US3446738A - Ester base lubricant compositions containing an aromatic amine and an organic thiophosphite or thiophosphonate - Google Patents

Description

United States Patent 3,446,738 ESTER BASE LUBRICANT COMPOSITIONS CONTAINING AN AROMATIC AMINE AND AN ORGANIC THIOPHOSPHITE OR THIOPHOSPHONATE Tai S. Chao, Homewood, and Daniel B. Eickemeyer, Park Forest, 111., assignors to Sinclair Research, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Feb. 10, 1964, Ser. No. 343,481 Int. Cl. Cm 1/24 US. Cl. 25246.7 12 Claims ABSTRACT OF THE DISCLOSURE Ester base lubricating compositions of high temperature oxidative resistance are provided containing small amounts of each of an ester base fluid soluble aromatic amine, such as N-phenyl-alpha-naphthylamine, and an ester base fluid soluble organic thiophosphite or thiophosphonate, such as trilauryltrithiophosphite or dicresylphenylthiophosphonate. While these phosphorous compounds are not by themselves effective high temperature antioxidants in ester base lubricating oils, their combination with the aromatic amines affords oxidative resistance to ester base lubricating oils at high temperatures in excess of 400 F.

This invention relates to ester-based lubricant compositions containing a novel combination of additive agents. More particularly the present invention relates to esterbased lubricant compositions which exhibit increased oxidation resistance.

Organic compounds, such as lubricating oils, undergo oxidation upon exposure to air. This process is accentuated by elevated temperatures such as occur in engines and other operating machinery. When such organic compositions are used as motor or machnery lubricants, their stability is still further drastically reduced due to their contact with metal surfaces which give up metallic particles into the lubricant. Such abraded or dissolved metals or metal salts appear to act as oxidation catalysts in the lubricant causing the formation of primary oxidation products which in turn cause further degradation of the organic compounds present in the composition. Problems of this nature are encountered in mineral oils but appear to be particularly limiting in synthetic oleaginous fluids exemplified by esters.

The development of modern high speed jet turbine aircraft engines necessitates the search for lubricants which are resistant to high temperature oxidative degradation. Jet turbines are actuated by the energy of a burning fuel and are used to drive compressors which provide large amounts of air for the burning of the fuel. The combustion of the fuel provides the energy for driving the compressors with the remainder of the useful energy going into the propulsion of the aircraft. Jet turbine bearings are lubricated by pumping a lubricant to the bearings from a reservoir in a closed system. The design of more powerful jet turbines has led to an increase in the lubricant reservoir temperature and to greater difiiculty in maintaining lubricant stability under the more severe conditions. For example, a lubricant which will operate satisfactorily at a reservoir temperature of 250 F. may sludge badly, build up viscosity, develop high acidity and corrode metals at a reservoir temperature of 440 F.

Thus jet turbine service requires a lubricant of superior thermal and oxidation stability as well as satisfactory physical characteristics in terms of viscosity, flash point, volatility, and load carrying properties. To arrive at such a lubricant it has been the general practice to add an antioxidant and other additives, such as foam inhibitors, anti-wear agents, etc., to a base fluid of suitable properties.

3,446,738 Patented May 27, 1969 Numerous oxidation and corrosion inhibitors have been found for use in lubricating compositions and many combinations thereof also have been tested. For instance, anti-oxidants such as phenothiazine; phenyl-tx-naphthylamine; S-ethyl-IO, 10-diphenylphenazasiline; etc. are well known in the art. The known inhibitors, however, are not adequate to provide the superior oxidation resistance now needed. Moreover, the effectiveness of these known inhibitors is greatly impaired in the presence of metal.

It is the object of this invention to provide an ester base synthetic lubricant having superior resistance toward oxidative and thermal degradation. It is a further object to protect and improve this resistance against the detrimental effects of metals with the use of suitable additives.

The present invention provides an improved ester-based lubricant composition containing small amounts effective to retard oxidation, of each of a defined sulfur and phosphorous-containing organic compound and an aromatic amine.

The sulfur phosphorous-containing organic compounds of our composition used in minor amounts are solublein the base ester oil to the extent present and have the formula:

where X is O or S, at least one being S n=0 or 1, at least three ns being 1 R R R are alkyl or aromatic groups R R and R are aromatic, including mixed aryl-alkyl, or alkyl, including cycloalkyl, hydrocarbon radicals of up to about 18 carbon atoms, and preferably of about 4 to 12 carbon atoms, whose adjacent carbon atoms are no closer than 1.40 A. (i.e. a non-olefinic, non-acetylenic). In any given compound the R radicals may be the same or differently selected from the group of radicals given above. Exemplary of the R aromatic radicals are phenyl and naphthyl groups, which groups may be substituted with non-deleterious substituents such as one or more lower alkyl radicals. The R alkyl radicals may be straight chain, branched, or cyclic alkyls which may be substituted with non-deleterious substituents, for example, ethyl, butyl, hexyl, octyl and iso-octyl.

Especially effective sulfur and phosphorous-containing compounds for use with the aromatic amines in our lubricant composition are dicresyl phenylthiophosphonate, trilauryl trithiophosphite, 0,0,0-tributyl thiophosphate, phenylethylene thiophosphite, etc. Other thiophosphonates, thiophosphites, thiophosphates and other esters of phosphorous-containing acids which contain one or more sulfur atoms in the molecule can also be used. Examples of other suitable thiophosphonates include triphenyl thiophosphonate, tricresyl thiophosphonate, diethyl cresyl thiophosphonate, lauryl methyl benzene thiophosphonate, dicresyl lauryl thiophosphonate, dioctyl phenylthiophosphonate, dilauryl chloromethyl dithiophosphonate. Examples of other suitable thiophosphites include tributyl triothiophosphite, trioctyl trithiophosphite, tricresyl trithiophosphite, trilauryl dithiophosphite, trioctyl monothiophosphite, dioctyl monothiophosphite and S,S-dioctyl phenyl dithiophosphite. Examples of other suitable thiophosphates include dilauryl thiophosphate, lauryl ethyl thiophosphate, monophenyl thiophosphate, diphenyl thiophosphate, dicresyl octyl thiophosphate, dioctyl dithiophosphate, dioctylphenyl dithiophosphate, trilauryl trithiophosphate, and trilauryl tetrathiophosphate. Examples of other 8- and P-containing compounds suitable for use as antioxidants with aromatic amines include trioctyl thiophosphinate, trioctyl dithiophosphinate, tricresyl thiophosphinate, S-lauryl diphenylthiophospinate, dilauryl amidothiophosphate, di-isoamyl amidothiophosphate and N- butyl dioctyl amidothiophosphate.

The aromatic amine component of the invention is soluble in the ester fluid to the extent present and can be represented by the following general formula:

wherein Q is a monovalent hydrocarbon of 1 to 20 carbons, preferably 6 to 12 carbon atoms, whose adjacent carbon atoms are no closer than 1.40 A. (i.e. a nonolefinic, non-acetylenic, monovalent hydrocarbon), and Q is an aromatic hydrocarbon radical of 6 to 12 or 16 carbon atoms. Thus Q can be an alkyl group, including cycloalkyl, or an aromatic group. Preferably both Q and Q are aromatic, and often at least one is a fused ring aromatic, e.g. naphthyl. Q and Q can be substituted with non-interfering substituents such as alkyl groups and amine groups, preferably alkyl or aromatic amines, and Q and Q can be linked together by means of a non-interfering element such as carbon, sulfur and oxygen. Illustrative of suitable amines are phenothiazine, N-phenyl-unaphthyl amine; di(a-naphthyl amine); N,N'-diphenyl para-phenylene diamine; N,N'-dioctyl para-phenylene diamine, N,N'heptylphenyl para-phenylene diamine; diphenyl amine, n-butyl phenyl(a-naphthyl)amine, di-betanaphthylamine, N-phenyl-decyl amine, N-phenyl-isooctyl amine, diphenyl amine, monomethylaniline, phenoxazine and carbazole.

The additives of the invention are incorporated in the base oil in amounts sufiicient to retard oxidation of the oil, and the concentrations employed for optimum results may be dependent on the particular base oil and second additive component selected. Ordinarily about 0.05 to preferably about 0.1 to 2%, by weight of each of the phosphorous-sulfur compound and the amine additive component provide satisfactory results.

The lubricant composition of this invention includes as the major component a base oil which is an ester of lubricating viscosity which may be, for instance, a simple ester or compounds having multiple ester groupings such as complex esters, dior other polyesters, and polymer esters. These esters are usually made from monoand poly-functional aliphatic alcohols or alkanols, and aliphatic monoand poly-carboxylic or alkanoic acids. 'Frequently, the alcohols and acids have about 4 to 12 carbon atoms. The reaction product of a mono-functional alcohol and a monocarboxylic acid is usually considered to be a simple ester. A diester is usually considered to be the reaction product of 1 mole of a dicarboxylic acid, say of 6 to 10 carbon atoms, with 2 moles of a monohydric alcohol or of 1 mole of a glycol, for instance of 4 to 10 carbon atoms, with two moles of a monocarboxylic acid, e.g. of 4 to 10 carbon atoms. The diesters frequently contain from to 40 carbon atoms.

A complex ester is usually considered to be of the type XY-ZYX in which X represents a monoalcohol residue. Y represents a dicarboxylic acid residue and Z represents a glycol residue and the linkages are ester linkages. Those esters, wherein X represents a monoacid residue, Y represents a glycol residue and Z represents a dibasic acid residue are also considered to be complex esters. The complex esters often have to 50 carbon atoms.

Polymer esters or polyester bright stocks can be prepared by direct esterification of dicarboxylic acids with glycols in about equimolar quantities. The polyesterification reaction is usually continued until the product has a kinematic viscosity from about 15 to 200 centistokes at 210 F., and preferably to 130 centistokes at 210 F.

Although each of these products in itself is useful as a lubricant, they are particularly useful when added or blended with each other in synthetic lubricant compositions. These esters and blends have been found to be especially adaptable to the conditions to which turbine engines are exposed, since they can be formulated to give a desirable combination of high flash point, low pour point, and high viscosity at elevated temperatures, and need contain no additives which might leave a residue upon volatilization. In addition, many complex esters have shown good stability to shear. Natural esters, such as castor oil may be employed and also be included in the blends, as may be small amounts of a foam inhibitor such as a methyl silicone polymer or other additives or lubricant components to provide a particular characteristic, for instance, extreme pressure or load carrying agents, corrosion inhibitors, etc., can be added.

The monohydric alcohols employed in these esters usually contain about 4 to 20 carbon atoms and are generally aliphatic. Preferably the alcohol contains up to about 12 carbon atoms. Useful alkanols include butyl, hexyl, methyl, iso-octyl and dodecyl alcohols, C oxo alcohols and octadecyl alcohols. C to C branched chain primary alcohols are frequently used to improve the low temperature viscosity of the finished lubricant composition. Alcohols such as n-decanol, 2-ethyl-hexanol oxo alcohols, prepared by the reaction of carbon monoxide and hydrogen upon the olefins obtainable from petroleum products such as di-isobutylene and C olefins, other alcohols such as butyl carbitol, tripropylene glycol monoisopropyl ether, dipropylene glycol mono-isopropyl ether, and products such as Tergitol 3A3 which has the formula C H O(CH CH O) H, are suitable alcohols for use to produce the desired lubricant. If the alcohol has no hydrogens on the beta carbon atoms, it is neo-structured; and esters of such alcohols are often preferred. In particular, the neo-C alcohol-2,2,4-trimethyl-pentanol- 1-gives lubricating diesters or complex esters suitable for blending with diesters to produce lubricants which meet stringent viscosity requirements. Iso-octanol and isodecanol are alcohol mixtures made by the 0x0 process from C -C copolymer heptenes. The cut which makes up iso-octanol usually contains about 17% 3,4-dimethylhexanol; 29% 3,5-dimethylhexanol; 25% 4,5-dimethylhexanol; 1.4% 5,5-dimethylhexanol; 16% of a mixture of S-methylheptanol and S-ethylheptanol; 2.3% 4-ethylhexanol; 4.3% a-alkyl alkanols and 5% other materials.

Generally, the glycols contain from about 4 to 12 carbon atoms; however, if desired they could contain a greater number. Among the specific glycols which can be employed are 2ethyl-1,3-hexanediol, 2-propyl-3,3-heptanediol, 2-methyl-1,3-pentanediol, 2-butyl-1,3-butanediol, 2,4-diphenyl-1,3-butanediol, and 2,4-dimesityl-1,3-butanediol. In addition to these glycols, ether glycols may be used, for instance, where the alkylene radical contains 2 to 4 carbon atoms such as diethylene glycol, dipropylene glycol and other glycols up to 1000 to 2000 molecular weight. The most popular glycols for the manufacture of ester lubricants appear to be polypropylene glycols having a molecular weight of about -300 and 2-ethylhexanediol. The 2,2-dimethyl glycols, such as neopentyl glycol have been shown to impart heat stability to the final blends. Minor amounts of ether glycols or other materials can be present as long as the desired properties of the product are not unduly deleteriously affected.

One group of useful monocarboxylic acids includes those of 8 to 18 or even 24 carbon atoms such as stearic, lauric, etc. The carboxylic acids employed in making ester lubricants will often contain from about 4 to 12 carbon atoms. Suitable acids are described in US. Patent No. 2,575,195, and include the aliphatic dibasic acids of branched or straight chain structures which are saturated or unsaturated. The preferred acids are the saturated aliphatic carboxylic acids containing not more than about 12 carbon atoms, and mixtures of these acids. Such acids include succinic, adipic, suberic, azelaic, and sebacic acids and isosebacic acid which is a mixture of a-ethyl suberic acid, a,u-diethyl adipic acid and sebacic acid. This composite of acids is attractive from the viewpoint of economy and availability since it is made from petroleum hydrocarbons rather than the natural oils and fats which are used in the manufacture of many other where X is selected from the group consisting of sulfur and oxygen, at least one X being sulfur, n is or 1 with three ns being 1 and one It being 0, R R and R are selected from the group consisting of alkyl and aromatic hydrocarbon radicals of up to about 18 carbon atoms dicarhoxylic acids, Which al Oils a d fats e f ca and an ester base fluid soluble aromatic amine having the quently in short supply. The preferred dibasic acids are general formul sebacic and azelaic or mixtures thereof. Minor amounts of adipic used with a major amount of sebacic may also Q' be used with advantage.

The ester base oils to which incorporation of the additive combination of the invention is particularly adwhere Q is a non-olefinic, non-acetylenic monovalent hyvantageous are the oils commonly referred o as eodrocarbon radical of 1 to 20 carbon atoms and Q is an P y P Y p y having more than 0118 ester aromatic hydrocarbon radical of 6 to 16 carbon atoms,

P- These are the esters of aliphatic cafboxylic acids, said amounts being elfective to retard oxidation of said generally alkanoic acids, of about 4 to 12 carbon atoms, ester base fluid at temperatures in excess of 400 F., said and a p y y alkallol free of beta hydrogen, 6011- ester base fluid being an ester of alkanol of 4 to carbon raining n0 hydrogen on the beta carbon atoms. and atoms and alkane carboxylic acid of 4 to 18 carbon cluding the di(polyhydric alcohol) ethers. The polyhydric atoms,

alcohol generally contains about 2 t0 6 hydrOXy groups 20 2. The lubricant composition of claim 1, wherein Q is and abOllt 5 to 20, Preferably 5 to 12 carbon atoms Illusan aromatic hydrocarbon radical and Q and Q each have trative of the alcohols are those having the general for- 6 to 12 carbon atoms mula: 3. The lubricant of claim 2 wherein the sulfur and phosphorous-containing compound is present in an amount HOOH2 (J CHQ O. CHZ G CHZ OH of about .01 to 2% by weight and the aromatic amine is L I present in an amount of about 0.1 to 2% by weight.

n 4. The lubricant composition of claim 1 wherein the Whereln 1S 0 to 1 and R 15 a lower alkyl group, f ester base fluid is an ester of an alkanol having the general erably of about 1 to 4 carbon atoms, which can be straight formula: or branched chain, or a hydroxy methyl group. These esters can be made by reacting a mole of the alcohol with R l- R -I about 2 moles u to the stoichiometric equivalent of the carboxylic acid. P HOCH2 (]IJCH2 0 CH2 +-CH2 TOH Illustrative of polyhydric alcohols free of beta hydro- R R u gen are neopentyl glycol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, 2-butyl-2-ethylwherein n 15 0 to 1 and R 15 Selected from the group 0011- 1,3-propanediol, etc. Suitable aliphatic carboxylic acids Sisting 0f lower alkyl radicals and Y Y y with which the polyhydric alcohols free of beta hydro- 5. The lubricant composition of claim 4 wherein the gen may be esterified are n-butyric acid, isobutyric acid, aromatic amine is 'p y p y n-pentanoic acid, isopentanoic acid, n-heptanoic acid, iso- 40 The lubricant composition of Claim 5 wherein the heptanoic acid, n-isoheptanoic acid, n-octanoic acid, isosulfur and phosphorous-containing compound and arooctanoic acid, pelargonic acid, n-decanoic acid, lauric acid, ma ine ar ea h pre e t in th am Imt of about myristic acid, stearic acid, n-dodecanoic acid, valeric acid, 00 0 n-hexabutyric acid, etc. 7. The lubricant composition of claim 6 wherein the The effectiveness of the combination of additives of sulfur and phosphorous-containing compound is dicresyl the present invention as an antioxidant in synthetic ester phenyl thiophosphonate. lubricants is apparent from the tests reported below. The 8. The lubricant composition of claim 6 wherein the times to the end of the inhibition period and to the end sulfur and phosphorous-containing compound is trilaurylof the test are designated Ti and Tr, respectively, and trithiophosphite. the volume of oxygen absorbed is designated Vt. It can 9. The lubricant composition of claim 1 wherein at be seen that the phosphorus and sulfur-containing addileast one of R R or R is an aromatic hydrocarbon tives of the invention are not, by themselves, effective radical of up to 18 carbon atoms. antioxidants. However, their combinations with the aro- 10. A lubricant composition consisting essentially of a matic amines are quite effective. major amount of an ester base fluid of lubricating viscosity TABLE I Base Oz Absorption Test Data Test Weight Weight Ti Tt Vt No. Fluid Aromatic Amine Percent Sulfur-Phosphorous Additive Percent (min.) (min.) (ml.) None None 10 99 2, 500

Dicresylphenylthiphosphonate. 1. 0 10 96 2, 500

0. 5 None 103 2, 500

0. 5 Dicresylphenylthiophosphonate.. 1. 0 243 338 2, 500

0. 5 Trilauryltrithiophosphite l. 0 257 257 2, 500

0. 5 0,0, O-tributylthiophosphate. 1. 0 143 195 2, 500

0. 5 Phenylethylenethiophosphate 1 0 197 284 2, 500

1 Test conditions=450 F. 1 cu. ft. Oz/hL, g. sample.

2 20% diisooctyl azelate arid complex ester of neopentyl glycol, azelaic acid and isooctyl alcohol (mole ratio 112:2).

It is claimed:

1. A lubricant composition consisting essentially of a major amount of an ester base fluid of lubricating viscosity and small amounts of each of an ester base fluid soluble sulfur and phosphorous-containing organic compound having the following structural formula:

where X is selected from the group consisting of sulfur and oxygen, at least one X being sulfur, R R and R 75 are selected from the group consisting of alkyl and aromatic hydrocarbon radicals of up to about 18 carbon atoms and an ester base fluid soluble aromatic amine having the general formula:

wherein Q is a non-olefinic, non-acetylenic monovalent hydrocarbon radical of 1 to 20 carbon atoms and Q is an aromatic hydrocarbon radical of 6 to 16 carbon atoms, said amounts being effective to retard oxidation of said ester base fluid at temperatures in excess of 400 F., said ester base fluid being an ester of alkanol of 4 to 20 carbon atoms and alkane carboxylic acid of 4 to 18 carbon atoms.

11. A lubricant composition consisting essentially of a major amount of an ester base fluid of lubricating Viscosity and small amounts of each of an ester base fluid soluble thiophosphonate having the following structural formula:

wherein X is selected from the group consisting of sulfur and oxygen, R R and R are selected from the group consisting of alkyl and aromatic hydrocarbon radicals of up to about 18 carbon atoms and an ester base fluid soluble aromatic amine having the general formula:

wherein Q is a non-olefinic, non-acetylenic monovalent hydrocarbon radical of 1 to 20 carbon atoms and Q' is an aromatic hydrocarbon radical of 6 to 16 carbon atoms, said amounts being eflective to retard oxidation of said ester base fluid at temperatures in excess of 400 B, said ester base fluid being an ester of alkanol of 4 to 20 carbon atoms and alkane carboxylic acid of 4 to 18 carbon atoms.

12. A lubricant composition consisting essentially of a major amount of an ester base fluid of lubricating viscosity and small amounts of each of an ester base fluid soluble thiophosphonate having the following structural formula:

R1O\ R2OP=S n R R and R are selected from the group consisting of alkyl and aromatic hydrocarbon radicals of up to about 18 carbon atoms and an ester base fluid soluble aromatic amine having the general formula:

UNITED STATES PATENTS 2,157,452 5/1939 Humphreys 252-466 2,188,943 2/1940 Evers 252-466 2,242,260 5/1941 Prutton 252-46.6 3,282,905 8/1945 Pedersen 252-46.6 2,815,327 12/1957 Mehr 6t al. 252-475 3,159,664 12/1964 Bartlett 252-466 3,218,256 11/1965 Edwards 6: a1. 252-475 DANIEL E. WYMAN, Primary Examiner.

W. CANNON, Assistant Examiner.

US. Cl. XR. 252-466 P0405) UNITED STATES PATENT OFFICE (5/69) r CERTIFICATE OF CQRKECIION Patent No. 3, ,73 Dated y 7, 9 9

Inventor(s) Tali s. Chao and Daniel B. Eickemeyer It is certified that: error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

I "3,282,905" should read --2,382,9o5--.

JAN 6 "I970 (SEAL) Atteat:

Edward Flemhm WILLIAM E. S-OHUYLER, .m. Attesting Officer Oozmnissioner of Patents