US3413225A

US3413225A - Functional fluid containing azo benzene derivatives as antioxidants

Info

Publication number: US3413225A
Application number: US560790A
Authority: US
Inventors: Dmuchovsky Basil; Richard W Weiss
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1966-06-27
Filing date: 1966-06-27
Publication date: 1968-11-26
Anticipated expiration: 1985-11-26
Also published as: CH491191A; DE1644916A1; NL6708849A; BE700490A; ES342328A1; GB1201961A

Description

United States Patent 3,413,225 FUNCTIONAL FLUID CONTAINING AZO BEN ZENE DERKVATIVES A ANTEUXHDANTS Basil Dmuchovsky and Richard W. Weiss, St. Louis, Mo.,

assignors to Monsanto Company, St. Louis, M0., a corporation of Delaware No Drawing. Filed June 27, 1966, Ser. No. 560,790

16 Claims. (Cl. 252-475) ABSTRACT OF THE DISCLOSURE Compositions of the class which exhibit improved oxidative resistance by the incorporation of an azo benzene compound into a class of base stocks representative of which are polyphenyl ethers, polyphenyl thioethers, mixed polyphenyl ethers-thioethers, phenylmercaptobiphenyls, phenoxybiphenyls and mixed phenoxyphenylmercaptobiphenyls. The compositions have many uses, among which are use as jet engine lubricants, heat transfer fluids and hydraulic fluids.

This invention relates to new phenoxy and thiophenoxy azobenzene compounds, to functional fluid compositions having improved oxidative stability and more particularly to compositions comprising a functional fluid and a stabilizing amount of an azo compound.

Many different types of materials have been utilized as functional fluids and functional fluid: are used in many different types of applications. Such fluids have been used as electronic coolants, atomic reactor coolants, diffusion pump fluids, synthetic lubricants, damping fluids, bases for greases, force transmission fluids (hydraulic fluids), heat transfer fluids, die casting release agents in metal extrusion processes and as filter mediums for air conditioning systems. Because of the wide variety of applications and the varied conditions under which functional fluids are utilized, the properties desired in a good functional fluid necessarily vary with the particular application in which it is to be utilized with each individual application requiring a functional fluid having a specific class of properties.

Of the foregoing the use of functional fluids as lubricants, particularly jet engine lubricants, has posed what is probably the most difficult area of application. As the operating temperatures for lubricants have increased it has become exceedingly diflicult to find lubricants which properly function at these high temperatures for any satisfactory length of time. Thus, the requirements of a jet engine lubricant are as follows: The fluid should possess high and low temperature stability, foam resistance, good storage stability and be noncorrosive to metal mechanical members which are in contact with the fluid. Such fluids should, in addition, possess adequate temperature-viscosity properties and satisfactory lubricity, that is, the lubricants must not become too thin at the very high temperatures to which they are subjected nor must they become too thck at lower temperatures and must at the same time be able to provide lubricity over such range of temperatures. In addition, such lubricants should not form deposits which interfere with the proper operation of a jet engine.

As the speed and altitude of operation of jet enginecontaining vehicles increases, lubrication problems also increase because of increased operating temperatures and higher bearing pressures resulting from the increased thrust needed to obtain high speeds and altitudes. As the service conditions encountered become increasingly severe the useful-life of the functional fluid is shortened, primarily due to their deficiency in oxidative stability above 500 F. In general, as the operating requirements of a jet engine are increased, engine temperatures increase and oil temperatures in the range of 600 F. and higher are encountered.

The useful life of any lubricant can be adjudged on the basis of many criteria such as the extent of viscosity increase, the extent of corrosion to metal surfaces in contact with the lubricant and the extent of deposits. Those skilled in the art have found many ways to improve lubricants and to thus retard or prevent the effects which shorten the useful life of a lubricant. Thus, it is a general practice to add small amounts of other materials, or additives, to lubricants in order to affect one or more of the properties of the base lubricant. It is diflicult, however, especially as operating temperatures are increased, to find additives which will still perform the function for which they are added and yet not inject other problems such as increasing corrosion and engine deposits.

As is seen from the foregoing temperature characteristics of a jet engine, a functional fluid can attain temperatures of up to 600 F. and higher which can result in oxidative and thermal degradation of a lubricant. The stabilization of lubricants at these high operating temperatures through the use of additives presents an extremely complex and difficult problem since antioxidants which have been utilized in lubricating oil compositions, such as phenolics and amine derivatives, decompose at such high temperatures thereby producing deposits and sludge. In addition, such decomposition products can at high temperatures promote oxidation thereby subjecting a lubricant to an increased rate of oxidative degradation. It is, therefore, a fundamental requirement for an antioxidant which is to be used in a high temperature lubricant that it perform its desired function without forming sludge or deposits. It is thus of particular importance that a functional fluid have improved oxidation resistance without forming sludge and deposits in the many functional fluid systems and applications as aforedescribed.

It has now been found that the oxidative stability and thus the useful life of functional fluids can be greatly extended, even under the severe conditions encountered in jet engines and other devices operating at temperatures of the order of 600 F. and higher, by the addition to functional fluids of an azo compound, said azo compound being selected from (A) A compound represented by the structure wherein a and b are whole numbers having a value of 0 to 5, R and R are each selected fro-m the group consisting of alkyl, substituted alkyl, aryl, substituted aryl, amino, substituted amino, cyano, nitro, halogen, sulfonic, carboxyl, carboalkoxy, phenoxy, substituted phenoxy, phenylmercapto, substituted phenylmercapto, alkoxy and hydroxyl and when a or b has a value of 2 to 5 any two Rs or R s which are attached to adjacent carbon atoms within the phenylene ring can together form a carbocyclic or substituted carbocyclic ring, and

(B) Mixtures thereof.

The functional fluids, to which an azo compound is added to provide the com-positions of this invention, hereinafter referred to as base stocks, include, but are not limited to, polyphenyl ethers, polyphenyl thioethers, mixed polyphenyl etherthioethers, phenoxybiphenyls, phenylmercapto biphenyls, mixed phenoxy phenylmercapto biphenyls and mixtures thereof. 'It is also contemplated within the scope of this invention that the phenyl and phenylene groups in the aforedescribed base stocks can be partially or totally replaced with a heterocyclic group such as thiophene and pyridene.

Whereas the incorporation of any foreign element into a base stock can alter properties of a functional fluid, the concentration of an azo compound in the base stock is adjusted in terms of the particular system and the base stock which is utilized in this system to provide functional fluid compositions of this invention which contain additive amounts of an azo compound sufficient to improve the oxidative stability of a base stock while not adversely affecting critical base stock properties. It has generally been found that the preferred additive concentrations of an azo compound for the base stocks described above are generally from about 0001 Weight percent to about 10 weight percent, preferably from about 0.05 weight percent to about 5 weight percent.

Therefore, included within the present invention are composition comprising a base stock and a Stabilizing amount of an azo compound, that is, an azo compound is added, in a concentration sutficient to improve the oxidative stability of the base stock. The functional fluid compositions of this invention can be compounded in any manner known to those skilled in the art for the incorporation of an additive into a base stock as for example by adding an azo compound to the base stock with stirring until a homogeneous fluid composition is obtained.

Typical examples of azo compounds are Typical examples of base stocks which are suitable as base stocks for this invention are represented by the structure 4)a wherein A, A A and A are each a chalkogen having an atomic number of 8 to 16, X, X X X and X each are selected from the group consisting of hydrogen, alkyl, haloalkyl, halogen, phenyl, alkaryl, hydroxyl, alkoxy, aralkyl and substituted aralkyl; w, y and z are whole numbers each having a value of 0 to 8; c is a whole number having a value of from 1 to 4; d is a whole number having a value of from 1 to 5 and e is a whole number having a value of 0 to 1 provided that when e is 0, y can have a value of 1 to 2. Typical examples of such base stocks are 2- to 7-ring 0-, mand p-polyphenyl ethers and mixtures thereof, polyphenyl thioethers and mixtures thereof, mixed polyphenyl etherthioether compounds in which at least one of the chalkogens represented by A, A A and A is dissimilar with respect to any one of the other chalkogens, phenoxybiphenyls, phenylmercaptobiphenyls, mixed phenoxy phenylmercaptobiphenyls and mixtures thereof. It is also contemplated within the scope of this invention that the phenyl and phenylene groups in the aforedescribed base stocks can be partially or totally replaced with a heterocyclic group such as thiophene and pyridene.

Typical examples of polyphenyl ethers, that is, when A, A A and A are oxygen and e has a value of 1 are those having all their ether linkages in the meta position since the all-meta linked ethers are the best suited for many applications because of their wide liquid range and high degree of thermal stability. However, mixtures of the polyphenyl ethers, i.e., either isomeric mixtures or mixtures of homologous ethers, can also be used to obtain certain properties, e.g., lower solidification points. Examples of the polyphenyl ethers contemplated are the bis(phenoxyphenyl) ethers, e.g.,

bis(m-phenoxyphenyl) ether;

the bis(phenoxyphenoxy)benzenes, e.g.,

m-bis(m-phenoxyphenoxy)benzene,

m-bis(p-phenoxyphenoxy)benzene,

o-bis o-phenoxyphenoxy benzene;

the bis( henoxyphenoxyphenyl) ethers,

e.g., bis[m-(m-phenoxyphenoxy)phenyl] ether,

bis pp-phenoxyphenoxy phenyl] ether,

m-[ (m-phenoxyphenoxy) (o-phenoxyphenoxy] ether and the bis(phenoxyphenoxyphenoxy)benzenes, e.g.,

m-bis [mm-phenoxyphenoxy) phenoxy] benzene,

p-bis [p- (m-phenoxyphenoxy phenoxy]-benzene,

m-bis [m- (p-phenoxyphenoxy phenoxy] benzene and 1,3,4-triphenoxybenzene.

It is also contemplated that mixtures of the polyphenyl ethers can be used. For example, mixtures of polyphenyl ethers in which the non-terminal phenylene rings (i.e., those rings enclosed in the brackets in the above structural representation of the polyphenyl ethers contemplated) are linked through oxygen atoms in the meta and para positions, have been found to be particularly suitable as lubricants because such mixtures possess lower solidification points and thus provide compositions having wider liquid ranges. Of the mixtures having only meta and para linkages, a preferred polyphenyl ether mixture of this invention is the mixture of S-ring polyphenyl ethers where the non-terminal phenylene rings are linked through oxygen atoms in the meta and para position and composed, by weight, of about m-bis(m-phenoxyphenoxy)benzene, 30% m-[(m phenoxyphenoxy) (pphenoxyphenoxy)]benzene and 5% m-bis(p-phenoxyphenoxy)benzene. Such a mixture solidifies at about -10 F. whereas the three components solidify individually at temperatures above normal room temperatures.

Examples of substituted polyphenyl ethers are l-(pmethylphenoxy)-4-phenoxybenzene, 2,4 diphenoxy 1 methylbenzene, bis[p-(p-methylphenoxy)phenyl] ether, bis[p-(p-tert-butylphenoxy)phenyl] ether and mixtures thereof.

Typical examples of phenoxybiphenyl compounds, that is, when 2 has a value of 0 and A, A A and A are oxygen are 3,3'-diphenoxybiphenyl, 3,2'-diphen0xybiphenyl, 3,4- diphenoxybiphenyl, 3,4-diphenoxybiphenyl, o-, mand pphenoxybiphenyl and triand tetra-substituted phenoxybiphenyls. It is also contemplated that mixtures of the above phenoxybiphenyls can be utilized as base stocks, for example, mixtures containing from 1 to 25% of a monophenoxybiphenyl, from 25% to of a diphenoxybiphenyl having at least one phenoxy group in the meta position with respect to the biphenyl nucleus and from 1 to 40% of a triand/ or tetra-substituted phenoxybiphenyl.

Typical examples of polyphenylthioethers, that is, when A, A A and A are sulfur and e has a value of l are o-bis-(phenylrnercapto)benzene, m-bis(phenylmercapto)benzene, bis-(m-phenylrnercaptophenyl) sulfide, m-phenylmercaptophenyl-p-phenyl-mercaptophenyl sulfide, the trisphenylmercaptobenzenes, such as 1,2,4-trisphenylmercaptobenzene, m-bis (p-phenylmercaptophenyl'mercapto) benzene, m-bis(m-phenylmercaptophenylmercapto)benzene, bis [m- (m-phenylmercaptophenylmercapto phenyl] sulfide, m-(m-c'hloropheny1mercapto)m-phenylmercaptobenzene, m-chlorodiphenyl sulfide, bis(o-phenylmercaptophenyl) sulfide, m-bis(m-phenylmercaptophenylmercapto)benzene, 1,2, 3 -tris phenylmerc apto -benzene, o-bis(o-phenylmercaptophenylmercapto)benzene, m-bis(p-phenylmercaptophenylmercapto)benzene and mixtures thereof.

Typical examples of phenylmercaptobiphenyls, that is, where e has a value of 0 and A, A A and A are sulfur are 3,3'-bis(phenylmercapto)rbiphenyl, 0-, m-, and pphenyl mercapto-biphenyl, 3,4-phenylmercaptobiphenyl, 3, 2diphenylmercaptobiphenyl, m-chloro-phenylmercapto 3-phenylmercaptobiphenyl and mixtures thereof.

Typical examples of mixed polyphenyl ether-thioethers, that is, where e has a value of l and at least one of the chalkogens represented by A, A A and A is dissimilar with respect to any other chalkogen are Typical examples of a mixed phenoxy-thiophenoxybiphenyl, that is, where e has a value of 0 and one of the chalkogens represented by A, A A and A is dissimilar with respect to any other chalkogen are phenylmercaptophenoxybiphenyl, o-phenylmercaptophenyl-m-phenoxyphenoxybiphenyl and mixtures thereof.

It is also contemplated within the scope of this invention that the aforedescribed base stocks "can be blended together to provide mixtures comprising two or more of the above base stocks. A typical mixture of a polyphenyl thioether and a mixed polyphenyl ether-thioether is one which contains by weight from about 45% to about 55% n1- phenoxyphenyl m-p'henylmercaptophenyl sulfide, from about to about bis(m-phenylmercaptophenyl) sulfide and from about 18% to about 25 bis(m-phenoxyphenyl) sulfide. Particularly useful mixtures are those containing the above mixtures and m-bis(phenylmercapto)benzene in about equal weight proportions. Typical examplesof mixtures containing polyphenyl thioethers, a mixed polyphenyl ether-thioether and halogenated polyphenyl ethers which are suitable as lubricants under high temperature conditions are as follows in weight percent:

It is also contemplated that any of the individual base stocks as described above or mixtures thereof in admixture with additives of this invention can also be utilized to provide compositions of this invention.

The followng non-limiting example will illustrate a preparaton of an azo compound of this invention.

Example 1 To a 2-liter reaction flask equipped with stirrer, addition funnel and reflux condenser was added grams of zinc dust, 120 grams of a solution consisting of 50% potassium hydroxide in water and 600 ml. of ethanol. To the flask was then added 48 grams of m-phenoxynitrobenzene over a period of about 30 minutes. The mixture was heated to the reflux temperature of ethanol and the reaction was continued for an additional 8 hours. The reaction mixture was filtered to remove the zinc dust and the 3,3'-diphenoxyazobenzene crystallized upon cooling of the ethanol solution. The 3,3'-diphenoxyazobenzene was recrystallized from an acetone-ethanol mixture. The 3,3-diphenoxyazobenzene had the following analysis: Percent carbon, 78.1; percent hydrogen, 4.83; percent nitrogen, 7.60.

The azo compound of the example and additional azo compounds were blended into base stocks to evaluate the oxidative stability of the resulting functional fluid compositions.

Following the procedure of Example 1, additional phenoxy and thiophenoxy azo compounds of this invention can be prepared. Thus, 3,3-dithiophenoxy azobenzene is prepared by the reduction of In-thiophenoxy nitrobenzene. Additionally, 3,3-(m-phenoxyphenoxy) azobenzene can be prepared by the reduction of 3-(m-phenoxyphenoxy) nitrobenzene.

The major bench scale method used for evaluating the oxidative stability of a lubricant is the procedure given in Federal Test Method, Standard No. 791, Method No. 5308 according to which the lubricant to be tested is heated at a specified temperature in the presence of certain metals and oxygen and the viscosity increase of the lubricant is determined. Additionally, information as to the corrosivity of a lubricant to metals and the degree of sludge and deposit formation can also be obtained.

Various functional fluid compositions containing an azo compound were tested according to the above procedure except that the temperature was held at 650 F. instead of 500 F. and the metal specimens used were, as specified in said procedure, steel, copper, silver, titanium, magnesium alloy and aluminum alloy. The viscosity of the fluid before and after testing was determined at F.

In Table I the percent stabilization is determined by the following formula:

Percent stabilization:

7 percent viscosity increase of the base stock plus azo compound after 24 hours at 65 F.

In Table I the base stock that was used was a mixture of -ring polyphenyl ether.

fective in controlling oxidative degradation of the base stock as is evidenced by the degree of stabilization of the compositions of this invention. Stabilization of a base stock is of particular importance in the many uses of Viscosity increase determined at 18 hours.

2 Minus sign signifies additive is prooxidant.

Viseosity increase determined at 21 hours.

A hearing test was run which was modified from MIL-- 11-27502. The test time was 100 hours using an ERDCO bearing. The test conditions for Example 8 were a bearing temperature of 600 F., a bulk oil temperature of 600 F. and an oil in temperature of 550 F. The test conditions for Example 9 are the same as for Example 8 except that the bearing temperature was increased to 650 F. In Table II the base stock that was used was a mixture of S-ring polyphenyl ether. The stabilizer that was used was 3,3- diphenoxyazobenzene.

1 Test terminated and viscosity determined at 62.5 hours.

2 Viscosity determined at 100 hours.

As is demonstrated by Tables I and II, it is clearly evident that the incorporation of an azo compound of this invention into a base stock provides a functional fluid composition which has a high degree of resistance towards oxidative degradation and, therefore, a greatly extended useful life. In regard to the extension of useful life, it has been found that the test procedure described above correlates quite well with the results obtained under full-scale aircraft gas turbine bearing tests and under conditions of actual use. It has been found that the magnitude of change in viscosity at 100 F. as measured by the test procedure is representative of the extent of increased service life obtainable under actual conditions. Thus, for example, the decrease in viscosity increase of a composition incorporating an azo compound of this invention was on the order of about three times less than the base stock viscosity increase for the same period of time. Of equal significance are the results as are set out with respect to phenolic-type antioxidants, which antioxidants have been effective in the prior art for inhibiting oxidative degradation of organic substances. The results in Table I with respect to these phenolic antioxidants show that the rate of oxidation of a composition which incorporates these antioxidants is higher than the neat base stock alone. The higher rate of oxidation with the phenolic antioxidants demonstrates that a compound can act as a prooxidant in systems operating at high temperatures. Of equal significance are the results set out in Table II since the hearing test correlates quite well with actual gas turbine performance in measuring the overall deposit rating and viscosity changes which would be expected to occur in actual use. Thus, the test of the neat base stock had to be terminated at the end of 62.5 hours with a substantial increase in viscosity. The compositions of the invention maintained the required temperature-viscosity relationship and did not become too thick on prolonged use thereby maintaining proper lubrication of mechanical parts in contact with the fluid.

Tables I and II in addition significantly demonstrate that the azo compounds at low concentrations are effunctional fluids since the required fluid characteristics can be maintained over extended periods of time during use by the incorporation of an azo compound. The incorporation of an azo compound into a base stock to control oxidative degradation is of particular importance since when fluid degradation occurs, such degradation can manifest itself in numerous ways among which are viscosity change, increase in acid number, formation of insoluble materials, increased reactivity and discoloration. In a fluid system the particular properties of a fluid have to be maintained in order to continue useful operation in the particular system in which the fluids are employed. Thus, changes in viscosity can be produced by fluid degradation whereby polymeric products with high molecular weights are produced in the fluid system. Such high molecular weight products often become inprecipitation or sludging of the insoluble material. Such precipitation and sludging plugs filters and causes deposits to form on moving parts which are lubricated by the fluid thereby causing inadequate lubricating and interference with the proper functioning of the parts. Increased chemical reactivity is observed on fluid degradation as well as a build-up in acid number of the fluid. Such increased chemical reactivity and high acid number allows the particular system which incorporates the fluid to be chemically attacked by the fluid thereby causing pitting, wear and alterations of the close tolerances of mechanical members in contact with said fluid. Thus, premature overhaul of mechanical parts can be a direct consequence of fluid degradation. It is, therefore, of particular importance that a base stock be stabilized so as to extend the useful life of a fluid in a functional fluid system.

As a result of the excellent stabilization of functional fluids which incorporate an azo compound, lubrication of gas turbine engines is obtained over extended periods of time. Thus, this invention relates to a novel method of lubricating gas turbine engines which comprises maintaining on the bearings and other points of wear a lubricating amount of a composition of this invention.

In addition, as a result of the excellent control of oxidative degradation utilizing the functional fluid compositions of this invention, improved hydraulic pressure devices can be prepared in accordance with this invention which comprise in combination a fluid chamber and an actuating fluid composition in said chamber, said fluid comprising a mixture of one or more of the base stocks hereinbefore described and a minor amount, suflicient to stabilize said base stock, of an azo compound. In such a system, the parts which are so lubricated include the frictional surfaces of the source of power, namely the pump, valves, operating pistons and cylinders, fluid motors, and in some cases, for machine tools, the ways, tables and slides. The hydraulic system may be of either the constant-volume of the variable-volume type of system.

The pumps may be of various types, including centrifugal pumps, jet pumps, turbine vane, liquid piston gas compressors, piston-type pump, more particularly the variable-stroke piston pump, the variable-discharge or variable displacement piston pump, radial-piston pump, axial-piston pump, in which a pivoted cylinder block is adjusted at various angles with the piston assembly, for example, the Vickers Axial-Piston Pump, or in which the mechanism which drives the pistons is set at an angle adjustable with the cylinder block; gear-type pump, which may be spur, helical or herringbone gears, variations of internal gears, or a screw pump; or vane pumps. The valves may be stop valves, reversing valves, pilot valves, throttling valves, sequence valves, relief valves, Servo valves, non-return valves, poppet valves or unloading valves. Fluid motors are usually constantor variable-discharge piston pumps caused to rotate by the pressure of the hydraulic fluid of the system with the power supplied by the pump power source. Such a hydraulic motor may be used in connection with a variable-discharge pump to form a variable-speed transmission. It is, therefore, especially important that the frictional parts of the fluid system which are lubricated by the functional fluid be protected from damage. Thus, damage brings about seizure of frictional parts, excessive wear and premature replacement of parts.

The fluid compositions of this invention when utilized as a functional fluid can also contain dyes, pour point depressants, metal deactivator, acid scavengers, antioxidants, defoamers in concentration suflicient to impart antifoam properties, such as from about to about 100 parts per million, viscosity index improvers such as polyalkylacrylates, polyalkylmethacrylates, polycyclic polymers, polyurethanes, polyalkylene oxides, substituted and unsubstituted polyphenylene oxides and polyesters, lubricity agents and the like.

It is also contemplated within the scope of this invention that the base stocks as aforedescribed can be utilized singly or as a fluid composition containing two or more base stocks in varying proportions. The base stocks can also contain other fluids which include, in addition to the functional fluids described above, fluids derived from coal products, and synthetic oils, e.g., alkylene polymers (such as polymers of propylene, butylene, etc., and the mixtures thereof), alkylene oxide-type polymers (e.g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing the alkylene oxide in the presence of water or alcohols, e.g., ethyl alcohol, alkyl benzenes (e.g., monoalkyl benzene such as dodecyl benzene, tetradecyl benzene, etc.), and dialkyl benzenes (e.g., n-nonyl Z-ethylhexylbenzene); polyphenyls (e.g., biphenyls and terphenyls), halogenated benzene, halogenated lower alkyl benzene, halogenated biphenyl and monohalogenated diphenyl ethers.

While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.

The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition comprising (A) a major amount of a base stock selected from the group consisting of (1) polyphenyl ethers, (2) phenoxybiphenyls and (3) mixtures thereof; and

(B) an oxidation inhibiting amounts of an azo compound selected from the group consisting of (1) a compound represented by the structure wherein a and b are whole numbers having a value of 0 to 5 and R and R are each selected from substituents selected from the group consisting of alkyl, aryl, amino, N-phenylamino, N- dimethylamino, cyano, nitro, halogen, sulfonic, carboxyl, carboalkoxy, phenoxy, phenylmercapto, alkoxy, hydroxyl, trifluoromethyl, alphacumyl and mixtures thereof and (2) azo naphthalene.

2. A composition of claim 1 wherein each R contains from 0 to 18 carbon atoms and a and b each have a value of from 0 to 2.

3. A composition of claim 2 wherein R and R each have from 0 to 9 carbon atoms.

4. A composition of claim 3 wherein R and R are each selected from the group consisting of alkyl, phenyl, phenoxy, phenylmercapto, bromo, hydroxyl, alpha-cumyl and trifluoromethyl.

5. A composition of claim 4 wherein a and b each have a value of from 0 to 1.

6. A composition of claim 5 wherein the azo compound is azobenzene.

7. A composition of claim 4 wherein the azo compound is (B) (1) and R and R are each selected from the group consisting of phenoxy, phenylmercapto and bromo.

8. A composition of claim 7 wherein R and R are selected from phenoxy and phenylmercapto and occupy the 2- and 2-position relative to the azobenzene nucleus.

9. A composition of claim 1 wherein the base stock is (A) (1).

10. A composition of claim 9 wherein (A)(1) is an unsubstituted polyphenyl ether containing from 3 to 7 aromatic rings.

11. A composition of claim 4 wherein the base stock is (A) (1) and (A) (1) is an unsubstituted polyphenyl ether containing from 3 to 7 aromatic rings.

12. A composition of claim 7 wherein the base stock is (A) (1) and (A) (1) is an unsubstituted polyphenyl ether containing from 3 to 7 aromatic rings.

13. A composition of claim 11 wherein the polyphenyl ether is m-bis(m-phenoxyphenoxy)benzene.

14. A method of lubricating a gas turbine engine which comprises maintaining on points of wear a lubricating amount of a composition of claim 1.

15. A method of lubricating a gas turbine engine which comprises maintaining on points of wear a lubricating amount of a composition of claim 9.

16. A method of lubricating a gas turbine engine which comprises maintaining on points of Wear a lubricating amount of a composition of claim 11.

References Cited UNITED STATES PATENTS 2,718,501 9/1955 Harle 25247 3,198,734 8/1965 Morway 25252X OTHER REFERENCES Kor ger et al., Oxidation of Naphthenes, Chemical Abstracts, vol. 44 (1950), pp. 1683, 1684 and 1685.

DANIEL E. WYMAN, Primary Examiner.

W. H. CANNON, Assistant Examiner.