2. Antioxidants. Most oleaginous compositions will preferably contain a conventional quantity of one or more antioxidants in order to protect the composition from premature degradation in the presence of air, especially at elevated temperatures. Typical antioxidants include hindered phenolic antioxidants, secondary aromatic amine antioxidants, sulfurized phenolic antioxidants, oil-soluble copper compounds, phosphorus-containing antioxidants, organic sulfides, disulfides and polysulfides and the like.

Illustrative sterically hindered phenolic antioxidants include orthoalkylated phenolic compounds such as 2,6-di-tertbutylphenol, 4-methyl-2,6-di-tertbutylphenol, 2,4,6-tri-tertbutylphenol, 2-tert-butylphenol, 2,6-diisopropylphenol, 2-methyl-6-tert-butylphenol, 2,4-dimethyl-6-tertbutylphenol, 4-(N,N-dimethylaminomethyl)-2,8-di-tertbutylphenol, 4-ethyl-2,6-di-tertbutylphenol, 2-methyl-6-styrylphenol, 2,6-distyryl-4-nonylphenol, and their analogs and homologs. Mixtures of two or more such mononuclear phenolic compounds are also suitable.

Other preferred phenol antioxidants for use in the compositions of this invention are methylene-bridged alkylphenols, and these can be used singly or in combinations with each other, or in combinations with sterically-hindered unbridged phenolic compounds. illustrative methylene-bridged compounds include 4,4'-methylenebis(6-tert-butyl o-cresol), 4,4'-methylenebis(2-tert-amyl-o-cresol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-methylenebis (2, 6-di-tertbutylphenol), and similar compounds. Particularly preferred are mixtures of methylene-bridged alkylphenols such as are described in U.S. Pat. No. 3,211,652, all disclosure of which is incorporated herein by reference.

Amine antioxidants, especially oil-soluble aromatic secondary amines may also be used in the compositions of this invention. Although aromatic secondary monoamines are preferred, aromatic secondary polyamines are also suitable. Illustrative aromatic secondary monoamines include diphenylamine, alkyl diphenylamines containing 1 or 2 alkyl substituents each having up to about 16 carbon atoms, phenyl-t-naphthylamine, phenyl-ß-naphthylamine, alkyl- or aralkylsubstituted phenyl-ß-naphthylamine containing one or two alkyl or aralkyl groups each having up to about 16 carbon atoms, alkyl- or aralkylsubstituted phenyl-p-naphthylamine containing one or two alkyl or aralkyl groups each having up to about 16 carbon atoms, and similar compounds.

A preferred type of aromatic amine antioxidant is an alkylated diphenylamine of the general formula

R1 -C6-H4-NH-C6H4-R2

wherein R1 is an alkyl group (preferably a branched alkyl group) having 8 to 12 carbon atoms, (more preferably 8 or 9 carbon atoms) and R2 is a hydrogen atom, alkylaryl or an alkyl group (preferably a branched alkyl group) having 8 to 12 carbon atoms, (more preferably 8 or 9 carbon atoms). Preferred compounds are available commercially as Naugalube^® 438L, 640, and 680 manufactured by Crompton Corporation. Other commercially available aromatic amine antioxidants include Vanlube SL, DND, NA, 81, 961 and 2005 sold by the R.T. Vanderbilt Company, Inc. Another useful type of antioxidant for preferred inclusion in the compositions of this invention is comprised of one or more liquid, partially sulfurized phenolic compounds such as are prepared by reacting sulfur monochloride with a liquid mixture of phenols--at least about 50 weight percent of which mixture of phenols is composed of one or more reactive, hindered phenols--in proportions to provide from about 0.3 to about 0.7 gram atoms of sulfur monochloride per mole of reactive, hindered phenol so as to produce a liquid product. Typical phenol mixtures useful in making such liquid product compositions include a mixture containing by weight about 75% of 2,6-di-tert-butylphenol, about 10% of 2-tert-butylphenol, about 13% of 2,4,6-tri-tertbutylphenol, and about 2% of 2,4-di-tertbutylphenol. The reaction is exothermic and thus is preferably kept within the range of about 15°C to about 70°C, most preferably between about 40°C to about 60°C.

Mixtures of different antioxidants may also be used. One suitable mixture is comprised of a combination of (i) an oil-soluble mixture of at least three different sterically-hindered tertiary butylated monohydric phenols which is in the liquid state at 25°C, (ii) an oil-soluble mixture of at least three different sterically-hindered tertiary butylated methylene-bridged polyphenols, and (iii) at least one bis(4-alkylphenyl) amine wherein the alkyl group is a branched alkyl group having 8 to 12 carbon atoms, the proportions of (i), (ii) and (iii) on a weight basis falling in the range of 3.5 to 5.0 parts of component (i) and 0.9 to 1.2 parts of component (ii) per part by weight of component (iii). The antioxidant discussion above is as put forth in U.S. Pat. No. 5,328,619 which is incorporated herein by reference.

Other useful preferred antioxidants are those included in the disclosure of U.S. Pat. No. 4,031,023 which is herein incorporated by reference. The referenced antioxidants of the '023 patent are then included under the formula:



wherein R is a hydrocarbyl or substituted hydrocarbyl containing up to about 30 carbon atoms and having a valence of m + q; each R' is independently selected from hydrogen and a hydrocarbon-based group of up to about 20 carbon atoms; x and y are independently from 2 to 5; z is from zero to 5; q is from zero to 4 and m is from 1 to 5 with the proviso that m + q is from 1 to 6, have increased resistance to oxidative degradation and antiwear properties. Antioxidants are preferably included in the composition at about 0.1-5 weight percent.

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