US3432433A

US3432433A - Lubricant compositions

Info

Publication number: US3432433A
Application number: US666499A
Authority: US
Inventors: Eugene Wittner; Kenneth T Wendler
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1965-11-15
Filing date: 1967-09-08
Publication date: 1969-03-11
Anticipated expiration: 1986-03-11
Also published as: FR1499018A; NL6615998A; GB1102010A; DE1279271B

Description

United States Patent Claims ABSTRACT OF THE DISCLOSURE Lubricating compositions containing minor amounts each of an arylamine, an alkyl amine salt of monohaloalkylphosphonic acid and a s-triazine have excellent oxidation stability.

This application is a continuation-in-part of Ser. No. 507,668 filed Nov. 15, 1965 and now abandoned.

This invention relates to synthetic ester lubricating oils having exceptional oxidation stability. More particularly, it relates to synthetic ester oils containing aromatic amines, a salt of a monohaloallcylphosphonic acid and certain s-triazine compounds.

Synthetic lubricants have gained recent prominence in the field of lubrication because of stringent requirements of long life under extreme conditions imposed by certain new applications. Synthetic lubricants have low pour points and desirable viscosity characteristics and can generally be used at temperatures considerably above the decomposition temperature of most mineral oils. 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 said applications.

Although these synthetic lubricants are more stable than mineral oils, they nevertheless undergo oxidation when exposed to air, especially when subjected to elevated temperatures such as occur under normal operation. Oxidation stability is further impaired by dissolution of metals under operating conditions. Dissolved metals seem to catalyze oxidative degradation of the lubricant, thereby substantially shortening its useful life. Additives have traditionally been employed in small concentrations to impart resistance to oxidation to these lubricants. Much research effort has been directed to finding additives or combinations of additives Which are effective antioxidants for long periods of time yet which do not impart or cause undesirable side effects such as sludge and deposit formation, increased corrosion, viscosity change, discoloration, and so on. Available information regarding mineral oil formulation is generally of little aid in developing successful synthetic lubricants since entirely different side effects are likely to occur under the more extreme conditions to which synthetic lubricants are subjected.

According to the invention, a synthetic ester lubricant having excellent oxidation stability comprises a major amount of synthetic ester lubricating oil and minor amounts sufficient to increase the oxidation stability of the oil of an aryl amine, an amine salt of a monohaloalkylphosphonic acid and an s-triazine having the formula 3,432,433 Patented Mar. 11, 1969 where R, R R and R are hydrogen, C to C hydrocarbyl, or pyridyl, and R is C to C hydrocartbyl, C to C hydrocarbylamino, pyridyl, or pyridylamino. R, R R R and R may all be different, or some or all may be alike. The term hydrocarbyl is intended to mean a radical formed from a hydrocarbon by removal of a hydrogen atom. All hydrocarbyl groups within the claimed ranges free of aliphatic unsaturation are operable, whether they are alkyl, aryl, alkaryl, aralkyl, cycloalkyl, single or multi-ring, straight chain or branched. Representative groups include methyl, propyl, butyl, phenyl, naphthyl, tridecylphenyl, and the like.

The s-triazines to be used in compositions of the invention do not impart any antioxidant activity to the oils by themselves, but show remarkable activity in the presence of an aryl amine and an amine salt of a monohaloalkylphosphonic acid. These triazine compounds are, in general, substituted guanamines and substituted melamines. Preferred hydrocarbyl substituents are phenyl, benzyl and butyl. If desired mixtures of the triazines may also be used. Examples of s-triazines which may be used in accord with the invention are as follows:

2-amino-4-n-butylamino-6-phenyl-s-triazine 2,4-bis (n-butyl amino -6-phenyl-s-triazine 2-amino-4-sec-butylamino-6-phenyl-s-triazine 2,4-lbis sec-butylamino -6-phenyl-s-triazine 2, 4,6-tris n-butylamino -s-triazine 2-anilino-4, 6-bis n-butylamino) -s-triazine Z-n-butylamino-4,6-dianilino-s-triazine 2,4-diamino-6- (4-tertbutylphenyl) -s-triazine 2 ,4-bis (n-butyl amino -6- (4-ethylphenyl -striazine 2-amino-4-anilino- G-benzylamino-s-triazine 2,4-bis (octylamino) -6-phenyl-s-triazine 2,4,6-tris (octylamino) -s-triazine 2,4,-6- (trianilino -s-triazine 2,4-diamino-6-n-butylamino-s-triazine 2,4-diamino-6-sec-butylamino-s-triazine 2,4-diamino-6-anilino-s-triazine 2-methylamino-4,6-dianilino-s-triazine 2-n-octylamino-4,6-diani1ino-s-triazine 2- Z-pyridylamino) -4,6-di-n-butylamino-s-triazine 2,4 diamino- 6- (Z-pyridylamino) -s-triazine 2, 4-diamino-6-tridecylanilino-s-triazine 2,4-diamino-6-di-n-butylamino-s-triazine 2-amino-4,6-bis (di-n-butylamino -s-triazine These compounds are added in amounts of from about 0.1% to 5% by Weight of the final lubricating composition, preferably from 0.25 to 3% by Weight.

The aryl amines to be used in combination with the striazines and amine salts of monohaloalkylphosphonic acid described above have from 6 to 30, preferably 12 to 20 carbons, and are preferably diarylamines having the formula where R and R are monoor diaromatic rings, each ring being optionally substituted with one C -C alkyl group. Examples of suitable diaryl amines are phenyl-alphanaphthylarnine, phenyl-beta-naphthylamine, beta,betadinaphthylamine, alpha,beta-dinaphthylamine, p,p'-dioctyldiphenylamine, and diphenylamine. Particularly preferred amines are phenyl-alpha-naphthylamine and diphenylarnine. The diarylamines are beneficially present in an amount of from about 0.05 to 5%, preferably 0.1 to 3% by weight of the final lubricating composition. Amounts of about 1% by weight are preferred.

The salt to be used in combination with the triazine and arylamine described above is a salt of 0 C alkylamine and a monohaloalkylphosphonic acid, the haloalkyl group containing 1 to 4, preferably 1 to 2 carbon atoms. The haloalkylphosphonic acids used for preparing the salts for use in the invention generally have the formula Ri (OH)1 where R is monohaloalkl containing 1 to 4, preferably 1 to 2 carbon atoms. R preferably contains a chlorine atom substituted on the alpha carbon atom. Preferred halogens are fluorine, chlorine and bromine, especially chlorine.

Suitable alpha-monochloroalkylphosphonic acids for preparing the salts include monochloromethylphosphonic acid, 1-monochloroethylphosphonic acid, l-monochloropropylphosphonic acid, l-chloro-l-methyl-ethylphosphonic acid, l-chloro-butylphosphonic acid and l-chlorol-methyl-propylphosphonic acid.

Amines which form eifective salts of the phosphonic acids are primary to secondary alkyl amines having at least 8, preferably 8 to 30, and more preferably 12 to 24 carbon atoms per molecule. Branched tertiary-alkyl primary amines are preferred; branched in this context means having at least 2 hydrocarbon substitutents attached to the main carbon chain. As the tertiary-alkyl radical, the radical of polyisobutylene and polypropylene, and mixtures of these are particularly preferred. Examples of these amines are 1,1,3,3-tetramethylbutylamine, 1,1,3,3,5,5 hexamethylhexylamine, 1,1,3,3,5,5,7,7 octamethyloctylamine and 1,1,3,3,5,5,7,7,9,9-decamethyl-decylamine. Tertiary alkyl methyl primary amines, such as 2,2,4,4-tetramethylpentylamine and 2,2,4,6,6-hexamethyl hexylamine are also suitable.

Other primary amines having 8 to 30 carbons which are appropriate for forming the salts of the invention are described in Bortnick, U.S. 2,606,923, issued Aug. 12,

1952, and Bortnick, U.S. 2,611,782, issued Sept. 23, 1952.

These include tert-tridecylamine,

C2115 (i-C Hn--NH2) as 'well as isoheptyl diethyl carbinylamine, is'ooctylethyl propylcarbinylamine, etc. Primary amines of this type are commercially available from Rohm and Haas Company under the trade name of Primenes. The amine may also be a polyamine, such as a diamine or triamine, and may contain other non-reactive groups, such as amide or ether groups, in the carbon chain.

Some specific examples of secondary amines for making the phosphonic acid salts are diamylamine, dihexymine, butyl-2-ethylhexylamine, dilaurylamine, methyloleylamine, ethyloctaylamine, isoamylhexylamine, dicyclohexylamine, dicyclopentylamine, cyclohexyloctylamine, cyclohexylbenzylamine, benzyloctylamine, benzyl-Z-ethylhexylamine, allyloctylamine, dodecyI-Z-ethyl-hexylamine, 1 -isobutyl-3-methylbutyl -3,3,3-methylcyclohexylamine, di(1 isobutyl-3-methylbutyl)-amine; N-n-dodecyldiethylenetriamine, N-n-tetradecyldiethylenetriamine, octylethylene diamine, N-2-ethylhexy1 N-hexadecyl triethylene tetramine, heptyl trimethylene diamine, N-tetradecyl tripropylene tetramine, N,N'-diallyl trimethylene diamine, 3-hexyl-morpholine, and the like.

The phosphonic acid-amine salts for use in the invention can be prepared by direct neutralization of haloalkylphosphonic acid with a substantially stoichiometric amount of amine. The reaction occurs at normal or moderately elevated temperatures and may be carried out in the presence of an inert diluent or solvent, such as a hydrocarbon, alcohol, ether, ketone, etc. Preparation of these salts is described in Watson et al., U.S. 2,858,332, issued Oct. 28, 1958.

The phosponic acid-amine salts useful in the invention may also be modified with an alkali metal as described in Price et al., U.S. 3,112,267, issued Nov. 26, 1963. The full amine salt of the phosphonic acid is prepared and is then treated in a low-boiling solvent with an alkali metal hydroxide, carbonate, or alcoholate such that one of the amine groups is replaced with an alkali metal. Preferred alkali metals are sodium, potassium, and lithium.

The amine-phosphonic acid salts are used in amounts of from about 0.005 to 5% by weight, preferably about 0.01 to 3% by weight of the lubricating composition.

Preferred s-triazine constituents have the formula:

where R and R are hydrogen, C to C hydrocarbyl, or pyridyl, and R is C to C hydrocarbyl or All of the Rs may be the same or different, except that not all of the carbon substituents may be amino since this compound, melamine, is insoluble in the ester base oils. These compounds are particularly and importantly preferred because they substantially inhibit copper corrosion in addition to being good antioxidants. Low copper corrosivity is important because copper parts are generally found in contact with turbine oils in jet engines. Although copper corrosion inhibitors may be added, further additives are expensive and might cause problems of incompatability with other additives. Thus, it is preferred to have at least one, preferably two NH groups on the triazine ring. Examples of preferred compounds are 2,4-diamino-6-tridecylanilines-triazine.

N NH NH; 2,4-diamino-fi-anilino-s- I triazine. V N Hz N n-C4HHNH -NII 2,4-diamino-6-n-butylaminol striazine. NHz

N NHz +0.11, 2,4diamino-6(4-tert-butyl- H phcnyl)-s-triazine. V l NHZ 2,4-diamino-G-di-n-butyl- N (11-04119) 2N NH H amino) -s-triazine.

NH2 NH-n-C4H 2-amino-4-butylamino-6- I phenyl-s-triazine.

2amino4-anilino-6-benzyl- N H2 NH CHM I arnino-s-triazine.

chloromethylphosphonic acid and C primary amine (MCMPA), phenyl-alpha-naphthylamine (PAN) or diphenylamine (DPA). Other runs combined the MCMPA with either PAN or DPA. The majority of the runs were made using as an oxidation inhibitor 1.0% wt. of a triazine alone or in combination with MCMPA, PAN and DPA. In all cases, the tabulated results are mean values of duplicate tests.

Results of the air oxidation tests are given in Table 1 below. The only runs not containing 1.0% wt. triazine are those listed in the first line of Table I. Oxidation stability was determined by the length of time (oxidation life) for absorption of 3 millimoles of oxygen per gram of oil. This criterion was used instead of the more conventional induction period measurement since oils of the invention exhibited unconventional oxidation characteristics; in most cases there was a short period of rapid oxidation followed by a period in which little oxidation occurred, followed by another period of rapid oxidation.

TABLE I.450 F. MICRO AIR OXIDATION TESTS .Oxidation Lite, Hours 0.2% Wt. MCMPA 1% PAN 1% DPA 1 1 (7) 1 0.2% MCMPA 0.2% MCMPA plus F7 2317. DPA plus 1% PAN 2(2-pyridylamino)-4,6-bis (n-butylamino)-s-triazine 2-methylamin04,G-dianilino-s-triazine 2-n-octylamino-4,6-dianilino-s-tiiazine 2-see-buty1amino-4,6-dianilino-s-triazine 2-isobutylamino-4,G-dianilino-s-triazine 2-tertbutylamino-4,G-dianilino-s-triazine 2-anilino-4,6-dlbenzylamino-s-t1iazine 2-amino-4-anilino-6-b enzylamino-s-triazine 1 100 gm. sample, 9 liters/in air flow, other conditions same.

To illustrate the efficacy of the additive combination of the invention, air oxidation tests were conducted on samples of various ester-base lubricants. The tests were carried out at 450 F. by passing a stream of air at the rate of 4.2 liters per hour through a 20 gram sample of the appropriate ester fluid. To more closely approximate actual operating conditions, 20 ppm. each of iron or iron and copper were added as octoates. The base stock for all tests was a mixture of 67% C -C acid esters of pentaerythritol and 33% 0 -0 acid esters of dipentaerythritol. Comparative runs were conducted using the base stock alone, others were conducted using the base stock plus one additive, i.e. the salt of mono- These results show that the s-triazines themselves have essentially little or no antioxidant activity, but that they act to complement the aryl amine additives to impart improved stability to ester oils. In addition, it is apparent that the antioxidant activity of the triazine-arylamine combination is surprisingly greatly enhanced by the presence of the MCMPA salt which is 'known as an extreme pressure agent, which by itself shows essentially no antioxidant activity. It is at once evident that the s-triazines, aryl amines and MCMPA salt coact in such a manner as to significantly enhance the antioxidant properties of the ester oils over the properties obtained using any of the additives alone or any of the additives in combination.

TABLE II.-SYNTHETIO OIL OXIDATION TESTS Iron Catalyst Copper Catalyst s-Triazine A Acid No. A Vis at A Acid No A Vis. at

F. 100 percent percent None 27. 3 294 23. 7 198 2-amin0-4-n-butylamino-fi-phenyl-s-triazine. 8. 8 77 3. 0 33 2,4-bis (n-butylamion) -6-phenyl-s-triazine 11. 0 142 6. 0 88 Mixture of 2-amin0-4-sec-butylamino-6-phenyl-s-briazine and 2,4-bis(see-butylamino)-6-pheny1-s-triazine 10. 3 73 6. 9 52 2,4,fi-tris(n-butylamino)-s-triazine 9. 9 b4 5. 4 60 2-anilino-4,6-bis(n-butyl-amino)-s-triazi.ne 7. 2 55 9. 2 74 2-n-butylamlno-4,fi'dianilino-s-triazine 4. 7 40 8. 7 83 The enhancement in activity is more than the sum of the individual additives. In other words, the compositions 8 in Smolin and Rapoport, s-Triazines and Derivatives, Interscience Publisher New York, 1959.

TABLE III.CORROSION OXIDATION TESTS Corrosion, mg./cm. A A Vis. at s-Triazine, 1.0% wt. Acid N0. 100 F., Mg Al Cu Fe Ag Ti Percent None 1.63 +0.03 1.08 +0.02 +0.03 +0.01 1.8 91.0 2,4,6-tris(n-butyl-amino)s-triazine. +0.03 +0.13 1.00 +0.04 0.07 +0.03 2.0 19.4 2-anilino-4,6bis(n-butylamino)s-triaz' +0.03 +0.07 0. 53 +0.06 0. 02 +0.05 0.9 18.1 2,4-dianilino-fi-methyl-amino-s-triazine.. +0. 02 +0.09 0.34 +0. 03 +0.04 +0. 05 1.1 18.7 2-n-butylamino-4,6-dianilino-s-triazine 0. 27 +0.03 0. 60 +0.04 0.05 +0.03 1.8 20.8 2,4-dianilino-G-n-octylamino-s-triazine +0.06 +0. 09 0. 76 +0.03 0. 05 0. 05 1.4 24.2 2-isobutylamino4,fi dianilino-s-triaizne +0.19 +0. 05 0. 58 +0.03 0. 01 +0.03 1.7 21.5 2-sec'butylamino-4,o'dianilino-s-triazine +0.02 +0. 07 1. 10 +0.04 0.00 0.00 2.1 23.4 2-tert-butylamino-4,fi-dianilino-s-triazine--- 0. 21 +0.05 0. 46 0. 01 +0.03 +003 12 23.9 2-amino-4-n-butylamino-6phenyl-s-triazine +0.09 +0.07 --0. 39 +0.05 +0.06 +0.03 1.5 23.7 2,4-di-n-butylamino-B-phenyl-s-triazine +0.06 +0. 05 0.67 +0. 09 +0.12 +0.02 1.3 25.9 Mixture of 2-alnino-4-sec-butylamino-6-phenyl-s 2,4-bis(sec-butylamino)6-phenyl-s-triazine. +0.04 +0. 02 -0.02 0.00 +0.01 0.02 1.0 21.1 2-amino-4,6-dianilino-s-triazine +0. 05 +0.07 0. 01 0.00 0.00 +0.4 4.0 16.7 2,4-dlanilino-fi-dimethylamino-s-triazine 0. 57 +006 0. 55 +0. 02 0.03 +0. 01 3.2 25.5 2-anilino-4,fi-diamino-s-triazine +0.15 +0.08 0.01 +0.03 0.01 +0.09 0.6 5.4

of this invention exhibit synergistic antioxidant activity.

Additional oxidation tests were conducted to more accurately determine oxidation stability of oils of the invention by measuring the acidity and viscosity increase of the oils under oxidative conditions. The base oil used for these tests was the same monoand dipentaerythrityl ester mixtrue described above. All samples contained 1.0% wt. of a diarylamine(diphenylamine) and 0.2% wt. MCMPA amine salt. In these tests, 9 liters/hour of air were flowed through a 200 gram oil sample at 450 F. for 40 hours. The oils contained either 10 p.p.m. iron or copper catalysts, added as naphthenate, as indicated. The results shown in Table II above are averages of duplicate determinations.

These results show that the triazines are surprisingly insensitive to the presence of iron and copper oxidation catalysts. Tests using iron only as catalyst are considered to be very severe, more so even that combined ironcopper tests; nevertheless, triazine-containing lubricants performed very satisfactorily in these tests.

Further evidence of beneficial elfects attributable to composition of the invention is shown in the oxidationcorrosion tests results in Table III. The same oils as described above (monoand dipentaerythrityl ester base containing 0.2 wt. MCMPA, 1.0% diphenylamine, and 1% wt. of specified triazines) were subjected to the Pratt and Whitney Type II Corrosion-Oxidation Test, which is similar to the test described in Federal Test Method Standard No. 791a as method 5308.4. Fluid samples (100 gm.) were heated at 425 F. for 48 hours in the presence of 1.0 square inch of each of the metals listed in the table. Air was bubbled through at the rate of 5 liters/ hour. Corrosion was measured in weight loss per unit of surface area.

Low corrosivity to a number of different metals is essential for some applications, for instance, jet aircraft turbine lubrication, where the oil contacts parts made from a variety of metals and alloys. Also, the presence of corrosion products may be detrimental to the stability of the oil and may accelerate degradation of the oil. The results below indicate that the corrosion results for most oils of the invention are satisfactory for all metals except copper (acceptable limits are i030 mg./cm. In addition, it appears that the s-triazines substantially inhibit the high corrosivity of the base oil to magnesium, and ta least partly inhibit the corrosivity to copper. In all cases, viscosity increase and acid number increase were well within acceptable limits.

The triazine components of lubricants of the invention may be made by any of a variety of methods known to the art. The chemistry of these compounds, along with methods for their preparation, is completely described The following example describes the preparation of 2-amino4-n-butylamino-fi-phenyl-s-triazine, and is included for purposes of illustrating one method of prep aration.

. EXAMPLE I Preparation of 2-amino-4-n-butylamino-6-phenyl-s-triazine A mixture of 880 g. (4.7 moles) of benzoguanamine, 468.2 g. (4.28 moles) of n-butylamine hydrochloride and 282 g. of phenol was charged to a 3-liter, 3-necked, round-bottomed flask equipped with a thermometer, a nitrogen inlet, a mechanical stirrer and an air-cooled condenser. The mixture was warmed to 200 C. under nitrogen. The stirrer 'was started and the mixture was stirred and heated at 225 C. The reaction mixture became liquid and homogeneous at about 215 C. After 30 minutes of heating at 225- C. a white solid precipitate of ammonium chloride began to form. After 8 hours of heating at 225 C., the hot reaction mixture was poured cautiously with stirring into a solution of 300 g. of sodium hydroxide in 4 liters of Water contained in two 4-liter beakers. The lower phase, a white semisolid material was washed with water and then dissolved in about 5 liters of warm benzene. The mixture 'was filtered, the benzene solution was washed twice with 2-liter portions of 5% wt. aqueous sodium hydroxide, then with water until the washings were no longer basic. The benzene solution was concentrated to a volume of 800 ml., filtered, warmed to 65 C. and diluted with n-hexane to the point of incipient cloudiness. The precipitated product was recovered by filtration after cooling. It was pressed dry and recrystallized a second time from benzene/n-hexane. A yield of 239 g. (23% wt. of theory) of fine white crystals, M.P. -137 C., was obtained.

Calculated for C H N percent wt., C, 64.2; H, 7.0; N, 28.8. Found, percent wt., C, 63.6; H, 7.3; N, 29.1.

Suitable synthetic lubricant base stocks for the practice of the invention 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 carbons. 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-trimethyl-pentanol-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-hexanediol, 2-propyl-3,3-heptanediol, 2-butyl-1,3-butaneidol, 2,4-dimesityl-1,3-butanediol, and polypropylene glycols having molecular Weights of from about 100 to 300. Alcohols having 3, 4, 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, caprylic, lauric, palmitic, pimelic, and mixtures thereof. Preferred acids are sebacic, azelaic, glutaric, adipic, and their mixtures.

Examples of suitable ester base oils are ethyl almitate, ethyl laurate, butyl stearate, di-(Z-ethylhexyl)sebacate, di- (2-ethylhexyl)azelate, ethyl glycol dilaureate, di-(Z-ethylhexyl) phthalate, di-(l,3-methylbutyl) adipate, di-(lethylpropyl) azelate, diisopropyloxylate, 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% 1,1,1-trimethylyl 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, dipentaerythritol, and trimethylol-propane. Examples of these esters are pentaerythrityl tetr-abutyrate, pentaerythrityl tetravalerate, pentaerythrityl tetracaproate, pentaerythrityl dibutyratedicaproate, pentaeryth-rityl butyratecaproate 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 tributyratetricaproate, dipentaerythrityl trivalerate trinonylate, di-

pentaerythrityl mixed hexaesters of C fatty acids and trimethylolpropane heptylate. Pentaerythrityl esters of mixtures of 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 80 H PO S001 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.

We claim as our invention:

1. A lubricant composition comprising a major amount of a synthetic ester lubricating oil and an oxidation inhibitor consisting of (a) 0.05 to 5.0% wt. of an arylamine selected from the group consisting of diphenylamine and 10 phenyl-alpha-naphthylamine, (b) 0.1 to 5% by weight of an s-triazine having the formula R3 R2 where R, R R and R are hydrogen, C to C hydrocarbyl, or pyridyl, and R is C to C hydrocarbyl, C to C hydrocarbylamino, pyridyl, or pyridylamino and (c) 0.005 to 5% by weight of the salt of a C alkyl amine and a monohaloalkylphosphonic acid, wherein the haloalkyl radical contains from 1 to 4 carbon atoms.

2. The composition of claim 1 wherein the arylamine is present in an amount of 0.1 to 3% by weight, the salt is present in the amount of 0.01 to 3% by weight and the s-triazine is present in an amount of 0.5 to 3% by weight.

3. An antioxidant containing lubricant composition comprising a major amount of synthetic ester lubricating oil, from .05 to 5% by weight of an arylamine selected from the group consisting of diphenylamine and phenylalpha-naphthylamine, from 0.005 to 5% by weight of the salt of a C primary or secondary alkyl amine or mixtures thereof and monochloromethylphosphonic acid, and from 0.1 to 5% by weight of an s-triazine having the formula where R and R are hydrogen, 0 -0 hydrocarbyl, or pyridyl, and R is C to C hydrocarbyl or 4. The composition of claim 3 wherein the arylamine is diphenylamine.

5. The composition of claim 3 wherein the arylamine is phenyl-alpha-naphthylamine.

6. The composition of claim 3 wherein R is NH 7. The composition of claim 3 wherein the s-triazine is 2-n-butylamino-4,6-diamino-s-triazine.

8. The composition of claim 3 wherein the s-triazine is 2-amino-4-anilino-6-benzylamino-s-triazine.

9. The composition of claim 3 wherein the s-triazine is 2,4-diamino-6-di-nbutylamino-s-triazine.

10. The composition of claim 3 wherein the s-triazine is 2,4-diamino-6- (4-tert-butylphenyl) -s-triazine.

References Cited UNITED STATES PATENTS 2,714,057 7/1955 Chenicek 252 XR 2,847,383 8/1958 Airs et al.

3,093,585 6/1963 Low et al. 2525l.5 XR 3,197,408 7/ 1965 Cupper et al 252-50* XR 3,247,111 4/1966 Oberright et al. 25250 XR 3,309,314 3/1967 Price et al 252-32.5 3,330,762 7/1967 Wendler et al. 25232.5

OTHER REFERENCES Barnes et al.: Synthetic Ester Lubricants, Lubrication Engineering, August 1957, pp. 454-458.

PATRICK P. GARVIN, Primary Examiner.

U.S. Cl. X.R. 252-50, 56