US3378490A - Lubricant compositions and antioxidants therefor - Google Patents

Description

United States Patent 3,378,490 LUBRICANT CQMPOSITTONS AND ANTIQANTS THEREFUR Bruce W. Hotten, Orinda, Calih, assignor to Chevron Research Company, San Francisco, Calif., a corporation of Delaware No Drawing. Filed 0st. 8, 1965, Ser. No. 494,234

' 8 Claims. (Cl. 25242.1)

ABSTRACT OF THE DISCLUSURE Lubricant compositions having superior antioxidant properties comprising a major portion of an oleaginous lubricant and a minor portion of an N N*, N trihydrocarbyl melamine in which the hydrocarbyl groups are aralkyl or alkaryl groups.

This invention relates to lubricant compositions inhibited from oxidations and, as antioxidants therefor, certain substituted melamines. More particularly, it relates to metal-containing greases inhibited from oxidation with certain benzyl and phenyl-substituted melamines.

Composition-s which are employed in lubricating modern automobile engines, machinery, etc., are becoming increasingly subject to attack by oxidation under the severe operating conditions encountered in these machines. This is primarily due to the increased speeds and correspondingly high temperatures at which the machines are being operated. Thus, When the lubricants are attacked by oxidation, the resulting buildup in oxidative products in the lubricants often results in increasing wear upon the parts being lubricated with resultant early failure of the equipment being lubricated.

This increased corrosivity is especially pronounced in the case of metal-ion containing lubricants, such as automatic transmission fluids and metal-soap gelled greases. In particular, lithium soap greases, which are often employed in high temperature applications because of their high dropping points, are thus often subject to such oxidative attack.

It is thus particularly desirable to provide additives for lubricants suchas those illustrated which will successfully. inhibit oxidation of the lubricants and increase the protective lives of the lubricants.

It has now been found that improved lubricant compositions highly resistant to oxidation can be prepared from a major portion of an oleaginous lubricant and a minor portion sufiicient to inhibit oxidation of an N N N triin which m is 0 to l, n is 1 to and R is a hydrocarbyl group of 1 to 30 carbon atoms, and the total number of carbon atoms substituted on each of the phenyl groups is from 4 to 90.

The three phenyl groups in each molecule of the substituted melamine should be substituted by hydrocarbyl radicals containing a total of at least 4 carbon atoms in addition to the possible linking carbon if there is a benzyl link with the melamine nucleus. It is preferred that the substituent groups be aliphatic hydrocarbon radicals. Examples of suitable substituent groups include methyl,

Patented Apr. 16, 1968 ethyl, propyl, butyl, octyl, decyl, dodecyl, octadecyl, etc. Branched-chain radicals, such as isoand tertiary-butyl and polymerized olefins (e.g. propylene tetramer) are suitable. Cycloaliphatic groups, such as cyclohexy-l, bornyl, etc. may also be used. Olefinic substituents may also be present, although the presence of a double bond is not preferred. An example of a preferred radical is one derived from a branched alkylaniline marketed by Monsanto Corporation as a C-12 alkylaniline. The preferred antioxidants of this invention are thus substituted on each phenyl ring with alkyl groups of from 4 to about 30 carbon atoms.

The hydrocarbyl melamines are made by several known methods, but they can be most conveniently prepared by reacting about 1 mol of cyanur-ic chloride with 3 mols of a suitable amine in the presence of a base, such as calcium hydroxide. Another suitable method of preparation involves mixing together about 1 mol of melamine with 3 mols of a suitable amine and heating the mixture to drive off ammonia.

The materials are employed in the compositions in amounts sufiicient to inhibit oxidation. Amounts from 0.1% to 5% by Weight are usually suificient.

While the melamines of this invention are effective in lubricating compositions of warious types, they are most effective in those compositions which, as previously noted, are made particularly susceptible to oxidation by the presence of metallic ions. More specifically, they are most effective in metallic soap thickened greases. Examples of the thickeners which are employed in such greases include the metal soaps which are usually the salts of saturated fatty acids containing more than 10 carbon atoms (stearic, palmitic, lauric, etc.) and the salts of oleic acid, an unsaturated fatty acid. The metallic ions which are employed include aluminum, barium, cadmium, calcium, lead, magnesium, strontium, and zinc. Greases in which the additives of this invention are most especially useful are the lithium-soap thickened greases which are often employed in high temperature operations because of the high dropping points of the greases. In the applications susceptibility to oxidation because of the high temperatures encountered becomes most important.

The oleaginous lubricants which comprise the bases for the compositions of this invention are those oily or greasy materials most commonly employed in the lubrication. Examples of these materials are natural and synthetic oils and greases made from these oils. Base materials which are not suitable for the compositions of this invention and are not classified as oleaginous lubricants are those inorganic substances sometimes used in lubricating functions, such as molybdenum disulfide, tungsten disulfide, graphite, ground basalt, etc.

The oils which can be used as base oils for the compositions of this invention include a wide variety of lubricating oils, such as naphthenic-base, parafiin-base, and mixed-base lubricating oils, other hydrocarbon lubricants, e.g. lubricating oils 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., alkylene oxide polymers prepared by polymerizing alkylene oxide, e.g., propylene oxide polymers, etc., in the presence of water or alcohols, e.g., ethyl alcohol), carboxylic acid esters (e.g., those which were prepared by esterifying such carboxylic acids as adipic acid, azelaic acid, su-beric acid, sebacic acid, alkenylsuccinic acid, fumaric acid, maleic acid, etc., with the alcohols, such as butyl alcohol, hexyl alcohol, Z-ethylhexyl alcohol, pentaerythritol, etc.), liquid esters of acids of phosphorus, alkylbenzenes, polyphenyls (e.g., biphenyls and terphenyls), alkylbiphenyl ethers, polymers of silicon (e.g., tetraethyl silicate, tetraisopropyl silicate, tetra(4 methyl-Z-pentoxy) disiloxane, poly- (methyl) siloxane, and poly(methylphenyl) siloxane, etc.

The base oils can be used individually or in combinations, wherever miscible or wherever made so by use of mutual solvents.

The following examples illustrate the preparation of the substituted melamine antioxidants of this invention. The first two examples illustrate the preparation of amines which are used in preparing the additives and are prepared from commercially available chlorides. The examplcs are only illustrative and are nonlimiting of the invention.

Example 1.Preparation of alkylbenzylamine with hexamethylenetetramine 1700 g. mols) of a chloromethylalkylbenzene substituted by an average of two methyl and one ethyl group per benzene ring marketed by International Mineral and Chemical Company was stirred with 1400 g. (10 mols) of hexamethylenetetramine for a period of ten hours at room temperature. The mixture was then allowed to stand for two weeks. To the reaction mixture were added 6 l. of distilled water and 2.4 l. of concentrated NI-I OH, and it was refluxed for two hours. 300 ml. of 38% formaldehyde solution was added to the mixture, and it was stirred for one-half hour. An oily layer developed, and it was then separated from the mixture and washed with 10% NaOH solution. 1.1 liters of concentrated HCl was then added to the mixture. The mixture was then placed in a distillation apparatus, and the water and aldehyde were distilled off to a pot temperature of 125 C. The residue was made basic with KOH and washed with water. The yield was 824 grams of alkylbenzylamine having a basic nitrogen content of 7.5% (theoretical equal 9.0%

Example II.Preparation of alkylbenzylamine by the Gabriel synthesis 278 g. 1.5 mol) of potassium phthalimide was mixed with 263 g. (1.5 mol) of the same chloromethylalkylbenzene which was used in Example I. The mixture was placed in 0.4 l. of dimethylformamide and heated for three hours at 100 to 160 C. The product was then Washed free of Clwith water and heated with 50 g. (1.5 mol) of hydrazine for one hour at 100 C. One liter of isopropanol and 150 ml. of 38% I-ICl (1.5 mol) were added to the mixture, which was then stirred in a batch blender and filtered. The filtrate was made basic with KOH and washed free of chloride ion. The yield was 43 g. of material having a basic nitrogen content of 8.0% (theoretical for alkylbenzylamine equal to 9.0%).

9.8% nitrogen (theoretical for tris-melamine equal to 9.8).

Example IV.--Preparation of substituted melamines from cyanuric chloride and amines 6 g. (0.3 mol) of cyanuric chloride, 4 g. (0.1 mol) of calcium hydroxide, 18 g. (0.1 mol) of the amine prepared in Example II, and 50 g. of toluene were placed in a reaction vessel and refluxed for four hours. The material was then filtered, and the filtrate was water-washed free of chloride ion and evaporated, yielding 17 g. of a tan resin having a melting temperature of 38 to 45 C. and having 14% nitrogen (theoretical for tris-rnelamine equal to 15% Example V.Preparation of substituted melamines from reaction of melamine and amine 21 g. (0.17 mol) of melamine and 97 g. (0.5 mol) of the amine prepared in Example II were heated for elevenhours at 100 to 190 C. until all ammonia had been driven off. This reaction yielded 40 g. of a brown resin.

In order to demonstrate the etfectiveness of the compounds of this invention in reducing oxidation of a grease and increasing bearing life of bearings lubricated by the grease, greases containing small quantities of the material were subjected to a bomb oxidation test and a hearing life test.

The bomb oxidation test, ASTM D-942-50, briefly involves placing a 20-gram sample of the grease in a bomb, and subjecting the sample to an initial pressure of p.s.i. of oxygen at 200 for 100 hours and then measuring the pressure loss at the end of the period. In general, the higher absorption of oxygen indicates greater oxidation of the sample.

The bearing life test used is known as the Navy High Speed Bearing Test and is described in Federal Test Method No. 331.1. In this test a ball bearing was operated at 10,000 r.p.m. continuously for approximately 22 hours at 300 F. while being lubricated with the subject grease sample. The apparatus was then cooled to room temperature during a period of two hours. This procedure of operating and cooling was repeated until there was bearing failure. The number of hours to bearing failure is indicated as Bearing Life.

The table following shows the results of the abovementioned test. The base grease was a synthetic oil (bis-2- ethylhexyl sebacate) thickened with 15% by weight of a lithium stearate soap. The bearing life for each sample and the geometric means of the bearing life is given. Comparative data for an uninhibited grease and greases inhibited with conventional antioxidant, zinc dithiocarbamate, is included.

Concentra- Bomb Oxidation, p.s.i. drop Bearing Life Antioxidant Additive tion, Wt. (Geometric percent 100 hrs. 200 hrs. Mean) None 27 53;(236;) 376 Tris(alkyiphenyl) melamine of Example III 2 4 8 691; 406

30 Tris(alkylbenzyl) melamine of Example IV 2 3 4 440; 3)04 370 Tris(a1kylbenzyl) melamine of Example V 2 4 6. 5 Do 5 262; 913; 655

(540) Zincdibutylthiocarbamate 2 3. 3 1(96; )76

Example III.--Preparation of substituted melamine from cyanuric chloride and alkyl aniline 783 g. (3 mols) of a branched-chain alkyl aniline having an average of 12 alkyl carbon atoms on each benzene ring (tetrapropenyl substituted) was placed in a reaction vessel. 184 g. (1 mol) of cyanuric chloride in 600 ml. of toluene was added to the aniline dropwise with stirring. An exothermic reaction resulted with a temperature reaching about 100 C. The mixture was stirred for one hour and filtered. The filtrate was evaporated and waterwashed, yielding 420 g. of a brown, resinous material having a melting range from 33 to 53 C. and having 75 5 6 oleaginous lubricant and a minor portion suflicient to 4. The composition of claim 3 wherein the metallic-ion inhibit oxidation of an N N N trihydrocarbyl melamine containing thickener is a soap. of the formula: 5. The composition of claim 4 in which the soap is a N lithium soap. 5 6. The composition of claim 1 in which R is an alkyl z)mNHO NH( H2)m group of l to 24 carbon atoms.

1; l; h 7. The composition of cla'un 6 in which m is 1, n is 1 and R is an alkyl group of about 12 carbon atoms. (3) 8 The composition of claim 6 in which mis 0, n is 3 NH""(C 2)m (R) 10 and R is an alkyl group of 1 to 2 carbon atoms.

References Cited UNITED STATE PAT NT in which m is 0 to 1, n is l to 5 and R is a hydrocarbyl S E S group of 1 to 30 carbon atoms and the total number of 15 2387547 10/1945 widriler et a1 260 249'6 carbon atoms in- R on each phenyl ring is from 4 to 90. 3250708 5/1966 Dazz} et 252*50 2. The composition of claim 1 wherein the oleaginous 3312698 4/1967 Dazzl et 252 5O lubricant is a grease.

3. The composition of claim 2 wherein the grease is DANIEL WYMAN P'lmary Examiner thickened by a metallic-ion containing thickener. 20 I. VAUGHN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,378 ,490 April 16 1968 Bruce W. Hotten It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 75, after "composition" insert comprising Signed and sealed this 18th day of November 1969.

(SEAL) Attest:

Fletcher, Jr. Aimin Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.