkali metals. It also forms salts with divalent heavy metals such as Ba, Ca and Sr which contain 2 molecular equivalentsof the ester for each mole of heavy metal.

Although we have not as yet definitely determined the chemical structure of the complex esters, we belive that the monocarboxylic acid replaces one of the alcohol groups of a dithiophosphoric acid di-ester, the replacement probably resulting in a mixed acid. anhydride-alcohol ester of dithiophosphorlc acid corresponding to the formula wherein R is the residue of a monocarboxylic acid and R1 is the residue of an alcohol or phenol. This formula, which represents a replacement of one of the alcohol groups of a di-ester of dithiophosphoric acid by a carboxylic acid group, is

consistent with the formation of heavy metal salts as well-as with the behavior of these salts in crankcase oils.

7 Although the complex dithiophosphoric acid esters may be added to lubricating oils as such or, for some purposes in the form of a neutral ester wherein the hydrogen of the SH group has been replaced by an alkyl radical, we prefer to employ these compounds in the form of their heavy metal salts. The preferred heavy metals are those of the alkaline earth metal group; that is, calcium, barium and strontium, but the zinc salts are frequently of value and the Mg, Al, Cr, Ni and Sn salts may also be used. The salts of these and similar polyvalent metals have the following probable structural formula wherein R is the residue of a monocarboxylic acid, Rl is an ester-forming radical such as an alkyl or phenyl radical, M is a polyvalent metal and :1: is the valence of M. These salts are preferably prepared by agitating a reactive oxide of the metal with a solution of the complex ester in a mixture of'alcohol and toluol.

One oi the principal advantages of the compounds of the present invention resides in the improved oil solubility that is obtained by the incorporation of an oil-soluble monocarboxylic acid into a dithiophosphoric acid ester molecule. Many dithiophosphoric acid di-esters, when used in the form of their heavy metal salts, lack suificient solubility in hydrocarbon oil of the type used as crankcase oils to be manufactured and sold in the form 01' concentrates of 25-50% strength, and the. incorporation of oil-soluble or oil-solubilizing monocarboxylic acid radicals such as higher fatty acid radicals into such compounds presents a ready means or improving their onsolubility to the desired extent. This is particularly true of the dithiophosphoric acid esters of alcohols of relatively low molecular weight such as propyl, butyl, amyl and hexyl alcohols; the calcium, barium and zinc salts of the dithiophosphoric acid di-esters of these alcohols possess excellent antioxidant properties for crankcase oils but the low molecular weight of the alkyl groups renders them rather dimcultly soluble in motor oils. By the replacement of a part of the alkyl radicals of these esters with hydroaromatic or higher fatty acid groups in accordance with the present invention the solubilities of these salts in lubricating oils is greatly improved without substantially increasing the cost thereof.

From the foregoing it is evident that any suitable esterifyina agents may be used in preparing complex dithiophosphoric acid esters for use in practising the present invention. Lower aliphatic alcohols which may be used either singly or in admixture are methyl, ethyl and the various isomeric butyl and amyl alcohols, and particularly the cheap mixtures of amyl alcohols sold commercially as fused oil and those obtained from low-boiling petroleum fractions and sold as "Pentaso Higher aliphatic alcohols such as hexyl, heptyl, octyl, nonyl, decyl, lauryl. myr styl, stearyl, oleyl and octadecyl alcohols and the like also may be used, either singly or in admixture.

Certain fractions containing substantial quan-- titles of alcohol mixtures can also be used in preparing the compounds of the present invention such as, for example, the mixtures of branchedchain alcohols obtained as by-products in the commercial hydrogenation of oxides of carbon in the presence of promoted copper chromite catalysts. Among the most important sources of alcohol mixtures of this type are the so-called "H. T. P." alcohols sold by E. I. du Pont de Nemours 8; Company described in detail in our copending application Serial No. 421,650, filed December 4, 1941. One of the most important fractions from this source is the so-called "3-24" alcohol fraction, which has the following composition:

Boiling range --Approximately 160-200 C. Specific gravity at 15.6'/l5.6 C.. 0.8610-0.8660 Weight per U. S. gallon at 68 F lbs- 7.17 Saybolt viscosity at 100' l." seconds About 32 Solubility in water Less than 1.0% Solubility in HaS04- Not less than 85% in 85% H2504 Approximate composition:

present.

Another class of mixed higher branched-chain alcohols that we have found suitable for use in the preparation of complex dithiophosphate heavy metal salt additives for crankcase lubricants are those obtained by the'reduction of the corresponding higher aliphatic ketones with hydrogen. Thus, rearrangement of alpha, betaunsaturated ketones produced by the condensation of ketones of lower molecular weight may be employed. Typical alcohols that can be produced cheaply by the method are 4-methyl hexanol-2, 5-methyl hexanol-3, 4- methyl heptanol-2 and 5- methyl heptanol-a. We have found, however. that the higher aliphatic ketones of the type foundin the duPont alcohols are frequently advantageous in lubricating oils, for they appear to act as additional solubilizing agents for the complex dithiophosphate heavy metal salts prepared from the c0rresponding alcohols and prevent the deposition of sludges at low temperatures, and the hydrogenation of the ketones present in these alcohol mixtures is not recommended.

In addition to the aliphatic alcohols and alco. hol mixtures, the aromatic alcohols such as benzyl alcohol and particularly the phenols form another important class of ester-forming compouhds for' use in preparing'the additives of the present invention. Phenols such as phenol itself, cresol, xylol and xylenol may be used but better results are usually obtained when higher alkyl phenols having larger oil-solubilizing aliphatic groups are employed. Typical phenols of this.

class are p-tertiary amyl phenol, tertiary butyl phenols and particularly the di-alkyl phenols such as 2,4-dipr0pyl, dibutyl or diamyl phenols. Complex esters of dithiophosphoric acid with phenols of these classes are both oil-soluble and heat-stable, and when used in the form of their heavy metal salts they possess excellent detergent properties for crankcase oils.

A wide variety of organic monocarboxylic acids is available" for use in admixture with the alcohols and phenols defined above in preparing the complex dithiophosphoric acid esters of the invention. Although any cyclic or acyclic monocarboxylic acids may be used, we prefer to employ only those acids of these classes which contain one or more oil-solubilizing groups; 1. e., carboxylic acids containing aliphatic or cycloaliphatic radicals. For this reason we prefer to avoid aromatic monocarboxylic acid of low molecular weight, although acids of this class such as benzoic acid may be employed in conjunction with higher aliphatic alcohols such as lauryl and particularly octadecyl alcohols. On the other hand, we have found that monocarboxylic acids of the hydroaromatic series such as dihydroabietic and particularly naphthenic acids will materially improve the oil solubility of complex dithiophosphoric acid esters and their heavy metal salts when chemically combined therein, and complex esters containing these acids are specifically included within the scope of the present invention when added to lubricating oils.

The most important class of organic monocarboxylic acids for use in the preparation of oilsoluble complex dithiophosphoric acid esters are the higher aliphatic monocarboxylic acids. by which term we include all those carboxylic acids of the aliphatic series which contain at least 6 carbon atoms. Representative acids of this clas which may be employed are caproic and other isomeric fatty acids of six carbon atoms, capryllc,

pelargonic, lauric, myristic, palmitic and stearic acids. Fatty acid mixtures obtained from animal and vegetable oils and fats, such a coconut oil and palm oil may also beused. Mixtures containing substantial quantities of unsaturated higher fatty acids, such as cottonseed oil fatty 1 0.1-5% by weight.

As has been stated, the complex dlthiophos phoric acid esters containing monocarboxylic acids chemically combined therein are preferably employed in crankcase oils in the form of their heavy metal salts in concentrations of about However, solutions of these salts in mineral oils are most conveniently manufactured and sold in the form of concentrates containing from 25-50% of additive, and for this reason it should be understood that the invention in its broader aspects is not limited to the preferred range of concentrations in which these compounds are used in the crankcase oil under service conditions. Moreover, th compounds defined above are frequently advantageously employed in admixture with other additives which may cooperate therewith to give improved heat- .stability, detergency or sludge dispersing proper- I Y@ S. QY Alk Alk wherein Alk represents an alkyl chain, preferably of 3, 4, or more carbon atoms, Y is hydrogen or an alkyl radical, M is a divalent heavy metal such as Ba, Ca or Zn and a: is a small whole number which is preferably one or two. These compounds are preferably added to the crankcase oil in amounts of 0.5-1.5 parts by weight for each part of the complex dithiophosphoric acid parts by weight of amyl. alcohol, 50 parts of 13-24 alcohol, 21 parts of lauryl alcohol and 40 parts of lauric acid were mixed together and 72 parts of PzSs were added. The mixture was heated with agitation at 95-105" C. for about 2.5 hours, or until the evolution of His was substantially complete. Th product was decanted from the small remaining amount of Pass and was obtained as a reddish-yellow liquid.

215 parts by weight of the complex dithiophosphoric acid ester obtained by thi procedure was dissolved in a mixture of 56.5 parts of ethyl alcohol and 125 parts of "Solvesso No. 1 (an aromatic petroleum solvent consisting mainly of toluol) and 445 parts of finelyc-ground barium oxide was added to this solution while stirring vigorously and maintaining the temperature at about aoj-ss 0. After filtering the resulting so- I lution from insoluble matter the alcohol was removed by vacuum distillation, the residue was dissolved in 10-W grade motor oil and the remaining volatile solvent was removed by a second vacuum distillation. The product was obtained as a clear, 50% solution of the bariumsalt of the complex dithiophosphoric acid ester in lubricating oil.

Example 2 as parts by weight of fusel Oil, 28 parts of lauryl alcohol, parts of palmitic acid and 56 parts of P285 were reacted by heating together with vig- 'orous agitation at 95-105 C. for about 2 hours, or until the evolution of HzSwas complete.

518 parts by weight of the complex acid ester was dissolved in a mixture of equal parts of ethanol and toluol, filtered, and 83.25 parts by weight of 92% barium oxide was added. After agitation to complete the salt formation at 30-35 C. the. insolubles were filtered off, and the solution was evaporated under a, vacuum and dissolved in a lubricating oil of 10-W grade. The last traces of the toluol were then stripped oil by vacuum evaporation. A 50% solution of the product in lubricating oil was clear at ordinary atmospheric temperatures.

Example 3 in an alcohol-toluene mixture, and the barium salt formed by neutralization with 92% barium oxide on the basis of 448 parts of the complex dithiophosphoric acid ester for each 8325 parts of: The solvent was driven off added barium oxide. and the salt dissolved in lubricating oil of 10-W and 30 grade to form clear 50% the preceding examples.

Example 4 A mixture of 50 parts by weight of amyl alcohol, 50 parts B-24 alcohol and 50 parts of lauric acid were reacted with 76 parts of P2S5 as in the preceding example. The equivalent combining weight of the product was determined by its neutralization number as being 340 and therefore the complex dithiophosphoric acid ester was neutralized by adding 83.25 parts by weight of 92% barium oxide for each 340 parts of the acid ester as described above. The product was dissolved in 10-W grade lubricating oil to form a clear 50% solution.

Ezcample 5 p 50 parts by weight of amyl alcohol, 50. parts of 3-24 alcohol, 21 parts of lauryl alcohol and 40 parts of hydrogenated rosin were mixed with 74 parts of P285 and the mixture was heated at -115 C. for about two hours. .After dissolving the product in ethanol and toluene, filtering, and neutralizing by the addition of the theoretical amount of ZnO which was 41 parts by weight of zinc oxide for each 189 parts of the complex ester, The insolubles. were filtered oil and the solution evaporated under a vacuum and dissolved in lubricating oil to a 40% solution. In the same manner the barium salt was also prepared.

Example 6 Complex esters wereprepared containing dichlorostearic acid, p-hydroxyphe'nyl stearic acid,

naphthenic acid and other fatty acids in the solutions as in v manner described in the preceding examples and converted to their heavy metal salts in the usual manner. The reagents employed and the combining weights of the complex dithiophosphoric acid esters formed are shown in the following table wherein the quantities given are in parts by weight p-Terti a ry Erh' i gA-diamyl pheno Naphthenic Myristic Palmitic 9,l-dichloro-stcaric p-IIydroxy-phcnylstearic...

Phenol ms, Neutralization N0 534 Example 7 Representative samples of the products prepared as described in the preceding examples were tested for efilciency by the Underwood oxidation test. This test consists in heating 1500 cc. of the oil under test to 325 F. and continuously spraying a portion of the heated oil against a 2" x 10''- freshly sanded copper strip and two freshly sanded hearings to be tested for corrosion for five hours while permitting free circulation of air through the apparatus. Samples of the oxidized oil were then examined for specific gravity, neutralization number, and naphtha insoluble and the bearings under test were weighed to determine loss by corrosion. The results were as follows:

The oil used in all the above tests was a Mid- Continent-base solvent-refined S. A. E. IO-grade motor oil to which 0.01% FeaOa was added in the form of iron naphthenate. A slightly different oil of the same base was used in testing the product of Example 6-No.' 3. In all cases 0.5% of the barium salt of the complex dithiophosphoric acid ester was used in the oil tested.

Iron naphthenate is known to be a powerful promoter of oxidationand decomposition in luposition caused by iron salts of naphthenic acids "In order to reproduce the conditions existing in ples.

is another important advantage of the present invention. Example 8 Another widely used test for accelerated oxidation in crankcase oils is known as the Catalytic Indiana test. The apparatus consists of a constant temperature bath maintained at 341 F. in which a number of large glass test tubes are immersed. 300 cc. samples of the oil under test are poured into these tubes and air at the rate of 10 liters per hour is bubbled through the oil.

the crankcase of an engine weighed strips of copper-lead alloy are suspended in the oil sam- As metallic surfaces, particularly copper, greatly accelerate th rate of oxidation and decomposit on of the oil in the presence of oxygen this is an important factor in the test. Bearing corrosion rates can also be determined by again weighing the strips after '70 hours immersion, which is the usual test period.

The bar'um salts of representative samples of the complex dithiophosphoric acid esters prepared as described in preceding examples were also evaluated by this test. A Mid-Continent solvent-refined S. A. E. 10-grade oil was used. In all cases except the control the oil contained 1% by we ght of the additive. The results are shown After complet'on of the tests the oil was removed and the amount and character of any sludge adhering to the walls of the tubes was noted. In all cases where additive was present in the oil there was only a slight amount of sludge, and these deposits were soft and easily removed by brushing.

Polyvalent metal salts of complex dithiophosphoric acid esters and their methods of preparation are not claimed as such since they constitute the subject matter of our copending application Serial No. 489,820 which was filed-lune 5, 1943, as a continuation in partof the present application.

What we claim is:

1. A lubricating composition comprising a hydrocarbon lubricating oil having dispersed there-.

. in a heavy metal salt of a complex dlthiophos;

phoric acid ester in which a monocanboxylic acid r s chemically combined with the dithiophosphoric acid radical.

2. A lubricating composition comprising a hydrocarbon lubricating oil having dispersed therein a heavy metal salt of a complex dithiophosphoric acid ester in which is chemically-combired with the dlthiophosphoric acid radical a monocarboxylic acid containing an oil-solubilizing radical selected from the group consisting of aliphatic and hydroaromatic radicals containing at least six carbon atoms.

3. A lubricating composition comprising a hydrocarbon lubricating oil having dispersed therein a heavy metal salt of a complex dithiophosphoric acid ester in which an aliphatic monocarboxylic acid is chemically combined with the dithiophosphoric acid radical.

4. A lubricating composition comprising a hydrocarbon lubricating oil having dispersed therein a heavy metal salt of a complex dithiophosphoric acid ester in which is chemically combined with the dithiophosphoric acid radical an aliphatic monocarboxylic acid containing at least six carbon atoms. v

5. A lubricating composition comprising a hydrocarbon lubricating oil having dispersed there'- in a heavy metal salt of a complex dithiophosphoric acid ester in which a naphthenic acid is chemically combined with the dithiophosphoric acid radical.

6. A lubricating composition comprising a hydrocarbon lubricating oil having dispersed therein a heavy metal salt of a complex dithiophosphoric acid ester'in which dihydroabietic acid is chemically combined with the dithiophosphoric acid radical. 1 I

7. A lubricating oil composition comprising a hydrocarbon lubricating oil having dispersed therein a heavy metal salt of a mixed ester of dithiophcsphoric acid wherein both a member of the group consisting of monohydric alcohols and monohydric phenols and a monocarboxylic acid are chemically combined with the dithiophosphoric acid radical.

8. A lubricating composition comprising a hydrocanbon lubricating oil having dispersed therein a heavy metal salt of a mixed ester of dithiothe group consisting of monohydric alcohols and monohydric phenols and an aliphatic monocarboxylic acid containing at least six carbon atoms are chemically combinedv with the dithiophosphoric acid radical.

10. A lubricating composition comprising a hydrocarbon lubricating oil having dispersed therein a polyvalent metal salt of a mixed ester of dithiophosphoric acid wherein both a member '25 of the gorup consisting of monohydric alcohols ELMER W. COOK. WILLIAM D. THOMAS, J R.