US3330763A - Lubricants containing an amino thiocyanate and a cyclic amine - Google Patents

Description

United States Patent 3,330,763 LUBRICANTS CONTAINING AN AMINO THIO- CYANATE AND A CYCLIC AMINE John G. Damrath, In, East Alton, 131., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Jan. 3, 1966, Ser. No. 517,915 5 Claims. (Cl. 25247.5)

This invention relates to improved synthetic ester lubricating compositions which have excellent extreme-pressure and antiwear properties and which are not corrosive to lead.

Recently, synthetic lubricants have gained prominence in the field of lubrication because of stringent requirements of various new lubricant applications. These lubricants, which are frequently esters, ethers, silicones, or polymeric hydrocarbons are generally designed for special applications where conventional mineral oils are not satisfactory. Synthetic oils have low pour points and desirable viscosity characteristics and, with proper inhibition, can generally be used at temperatures considerably above the decomposition temperatures of most mineral oils. Accordingly, these oils have found use in jet aircraft, missiles, and the like, Where wide temperature ranges and extreme operating conditions are likely to be encountered. Proper lubrication of aircraft gas turbines, for example, requires ability to function at bulk oil temperatures as low as 65 F. to as high as 450 to 500 F. for some applications.

While synthetic esters are good base oils for formulating the gas turbine lubricants, their inherent properties are not suiiicient in all respects to meet generally accepted minimum requirements for proper lubrication for long periods of time. Accordingly, to meet commercial specifications, turbine oils generally contain one or more additives to improve various characteristics such as corrosion resistance, oxidation resistance, antiwear properties, etc. A proper choice of additives to optimize desirable lubricant properties involves detailed empirical studies, since additives used to correct one deficiency will often cause another; e.g., amine antioxidants enhance the oxidation stability of esters, but also aggravate corrosivity to certain metals. In addition, it is desirable to have as few additives as possible to achieve desired performance, since a large number of additives is likely to raise problems of incompatibility among the additives.

Antiwear properties are particularly difiicult to impart to synthetic ester oils, since at the very high temperatures of operation of these fluids, continuous films of lubricants are particularly difficult to maintain on parts subject to wear. Furthermore, compounds which do successfully impart antiwear properties to these esters are likely to be depleted under these extreme conditions or to react with or be rendered ineffective by other additive materials in the oil. In addition, many compounds which impart wear resistance are likely to decrease the oxidation stability or increase the corrosivity of the base oil.

It has now been discovered that synthetic lubricants having excellent antiwear characteristics comprise a major amount of a synthetic ester base lubricating oil and a minor amount, suflicient to enhance the antiwear properties, of certain hydrocarbyl ammonium thiocyanates.

The thiocyanate additives of the invention may be represented by the formula FR! R! R I N+ soN- L R where R is a hydrocarbyl group having a valence of n,

and having from 1 to 30 carbons each, R is independently hydrogen or C to C hydrocarbyl, and n is an integer 3,330,763 Patented July 11, 1967 from 1 to 2. The total number of carbon atoms in R and R is from 4 to about 30. The hydrocarbyl groups are preferably alkyl groups, because these compounds are superior inhibitors of lead corrosion. The Word hydrocarbyl is used in its accepted meaning as representing a radical formed from a hydrocarbon by removal of a hydrogen. The hydrocarbyl groups represented by the Rs in the above formula may be any aliphatically saturated radical composed solely of carbon and hydrogen, whether they be alkyl, cycloalkyl, aryl, alkaryl, aralkyl, single ring, multi-ring, straight chain or branched chain. Representative groups are methyl, tert-butyl, isooctyl, dodecyl, octadecyl, eicosyl, cyclohexyl, phenyl, naphthyl, anthryl, benzyl, phenethyl, etc.

The thiocyanate additives of the invention are used in amounts sufficient to increase the load-carrying ability of the synthetic ester oil. Appropriate concentrations are generally in the range of from about 0.01 to about 5% by weight, preferably 0.05 to 3% by weight of the final lubricant composition. Lower amounts may be used, but the resulting increase in EP properties is generally insufficient to justify addition of the thiocyanate; higher amounts are also operable but may cause ancillary problems, such as sludging.

The hydrocarbyl ammonium thiocyanates useful in compositions of the invention may be considered to be neutral salts of thiocyanate acid or hydrocarbyl thiocyanic acid and monoto trihydrocarbyl monoto diamines, where the total number of carbons in the hydrocarbyl substituents is at least 4, preferably from 4 to about 30. The salts may be primary, secondary, tertiary, or quaternary ammonium salts; primary and secondary, especially primary salts are preferred since extreme-pressure activity seems to decrease with the number of hydrocarbyl substituents on the nitrogen atom. A total of at least about four carbon atoms on the amine is necessary to achieve solubility. The upper limit on the number of carbon atoms is less well defined, but is governed by considerations of solubility and practicality, e.g., the amount of additive required to achieve an effective concentration of the salt. In general, it is unnecessary to have a total number of alkyl carbons in excess of about 30.

Examples of suitable primary amines for use in preparing salts of the invention are butylamine, n-hexylamine, Z-ethylhexylamine, decylamine, dodecylamine, pentadecylamine, octadecylamine, eicosylamine, pentacosylamine, phenethylamine, octylphenylamine, naphthylamine, etc. Particularly appropriate amines are mixtures of tertiary alkyl primary amines having 18 to 22 carbons, such as those marketed by Rohm and Haas as Primene JM-T. Examples of suitable secondary amines are diisobutylamine, di(2-ethylhexyl)amine, dicaprylylamine, N- methylhexylamine, N-(Z-ethylhexyl)dodecylamine, N-isobutyl-caprylylamine, diphenylamine, phenyl-a-naphthylamine, dioctyldiphenylamine, and phenyloctylamine. Examples of suitable tertiary amines are tri(2-ethylhexyl) amine, tricaprylylamine, tri(decyl)amine, N-metiiyl-dicaprylylamine, N isobutyl di(2-ethylhexyl)amine, N- methyl-N-isobutyl caprylylamine, N-ethyl-N-isobutyl dodecylamine, N isopropyl N-(Z-ethylhexyl)octadecylamine, N-hexyl diisobutylamine, and -N,N-diisobutyl eicosylamine, N-phenyl diisobutylamine, and N-caprylyl diphenylamine. Some examples of diamines for use in the invention are ethylene diamine, propylene diamine, isobutylene diamine, octadecylene diamine, polyisobutylene ethylene diamine, etc.

Some examples of suitable thiocyanates of the invention are octadecyl ammonium thiocyanate, eicosyl ammonium thiocyanate, Z-ethylhexyl ammonium thiocyanate, di(2- ethylhexyl) ammonium thiocyanate, tricaprylyl ammonium thiocyanate, tricaprylyl-N-methyl ammonium thiocyanate, polyisobutylene ethylene diamine dithiocyanate, octadecyl cyclohexylamine thiocyanate, diethyl cyclohexylarnine thiocyanate, butyl phenylarnine thiocyanate, etc.

To illustrate the effectiveness of the thiocyanates of the invention in imparting load-carrying ability to synthetic ester oils, various tests were carried out. Lubricants according to the invention were formulated using several different thiocyanates in a base oil consisting of 95% C to 0, mixed acid esters of pentaerythritol and 5% C -C mixed acid esters of dipentaerythritol containing 1% phenyl-a-naphthylamine. These oils were subjected to the Shell 4-Ball Wear Test and the Ryder Gear Test to test their load-carrying properties. The 4-Ball Wear Test is Federal Test Method Standard 791a, Test Method 6503. The Ryder Gear Test was conducted as directed in Federal Test Method Standard 791, Test Method 6508.

The results of these tests are described in Table 1 below.

To illustrate the lead corrosion inhibiting properties of the thiocyanate EP agents, SOD Lead Corrosion and MacCoull-Ryder Lead Corrosion tests were run on a typical synthetic base oil with and without varying amounts of these additives. The MacCoull-Ryder test is described in detail in SAE Journal 50, 8, page 338 (August 1942); this test was run for one hour at 325 F. Corrosion was measured in grams of weight loss. In the SOD lead corrosion test, rapidly rotating panels of lead and copper were heated in the oil sample for one hour at 325 F. or five hours at 375 F. while air was bubbled through the sample. This test is described in Federal Test Method Standard No. 791a, Method 4321.1. The base oil used was a mixture of 67% w. C -C alkanoic acid esters of pentaerythritol and 33% w. C -C alkanoic acid esters of dipentaerythritol, containing 1.0% wt. phenyl-a-naphthylamine. The results are tabulated in Table II below.

TABLE I.RESULTS OF LOAD-CARRYING CAPACITY TESTS Shell Shell Concentration, it-Ball Ball Ryder Gear Additive percent wt. Mean Weld Load, p.s.i.

Hertz Load, kg. Load, kg.

None 18. 0 126 1,800 Pt ene .TMT-HSCN 1 l. 0 224 3,690 Do 0. 5 42.0 224 3, 700 Do 0.1 200 3, 330 Do 0.05 180 2, 280 Z-ethylhexyl ammonium thiocyanate 0. 35 34. 4 200 2,800 Di(2-ethy1hexyl) ammonium thiocyanate 0. 45 37. 7 200 2, 750 Tri(caprylyl) ammonium thiocyanate 0. 56 23. 7 141 2, 210 Tri(caprylyl)-N-methyl ammonium thiocyanat 0. 65 28. 5 126 2, 100 PIB ethylene diamine dithiocyanate 2 0. 38 178 Tridecylphcnyl ammonium thiocyanate- 0. 50 40. 0 178 1 Prirnene J MT is a commercial mixture of tort-CW0 alkyl primary amines marketed by Rohm and Haas.

= P113 is polyisobutylene of about 300 mol weight.

These results show the effectiveness of ammonium thiocyanates as EP agents, and also indicate that at equivalent concentrations, EP effectiveness decreases as more hydrocarbyl groups are attached to the amine nitrogen.

The thiocyanates of the invention are not only excellent extreme-pressure agents, they also function as very good lead corrosion inhibitors in synthetic esters. Lead is corroded much more easily than other metals, such as steel, aluminum, copper, magnesium and silver; also, lead corrosion is not predictable from corrosion results of other metals. Some additives, for example 2,2-dipyridylamine, which are corrosion inhibitors for most metals, actually promote lead corrosion. Synthetic ester base stocks exhibit some mild lead corrosion, and this corrosion is often severely aggravated by other additives. It is very difficult to predict particular additives which will be corrosive to lead, since the lead corrosion function seems to be unrelated to the normal corrosion function. Nevertheless, the additives of the invention substantially reduce lead corrosion regardless of the nature of the additives or type of ester base stock which induces it.

Cyclic amine additives, which are useful as antioxidants, are known to cause lead corrosion. Accordingly, the thiocyanates of the invention are particularly useful when used in combination with one or more of these additives. By the term cyclic amine is meant herein a primary to tertiary amine, each non-hydrogen substituent of which is a monoto diuuclear cyclic radical having from 02 alkyl substituents of 1-12 carbons. Secondary amines are preferred; amines in which the cyclic radicals are are matic rings are also preferred. Examples of amines which may be used advantageously with the thiocyanates of the invention are phenyl-m-naphthylamine, phenyl-B-naphthylamine, diphenylamine, di-a-naphthylamine, triphenylamine, 2,2'-dipyridylamine, Z-aminopyridine, p,p-dioctyldiphenylamine, 2,6-diaminopyridine, phenyl-Z-pyridylamine, 3-aminoquinoline, etc. These amines are usually present in an amount of from about 0.2 to about 5% by weight of the final composition.

TABLE II.-RESULTS OF LEAD CORROSION TESTS Pass=6 mgJcm. at 375 F., 5 hours.

2 Pass=0.1000 gm. maximum.

3 Neutral salt of a mixture of Ora-C22 tort-alkyl primary amines and thioeyanio acid.

These results show that the base oil fails both lead corrosion tests, but passes when as little as 0.05% weight of a thiocyanate is added. Addition of 0.2% wt. of the salt ahnost completely eliminated lead corrosion.

'In general, any synthetic ester lubricating oil is a satisfactory base for compositions of the invention. Suitable synthetic lubricant base stocks are esters of alcohols having 1 to 20, especially 4 to 12 carbons and aliphatic carboxylic acids having from 3 to 20, especially 4 to 12 car bons. The ester base may comprise a simple ester (reaction product of a monohydroxyalcohol and a monocarboxylic acid), a polyester (reaction product of an alcohol and an acid, one of which has more than one functional group), or a complex ester (reaction product of a polyfunctional acid with more than one alcohol, or of a polyfunctional alcohol with more than one acid). Also, excellent synthetic lubricants may be formulated from mixtures of esters, such as major proportions of complex esters and minor amounts of diesters.

Monohydric alcohols suitable for making ester base stocks include methyl, butyl, isooctyl, dodecyl and octadecyl alcohols. Oxo alcohols prepared by the reaction of olefins with carbon monoxide and hydrogen are suitable. Neo alcohols, i.e., alcohols having no hydrogens on the beta carbon atom are preferred. Examples of such alcohols are 2,2,4-trimethylpentanol-1 and 2,2-dimethyl propanol.

Polyalcohols used for the production of base oil esters preferably contain 1 to 12 carbons. Examples of dialcohols are 2-ethyl-1,3-hexar1ediol, 2-propyl-3,3-heptanediol, 2-butyl-l,3-butanedio1, 2,4*dimesityl-1,3-butanediol, and polypropylene glycols having molecular weights of from about 100 to 300. Alcohols having 3, 4, 5 or more hydroxyl groups per molecule are also suitable and are preferred; examples of these polyols are pentaerythritol, dipentaerythritol, and trimethylolpropane. Mixtures of alcohols may also be used.

Suitable carboxylic acids for making the ester base oils include monoand dibasic aliphatic carboxylic acids. Examples of appropriate acids are 'butyric, valeric, sebacic, azelaic, suberic, succinic, caproic, adipic, ethyl suberic, diethyl adipic, oxalic, malonic, glutaric, pentadecanedicarboxylic, diglycolic, thiodiglycolic, acetic, propionic, caprylie, lauric, palmitic, pimelic, and mixtures thereof. Preferred acids are sebacic, azelaic, glutaric, adipic, and their mixtures.

Examples of suitable ester base oils are ethyl palmitate, ethyl laurate, butyl stearate, di-(Z-ethylhexyDsebacate, di(Z-ethylhexyl) azelate, ethyl glycol dilaurate, di- (2-ethy1hexyl) phthalate, di(1,3-methylbuty1) adipate, di- (Z-ethylpropyl) azelate, diisopropyl oxylate, dicyclohexyl sebacate, glycerol tri-n-heptoate, di(undecyl) azelate, and tetraethylene glycol di-(Z-ethylene caproate), and mixtures thereof. An especially preferred mixture of esters consists of about 5080% Wt. bis (2,2,4-trimethylpentyl) azelate and 20 to 50% Wt. 1,1,1-trimethyly1 propane triheptanoate.

Especially preferred esters for use as base stocks in the present invention are esters of monocarboxylic acids having 3 to 12 carbons and polyalcohols such as pentaerythritol, dipentaerythrit-ol, and trimethylolpropane. Examples of these esters are entaerythrityl butyrate, pentaerythrityl tetrabutyrate, pentaerythrityl tetravalerate, pentaerythrityl tetracaproate, pentaerythrityl dibutyratedicaproate, pentaerythrityl butyrate caproate divalerate, pentaerythrityl butyrate trivalerate, pentaerythrityl butyrate tricaproate, pentaerythrityl tributyratecaproate, mixed C saturated fatty acid esters of pentaerythritol, dipentaerythrityl hexavalerate, dipentaerythrityl hexacaproate, dipentaerythrityl hexaheptoate, dipentaerythrityl hexacaprylate, dipentaerythrityl tributyratecaproate, dipentaerythrityl trivalerate trinonylate, dipentaerythrityl mixed hexaesters of C fatty acids and trimethylolpropane heptylate. Pentaerythrityl esters of mixtures of C C acids are excellent base oils, and are commercially available from Hercules Chemical Company.

Ester oils may be prepared by simple reaction of the alcoholic and acidic reactants in proportions suitable for producing the desired product; preparation preferably takes place in a solvent such as an aromatic hydrocarbon, and in the presence of a catalyst, such as HCl, HF, HBr, H H PO SOCI BF etc. Preparation of suitable esters is described in Eickemeyer, US. 3,038,859, issued June 12, 1962, and Young, US. 3,121,109, issued Feb. 11, 1964.

Compositions of the invention may also contain other additives to further improve properties of the oil. Examples of other such additives are extreme-pressure agents, viscosity index improvers, anti-corrosion agents, detergents, antifoamants, etc.

I claim as my invention:

1. A lubricant composition comprising a major amount of a synthetic ester lubricating oil and minor amounts, sufiicient to increase load-carrying ability of the oil, of an ammonium thiocyanate having the formula where R is a hydrocarbyl group having a valence of n and having from 1 to 30 carbons, each R is independently hydrogen or C to C hydrocarbyl, and n is an integer from 1 to 2 and from 0.2 to 5% by weight of a cyclic amine, each non-hydrogen substituent of which is a phenyl, pyridyl or naphthyl radical having from 0 to 2 alkyl su'bstituents of 1-12 carbons.

2. The composition of claim 1 wherein the thiocyanate is present in the amount of from 0.01 to 5% by weight of the final lubricating composition, and wherein the total number of carbon atoms in R and all Rs is from 4 to about 30.

3. The composition of claim 2 wherein hydrocarbyl is alkyl.

4. The composition of claim 2 wherein the ammonium thiocyanate is a neutral salt of a primary amine having from 4 to 30 carbon atoms and thiocyanic acid or a mixture of these salts.

5. The composition of claim 1 wherein the cyclic amine is phenyl-a-naphthylamine.

References Cited UNITED STATES PATENTS 2,362,890 11/ 1944 Dietrich 25247 3,218,256 ll/1965 Edwards et al. 252-47.5

DANIEL E. WYMAN, Primary Examiner.

PATRICK P. GARVIN, Examiner.

L. G. XIARHOS, W. H. CANNON, Assistant Examiners.

Claims (1)

1. A LUBRICANT COMPOSITION COMPRISING A MAJOR AMOUNT OF A SYNTHETIC ESTER LUBRICATING OIL AND MINOR AMOUNTS, SUFFICIENT TO INCREASE LOAD-CARRYING ABILITY OF THE OIL, OF AN AMMONIUM THIOCYANATE HAVING THE FORMULA