US3236774A

US3236774A - Antioxidant composition and synthetic lubricant containing it

Info

Publication number: US3236774A
Application number: US216070A
Authority: US
Inventors: John W Thompson; Gerald S Cassell
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1962-08-10
Filing date: 1962-08-10
Publication date: 1966-02-22
Anticipated expiration: 1983-02-22
Also published as: FR1365022A; GB1016935A

Description

United States Patent 3,236,774 ANTIOXIDANT COMPOSITION AND SYNTHETIC LUBRICANT CONTAINING IT John W. Thompson and Gerald S. Cassell, Kingsport,

Tenn., assignors to Eastman Kodak Company, Rochester, N.Y a corporation of New Jersey No Drawing. Filed Aug. 10, 1962, Ser. No. 216,070 Claims. (Cl. 25246.7)

This invention relates to ester type synthetic lubricants and to the problem of protecting them from oxidative degradation.

Synthetic lubricants of the ester type have replaced petroleum oils in many lubricant and hydraulic fluid applications Where severe service conditions are encountered. As an example, esters such as bis(2-ethylhexyl)sebacate are used almost universally as lubricants in aircraft turbine engines of the pure jet and prop-jet types. However, under such severe service conditions, these organic esters as a class are very susceptible to oxidation. Consequently, in formulating satisfactory jet engine lube oils from esters and the like, measures must be taken to protect these esters from oxidative attack under these severe service conditions.

Phenothiazine has been one of the most used anti oxidants for ester type synthetic lubricants. It has been reasonably satisfactory for moderately high jet engine temperatures. However, as is well-known, phenothiazine is a dirty antioxidant, causing the formation of insoluble sludges during lubricant use. In addition to such sludging characteristics, phenothiazine does not appear to stabilize ester lubricants satisfactorily at the higher temperatures for which current militry and civil jet engines are being designed. a

A problem, therefore, to which this invention provides a solution is how to minimize, if not eliminate, the sludging characteristics of phenothiazine under the more severe service conditions and particularly higher temperatures, as well as to increase the stabilizing action of the phenothiazine at these higher temperatures.

This invention is based upon the discovery that small amounts of acidic phosphorus compounds greatly improve the antioxidant properties of arylamine type antioxidants and particularly phenothiazine in ester lube oils for aircraft jet engines. The acidic phosphorus compounds have been found to retard the sludging or dirtiness caused by the arylamine antioxidants and to increase the antioxidant action or stabilizing action of the arylamine antioxidants.

I" In summary, this lnvention comprises an antioxidant composition particularly useful for ester type synthetic lubricants. In addition, this invention broadly comprises an ester type synthetic lubricant containing the antioxidant composition at an efiective or protective concentration.

The antioxidant composition of this invention comprises a mixture consisting essentially of an arylamine antioxidant portion and at a minor concentration relative to the arylamine antioxidant portion an acidic phosphorus portion. The arylamine antioxidant portion of the composition consists essentially of at least one arylamine antioxidant. Examples of an arylamine antioxidant include phenothiazines such as phenothiazine, phenothiazine derivatives containing substituents on the nitrogen atom and phenothiazine derivatives containing substituents on the rings, alkylated diphenylamines, N-phenylnaphthylamines and dinaphthylamines. Prefered arylamine antioxidants include N-alkylphenothiazines wherein the N-alkyl group has 1-18 carbon atoms, N-phenyl-l-naphthylamine and p,p'-dialkyl diphenylamines such as p,p'-dioctyldiphenylamine, wherein the p and p-alkyl groups each have 1-18 carbon atoms. In preferred embodiments of this invention the arylamine antioxidant portion consists essentially of a mixture of an N-alkylphenothiazine and a p,p-dialkyldipldienylamine. Typical examples of such a mixture inc u e:

N-ethylphenothiazine and p,p'-dioctyldiphenylamine N-butylphenothiazine and dinonyldiphenylamine N-octylphenothiazine and p,p'-dibutyldiphenylamine N-d-odecylphenothiazine and p,p-dioctyldiphenylamine N-ethylphenothiazine and N-phenyl-l-naphthylamine N-acetylphenothiazine and p,p'-dioctyldiphenylamine N-methylphenothiazine and N-phenyl-Z-naphthylamine N-decylphenothiazine and diphenylamine N-ethylphenothiazine and di-l-naphthylamine The weight ratio of the N-alkylphenothiazine to the p,p'- dialkyldiphenylamine is generally in a range from about 1:3 to about 3:1 and preferably in a range from about 2:3 to about 3:2.

The acidic pohsphorus portion of the antioxidant composition of this invention consists essentially of at least one acidic phosphorus compound. This is a compound having at least one acid (OH) group attached to a phosphorus atom. Such a compound is present in phosphoric acid, phosphorous acid and organic partial esters of these acids. The organic partial esters of these acids are preferred since they are more soluble in the esters normally employed as synthetic lubricants, and are less extractable therefrom by aqueous solutions. The organic partial esters of phosphoric acid include alkyl dihydrogen phosphates, dialkyl hydrogen phosphates, aryl dihydrogen phosphates, diaryl hydrogen phosphates, alkylaryl dihydrogen phosphates and di(alkylaryl)hydrogen phosphates. It is preferred that the alkyl groups in these compounds that have such contain 18 carbon atoms. The organic partial esters of phosphorous acid include alkyl dihydrogen phosphites, dialkyl hydrogen phosphites, aryl dihydrogen phosphites, diaryl hydrogen phosphites, alkylaryl dihydrogen phosphites and di(alkylaryl)hydrogen phosphites. Here, too, it is prefered that the alkyl groups in these compounds that have such contain 1-8 carbon atoms. Under the concepts of this invention the acidic phosphorus portion of the antioxidant composition of the invention can consist essentially of a mixture of acidic phosphorus compounds. Generally, the acidic phosphorus esters are obtained commerically as mixtures of the monoalkyl and dialkyl derivatives and are referred to as alkyl acid phosphates and alkyl acid phosphites. These mixtures are within the concepts of this invention. Preferred, specific, acidic phosphorus compounds include ethyl acid phosphate, butyl acid phosphate, methyl acid phosphate and phosphorous acid.

Concentration of the arylamine antioxidant portion of the mixture which characterizes the antioxidant composition of this invention is generally greater than the concentration of the acidic phosphorus portion of the mixture. Usually, concentration of the arylamine antioxidant portion is broadly in a range from about 95.3 to about 99.95 by weight of the mixture and preferably in a range from about 97.6 to about 99.75. Concentration of the acidic phosphorus portion of the mixture usually is broadly in a range from about 0.05 to about 4.7% by weight of the mixture and preferably in a range from about 0.25 to about 2.4% by weight of the mixture.

The antioxidant composition is prepared by admixing the components thereof until a uniform blend is obtained.

The synthetic lubricant of this invention consists essentially of an organic ester base stock and at a protective concentration the antioxidant composition of this invention.

The organic ester base stock consists essentially of at least one organic ester which is an oil at 20 C. Such an ester is provided by various diesters of dibasic acids and alcohols, diesters of monobasic acids and glycols, triesters of monobasic acids and trihydric alcohols such as trimethylolethane, trimethylolpropane and the like, pentaerythritol tetraesters, and polyesters such as those obtained from a dibasic acid and a glycol and chain terminated with either an alcohol or a monobasic acid. Typical organic esters include:

2-butyl-2-ethyll ,3-propanediol dipelargonate 2-ethyl-2-isobutyl-l,3-propanediol diundecanoate 2,2-diethyl-l,3-propanediol dipelargonate Bis(2,2,4-trimethylpentyl)azelate Bis(2,2,4-trimethylpentyl)undecanedioate Bis 2-methyl-2-norcamphanylmethyl sebacate 1,l-cyclopentanedimethanol dipelargonate Trimethylolpropane triheptanoate Pentaerythritol tctrahexanoate Bis(2-ethylhexyl)sebacate Esters of alcohols and oleic acid dimers and trirners Polyester of azelaic acid, neopentyl glycol and 2,2,4-trimethylpentanol at a mole ratio of 1:1:0.25

Polyester of azelaic acid, 2-butyl-2-ethyl-1,3-propanediol and octanoic acid at a mole ratio of 1:1:0.25

Concentration of the antioxidant composition of this invention in the synthetic lubricant in general depends upon the ester base stock and on the degree of stability desired. However, in general, a concentration of the antioxidant composition in a range from about 0.1005 to about 5.2% by weight of the ester base stock and preferably in a range fro-m about 0.201 to about 4.05% by weight of the ester base stock gives satisfactory results. At these concentrations, the concentration of the arylamine antioxidant portion of the antioxidant composition is in a general range from about 0.1 to about by Weight of the ester base stock and preferably in a range from about 0.2 to about 4% by weight of the ester base stock. Similarly, at these concentrations, the acidic phosphorus portion of the antioxidant composition is present at a concentration in a general range from about 0.0005 to about 0.2% by weight of the ester base stock and preferably in a range from about 0.001 to about 0.05% by weight of the ester base stock.

Besides the ester base stock and antioxidant composition, the synthetic lubricant of this invention can also comprise other additives such as lubricity improvers, anticorrosion agents, metal deactivators, detergents, dyes and phenolic antioxidants.

The synthetic lubricant of this invention is prepared merely by admixing the components thereof until a uniform blend, usually in the form of a solution, is obtained. In admixing the components of the synthetic lubricant, the antioxidant composition can be added as such to the ester base stock or the components of the antioxidant composition can be individually added to the ester base stock whereby the antioxidant composition is formed in the ester base stock.

The synthetic lubricant of this invention is suitable for a variety of severe service uses. Indeed specific embodiments thereof satisfy military and civil jet engine specifications such as MILL7808D, MILL25,336, MIL-L9236B, MILL27,502, DERD 2487 and others. In addition the synthetic lubricant has utility under less severe service conditions as a hydraulic fluid, industrial lubricant, coolant fluid and automotive lubricant.

This invention is further illustrated by the following examples of various aspects thereof, including preferred specific embodiments of the invention. This invention is not limited to these specific embodiments unless otherwise indicated.

Specific embodiments of the antioxidant composition of this invention are formulated as follows:

EXAMPLE 1 Components: Parts by Weight N-ethylphenothiazine p,p-Dioctyldiphenylamine 100 Ethyl acid phosphate 0.1

EXAMPLE 2 Components:

N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100 Ethyl acid phosphate 0.5

EXAMPLE 3 Components:

N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100 Ethyl acid phosphate 0.75

EXAMPLE 4 Components:

N-ethylphenothiazine 100 p,p'-Dioctyl-diphenylamine 100 Ethyl acid phosphate 1 EXAMPLE 5 Components:

N-ethylphenothiazine 100 p,p'-Di0ctyl-diphenylamine 100 Ethyl acid phosphate 2 EXAMPLE 6 Components:

N-ethylphenothiazine 100 p,p'-Dioctyl-diphenylamine 100 Ethyl acid phosphate 10 EXAMPLE 7 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Dodecyl acid phosphate 1 EXAMPLE 8 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 2,2 dimethyl 1,3 propanediol cyclic hydrogen-phosphate 0.6

EXAMPLE 9 Components:

N-ethylphenothiazine 100 p,p'-Dioctyl-diphenylamine 100 o-Phosphoric acid 0.36

EXAMPLE 10 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 o-Phosphoric acid 0.42

EXAMPLE 11 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 2,2 dimethyl 1,3 propanediol cyclic hydrogen-phosphite 1 EXAMPLE 12 Components:

N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100 Diethyl hydrogen phosphite 0.44

EXAMPLE 13 Components:

N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100 Bis(2-ethylliexyl) hydrogen phosphite 1 3 K EXAMPLE 14 Components: Parts by weight N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Ethyl acid phosphate 1 EXAMPLE 15 Components:

N-ethylphenothiazine 100 N-phenyl-l-naphthylamine 100 Ethyl acid phosphate 0.5

EXAMPLE 16 Components:

N-ethylphenothiazine 100 p,p' Dioctyldiphenylamine 100 Butyl acid phosphate 1.3

EXAMPLE 17 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Diphenyl hydrogen phosphate 1.2

EXAMPLE 18 Components:

N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Methyl acid phosphate 0.6

Each one of the antioxidant compositions of the foregoing specific formulations are prepared merely by admixing the components at room temperature until a uniform blend is obtained.

Specific embodiments of the synthetic lubricant of this invention are formulated as follows.

EXAMPLE 19 Components: Parts by weight Ester base stock2-buty1-2-ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant composition N-ethylphenothiazine -l00 p,p'-Dioctyldiphenylamine 100 Ethyl acid phosphate 0.1

EXAMPLE 20 Components:

Ester base stock-2-butyl-2-ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant composition N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100 Ethyl acid phosphate 0.5

EXAMPLE 21 Components:

Ester base stock2-butyl-2-ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant composition- N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Ethyl acid phosphate 0.75

EXAMPLE 22 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,00 Antioxidant composition N-ethylphenothiazine 100 p,p'-Dioctyldiphenyl-arnine 100 Ethyl acid phosphate :1

EXAMPLE 23 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant composition- N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Ethyl acid phosphate 2 6 EXAMPLE 24 Components: Parts by weight Ester base stock2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant composition N-ethylphenothiazine p,p'-Dioctyldiphenylamine 100 Ethyl acid phosphate 10 EXAMPLE 25 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant composition N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Dodecyl acid phosphate 1 EXAMPLE 26 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant composition N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 2,2 dimethyl 1,3 propanediol-cyclic hydrogen-phosphate 0.6

EXAMPLE 27 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant composition N-ethylphenothiazine 100 p,p'-Diocty1diphenylamine 100 o-Phosphoric acid 0.36

EXAMPLE 28 Components:

Ester base stock-2 butyl 2 ethyl-1,3-pr0- panediol dipclargonate 10,000 Antioxidant composition N-ethylphenothiazine 100 p,p'-Dioctyldipheny1amine 100 o-Phosphoric acid 0.42

EXAMPLE 29 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipel-argonate 10,000 Antioxidant composition N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 2,2 dimethyl 1,3 propanediol-cyclic hydrogen-phosphite 1 EXAMPLE 30 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant composition N-ethylphenothiazine 100 Samples 615 in Table I, it will be noted, have the anti- Diethyl hydrogen phosphite 0.44

EXAMPLE 31 Components:

Ester base stock-2 butyl 2 ethyl-1,3-propanediol dipelargonate 10,000 Antioxidant composition- N-ethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 Bis(2-ethy1hexyl)hydrogen phosphite 1 7 EXAMPLE 32 Components: Parts by weight Ester base stock2 butyl 2 ethyl-1,3-propanediol dipelargonate Antioxidant composition 8 EXAMPLE 37 Components: Parts by weight Ester base stookBis(2,2,4-trimethylpentyl) azelate 10,000 Antioxidant composition N-dodecylphenothiazine 100 N-ethylphenothiazine 100 p,p-Dioctyldiphenylamine 100 p,p'-D1octyldiphenylamlne 100 Ethyl acid phosphate 1 Ethyl ac1d phosphate 1 EXAMPLE 38 EXAMPLE 10 Components: Components: Ester base stock1lrimethylolpropane tri- Ester base stock2 butyl 2 ethyl-1,3-p1oheptanoate 10,000

panediol dipelargonate 10,000 Antioxidant composition Antioxidant composition- N-ethylphenothiazine 100 Nethylphenothiazine 100 p,p'-Dioctyldiphenylamine 100 N-phenyl-l-naphthylamine 100 Ethyl acid phosphate l Ethyl and phosphate The synthetic lubricant compositions of the foregoing formulations are prepared merely by admixing the various EXAMPLE 34 components specified in the formulations. Such mixing components! is preferably undertaken at room temperature and is Ester P2186 Y Y s 'P continued until the components of the antioxidant com- P F dlpelargqqate 10,000 position are dissolved in the ester base stock.

AntlOXldaHt P The effectivenes of the antioxidant composition of this e v p q 100 25 invention and the stability of the. synthetic lubricant of PBP Q Y P Y 100 this invention are demonstrated by the following test data Butyl acld Phosphate obtained in actual tests on samples of synthetic lubricants formulated as indicated in the following tables. The EXAMPLE tests and measurements employed in the testing are as Components: 30 follows.

Ester base stock-2Hbutyl-2-ethyl-L3-pro- AF oxzdatzon test i f dlpel'aTgqllate 10,000 This test, which indicates the oxidation stability of the Annoxldant f P synthetic lubricant at high temperatures, is described in N"3,thY lPhen" th1aZme 1 100 a paper entitled Materials for High Temperature Jet P 'Dloctyldlphenylamme 100 39 Engine Lubricants (H. E. Adams) in W.A.D.C. Tech Drphenyl hydrogen phosphate nical Report 59244 (Air Force, 1959). The test conditions employed in this test are selected to simulate high EXAMPLE 36 temperature jet engine and bearing rig operation condi- Components: tions.

Ester base st0ck-2 butylr2-ethyl-l,3-pro- 40 In this test a 250 milliliter sample of the lubricant is paned-iol dipelargonate 10,000 heated at 425 F. in a Pyrex test tube while 96 liters of Antioxidant composition air per hour are blown through it. A freshly polished N-ethylphenothiazine 100 metal panel is immersed in the lubricant. The test tube is p,p'-Dioctyldiphenylamine 100 capped with a Pyrex fitting which allows volatile products Methyl acid phosphate 0.6 40 to escape from the tube. The lubricant in the tube is TABLE I Additives Viscosity acid N 0. at- Sludge rating (hours) Sample Gone. in Gone. in

N 0. percent Acidic phosphorus percent Arylamines by wt. compound by wt. 120 hrs. 120 hrs. 20 40 of ester of ester base stock base stock 1 No11e None 104.7 12.4 0

(at 20 hrs.) (at 20 hrs.) N-ethylphenothiazine 2 d0.. 23.8 5. 26 8 10 10 (at 60 hrs.) (at 60 hrs.) p,p-Dioctyldiphenylamine 2 .-..d0 116.5 13.63 2 N th 1 hen thiaziue (at 20 hm) (at 20 hrs') -8 O p,p-D io t :tyldiphenylam 1e" 0 1 2 G 8 9 None. Ethyl acid phosphate 0.0075 30.98 17.14 0 N th 1 hen thia inc 1 (M20 hrs') (M20 his) -e 0 Z i p i g ldi nen mmma 1 M01 364 O 0 1 2 8 8 1 11i g g gggfg gg g do 0.005 20.0 3.07 0 0 0 0 o 2 if i tfilfi lfifiglinnsi i W m 0 0 1 2 3 en f, fi :f 1 d0.... 0.1 22.3 a. 07 1 1 1 4 4 5 i f fi iggl sfl lgggfg g }Dodecylacid phosphate.-- 0.01 21.2 a. 01 0 1 1 2 3 a N-ethylpheuothiazine 1 2,2-dimethyl1,3-propane 0.006 22.5 4. 23 1 1 2 3 3 4 diol cyclic hydrogen p,p-Dioctyldiphenylaminm. 1 phosphate. 12 g igig ggiflf gfigf gfig }o-Phosphoric acid 0.0030 20.8 3. 20 0 0 0 1 1 1 13 g fi g gfif figf fi 1 do 0. 0042 22.5 3.27 1 1 1 2 5 4 14 N-ethylphenothiazine 1 }Diethyl hydrogen phos- 0.0044 0 0 0 4 p,p-Dioctyldiphenylarnine. 1 phite. 15 N-ethylphenothiazino 1 }Bis(2-ethylhexyl) hydro- 0.01 22.0 3.85 0 0 0 2 3 4 p,p-Dioctyldiphenylaminen 1 gen phosphite.

heated in 20 hour cycles and at the end of each cycle the tube is cooled, a 10 milliliter sample of the lubricant is Withdrawn for analysis and the lubricant lost by evaporation is replaced with fresh lubricant. Ordinarily the test is conducted for 6 cycles or 1 20 hours. The 10 rnil liliter samples are analyzed for viscosity in centistokes at 100 F. (ASTM Method D445), acid number (in milligrams of KOH per gram) (ASTM Method D974) sludge content. Sludge content is determined by filtering a 2 milliliter sample of the lubricant through a Whatman No. 2 filter paper (4.25 centimeters), washing the paper with 25 milliliters of Stoddard solvent, drying the paper and then rating the sludge deposit on the paper according to a scale from to 10, 0 being equivalent to clean and 10 designating hea-vy deposit.

In the first series of tests the ester base stock in each sample consisted essentially of 2-tbutyl-2-ethyl-1,3-propanediol dipel-angonate and was characterized by an acid number (milligrams of KOH per gram) of 0.03, a viscosity at 65 F. of 15,084 centistokes, a viscosity at 100 F. of 14.32 centistokes and a viscosity at 210 F. of 3.33 centistokes, an open cup flash point of 443 F. and a pour point of less than -70 F. The test samples containing additives were prepared from this ester base stock and the specific additives at specific concentrations indicated in the preceding Table I. These test samples were prepared merely by admixing the additives into the ester base stock until in each case a uniform blend was obtained. The metal panels employed in these particular tests were made of steel and each had the dimensions: 1 inch by 1 inch by inch. The test results and other test conditions in this first series of tests are set out in the preceding Table 1.

Samples 6-15 in Table I, it will be noted, have the antioxidant compositions of Examples 1-2, -10 and 12-13, and correspond in formulation to the specific synthetic lubricants of Examples 19-20, 23-28 and 30-31.

In the case of Samples 1, 3 and 5, the AF oxidation test procedure was stopped after 20 hours due to the obviously rapid oxidation of the samples, and viscosity and acid number measurements were then made on these samples. In the case of sample 2, the AF oxidation test procedure was terminated after 60 hours, because of the highly oxi- 10 dized condition of the sample, and viscosity and acid number measurements were then made on the sample. All other samples (4 and 6-15), were subjected to the AF oxidation test for the full 120 hours.

A comparison of the test data of Sample 6 with the test data of Samples 1-5 demonstrates the need for an etfective antioxidant composition in the ester base stock and the fact that the antioxidant composition in Sample 6 is effective. Comparison of the data of Samples 6-15 with the data of Sample 4 reveals the dramatic effect of various acidic phosphorus compounds on the antioxidant activity of the arylamine antioxidant mixture of Sample 4, especially in regard to reduction in sludging tendency.

In the next test series summarized in the following Table 11, test samples of synthetic lubricants were prepared from difierent ester base stocks and with various arylamine antioxidants and ethyl acid phosphate. In this series of tests, the ester base stock identified in Table II as BEPD consisted essentially of 2-butyl-2-ethyl-1,3-propanediol dipelargonate and had an acid number (milligrams of KOH per gram) of 0.03, a viscosity at F. of 15,084 centistokes, a viscosity at 100 F. of 14.32 centistokes, a viscosity at 210 F. of 3.33 centistokes, an open cup flash point of 443 F. and a pour point of less than F. The ester base stock identified in Table 11 as TMPZ consisted essentially of bis(2,2,4-trimethylpentyl) azelate and had an acid number (milligrams of KOH per gram) of 0.06, a viscosity at 65 F. of 8,940 centistokes, a viscosity .at 100 F. of 13.14 centistokes, a viscosity at 210 F. of 3.45 centistokes, an open cup flash point of 425 F. and a pour point less than F. The ester base stock identified in Table II as TMPTH consisted essentially of trimethylolpropane triheptanoate and was characterized by an acid number (milligrams of KOH per gram) of 0.07, a viscosity at 65 F. of 17,911 centistokes, a viscosity at F. of 16.09 centistokes, a

viscosity at 210 F. of 3.66 centistokes, an open cup flash point of 450 F., and a pour point of less than -65 F. The test samples were prepared by admixing the components thereof until solutions Were formed. The metal panels employed in these particular tests were made of steel and each had the dimensions: 1 inch by 1 inch by inch. The test results and test sample formulations are set forth in the following Table II.

TABLE II Sample composition Test results Sample Gone. in Acidic Gone. in Hours 0. Ester base Arylarmnes percent by phosphorus percent by Property stock wt. of ester compound wt. of ester base stock base stock 0 20 40 60 80 100 Viscosity" 15.03 17.95 19.64 21.63 23.63 26.48 31.91 1 BEPD N-dodccylphenothiazme 1 }None Acid No 0.05 2.20 3.68 3.46 3.27 4.75 5.36 p,p-dioctyldiphenylamme l Sludfige 0 0 0 1 2 2 4 re mg. Viseosity 15.03 16.44 17.29 18.36 19.72 20.96 22.48 2 BEPD N-dodecylphenothiazine-. 1 }Ethyl acid 001 Acid No 0.14 0.96 1.37 2.08 4.09 2.77 p,p-dioctyldiphenylamine 1 phosphate. Sludtge 0 0 0 0 1 1 2 re mg. Viscosity" 15.03 16.17 18.77 3 BEPD N-ethylphenothiazme 1 }None Acid No 0.04 1.00 3.44 N-phenyl-l-naphthylamine 1 Sludge 0 6 7 rating. isc0Sity 15.03 15.81 20.16 4 BEPD N-ethylphenothiazine 1 Ethyl acid 0 005 Acid No 0.10 0.72 4.42 N-phenyl-l-naphthylamine.. 1 phosphate. Sludge 0 2 3 ra mg. iseosity 13.58 15. 30 16.38 17.84 19.42 21.61 23.47 5 TMPZ N-ethylphenothiazine 1 }None Acid No 0.15 1.69 2. 77 2.64 3.16 3.70 3.66 p,p-dioctyldiphenylamine 1 Sludgge 0 0 2 4 6 8 8 In mg. Viscosity 13.58 15.07 16.14 17.39 19.30 20.16 22.68 6 TMPZ N-ethylphenothiazine 1 Ethyl acid 0 01 Acid No 0.43 0.96 1.99 2.05 3.10 3.19 4.12 p,p-dioetyldiphenylamine 1 phosphate. Sludtge 0 0 0 1 3 3 3 ra mg. iscosity 16. 62 20.19 22.40 24.81 28.07 32.09 38.39 7 TMPTH N-ethylphenothiazine 1 }None Acid No 0.03 1.27 1.98 2.55 3.91 3.95 5.52 p,p-dioctyldiphenylamine 1 Sludtge 0 0 0 1 2 2 2 ra mg. Viscosity 16.62 19.50 20.28 22.85 24.65 26.42 29 38 8 TMPTH N-ethylphenothiazine 1 Ethyl acid 0 01 Acid No 0.23 0.95 1.51 2.09 2.91 2 87 3.17 p,p-dioctyldiphenylamine 1 phosphate. Sludtge 0 0 0 0 1 l l ra mg.

1 1 Sample 2 in Table II has the specific antioxidant composition of Example 14 and corresponds in formulation to the specific synthetic lubricant of Example 32. Sample 4 in Table II has the specific antioxidant composition of oxidant compositions of Examples 17 and 18, respectively, and corresponded in formulation to the specific synthetic lubricants of Examples 35 and 36, respectively.

These data of Table III dramatically illustrate the bene- Example 15 and corresponds in formulation to the specific 5 ficial efiect of acidic phosphorus compounds on arylsynthetic lubricant of Example 33. Samples 6 and 8 amine antioxidants in stabilizing synthetic lubricants of have the specific antioxidant composition of Example 4 the ester type. These data show that acidic phosphorus and correspond in formulation to the specific synthetic compounds substantially reduce sludging of synthet1c lubricants of Examples 37 and 38, respectively. lubricants of the ester type, when containing arylamlne These data of Table II demonstrate the outstanding 10 antioxidants. effectiveness .of the various specific embodiments of the Thus, there is provided an antioxidant composition antioxidant composition of this invention in protecting which is particularly useful for synthetic lubricants of several different ester base stocks from oxidative attack, the ester type, which are intended for severe servlce and particularly in reducing sludging. In addition, these use. Moreover, there is provided a synthetic lubricant data demonstrate the outstanding stability of a number which has a high degree of protection relat1ve to oxidaof specific embodiments of the synthetic lubricant of this tive degradation, particularly under severe service coninvention. ditions.

In the next series of tests which are summarized in the Other features, advantages and specific embodiments following Table III the ester base stock that was used of this invention will be apparent to those in the exercise consisted essentially of 2-butyl-2-ethyl-1,3-propanediol diof ordinary skill in the art after reading the foregoing pelargonate and was characterized by an acid number disclosure. In this connection, while this IHVCIllZlOIl has (milligrams of KOH per gram) of 0.03, a viscosity at been described in considerable detail relative to spec1fic of 15,054 Centistokes, t1 Viscosity at 00 F. of embodiments thereof, variations and modifications of 14-32 Centistokes, a Viscosity at Of -33 C tithese specific embodiments can be effected within the Stokes, an p p as point 0f 4 3 F. and a pour point spirit and scope of the invention as disclosedand claimed. of 1655 than TO test Samples of this Stock Were The embodiments of the invention in which an excluadded N'etbylpbenothiazine and PM- y p y sive property or privilege is claimed are defined as follows: amine, the concentration of each one of these arylamines 1 A ti idant composition comprlsing a mixture in the ester base Stock being 1% y Weight of the ester consisting essentially of (1) an arylamine antioxidant porbase stock. Where indicated in the following Table III, i consisting e entially of (a) N-alkylphenothiazlne specific acidic phosphorus compounds were added to h i h N- 1k 1 group h .143 carbon atoms and various ones of the test samples. In each case the addi- (b) -d-ialkyldi henylamine wherein the p and p -alkyl tives and ester base stock were admixed until a solution ou each have 1-18 carbon atoms, the vvelght 111 1 f was formed. In the stability testing of these test samples, th N-alkyl-phenothiazine to the p,p-d1alkyld1phenyl the degree of metal to lubricant contact was increased by amine b i i a range f bo t 1: 3 to about 3:1, and replacing the smaller metal panels with larger metal panels 2) an acidic phosphorus portion consisting essentially (11/2 inches y 6 inches y /16 inch) and y using both of at least one acidic phosphorus compound selected from steel and aluminum panels except where otherwise indithe group consisting of an alkyl acid phosphate wherein cated. Formulations of the various test samples and test the alkyl group contains from 1 to 10 carbon atoms, 0- results are set out in the following Table III. phosphoric id, diphenyl hydrogen h hate, d ethyl TABLE III Gone. in Hours Sample Acidic phosphorus compound percent by Metal panels used Property No. wt. of ester base stock 0 20 40 Viscosity 15. 03 23. 03 31.13 42.96 N m teel only {Acid N0 0.04 5.55 9.06 17.97

Sludge rating. 0 1 4 6 Viscosity 15. 03 24.80 37. 59 56.36 95.72 2. None... Steel plus a1uminum {Acid No 0.04 6.55 9.65 10.49 10.71 Sludge rating. 0 3 3 6 iscosity 15. 03 16.20 17.05 18.06 19.16 .35 21.72 3 Ethyl acid phosphate 0.0075 do {Xcid No 0.11 0.69 1.16 1.38 1.84 3.38 3.12 Sludge rating. 0 1 0 0 1 1 1 Viscosity 15. 03 16.47 17.21 18.44 19.59 21.01 22.60 4 Butyl acid phosphate 0.013 (10 {Acid No 0.12 2.46 1.75 1.96 1.53 3.19 Sludge ratin 0 2 2 2 2 2 2 4 Viscosity 15. 03 16.28 17.15 18.25 19.86 21.06 22.73 2,?rd1rnethyl-1,3-propa11ed1ol- 5 cyclie-hydrogen-phosphite. {g gg gg 3 3 3 8 2 Viscosity 14. 91 16.17 17.03 18.11 19.01 20.05 21.47 6 Diphenylhydrogenphosphatc. 0.012 .d0 {Acid No 0.21 1. 26 1. 64 1.89 2.57 3.27 Sludge rating. 0 1 2 2 3 5 6 iscosity .14.91 16.17 17.08 17.73 18.41 19.41 20.95 7 Methyl acid phosphate 0.006 do {from No 0.14 1.38 2.10 2.46 2.15 3.27 3.40 Sludge rating- 0 0 0 0 O 0 2 Sample 3 of Table III, it will be observed, had the antioxidant composition of Example 3 and corresponded in formulation to the specific synthetic lubricant of Example 21. Sample 4 contained the antioxidant composition of Example 16 and corresponded in formulation to the specific synthetic lubricant of Example 34. Sample 5 had the antioxidant composition of Example 11 and corresponded in formulation to the specific synthetic lubricant of Example 29. Samples 6 and 7 contained the antihydrogen phosphite, bis(2-ethyl hexyl)hydrogen phosphite and 2,2-dimethyl-1Q3 propanediol-cyclic-hydrogenphosphite, the concentration of said arylamine antioxidant portion being in a range from about 95.3 to about 99.95% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.05 to about 4.7% by weight of said mixture.

2. An antioxidant composition comprising a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of (a) N-alkylphenot hiazine wherein the N-alkyl group has 1-"18 carbon atoms and (b) p,p'-dialkyldiphenylamine wherein the p and p-alkyl groups each have 1- 18 carbon atoms, the weight ratio of the N-a'lkylphenothiazine to the p,p-dialkyldiphenylamine being in a range from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of at least one acidic phosphorus compound selected from the group consisting of an alkyl acid phosphate wherein the alkyl group contains from 1 to 10 carbon atoms, o-phosphoric acid, diphenyl hydrogen phosphate, diethyl hydrogen phosphite, bis(2-ethylhexyl)hydrogen phosphite and 2,2- dilmethyl 1,'3 =propanediol-cyclic hydrogen-phosphite, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

3. An antioxidant composition comprising a mixture consisting essentially of ('1) an arylamine antioxidant portion consisting essentially of N-ethylp-henothiazine and p,p'-dioctyldiphenylamine, the Weight ratio of said N-ethylphenothiazine to said p,p-dioctyldiphenylamine being in a range-from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of at least one acidic phosphorus compound selected from the group consisting of an alkyl acid phosphate wherein the alkyl group contains from 1 to 1 carbon atoms, o-phosphoric acid, diphenyl hydrogen phosphate, diethyl hydrogen phosphite, bis(2-ethylhexyl) hydrogen phosphite and 2,2- dirnethyl 1,3 propanediolcyclic-hydrogen-p hosphite, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by Weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

4. An antioxidant composition comprising a mixture consisting essentially of 1) an arylamine antioxidant portion consisting essentially of N-ethylphenothiazine and p,p-dioctyldiphenylamine, the Weight ratio of said N- ethylphenot hiazine to said p,p'-dioctyldiphenylamine being in a range from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of ethyl acid phosphate, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by Weight of said mixture.

5. An antioxidant composition comprising a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of N-et'hylphenothiazine and p,p-dioctyldiphenylamine, the weight ratio of said N- ethylphenothiazine to said p,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2, .and (2) an acidic phosphorus portion consisting essentially of dodecyl acid phosphate, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

6. An antioxidant composition comprising a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of N-ethylphenothiazine and p,p'-dioctyldiphenylamine, the weight ratio of said N- ethylphenothiazine to said p,p'-dioctyldiphenylamine being in a range from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of o-phosphoric acid, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

7. An antioxidant composition comprising a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of N-ethylphenothiazine and p, p-dioctyldiphenyla-mine, the weight ratio of said N-ethylp'henothiaizne to said p,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of butyl acid phosphate, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75 by Weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

8. An antioxidant composition comprising a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of N-ethylphenothiazine and p,p'dioctyldiphenylamine, the weight ratio of said N- ethylphenothiazine to said p,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of diphenyl hydrogen phosphate, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by Weight of said mixture.

9. An antioxidant composition comprising a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of N-ethylphenothiazine and p,p'-dioctyldiphenylamine, the weight ratio of said N- ethylphenothiazine to said p,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of methyl acid phosphate, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

10. An antioxidant composition comprising a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of N-ethylphenothiazine and p,p'-dioctyldiphenylamine, the Weight ratio of said N- ethylphenothiazine to said p,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of 2,2- dimethyl-l ,3 -propanediol-cyclic-hydrogen-phosphite, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

11. An antioxidant composition comprising a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of N-ethylphenothiazine and p,p-dioctyldiphenylamine, the weight ratio of said N- ethylphenothiazine to said p,pdioctyldiphenylamine being in a range from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of diethyl hydrogen phosphite, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by Weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

12. An antioxidant composition comprising a mixture consisting asentially of (1) an arylamine antioxidant portion consisting essentially of N-ethylphenothiazine and p,p-dioctyldiphenylamine, the weight ratio of said N- ethylphenothiazine to said p,p-dioctyldiphenylamine being in a range from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of bis- (2-ethylhexy1)hydrogen phosphite, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

13. A11 antioxidant composition comprising a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of N-dodecylphenothiazine and p,p'-dioctyldiphenylamine, the weight ratio of said N-dodecylphenothiazine to said p,p'-dioctyldiphenylamine being in a range from about 2:3 to about 3:2, and (2) an acidic phosphorus portion consisting essentially of ethyl acid phosphate, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

14. A synthetic lubricant consisting essentially of (A) an organic ester base stock and (B) at a concentration in a range from about 0.20 to about 4.05% by weight of said organic ester base stock a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of (a) N-alkylphenothiazine wherein the N- alkyl group has 1-18 carbon atoms and (b) p,p-dialkyldiphenylamine wherein the p and p-alky1 groups each have 1-18 carbon atoms, the weight ratio of the N-alkylphenothiazine to the p,p'-dialkyldiphenylamine being in a range from about 1:3 to about 3:1, and (2) an acidic phosphorus portion consisting essentially of ethyl acid phosphate, the concentration of said arylamine antioxidant portion being in a range from about 95.3 to about 99.95% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.05 to about 4.7% by weight of said mixture.

15. A synthetic lubricant consisting essentially of (A) an organic ester base stock and (B) at a concentration in a range from about 0.20 to about 4.05% by weight of said organic ester base stock a mixture consisting essentially of (1) an arylamine antioxidant portion consisting essentially of (a) N-alkylphenothiazine wherein the Nalkyl group has 1-18 carbon atoms and (b) p,-p'- dialkyldiphenylamine wherein the p and p-alkyl groups each have 118 carbon atoms, the weight ratio of the N-alkylphenothiazine to the p,p-dialkyldiphenylamine being in a range from about 2:3 'to about 3:2, and (2) an acidic phosphorus portion consisting essentially of ethyl acid phosphate, the concentration of said arylamine antioxidant portion being in a range from about 97.6 to about 99.75% by weight of said mixture and the concentration of said acidic phosphorus portion being in a range from about 0.25 to about 2.4% by weight of said mixture.

References Cited by the Examiner UNITED STATES PATENTS 2,743,234 4/1956 Matuszak et al. 25246.7 2,930,758 3 1960 Tierney et al. 25246.7 3,038,858 6/1962 Verley 25247 3,038,859 6/1962 Eickemeyer et al. 25247 FOREIGN PATENTS 847,399 9/ 1960 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

Claims

1. AN ANTIOXIDANT COMPOSITION COMPRISIN A MIXTURE CONSISTING ESSENTIALLY OF (1) AN ARYLAMINE ANTIOXIDANT PORTION CONSISTING ESSENTIALLY OF (A) N-ALKYLPHENOTHIAZINE WHEREIN THE N-ALKYL GROUP HAS 1-18 CARBON ATOMS AND (B) P,P''-DIALKYLDIPHENYLAMINE WHEREIN THE P AND P''-ALKYL GROUPS EACH HAVE 1-18 CARBON ATOMS, THE WEIGHT RATION OF THE (-ALKYL-PHENOTHIAZINE TO THE P,P''-DIALKYLDIPHENYLAMINE BEING IN A RANGE FROM ABOUT 1:3 TO ABOUT 3:1, AND (2) AN ACIDIC PHOSPHORUS PORTION CONSISITING ESSENTIALLY OF AT LEAST ONE ACIDIC PHOSPHORUS COMPOUND SELECTED FROM THE GROUP CONSISTING OF AN ALKYL ACID PHOSPHATE WHEREIN THE ALKYL GROUP CONTAINS FROM 1 TO 10 CARBON ATOMS, OPHOSPHORIC ACID, DIPHENYL HYDROGEN PHOSPHATE, DIETHYL HYDROGEN PHOSPHITE, BIS(2-ETHYLTHEXYL)HYDROGEN PHOSPHITE AND 2,2-DIMETHYL-1,3-PROPANEDIOL-CYCLIC-HYDROGENPHOSPHITE, THE CONCENTRATION OF SAID ARYLAMINE ANTIOXIDANT PORTION BEING IN A RANGE FROM ABOUT 95.3 TO ABOUT 99.95% BY WEIGHT OF SAID MIXTURE AND THE CONCENTRATION OF SAID ACIDIC PHOSPHORUS PORTION BEING IN A RANGE FROM ABOUT 0.05 TO ABOUT 4.7% BY WEIGHT OF SAID MIXTURE.