US2691000A

US2691000A - Lubricating oils

Info

Publication number: US2691000A
Application number: US282472A
Authority: US
Inventors: Elliott John Scotchford
Original assignee: CC Wakefield and Co Ltd
Current assignee: CC Wakefield and Co Ltd
Priority date: 1951-04-23
Filing date: 1952-04-15
Publication date: 1954-10-05
Anticipated expiration: 1971-10-05
Also published as: FR1058007A; NL75960C; GB714497A; BE510842A; DE942586C

Description

, spent.

Faerie.

Patented Oct. 5, 1954 UNITED STATES PATENT OFFICE 2,691,000 LUBRICATING OILS 13 Claims.

This invention is for improvements in or relating to lubricants which are to be used under conditions which tend to disrupt the lubricant film, which disruption more particularly takes place when the pressure between the bearing surfaces is very great.

Where the lubricant is required to lubricate surfaces under the above conditions, the film rupture strength becomes more important than the coeflicient of friction. For example, under the extreme pressures obtaining in hypoid gears, if the oil film is ruptured, the metal surfaces will contact one with the other, thereby leading to loss of eificiency, excessive wear and ultimately to failure of the mechanism.

There have already been provided lubricants which have a high film-rupture strength. Such lubricants are generally known in the trade as extremepressure lubricants.

These extreme-pressure lubricants originally consisted of lubricating oil which contained sulphur, either in the form of flowers of sulphur or as a colloidal dispersion. The sulphur, however, was liable to precipitation and it was later proposed to prepare these extreme-pressure lubricants by treating a fatty oil, for example, an animal oil, with thionyl-chloride or with similar reagents, such as sulphur monochloride, sulphur dichloride, etc, and then to add the product of this reaction to a mineral oil.

- A theory as to the action of extreme pressure lubricants has been that the sulphur reacts with metallic surfaces and forms a very thin coating of iron sulphide and that this sulphide film is sufficient to prevent the metallic surfaces coming into contact with one another should the lubricant film be ruptured. If this theory is, in fact, correct, then it is obvious that the sulphur contained in the oil must be in such form as to be capable of reacting with the metallic surfaces which it is desired to lubricate. On the other hand, the sulphur compound must not be so reactive as to induce corrosion of the surfaces.

A large number of organic compounds have been proposed for use as extreme pressure agents, including various types of organic di and polysulphides, and the corresponding derivatives of selenium and tellurium. While the higher polysulphides are very effective in increasing the film rupture strength of the oil in which they are dissolved, they tend to be inherently unstable, corrosive, especially to copper and cuprous materials, and to exert a pro-oxidant effect upon the oil.

The disulphides, on the other hand, usually possess rather poor extreme pressure properties, insufficient to warrant their use except in conjunction with other extreme pressure additives such as organic halogen compounds. Thus, for example, it has been proposed to employa mixture of dibenzyl disulphide or of a dialkyl disulphide with a variety of organic chlorine compounds.

It is an object of the present invention to provide lubricating compositions having extreme pressure properties containing additives which do not substantially tend to increase the rate of oxidation of the oils in service.

It is a further specific object of the invention to provide additives capable of substantially increasing the film rupture strength of lubricating oils for turbines and/or hypoid gears without at same time increasing their tendency to oxidise or emulsify with water.

Thus at the present time many oils used for turbine lubrication consist of specially selected mineral oil blends stabilised against oxidation by the incorporation of antioxidant additives and containing also additives designed to protect fer rous metal parts against rusting or corrosion by, e. g., sea water. It is of course important that additional additives, incorporated in such oils for the purpose of enhancing their extreme pressure properties, should not interfere in any way with the normal functions of the two foregoing classes of additive. Many turbine oils, especially marine turbine oils used by the Admiralty, are controlled as regards oxidation stability, salt water corrosion of ferrous metals, demulsification value and corrosive action on cuprous metals, by a very rigid specification. It is necessary, therefore, that extreme pressure additives incorporated therein should not adversely affect compliance with its clauses.

Many of the more commonly employed extreme pressure additives are detrimental in one or more respects. Thus chlorine compounds generally tend to promote oxidation and are also prone to hydrolysis with the subsequent libersubstituted in the alpha position by dior polysulphide groups, and the corresponding derivatives of selenium or tellurium and may be represented by the general formula:

where the radical R is an alkyl, aryl or cycloalkyl 3 radical, X is sulphur, selenium or tellurium and n is 2, 3 or 4.

The radicals R may contain halogen substituents, although as already indicated the presence of halogen is to be avoided if the compounds are to be used in certain applications, particularly in the turbine oils.

It would appear that the presence of ester groups situated in the alpha position to the dior polysulphide groups exerts an activating influence with the consequent production of extreme pressure properties substantially in excess of those obtainable by the use of the simple aliphatic, aromatic or aryl substituted aliphatic dior polysulphides.

According to the present invention a lubricating composition comprises a mineral lubricating oil base and a minor proportion, sufficient substantially to increase the load-carrying capacity of the oil, of an ester of acetic acid substituted in the alpha position by sulphur, selenium or tellurium said ester having the general formula where R, is an alkyl, aryl or cycloalkyl radical which may contain halogen substituents, X is sulphur, selenium or tellurium and n is 2, 3 or 4.

The invention includes a turbine oil comprising a mineral lubricating oil base containing agents controlling oxidation stability and corrosion of ferrous metals and including also a minor proportion, sufiicient substantially to increase the load-carrying capacity of the oil, of an ester of acetic acid substituted in the alpha position by sulphur, selenium or tellurium said ester having the general formula where R is an alkyl, aryl or cycloalkyl radical, X is sulphur, selenium or tellurium and n is 2, 3 or 4.

Specific examples of compounds which may be employed as additives in accordance with the present invention are Diethyl dithiodiacetate C2H5OOC.CH2S

Di-n-butyl trithiodiacetate C4H0OOC.CH2S

Diphenyl dithiodiacetate OOC.CHz-S It has been found, surprisingly, that the presence of substituents such as alkyl groups or ester-substituted alkyl groups attached to the carbon atom adjacent to the radical X results in a considerable loss of load-carrying ability. Thus the presence of unsubstituted CH2 groups appears to be essential, in addition to the presence of ester groups in the alpha position in order to provide the outstanding extreme pressure properties to which reference has been made.

While it is believed that some, at least, of the additive compounds referred to above are new and have not been prepared heretofore, they may be prepared by methods known to the art. Thus, they may be prepared by the reaction of the corresponding oc-ChlOlO or abromo esters with sodium dior poly-sulphides in alcoholic solution, or by oxidation or the a-mercapto esters to give the corresponding disulphides, or by reaction of the amercapto esters with sulphur dichloride or sulphur mono-chloride in a non-ionising solvent to give the triand tetra-sulphides respectively.

Specific examples of additives employed in the present invention and methods of preparing them are as follows:

EXAMPLE I Preparation of dz'(n-butyl) dithiodiacetate An alcoholic solution of sodium disulphide was prepared by dissolving 26.4 grams of sodium sulphide crystals Na2S.9I-I2O and 3.52 grams of sulphur (0.11 mol in each case) in 150 mls. of alcohol at the boiling point.

The deep red solution so obtained was cooled to about 30 C. and 28 grams (0.1 mol.) of n-butyl monochloracetate was added dropwise with continuous stirring and cooling maintaining the temperature below about 60 C.

An almost instantaneous exothermic reaction took place and sodium chloride was precipitated.

At the conclusion of the reaction the mixture was diluted with water to about 500 ccs. total volume and the reaction product extracted with petroleum ether.

After washing the extract with water, it was dried over anhydrous sodium sulphate, filtered, and the solvent removed by distillation.

The product was a pale yellow liquid with a characteristic odour.

EXAMPLE 11 Preparation of dz'(n-butyl) trithiodiacetate This was prepared precisely as outlined in Example I, except that twice the amount of sulphur was used.

The product resembled the disulphide in appearance.

By adopting the procedure described in Examples I and II, it has been found possible to prepare substantially neutral chlorine-free products without difiiculty.

EXAMPLE I11 Preparation of dim-batyl) tetrathiodiacetate 37.05 grams of n-butyl thioglycollate (0.25 mol.) was dissolved in mls. benzene and cooled below 0 C. in a bath of 50% ice and 50% concentrated hydrochloric acid. 16.88 grams /8 mol.) of sulphur monochloride was dissolved in 50 mls. benzene and cooled in the same way.

The n-butyl thioglycollate solution was now added dropwise with stirring, keeping the temperature below 0 C. A brisk reaction took place with evolution of hydrogen chloride. After standing for two hours, the mixture was allowed to warm up to room temperature, the evolution of hydrogen chloride continuing for some hours. The solvent was removed at a temperature not exceeding 25 C.

The product was a yellow liquid.

By methods analogous to those described in Examples I and II, it has been found possible to prepare a variety of. compounds falling within the scope of the present invention, some examples of which are as follows:

Diethyldithiodiacetate, prepared by the method of Example I from ethyl monochloracetate.

(A mixture of the diand trisulphides in approximately 3:1 ratio containing 29.0% sulphur was actually made.)

Di (2-ethyl hexylltrithiodiacetate, prepared similarly from 2-ethyl hexyl. monochloracetate (as in Example II).

Dicyclohexyl dithiodiacetate, prepared similarlyfrom cyclohexyl monochloracetate.

Di tB-chloroethyl) dithiodiacetate prepared similarly from pl-chloroethyl chloracetate, which was prepared by reacting chloracetyl chloride with ethylene chlorhydrin.

Analysis showed that this product was a mixture of compounds formed by the replacement of some of the terminal chlorine atoms by disulphide groups.

Aryl esters such as diphenyl dithiodiacetate cannot readily be prepared by the foregoing methods as hydrolysis of the esters appears to take place. They may, however, be prepared via the Bunte salts by a. method similar to that described by Stoner and Dougherty in the Journal of the American Chemical Society, vol. 63, p. 987 (1941). Thus, for example, phenyl monochloracetate may be reacted in boiling 50 aqueous alcohol with sodium thiosulphate, and the product converted tov the disulphide by the addition of iodine.

Yields are usually rather poor and it is therefore generally preferred to employ the alkyl or cycloalkyl esters.

Selenium compounds such as di(nbuty1) diseleno-diacetate may be prepared by reacting the a-halo ester e. g. n-butyl, monochloracetate with sodium or potassium selenosulphate in aqueous alcoholic solution by the method employed by Stoner and Williams in the Journal of the American Chemical Society, vol. 70, page 1113 (1948).

The additives used will of necessity be soluble in the mineral oil base in the proportions in which they are to be employed. The preferred compounds are those which are miscible with oil in all proportions, although others of lower solubility may be satisfactorily used. The oil solubility will necessarily depend upon the nature of the groups R but in general complete miscibility with. oil. may be achieved by employing as radical R an aliphatic or cycloaliphatic radical having not less than four carbon atoms.

The. amounts of the additives employed. will depend upon the purpose for which the oil is to be. used. Any quantity from the minimum suflicient to impart a substantial increase in film rupture strength up to about per cent may be employed, but in general from about 0.5. per cent. to about 2.0 per cent is contemplated, especially for use in turbine oils.

The so-called inhibited turbine oils to which the compounds of this invention may be added normally contain antioxidant additives which may be of. the alkylated phenol type, e. g,.,, tertiary butyl cresol, 2.14 dimethyl-B-tertiary butyl phenol, 2:6 di-tertiary butyl-p-cresol, or sec.- ondary aromatic amines, e. g., diphenylamine,

6 phenyl a naphthylamine, phenyl-s-naphthylamine, and also anti-rusting additives which may be of various types, one preferred class of additives being the acid esters of the long-chain mono esters. of polyhydric alcohols described in patent application No. 191,166.

Some of the additives contemplated, notably the triand higher polysulphides, tend to be somewhat corrosive to copper and cuprous alloys at. elevated temperatures. In. such cases, it is desirable to incorporate also a copper stain inhibitor of the type disclosed in Patent No. 2,414,257, e. g., mercaptobenzothiazole, benzothiazoledisulphide, benzothiazole hydroxymethyl sulphide, or tetramethyl or tetraethyl thiuram disulphide.

The additives of the present invention may, if desired, be employed in conjunction with organic halogenated compounds in mineral lubricating oils to provide, for example, extreme pressure lubricants for hypoid gears. Oils containing such combinations of additives are capable of withstanding higher loads than oils which contain only the sulphur compound. As already stated, however, the presence of halogen compounds in turbine oils is undesirable.

To demonstrate the effectiveness of the compounds of the present invention as extreme pressure agents, tests were carried out on the wellknown Society of Automotive Engineers (S. A. E.) Testing Machine, a description of which may be found in the Co-ordinating Research Council (C. R. C.) Handbook (1946) on pages 458-462. This machine was operated at 500 R. P. M. using a standard loading rate of 75 to lbs/sec. and rubbing ratio of 14.6:1.

The additives were dissolved in a mineral oil blend (oil A) consisting of 70%. of a mineral .oil having a viscosity of about 170 seconds Redwood at 140 F. and 30% of a solvent refined mineral oil having a viscosity of about 65 seconds Redwood at 140 F.

The results obtained are. tabulatedv below, the. failure loads recorded being in general the mean of several tests.

Certain other closely related compounds were tested at the same time in order to demonstrate the superiority of the compounds of the present invention. In the majority of instances the percentages of additive used were adjusted to.- provide an. amount of added sulphur of between 0.23 and 0.28 per cent.

Percent Sulphur Percent provided Fallureload (lbs), by the additive Compound Dibenzyl disulphlde 26 Dibenzyl trisulphide E 25 125. (31.7% Diphenyl disulphide... Di(n-butyl) monothiodie etat c e. Di(n-butyl) diB-thiodipropionate.

l2. Di(n-butyl)dithiob.is

(ha-dimethyl) diacetats.

32 scattered results not exceeding 120.

I? This. compound hadv a rather limited oil-solubility.

It will be apparent from the foregoing tests that the compounds of the present invention (numbers 2 to 6) possess a marked advantage over:

(a) Conventional diand polysulphides (numbers 7 to 9);

(b) The corresponding monosulphides (number 10) (c) A closely related ester containing a disul- 8 of the oils to stain copper under the conditions of the standard copper strip corrosion test (I. P. 64/51, Procedure C, page 550, 1951 edition), i. e., immersion for 3 hours at 100 C., it has been found necessary in general to employ a copper stain inhibitor of the type already described, examples of satisfactory combinations of additives having been quoted in the foregoing table. In this connection it is generally phide group in the ,B-position to the ester group 10 preferred to use the diand. tri-sulphides since instead of the a-position (number 11), and the activity of the sulphur in the tetra-sulphides (d) A compound containing alkyl substituents is greater and more difficult to control. attached to the disulphide group (number 12). Comparative tests on certain of the oils were In order to obtain the best results, it would obtained by the use of a high speed disc testappear desirable to have the radicals R consist- 15 ing machine in which two discs of En. 36 caseing of relatively short alkyl chains, the introhardened steel of diameter 8 and 4", respecduction of large or cyclic groups tending to retively, were rotated in contact with one another duce load-carrying capacity. Thus it is preat speeds of 1800 and 7200 revolutions per minferred that the radicals R shall consist of alkyl ute, respectively, the sliding velocity being 3775 radicals having not more than six carbon atoms. feet per minute. The discs were immersed in To illustrate the effectiveness of the comthe oil under test, which was maintained at pounds of the present invention when employed 155-165 F., and the load on the discs was gradfor the purpose of imparting extreme pressure ually increased until scuffing took place. The properties to turbine oils, an inhibited turbine results were recorded as Sc loads at the incioil nf rm t B t sh Ad ty p fi adence of scuffing, the definition of the term Sc tion OM.88 was selected (oil B). This consisted being: of an oil similar to oil A. containing 0.5% of a p secondary aromatic amine type oxidation in- Poundshgdl i g ofhneoosf Contact hibitor and 0.07% of a ferrous metal corrosion eatlve curvature) inhibitor consisting of ethylene glycol mono- Six tests were carried out on each of the oils naphthenate acid phthalate. tabulated below, and the mean Sc loads quoted The following table illustrates the effect of for each oil. Oil C was a typical turbine oil of additives of the present invention on the propsimilar viscosity to oil B and containing antierties of oil B: oxidant and rust inhibitors.

Oxidation Test Acidity, Demulsi- Salt Water u Additives milligrams fication Add Demulsi- Corrosion KOH/gm. value after ficatiou R P M) dam will??? Seconds Seconds 1. None N 0.08 180 0.17 540 No rusting 150 2. Diethyl-dithio-diacetate (2%) 0.17 195 340 3. Di(n butyl)trithio diacetete (1.5%) 0.08 180 0.14 330 No rusting" 250 bcnzothiazole disulphide (0.1%).

4. Di(n-butyl)trithio-diacetate 1.0%) 0.20 130 0.17 480 do 21s mercaptobenzothiazole (0.05%). 5. Dicyclohexyl dithio-diacetate (1.5%) 0.08 135 6. Di(n-butyl)dlseleno-diacetatc (1.0%) 0.15 150 0.08 225 Very slight benzothiazolc disulphide (0.1%). rusting.

1 The somewhat high acidity in this instance was due to the presence of a trace of acid in the additive.

The methods employed for determining the various values quoted above were standard methods described in the Standard Methods for Testing Petroleum and its Products, and having the following references:

Acidity, I. P. 1/46, Method A (page 11951 edition).

Demulsification value, I. P. 19/51 (page 117- 1951 edition).

Oxidation test, I. P. 114/47 (page 363--1951 edition).

Salt water corrosion test, I. P. 125/51 (1951 edition, page 390) (modified in respect of salt water composition and duration, to comply with the requirements of British Admiralty Specification OM88).

It will be seen from the foregoing tests that the additives of the present invention not only greatly enhanced the load-carrying capacity of the turbine oil in which they were dissolved, but also left unaffected the essential properties of the oil, i. e., low acidity, low demulsification value, high resistance to oxidation and ability to inhibit corrosion of ferrous metals by salt water.

In order to eliminate completely all tendency In the case of oils 2 and 3, no scuffing was experienced in three and six tests, respectively, up to a limit of 12,550 lbs., after which the tests were discontinued. The other three tests on oil '2 were terminated at lower Sc loads, without any scufiing having occurred.

To provide illustrations of lubricating oil compositions suitable for use as extreme pressure lubricants for hypoid gears, compounds of the present invention were dissolved in a relatively viscous mineral oil blend designated oil D, which consisted of 27 parts by weight of a conventionally refined Pennsylvanian bright stock of viscosity 600 seconds Redwood at F., 34 parts of a conventionally refined Mid-Continent Failure Oil 2% Di(n-butyl) dithiodiacetate. 0.2% Mercaptobenzothlazol 91.9% Oil D B Hexachlorethaue 89.8% our) 3% DMZ-ethyl hexyl) trlthiodiacetatei: 0.1% Tetraethyl thiuram disulphide..."

The normal requirement for a good extreme pressure lubricant for hypoid gears is that it should withstand loads up to 350 lbs. under these conditions.

I claim:

1. A lubricating composition comprising a mineral oil containing a small amount sufficient to increase the load-carrying capacity of the oil of an ester of acetic acid substituted in the alpha position by an element selected from the group consisting of sulphur and selenium, said ester having the general formula in which R is a radical selected from the group consisting of alkyl, aryl and cycloalkyl radicals, X is an element selected from the group consisting of sulphur and selenium and n is an integer from 2 to 4 inclusive.

2. A lubricating composition comprising a mineral oil containing a small amount suflicient to increase the load-carrying capacity of the oil of an ester of acetic acid substituted in the alpha position by an element selected from the group consisting of sulphur and selenium, said ester having the general formula ROOC.CH2 (X) n-CH2-COOR in which R is a chlorine containing radical selected from the group consisting of alkyl, aryl and cycloalkyl radicals, X is an element selected from the group consisting of sulphur and selenium and n is an integer from 2' to 4 inclusive.

3. A lubricating composition comprising a mineral oil containing about 0.5% to about by weight of an ester of acetic acid substituted in the alpha position by an element selected from the group consisting of sulphur and selenium, said ester having the general formula in which R is a radical selected from the group consisting of alkyl, aryl and cycloalkyl radicals, X is an element selected from the group consisting of sulphur and selenium and n is an integer from 2 to 4 inclusive.

4. A lubricating composition comprising a mineral oil containing from 0.5% to 2.0% by weight of an ester of acetic acid substituted in the alpha position by an element selected from the group consisting of sulphur and selenium, said ester having the general formula ROOC.CH2 (X) n-CH2COOR ll) in which R is a radical selected from the group consisting of alkyl, aryl and cycloalkyl radicals, X is an element selected from the group consisting of sulphur and selenium and n is an integer from 2 to 4 inclusive.

5. A lubricating composition comprising a mineral oil containing a small amount suflicient to increase the load-carrying capacity of the oil of an ester of acetic acid substituted in the alpha position by an element selected from the group consisting of sulphur and selenium, said ester having the general formula in which R is an alkyl radical containing not more than six carbon atoms X is an element selected from the group consisting of sulphur and selenium and n is an integer from 2 to 4 inclusive.

6. A lubricating composition comprising a mineral oil containing from 0.5% to 2.0% by weight of an ester of acetic acid substituted in the alpha position by an element selected from the group consisting of sulphur and selenium, said ester having the general formula ROOC.CH2- (X) n--CH2.COOR

in which R is an alkyl radical containing not more than six carbon atoms X is an element selected from the group consists of sulphur and selenium and n is an integer from 2 to 4 inclusive.

7. A lubricating composition as claimed in claim 1 in which there is also incorporated a small amount of a compound selected from the group consisting of mercapto-arylene-thiazoles and derivatives of mercapto-arylene-thiazoles.

8. A lubricating composition as claimed in claim 1 in which there is also incorporated a small amount of an alkyl thiuram disulphide.

9. A lubricating composition as claimed in claim 1 in which there is also incorporated a small amount of berizothiazole disulphide.

10. A lubricating composition comprising a mineral oil containing as an additive from 0.5% to 2.0% by weight of di(n-butyl) dithiodiacetate.

11. A lubricating composition comprising a mineral oil containing as an additive from 0.5% to 2.0% by weight of di(n-butyl) trithiodiacetate.

12. A turbine oil comprising a mineral oil containing agents controlling oxidation stability and corrosion of ferrous metals and including also a small amount suificient to increase the load-carrying capacity of the oil of an ester of acetic acid substituted in the alpha position by an element selected from the group consisting of sulphur and selenium, said ester having the general formula ROOC.CH2 (X) n-CHaCOOR in which R is a radical selected from the group consisting of alkyl, aryl and cycloalkyl radicals, X is an element selected from the group consisting of sulphur and selenium and n is an integer from 2 to 4 inclusive.

13. An extreme pressure lubricant comprising a lubricating oil composition as claimed in claim 1 and including in addition to the ester of acetic acid an organic halogenated compound.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,073,841 Humphreys Mar. 16, 1937 2,317,666 Burwell Apr. 27, 1943 2,467,303 Frank Apr. 12, 1949 2,503,401 Mattano et al Apr. 11, 1950 2,649,416 Richter et a1 Aug. 18, 1953

Claims

1. A LUBRICATING COMPOSITION COMPRISING A MINERAL OIL CONTAINING A SMALL AMOUNT SUFFICIENT TO INCREASE THE LOAD-CARRYING CAPACITY OF THE OIL OF AN ESTER OF ACETIC ACID SUBSTITUTED IN THE ALPHA POSITION BY AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF SULPHUR AND SELEMIUM, SAID ESTER HAVING THE GENERAL FORMULA