2. Description of Related Art In developing lubricating oils, there have been many attempts to provide additives that impart antifatigue, antiwear, and extreme pressure properties thereto.

Zinc dialkyldithiophosphates (ZDDP) have been used in formulated oils as antiwear additives for more than 50 years. However, zinc dialkyldithiophosphates give rise to ash, which contributes to particulate matter in automotive exhaust emissions, and regulatory agencies are seeking to reduce emissions of zinc into the environment. In addition, phosphorus, also a component of ZDDP, is suspected of limiting the service life of the catalytic converters that are used on cars to reduce pollution. It is important to limit the particulate matter and pollution formed during engine use for toxicological and environmental reasons, but it is also important to maintain undiminished the antiwear properties of the lubricating oil.

In view of the aforementioned shortcomings of the known zinc and phosphorus- containing additives, efforts have been made to provide lubricating oil additives that contain neither zinc nor phosphorus or, at least, contain them in substantially reduced amounts.

Illustrative of non-zinc, i. e., ashless, non-phosphorus-containing lubricating oil additives are the reaction products of 2, 5-dimercapto-1,3,4-thiadiazoles and unsaturated mono-, di-, and tri-glycerides disclosed in U. S. Patent No. 5,512,190 and the dialkyl dithiocarbamate-derived organic ethers of U. S. Patent No. 5,514,189.

U. S. Patent No. 5,512,190 discloses an additive that provides antiwear properties to a lubricating oil. The additive is the reaction product of 2,5-dimercapto- 1,3,4-thiadiazole and a mixture of unsaturated mono-, di-, and triglycerides. Also disclosed is a lubricating oil additive with antiwear properties produced by reacting a mixture of unsaturated mono-, di-, and triglycerides with diethanolamine to provide an intermediate reaction product and reacting the intermediate reaction product with 2,5- dimercapto-1,3,4 thiadiazole.

U. S. Patent No. 5,514,189 discloses that dialkyl dithiocarbamate-derived organic ethers have been found to be effective antiwear/antioxidant additives for lubricants and fuels.

U. S. Patent Nos. 5,084,195 and 5,300,243 disclose N-acyl-thiourethane thioureas as antiwear additives specified for lubricants or hydraulic fluids.

The disclosures of the foregoing references are incorporated herein by reference in their entirety.

SUMMARY OF THE INVENTION The present invention relates to imidazole thione compounds of the formula wherein R,, R2, R3, and R4 are independently selected from the group consisting of alkyl, functionalized alkyl, and hydrogen.

In the above structural formulas, R,, R2, R3, and/or R4 can be a straight or branched chain, fully saturated or partially unsaturated, alkyl moiety, preferably having from 1 to 40 carbon atoms, e. g., methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, oleyl, nonadecyl, eicosyl, heneicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, triacontyl, pentatriacontyl, tetracontyl, and the like, and isomers and mixtures thereof. Additionally, R,, R2, R3, and/or R4 can be a straight or branched chain, a fully saturated or partially unsaturated hydrocarbon chain, preferably having from 1 to 40 carbon atoms, within which may be ester groups or heteroatoms, such as, oxygen, sulfur, and nitrogen, which may take the form of ethers, polyethers, sulfides, amines, and amides. This is what is meant by"functionalized alkyl."

The imidazole thione compounds of this invention are useful as ashless, non- phosphorus-containing antifatigue, antiwear, extreme pressure additives for lubricating oils.

The present invention also relates to lubricating oil compositions comprising a lubricating oil and a functional property-improving amount of at least one imidazole thione compound of the above formulas. More particularly, the present invention is directed to a composition comprising: (A) a lubricant, and (B) at least one imidazole thione compound of the formula: wherein R,, R2, R3, and R4 are independently selected from the group consisting of alkyl, functionalized alkyl, and hydrogen. DESCRIPTION OF THE PREFERRED EMBODIMENTS The imidazole thione compounds of the present invention are compounds of the formula:

wherein R, and R2 are independently selected from the group consisting of alkyl, functionalized alkyl, and hydrogen.

In the above structural formula, Rl, R,, R3, and/or R4 can be an alkyl moiety, preferably of I to 40 carbon atoms, more preferably of 1 to 18 carbon atoms, most preferably of 1 to 10 carbon atoms, and can have either a straight chain or a branched chain, a fully saturated or partially unsaturated hydrocarbon chain, e. g. methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, oleyl, nonadecyl, eicosyl, heneicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, triacontyl, pentatriacontyl, tetracontyl, and the like, and isomers, e. g., 2-ethylhexyl, and mixtures thereof. R,, R2, R3, and/or R4 can have from 1 to 40 carbon atoms, preferably 1 to 18 carbon atoms, most preferably of 1 to 10 carbon atoms, and can be either a straight chain or a branched chain, a fully saturated or partially unsaturated hydrocarbon chain, wherein said chains may contain ester groups or heteroatoms, such as oxygen and/or sulfur

and/or nitrogen, which may take the form of ethers, polyethers, sulfides, amines, amides, and the like. As employed herein, the term"alkyl"is also intended to include "cycloalkyl."Where the alkyl is cyclic, it preferably contains from 3 to 9 carbon atoms, e. g., cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, and the like. Cycloalkyl moieties having 5 or 6 carbon atoms, i. e., cyclopentyl or cyclohexyl, are more preferred.

Additionally, R, and R, and/or R3 and R4 can be fused together as part of a spiro cyclic alkyl group CH2 (CH2) nCH2, where n = 0-4.

As noted above, R,, R2, R3, and/or R4 can also be hydrogen; it is preferred, however, that no more than three of R,, R2, R3, or R4 be hydrogen. In other words, it is preferred that at least one of the ring carbon atoms of the imidazole thiones of the present invention have an alkyl or functionalized alkyl substituent, as defined herein, attached thereto. It is more preferred that all of R,, R2, R3, and R be alkyl and most preferred that they all be methyl.

Those skilled in the art will understand that analogous imidazole thiones useful as described in this invention can be prepared from cyanohydrins derived from any simple ketone or aldehyde. Preferred ketones for the preparation of these imidazole thiones include, but are not limited to, propanone, butanone, 3-methyl-2-butanone, 2- pentanone, 3-pentanone, 4-methyl-2-pentanone, 2-hexanone, 3-hexanone, 5- methyl-2-hexanone, 2-heptanone, 3-heptanone, 4-heptanone, 5-methyl-2-heptanone, cyclopentanone, cyclohexanone, cycloheptanone, and the like. Preferred aldehydes for

the preparation of these imidazole thiones include, but are not limited to, butanal, pentanal, hexanal, heptanal, 2-ethylheptanal, and the like.

The use of the imidazole thione compounds of this invention can improve the antifatigue, antiwear, and extreme pressure properties of a lubricant.

General Synthesis of Additives of this Invention The imidazole thione compounds of the present invention were synthesized as follows.

Into a 1000 mL three neck round bottom flask, equipped with a mechanical stirrer, thermometer, and dropping funnel, was placed 494 mL of (NH4) 2S (22.6%). To this was added with stirring a mixture of 106.8 mL of acetone and 131.6 mL of acetone cyanohydrin. The reaction was exothermic and the temperature rose to 50 °C. The mixture was heated to 60° C. and held for there for 1 hour, then cooled to 10 °C. The reaction mixture was filtered, and the product rinsed with ice water and dried. Yield: 106g.

Use with Other Additives The imidazole thione additives of this invention can be used as either a partial or complete replacement for the zinc dialkyldithiophosphates currently used. They can also be used in combination with other additives typically found in lubricating oils, as well as with other ashless, antiwear additives. The additives typically found in lubricating oils are, for example, dispersants, detergents, corrosion/rust inhibitors,

antioxidants, antiwear agents, antifoamants, friction modifiers, seal swell agents, demulsifiers, VI improvers, pour point depressants, and the like. See, for example, U. S. Patent No. 5,498,809 for a description of useful lubricating oil composition additives, the disclosure of which is incorporated herein by reference in its entirety.

Examples of dispersants include polyisobutylene succinimides, polyisobutylene succinate esters, Mannich Base ashless dispersants, and the like. Examples of detergents include metallic phenates, metallic sulfonates, metallic salicylates, and the like. Examples of antioxidants include alkylated diphenylamines, N-alkylated phenylenediamines, hindered phenolics, alkylated hydroquinones, hydroxylated thiodiphenyl ethers, alkylidenebisphenols, oil soluble copper compounds, and the like.

Examples of antiwear additives that can be used in combination with the additives of the present invention include organo borates, organo phosphites, organic sulfur-containing compounds, zinc dialkyldithiophosphates, zinc diaryldithiophosphates, phosphosulfurized hydrocarbons, and the like. The following are exemplary of such additives and are commercially available from The Lubrizol Corporation: Lubrizol 677A, Lubrizol 1095, Lubrizol 1097, Lubrizol 1360, Lubrizol 1395, Lubrizol 5139, and Lubrizol 5604, among others. Examples of friction modifiers include fatty acid esters and amides, organo molybdenum compounds, molybdenum dialkyldithiocarbamates, molybdenum dialkyl dithiophosphates, and the like. An example of an antifoamant is polysiloxane, and the like. An example of a rust inhibitor is a polyoxyalkylene polyol, and the like. Examples of VI improvers include olefin

copolymers and dispersant olefin copolymers, and the like. An example of a pour point depressant is polymethacrylate, and the like.

Representative conventional antiwear agents that can be used include, for example, the zinc dialkyl dithiophosphates and the zinc diaryl dithiophosphates.

Suitable phosphates include dihydrocarbyl dithiophosphates, wherein the hydrocarbyl groups contain an average of at least 3 carbon atoms. Particularly useful are metal salts of at least one dihydrocarbyl dithiophosphoric acid wherein the hydrocarbyl groups contain an average of at least 3 carbon atoms. The acids from which the dihydrocarbyl dithiophosphates can be derived can be illustrated by acids of the formula wherein R, and R6 are the same or different and are alkyl, cycloalkyl, aralkyl, alkaryl or substituted substantially hydrocarbon radical derivatives of any of the above groups, and wherein the Rs and R6 groups in the acid each have, on average, at least 3 carbon atoms. By"substantially hydrocarbon"is meant radicals containing substituent groups (e. g., 1 to 4 substituent groups per radical moiety) such as ether, ester, nitro, or halogen that do not materially affect the hydrocarbon character of the radical.

Specific examples of suitable R5 and R6 radicals include isopropyl, isobutyl, n-butyl, sec-butyl, n-hexyl, heptyl, 2-ethylhexyl, diisobutyl, isooctyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, butylphenyl, o, p-dipentylphenyl, octylphenyl, polyisobutene- (molecular weight 350)-substituted phenyl, tetrapropylene-substituted phenyl, p-octylbutylnaphthyl, cyclopentyl, cyclohexyl, phenyl, chlorophenyl, o-dichlorophenyl, bromophenyl, naphthenyl, 2-methylcyclohexyl, benzyl, chlorobenzyl, chloropentyl, dichlorophenyl, nitrophenyl, dichlorodecyl and xenyl radicals. Alkyl radicals having from about 3 to about 30 carbon atoms and aryl radicals having from about 6 to about 30 carbon atoms are preferred. Particularly preferred R5and R6 radicals are alkyl of from 4 to 18 carbon atoms.

The phosphorodithioic acids are readily obtainable by the reaction of phosphorus pentasulfide and an alcohol or phenol. The reaction involves mixing, at a temperature of about 20 °C. to 200 °C., 4 moles of the alcohol or phenol with one mole of phosphorus pentasulfide. Hydrogen sulfide is liberated as the reaction takes place.

Mixtures of alcohols, phenols, or both can be employed, e. g., mixtures of C3 to C30 alcohols, C6 to C30 aromatic alcohols, etc.

The metals useful to make the phosphate salts include Group I metals, Group II metals, aluminum, lead, tin, molybdenum, manganese, cobalt, and nickel. Zinc is the preferred metal. Examples of metal compounds that can be reacted with the acid include lithium oxide, lithium hydroxide, lithium carbonate, lithium pentylate, sodium oxide, sodium hydroxide, sodium carbonate, sodium methylate, sodium propylate, sodium phenoxide, potassium oxide, potassium hydroxide, potassium carbonate,

potassium methylate, silver oxide, silver carbonate, magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium ethylate, magnesium propylate, magnesium phenoxide, calcium oxide, calcium hydroxide, calcium carbonate, calcium methylate, calcium propylate, calcium pentylate, zinc oxide, zinc hydroxide, zinc carbonate, zinc propylate, strontium oxide, strontium hydroxide, cadmium oxide, cadmium hydroxide, cadmium carbonate, cadmium ethylate, barium oxide, barium hydroxide, barium hydrate, barium carbonate, barium ethylate, barium pentylate, aluminum oxide, aluminum propylate, lead oxide, lead hydroxide, lead carbonate, tin oxide, tin butylate, cobalt oxide, cobalt hydroxide, cobalt carbonate, cobalt pentylate, nickel oxide, nickel hydroxide, and nickel carbonate.

In some instances, the incorporation of certain ingredients, particularly carboxylic acids or metal carboxylates, such as, small amounts of the metal acetate or acetic acid, used in conjunction with the metal reactant will facilitate the reaction and result in an improved product. For example, the use of up to about 5% of zinc acetate in combination with the required amount of zinc oxide facilitates the formation of a zinc phosphorodithioate.

The preparation of metal phosphorodithioates is well known in the art and is described in a large number of issued patents, including U. S. Patent Nos. 3,293,181; 3,397,145; 3,396,109 and 3,442,804, the disclosures of which are hereby incorporated by reference. Also useful as antiwear additives are amine derivatives of dithiophosphoric acid compounds, such as are described in U. S. Patent No. 3,637,499, the disclosure of which is hereby incorporated by reference in its entirety.

The zinc salts are most commonly used as antiwear additives in lubricating oil in amounts of 0.1 to 10, preferably 0.2 to 2, wt. %, based upon the total weight of the lubricating oil composition. They may be prepared in accordance with known techniques by first forming a dithiophosphoric acid, usually by reaction of an alcohol or a phenol with P2S5 and then neutralizing the dithiophosphoric acid with a suitable zinc compound.

Mixtures of alcohols can be used, including mixtures of primary and secondary alcohols, secondary generally for imparting improved antiwear properties and primary for thermal stability. Mixtures of the two are particularly useful. In general, any basic or neutral zinc compound could be used, but the oxides, hydroxides, and carbonates are most generally employed. Commercial additives frequently contain an excess of zinc owing to use of an excess of the basic zinc compound in the neutralization reaction.

The zinc dihydrocarbyl dithiophosphates (ZDDP) are oil soluble salts of dihydrocarbyl esters of dithiophosphoric acids and can be represented by the following formula: wherein R5 and R6 are as described in connection with the previous formula.

Especially preferred additives for use in the practice of the present invention include alkylated diphenylamines, hindered alkylated phenols, hindered alkylated phenolic esters, and molybdenum dithiocarbamates.

Lubricant Compositions Compositions, when they contain these additives, are typically blended into the base oil in amounts such that the additives therein are effective to provide their normal attendant functions. Representative effective amounts of such additives are illustrated in TABLE 1.

TABLE 1 AdditivesPreferredWeight%MorePreferredWeight% V.I.Improver I-12 1-4 CorrosionInhibitor 0. 01-3 0.01-1.5 OxidationInhibitor 0. 01-5 0.01-1.5 Dispersant 01.-10 0.1-5 LubeOilFlowImprover 0. 01-2 0.01-1.5 Detergent/RustInhibitor 0. 01-6 0.01-3 PourPointDepressant 0.01-1.5 0.01-0.5 AntifoamingAgent 0.001-0.1 0.001-0.01 AntiwearAgent 0. 001-5 0. 001-1. 5 Seal Swellant 0. 1-8 Ol.-4 FrictionModifier 0. 01-3 0.01-1.5 LubricatingBaseOil Balance Balance

When other additives are employed, it may be desirable, although not necessary, to prepare additive concentrates comprising concentrated solutions or dispersions of the subject additives of this invention, together with one or more of said other additives (said concentrate when constituting an additive mixture being referred to herein as an additive-package) whereby several additives can be added simultaneously to the base oil to form the lubricating oil composition. Dissolution of the additive concentrate into the lubricating oil can be facilitated by solvents and/or by mixing accompanied by mild heating, but this is not essential. The concentrate or additive-package will typically be formulated to contain the additives in proper amounts to provide the desired concentration in the final formulation when the additive-package is combined with a predetermined amount of base lubricant. Thus, the subject additives of the present invention can be added to small amounts of base oil or other compatible solvents along with other desirable additives to form additive-packages containing active ingredients in collective amounts of, typically, from about 2.5 to about 90 percent, preferably from about 15 to about 75 percent, and more preferably from about 25 percent to about 60 percent by weight additives in the appropriate proportions with the remainder being base oil. The final formulations can typically employ about I to 20 weight percent of the additive-package with the remainder being base oil.

All of the weight percentages expressed herein (unless otherwise indicated) are based on the active ingredient (AI) content of the additive, and/or upon the total weight of any additive-package, or formulation, which will be the sum of the AI weight of each additive plus the weight of total oil or diluent.

In general, the lubricant compositions of the invention contain the additives in a concentration ranging from about 0.05 to about 30 weight percent. A concentration range for the additives ranging from about 0.1 to about 10 weight percent based on the total weight of the oil composition is preferred. A more preferred concentration range is from about 0.2 to about 5 weight percent. Oil concentrates of the additives can contain from about I to about 75 weight percent of the additive reaction product in a carrier or diluent oil of lubricating oil viscosity.

In general, the additives of the present invention are useful in a variety of lubricating oil base stocks. The lubricating oil base stock is any natural or synthetic lubricating oil base stock fraction having a kinematic viscosity at 100 °C of about 2 to about 200 cSt, more preferably about 3 to about 150 cSt, and most preferably about 3 to about 100 cSt. The lubricating oil base stock can be derived from natural lubricating oils, synthetic lubricating oils, or mixtures thereof. Suitable lubricating oil base stocks include base stocks obtained by isomerization of synthetic wax and wax, as well as hydrocrackate base stocks produced by hydrocracking (rather than solvent extracting) the aromatic and polar components of the crude. Natural lubricating oils include animal oils, such as, lard oil, vegetable oils (e. g., canola oils, castor oils, sunflower oils), petroleum oils, mineral oils, and oils derived from coal or shale.

Synthetic oils include hydrocarbon oils and halo-substituted hydrocarbon oils, such as, polymerized and interpolymerized olefins, alkylbenzenes, polyphenyls, alkylated diphenyl ethers, alkylated diphenyl sulfides, as well as their derivatives, analogs, homologues, and the like. Synthetic lubricating oils also include alkylene

oxide polymers, interpolymers, copolymers, and derivatives thereof, wherein the terminal hydroxyl groups have been modified by esterification, etherification, etc.

Another suitable class of synthetic lubricating oils comprises the esters of dicarboxylic acids with a variety of alcohols. Esters useful as synthetic oils also include those made from Cl to C12 monocarboxylic acids and polyols and polyol ethers.

Silicon-based oils (such as the polyalkyl-, polyaryl-, polyalkoxy-, or polyaryloxy-siloxane oils and silicate oils) comprise another useful class of synthetic lubricating oils. Other synthetic lubricating oils include liquid esters of phosphorus- containing acids, polymeric tetrahydrofurans, poly a-olefins, and the like.

The lubricating oil may be derived from unrefined, refined, rerefined oils, or mixtures thereof. Unrefined oils are obtained directly from a natural source or synthetic source (e. g., coal, shale, or tar and bitumen) without further purification or treatment.

Examples of unrefined oils include a shale oil obtained directly from a retorting operation, a petroleum oil obtained directly from distillation, or an ester oil obtained directly from an esterification process, each of which is then used without further treatment. Refined oils are similar to unrefined oils, except that refined oils have been treated in one or more purification steps to improve one or more properties. Suitable purification techniques include distillation, hydrotreating, dewaxing, solvent extraction, acid or base extraction, filtration, percolation, and the like, all of which are well-known to those skilled in the art. Rerefined oils are obtained by treating refined oils in processes similar to those used to obtain the refined oils. These rerefined oils are also

known as reclaimed or reprocessed oils and often are additionally processed by techniques for removal of spent additives and oil breakdown products.

Lubricating oil base stocks derived from the hydroisomerization of wax may also be used, either alone or in combination with the aforesaid natural and/or synthetic base stocks. Such wax isomerate oil is produced by the hydroisomerization of natural or synthetic waxes or mixtures thereof over a hydroisomerization catalyst. Natural waxes are typically the slack waxes recovered by the solvent dewaxing of mineral oils; synthetic waxes are typically the wax produced by the Fischer-Tropsch process. The resulting isomerate product is typically subjected to solvent dewaxing and fractionation to recover various fractions having a specific viscosity range. Wax isomerate is also characterized by possessing very high viscosity indices, generally having a VI of at least 130, preferably at least 135 or higher and, following dewaxing, a pour point of about-20 °C or lower.

The additives of the present invention are especially useful as components in many different lubricating oil compositions. The additives can be included in a variety of oils with lubricating viscosity, including natural and synthetic lubricating oils and mixtures thereof. The additives can be included in crankcase lubricating oils for spark- ignited and compression-ignited internal combustion engines. The compositions can also be used in gas engine lubricants, turbine lubricants, automatic transmission fluids, gear lubricants, compressor lubricants, metal-working lubricants, hydraulic fluids, and other lubricating oil and grease compositions. The additives can also be used in motor fuel compositions.

The advantages and the important features of the present invention will be more apparent from the following examples.

EXAMPLES Four-Ball AntiWear Testing The antiwear properties of the novel reaction product in a fully formulated lubricating oil were determined in the Four-Ball Wear Test under the ASTM D 4172 test conditions. The fully formulated lubricating oils tested also contained 1 weight percent cumene hydroperoxide to help simulate the environment within a running engine. The additives were tested for effectiveness in a motor oil formulation (see description in Table I) and compared to an identical formulation with and without any zinc dialkyldithiophosphate. In Table 2, the numerical value of the test results (Average Wear Scar Diameter, mm) decreases with an increase in effectiveness. TABLE 1 SAE 10W-30 Motor Oil Formulations ComponentFormulationA(wt%) Solvent Neutral 100 22.8 Solvent Neutral 150 60 SuccinimideDispersant 7.5 OverbasedCalciumPhenateDetergent 2.0 NeutralCalciumSulfonateDetergent 0. 5 RustInhibitor 0. 1 Antioxidant 0.5 PourPointDepressant 0. 1 OCPVI Improver 5.5 AntiwearAdditive'1.0

'In the case of No antiwear additive in Table I, solvent neutral 150 is put in its place at 1.0 weight percent. TABLE 2 Falex Four-Ball Wear Results CompoundFormulationWearScarDiameter, mm NoantiwearadditiveA0.93 ZincA0.46 dialkyldithiophosphate 2,2,5,5- A0.479,0.480 tetramethylimidazole thione In view of the many changes and modifications that can be made without departing from principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of the protection to be afforded the invention.