Corrosion Inhibitors for Boron-Containing Lubricants

1. Field of the Invention

This invention relates to lubricating oils, and more particularly to improved lubricating oils containing hydrocarbon derivatives of 2,5-di-mercapto-1,3,4-thiodiazole as copper corrosion inhibitors, terephthalic acid as a lead corrosion inhibitor, and certain boron and/or metal-boron derivatives having extreme pressure, anti-wear and friction reducing properties.

2. Description of the Prior Art

The use of boron containing compounds as extreme pressure and anti-wear additives for lubricating oils is known and appreciated by the prior art. For example, U.S. Pat. No. 3,313,727 to Peeler discloses compositions of amorphous alkali metal borates as a stable dispersion in lubrication oils. In particular, a boron compound, such as, the metaborates and tetraborates of sodium and potassium in combination with a lyophilic surface active agent, such as the carboxylates, phenates and sulfonates of alkaline earth metals, e.g. calcium and barium, when dispersed in lubricating oil compositions are said to improve the extreme pressure and anti-wear properties thereof.

U.S. Pat. No. 2,987,476 to Hartley et al. relates to a method for solubilizing boric acid and metal borates in liquid fuels for internal combustion engines and in lubricating oils and greases. Desirable compositions are prepared by hydrolyzing an organic ester of boric acid in the presence of three materials, namely, a lyophilic ionic surface active agent, a non-polar organic liquid and a water-miscible organic liquid. The resulting dispersible boron-containing product of this process is a complex of an inorganic boric acid compound with an oleophilic ionic surface active agent.

Another boron composition is disclosed in U.S. Pat. No. 3,598,855 to Cyba which relates to cyclic borates of polymeric alkanolamines formed by reacting a borylating agent with a polymeric alkanolamine. The additives thus formed are described as additives for a wide variety of petroleum products including lubricating oils.

U.S. Pat. No. 3,227,739 to Versteeg relates to lubricating oils containing additives formed by reacting certain amine type compounds with boric acid. The amine type compounds are prepared by reacting equal molar proportions of diethanolamine or dipropanolamine and a long chain 1,2-epoxide.

Another extreme pressure lubrication composition is disclosed in U.S. Pat. No. 3,185,644 to Knowles et al., which relates to lubricating compositions containing amine salts of boron-containing compounds. The amine salts are formed by reaction of a hydroxy substituted amine and a trihydrocarbyl borate. The amine-borate compounds thus formed are described as useful as load carrying additives for mineral and synthetic base lubricating oils.

As can readily be determined from the above, there is an ongoing effort to develop improved lubricating compositions which contain boron and/or boron derivatives.

Accordingly, it is an object of the present invention to provide an improved lubricating composition having enhanced extreme pressure, anti-wear and friction reducing properties.

Another object of the present invention is to provide a lubricating composition having improved copper and lead corrosion properties.

These and other objects are accomplished according to the present invention by adding to a lubricating composition a small but effective amount of a boron and/or metal boron additive in combination with copper and lead corrosion prevention additives.

This invention resides in a lubrication composition comprising a major amount of a lubricating oil and a minor amount of:

(A) An extreme pressure, anti-wear, and friction reducing boron compound having the formula: ##STR1## wherein R.sup.1 is hydrogen, alkyl, cyclic, alicyclic, aryl, alkylaryl, or arylalkyl radicals having from 1 to about 24 carbon atoms, R.sup.2 and R.sup.3 are straight or branched carbon chains, alkyl, cyclic, alicyclic, aryl, alkylaryl or arylalkyl radicals having from 2 to about 20 carbon atoms, Y is a number from 1 to 4, and X is either hydrogen, a transition metal having an atomic number between 21 and 30 or a Group IVA metal of the Periodic Table and mixtures thereof;

(B) A copper corrosion inhibitor comprising a hydrocarbon polysulfide derivative of 2,5-dimercapto-1,3,4-thiadiazole having the formula: ##STR2## wherein R.sup.4 and R.sup.5 are the same or different moieties selected from hydrogen or straight or branched chain alkyl, cyclic, alicyclic, aryl, alkylaryl or arylalkyl radicals having from 2 to about 30 carbon atoms, provided that R.sup.4 and R.sup.5 are not hand w and z are number from 1 to about 8; and

(C) A lead corrosion inhibitor comprising terephthalic acid.

The present invention resides in lubricating oil compositions having extreme pressure, anti-wear, friction reducing and corrosion inhibition properties which comprise a major amount of a lubricating oil and a minor amount of a mixture comprising a boron or metal-boron derivative, a hydrocarbon polysulfide derivative of 2,5-dimercapto-1,3,4-thiadiazole and terephthalic acid.

Extreme pressure, anti-wear and friction reducing lubricating additives prevent destructive metal-to-metal contact, under boundary lubrication conditions, by adsorption or reaction with relatively moving metal surfaces to form an adherent protective film of compounds which have a lower shear strength than that of the metal surfaces. This film acts in the capacity of a "boundary lubricant" and performs the function of lubrication when metal-to-metal contact occurs. Boundary conditions and boundary lubricant refer to the conditions and a suitable lubricant relating to the combination of applied load, fluid viscosity and rubbing speed, which do not allow hydrodynamic lubrication to exist. Hydrodynamic lubrication exists when a film of lubricant maintains separation between lubricated surfaces.

Many extreme pressure and anti-wear agents are oil soluble or easily dispersed as a stable dispersion in oil. Many of the E.P. agents which provide the high load capacity are chemically reactive, containing chlorine, sulfur or phosphorus which react with metal surfaces.

It has now been discovered that certain oil-soluble or dispersible boron or metal-boron derivatives prepared as described herein, when added to lubricating oils or grease, not only improve the ability of the lubricant to prevent seizure of the parts being lubricated but, in addition, greatly reduce the amount of friction and wear of such moving parts.

The terms "friction reducing and anti-wear" herein refer to the ability of a substance to reduce the coefficient of friction between sliding or rubbing surfaces and/or the ability of a substance to prevent metal-to-metal welding or bonding during rubbing at extremely high contact pressures. "Extreme pressure lubricant" refers to a fluid or other substance which provides lubrication during extreme pressure conditions, including boundary lubrication. The term boramid denotes certain boron-containing compounds, which, as will be further described hereinafter, may be produced by reacting the reaction product of a primary amine, an alkylene oxide or epoxide and boric acid, all of which are further described herein. Metal derivatives of boramids are the the reaction product of the desired metal and specified boramid compound.

The boron and metal-boron derivatives (boramid compounds) herein, however, suffer from the disadvantage of copper and lead corrosion. This problem is solved by adding a small but effective amount of a hydrocarbon polysulfide derivative of 2,5-dimercapto-1,3,4-thiadiazole as a copper corrosion inhibitor and terephthalic acid as a lead corrosion inhibitor.

The extreme pressure anti-wear and anti-corrosion additives, in addition to the corrosion inhibitors and anti-oxidants described herein may be incorporated in a wide variety of lubricating oils, for example, mineral oil, (including automobile engine oil), crude oil, synthetic oil, and such industrial oils, as cutting oil, metal working fluids and grease. For example, the additives may be added to lubricating oils derived from paraffins, naphthenic or mixed base crude petroleum oils that have been subjected to solvent and/or sulfuric-acid treatment, aluminum chloride treatment, hydrogenation and/or other refining treatments. In addition, the additives described herein may be incorporated in petroleum distillates, such as diesel fuel, jet engine fuel, furnace oil, gas oil and other light oils. The petroleum oils may be of virgin or cracked petroleum stock, or mixtures thereof, boiling in the range of about 100.degree. F. to about 1,100.degree. F. The petroleum oil may contain cracked components such as those derived from cycle oils or cycle cuts boiling above gasoline, usually in the range of about 450.degree. F. to about 750.degree. F. and may be derived by catalytic or thermal cracking. Oils of high or low sulfur content such as diesel fuels or oils may additionally be used including re-refined oils.

Preferred distillate lubrication oils which are improved by the addition of additives herein have an initial boiling point within the range of 350.degree. F. to about 475.degree. F., an end point in the range of about 500.degree. F. to about 1,100.degree. F., and a flash point not lower than 110.degree. F.

Lubricants derived from oil shale are particularly desirable for use herein. Oil shale is generally composed of a variety of compact sedimentary rock, generally laminated, that contains little or no oil but does contain organic material, derived from aquatic organisms or waxy spores and pollen grains, which is convertible to oil by heat. Crude shale oil, in combination with water, gas and spent shale containing a carbonaceous residue and mineral matter, is formed by the pyrolysis of oil shale. The hydrocarbons of shale oil are highly unsaturated, resembling the products of thermal cracking of petroleum, as would be expected because of the pyrolytic origin of shale oil. Once the shale oil is extracted, it may be subjected to conventional hydrotreating procedures to produce a variety of hydrocarbon products, including lubricants.

Synthetic lubricating oils as defined herein are those oils derived from a product of chemical synthesis (man-made oils). Typical examples of such compositions include the polyglycol fluids (i.e., polyalkylene glycol); silicones which consist of a silicone-oxygen polymer chain to which are attached hydrocarbon branches composed of either alkyl or phenyl groups; phosphates; polyphenyl esters; synthetic hydrocarbons and various esters of organic acids and alcohols. Others include lubricating oils derived from solid carbonaceous products, such as coal, and the like.

The polyalkylene glycol lubricating oils suitable for use herein preferably are derived from the reaction product of the appropriate alkylene oxides. The alkylene moiety of the above compositions have a carbon chain of from about 1 to about 10 carbon atoms, preferably from about 2 to 7 carbon atoms and a molecular weight within the range of from about 200 to about 2,000, especially from about 200 to about 1,000, most preferably from about 200 to about 800. Representative examples of suitable polyalkylene glycols include, polyethylene glycol, polypropylene glycol, polyisopropylene glycol, polybutylene glycol and the like.

Silicone lubricants have extra-ordinary low viscosity-temperature coefficients coupled with good oxidation stability. The lubricant contains a repeating silicon-oxygen backbone and has organic groups R, wherein R is methyl, phenyl, vinyl and the like. The silicones herein have an average molecular weight within the range of from about 400 to about 9,000.

The polyphenyl ethers suitable for use herein have from 3 to 7 benzene rings and from 1 to 6 oxygen atoms, with the stated oxygen atoms joining the stated benzene rings in chains as ether linkages. One or more of the stated benzene rings in these polyphenyl ethers may be hydrocarbonyl-substituted. The hydrocarbonyl substituents, for thermal stability, must be free of CH and aliphatic CH so that preferred aliphatic substituents are lower saturated hydrocarbon radicals (1 to 6 carbon atoms) like methyl and tertbutyl, and preferred aromatic substituents are aryl radicals like phenyl and tolyl. In the latter case, the benzene ring supplied in the hydrocarbonyl substituent contributes to the total number of benzene rings in the molecule. Polyphenyl ethers consisting exclusively of chains of from 3 to 7 benzene rings with at least one oxygen atom joining the stated benzene rings in the chains as an ether linkage have particularly desirable thermal stability.

Exemplary of the alkyl polyphenyl ethers suitable for use are 3-ring polyphenyl ethers like 1-(p-methylphenoxy)4-phenoxybenzene and 2,4-diphenoxy-1-methyl-benzene, 4-ring polyethers like bis[p-(p-methyl-phenoxy)phenyl]ether and bis[(p-tert-butylphenoxy)phenyl]ether, and the like.

Polyphenyl ethers consisting exclusively of benzene rings and ether oxygen atoms linking said rings are exemplified by the triphenoxy benzenes and aryl-substituted polyphenyl ethers such as biphenyl phenoxyphenyl ether, biphenylyloxyphenyl phenoxyphenyl ether, biphenylyl ether, dibiphenylyloxybenzene, bis(phenylyloxyphenyl) ether, and the like.

A preferred class of polyphenyl ethers comprises those consisting of benzene rings joined in a chain by oxygen atoms as ether linkages between each ring. Examples of the polyphenyl ethers contemplated in the class are the bis(phenoxy-phenyl)ethers (4 benzene rings joined in a chain by 3 oxygen atoms), illustrative of which is bis(m-phenoxyphenyl)ether. The bis(phenoxy-phenoxy)benzenes are particularly preferred in the present invention. Illustrative of these are m-bis(m-phenoxy-phenoxy)benzene, m-bis(p-phenoxy-phenoxy)benzene, o-bis(o-phenoxy-phenoxy)benzene, and so forth. Further, the polyphenyl ethers suitable for use herein include the bis(phenoxy-phenoxy-phenyl)ethers such as bis[m-(m-phenoxy-phenoxy)phenyl]ether, bis[p-(p-phenoxy-phenoxy phenyl]ether, m-(m-phenoxy-phenoxy)phenyl m-(o-phenoxy-phenoxy)phenyl ether and the bis(phenoxy-phenoxy-phenoxy)benzenes such as m-bis(m-phenoxy-phenoxy-phenoxy)benzene, p-bis[p-(m-phenoxy-phenoxy)phenoxy]benzene and m-bis[m-(p-phenoxy-phenoxy)phenoxy]benzene.

Synthetic lubricating oils derived from hydrocarbons are generally of two types, namely, dialkylated benzene, polymerized alpha-olefins and/or hydrogenated polymerized alpha-olefins. Dialkylated benzene herein is formed from the condensation product of the appropriate alkyl compound and has a carbon chain from about 5 to about 50 carbon atoms, preferably from about 8 to about 20 carbon atoms, and a molecular weight of from about 200 to about 1,500, preferably from about 300 to about 700. Representative compounds include di-n-decylbenzene, n-decyl-n-tetradecylbenzene, and n-nonyl-n-dodecylbenzene.

Alpha-olefins suitable for use in preparing lubricating oils herein are characterized by the formula RCH.dbd.CH.sub.2, wherein R is a radical selected from the group of hydrogen and alkyl radicals having from about 4 to about 18 carbon atoms, preferably from about 6 to about 10 carbon atoms, and having a molecular weight of from about 80 to about 300, preferably from about 100 to about 200. Typical compounds include 1-octene, 1-decene and 1-dodecene.

Phosphates suitable for use herein as synthetic lubricating oils are the phosphate esters having the formula O.dbd.P(OR).sub.3, wherein R is aryl or alkyl having from about 4 to about 20 carbon atoms, preferably from 6 to about 10 carbon atoms, and have a molecular weight within the range of from about 200 to about 1,000, preferably from about 300 to about 550. Representative compounds include trioctyl phosphate, tricresyl phosphate and dicresyl methyl phosphate.

Esters of organic acids which are suitable for use herein as synthetic lubricating oils preferably are selected from organic acids having carbon chains of from C.sub.4 to C.sub.40 carbon units. Organic acids which may be reacted with the alcohols herein include caproic, decanoic, sebacic, laurel, oleic, stearic, palmitic etc. Likewise, alcohols herein may be derived from either natural or synthetic origin for example, pentarythritol, trimethylolpropane, amyl, 2-ethylhexanol or laural alcohol, etc., may be used to form the desired ester. The esters are formed using conventional methods. For example, the esters may be prepared by reaction of the desired alcohol with the desired acid, acid anhydride or acid halide using conventional reaction conditions and techniques.

Synthetic lubricating oils which are improved by the addition of the additives herein additionally include those derived from solid carbonaceous products, conveniently prepared by blending finely ground carbonaceous materials with a solvent to form a slurry. The slurry is then introduced into a reaction vessel containing a conventional hydrogenation catalyst and is reacted under normal hydrogenating pressures and temperatures. After hydrogenation, solids that are present may conveniently be removed from the product stream. The product is next stripped of solvent. The balance of the product stream may be distilled to obtain products of various boiling ranges, for example, hydrocarbons boiling in the gasoline range and hydrocarbons boiling in the lubricating oil range. Some of the products are useful as fuels and oils, the remainder may be further treated by a conventional petroleum process including cracking, hydrocracking, and the like. Synthetic lubricating oils produced from solid carbonaceous products, such as coal, are primarily aromatic and generally have a boiling range of about 300.degree. F. to about 1,400.degree. F., a density of about 0.7 to about 1.1 and a carbon to hydrogen molecular ratio in the range of about 1.3:1 to about 0.66:1. A typical example is a lubricating oil obtained from a subbituminous coal, such as Wyoming-Montana coal, comprising a middle oil having a boiling range of from about 375.degree. F. to about 675.degree. F. A description of how to prepare synthetic lubricating oils from a carbonaceous material, for example coal, is set forth in greater detail in U.S. Pat. No. 3,957,619 issued to Chun et al. on May 18, 1976, the disclosure of which is incorporated herein by reference.

Alternatively, the synthetic oil improved herein may be a nonhydrocarbon oil of lubricating viscosity. Suitable examples include synthetic oils obtained by polymerization of lower molecular weight alkylene oxides, such as propylene oxide and/or ethylene oxide employing alcohol or acid initiators, such as lauryl alcohol or acetic acid. Other typical synthetic oils include esters, for example, di(2-ethylhexyl)-silicate, tricresylphosphate and silicate esters, such as tetra-(2-ethyl-hexyl)-orthosilicate and hexa-(2-ethylbutoxy)-disiloxane.

If desired, the extreme pressure, anti-wear and friction reducing additives described herein may be employed in conjunction with other additives commonly used in petroleum products. Thus, there may be added to the oil compositions of this invention other rust and corrosion inhibitors, emulsifying agents, antioxidants, dyes, haze inhibitors, anti-static agents, detergents, dispersants, viscosity index improvement agents, extreme pressure, anti-wear, friction reducing and pour point reducing agents in addition to the additives used herein. Soaps or other thickening agents may be added to the lubricating oil compositions to form compositions having the consistency of a grease. When other additives are employed, it may be desirable, although not necessary, to prepare additive concentrates comprising concentrated solutions of the herein boron or metal-boron derivatives together with said other additives whereby the several additives are added simultaneously. Dissolution of the additive or additive concentrate into the oil composition may be facilitated by mixing accompanied with mild heating, but this is not absolutely essential.

Metal-working fluids such as cutting and grinding fluids are defined as liquids applied to a cutting tool or apparatus to assist in a cutting or machining process by washing away chips or serving as a lubricant or coolant, for example, in milling, drilling, turning, cutting, threading, broaching, surface grinding, form grinding, flute grinding, and similar metal-working operations. These oils are preferably obtained from conventionally refined lubricating oils containing film-strength additives or sulfurized naphthene-base oils, which may additionally contain emulsifying agents. Representative fluids and agents include: water, water solutions or emulsions of detergents and oils, mineral oils, fatty oils, chlorinated mineral oils, sulfurized mineral oils and mixtures thereof.

The herein described extreme pressure, anti-wear friction reducing and anti-corrosion additives may be incorporated in the lubricating oils in any convenient way. Thus, the above-described additives may be added directly to the lubricating oil by dissolving the desired additive(s) in said oil at the desired level of concentration.

Normally, the additive comprising boron or metal-boron derivatives is blended with the lubricating oil from about 0.1 to about 15 percent by weight, preferably from about 0.5 to about 10 percent by weight of the oil composition. Alternatively, the additive(s) may be blended with suitable solvents to form concentrates that may readily be dissolved in the appropriate oil at the desired concentration. If a concentrate is employed, it ordinarily will contain at least 10 to about 80 percent by weight of the additive(s) and preferably from 25 to about 75 percent by weight of said additive(s). The solvent in such a concentrate may be present in amounts of about 35 to about 75 percent by weight. Suitable solvents which may be used for this purpose are naphtha, and light mineral oil (i.e., 150 neutral to 450 neutral) and mixtures thereof. The particular solvent selected should, of course, be selected so as not to adversely affect the other desired properties of the ultimate oil composition. Thus, the solvent for use in incorporating the additive in an oil or fuel oil should be compatible with the oil or fuel oil in terms of stability, boiling range, corrosiveness, etc.

The extreme pressure, anti-wear and friction reducing boron compounds of the present invention are represented by the following formula: ##STR3## wherein R.sup.1 is hydrogen, alkyl, cyclic, alicyclic, aryl, alkylaryl, or arylalkyl radicals having from 1 to about 24 carbon atoms, preferably from 1 to about 18 carbon atoms, R.sup.2 and R.sup.3 are the same or different, straight or branched carbon chains, alkyl, cyclic, alicyclic, aryl, alkyaryl, or arylalkyl radicals having from 2 to about 20 carbon atoms, especially from about 2 to about 10 carbon atoms, y is a number from 1 to 4, and X is either hydrogen or a metal selected from transition metals having an atomic number between 21 and 30 or a Group IVA metal of the Periodic Table and mixtures thereof.

The above group of compounds, including metal derivatives thereof are referred to herein as boramids. The above compounds are conveniently prepared by reacting a primary amine with an alkylene oxide or epoxide. The resulting product is then reacted with boric acid to give the corresponding boramid compound. Amines which are suitable for use herein include methylamine, ethylamine, propylamine, butylamine, octadecylamine, dodecylamine, cyclohexylamine, phenylamine, cocoamine, tallowamine and oleylamine and mixtures thereof. A wide variety of alkene oxides or epoxides may be used to prepare the precursor for the boramid compounds herein. Typical alkene oxides or epoxides which are suitable for use include ethylene oxide, propylene oxide, 1,2-epoxybutane, cyclohexene oxide, cyclooctene oxide, cyclododecene oxide, styrene oxide, and 1,2-epoxybenzene and mixtures thereof. Normally, the boron atom will comprise from about 0.5 to about 10 weight percent, especially from about 2 to about 5 weight percent of the boramid compound. The boramid and/or metal-boramid compounds produced in accordance with the procedure herein are preferably selected from the group consisting of methylaminodiethylate hydrogen borate, ethylaminodiethylate hydrogen borate, propylaminodiethylate hydrogen borate, butylaminodiethylate hydrogen borate, octadecylaminodiethylate hydrogen borate, dodecylaminodiethylate hydrogen borate, cyclohexylaminodiethylate hydrogen borate, phenylaminodiethylate hydrogen borate, oleylaminodiethylate hydrogen borate, cocoaminodiethylate hydrogen borate, tallowaminodiethylate hydrogen borate, and dodecylamino di(phenyl ethylate)hydrogen borate and mixtures thereof.

It should be noted that a transition metal having an atomic number between 21 and 30 or a Group IVA metal of the Perioic Table may be incorporated into the boramid compounds herein. When a transition metal or Group IVA metal is incorporated into said compound, the metal component will replace the hydrogen atom on the hydroxy portion of the structure. In addition, the Examples, as set forth hereinafter, recite cocoaminodiethylate hydrogen borate as boramid C/12, tallowaminodiethylate hydrogen borate as boramid T/12 octadecylaminodiethylate hydrogen borate as boramid 18/12, and dodecylamino di(phenyl ethylate)hydrogen borate as H-boramid-CDS. The corresponding metal-boron derivatives will, of course, incorporate the desired metal into the composition before the boramid nomenclature, for example, zinc boramid C/12, etc.

Metals are conveniently incorporated into the boramid compound using conventional methods and apparatus. Normally, the metal is reacted with the desired boramid compound in salt form. Thus the metal acetates, propanates, hexanates etc. are suitable for use. It should be noted that not all metal salts are desirable for incorporating the metal ion into the boramid compound. The metal carbonates, nitrates, oxalates, chlorides, sulfates, hydroxides and oxides, to name a few, are all undesirable as vehicles for imparting metal ions into the boramid compound. These metal salts present solubility problems, separation problems and in addition, undesirable ions are frequently left in the boramid compound.

Desirable metals are conveniently selected from first row transition metals of the Perioid Table. Transition metals which are suitable for use are selected from scandium titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc and mixtures thereof. Group IVA metals which are useful herein include tin and lead and mixtures thereof. Normally, the metal will comprise from about 1 to about 17 weight percent, preferably from about 5 to about 10 weight percent of the boramid compound.

Generally, when two different boramid compounds or derivatives thereof are blended together, a weight ratio of from about 1:20 to about 20:1, preferably from about 1:10 to about 10:1 is highly desirable for imparting extreme pressure, anti-wear and friction reducing properties to a lubricant.

Use of copper and lead in the construction of improved internal combustion engines has created problems in the use of boramid extreme pressure additives in lubricants for such engines. The primary problem being the leaching out of copper and lead from bearings used in said engines.

Copper corrosion in engine bearings is inhibited by adding to the lubrication composition a corrosion inhibiting amount, preferably from about 0.001 to about 5 weight percent, especially from about 0.005 to about 2.5 weight percent of a hydrocarbon polysulfide derivative of 2,5-dimercapto-1,3,4-thiadiazole having the formula: ##STR4## wherein R.sup.4 and R.sup.5 are the same or different moieties selected from hydrogen or straight or branched chain alkyl, cyclic, alicyclic, aryl, alkylaryl or arylalkyl radicals having from 2 to about 30 carbon atoms, preferably from 4 to about 16 carbon atoms and w and z are numbers from 1 to about 8, preferably from 1 to 4. It should be noted that R.sup.4 and R.sup.5 cannot be hydrogen at the same time because the compound would be rendered insoluble in lubricating oils. Thus, when R.sup.4 is hydrogen, R.sup.5 must be selected from one of the other moieties described above.

The herein-described polysulfide derivatives of 2,5-dimercapto-1,3,4-thiadiazole can be suitable prepared by several methods. For example, they can be prepared by reacting 2,5-dimercapto-1,3,4-thiadiazole with a suitable sulfenyl chloride, or by reacting the dimercaptan with chlorine and reacting the resultant disulfenyl chloride below, ##STR5## with a primary or tertiary mercaptan. Bis-trisulfide derivatives are obtained by reacting the dimercaptan with a mercaptan and a sulfur chloride in molar ratios of from 1:2:2 to 1:2:4 at a temperature of from about 120.degree. to 212.degree. F. Higher polysulfides may be prepared by reacting the thiadiazole di- or trisulfides with sulfur at temperatures of about 200.degree. F. to 400.degree. F. Another method of preparing the polysulfides of the present invention involves reacting 2,5-dimercapto-1,3,4-thiadiazole with a mercaptan and sulfur in the molar ratio of from 1:1:1 to 1:4:16 at temperatures of from about 160.degree. F. to about 300.degree. F.

Compounds produced in accordance with the above procedure preferably are polysulfides of 1,3,4-thiadiazole-2,5-bis(alkyl, di-tri or tetra sulfide) containing from 2 to about 30 carbon atoms. Desirable polysulfides include 1,3,4-thiadiazole-2,5-bis(octyldisulfide); 1,3,4-thiadiazole-2,5bis(octytrisulfide); 1,3,4-thiadiazole-2,5bis(octyltetrasulfide); 1,3,4-thiadiazole-2,5bis(dodecyldisulfide); 1,3,4-thiadiazole-2,5bis(dodecyltrisulfide); 1,3,4-thiadiazole-2,5bis(dodecyltetrasulfide); 2-lauryldithia-5-thiaalphamethylstyryl-1,3,4 thiadiazole; 2-lauryltrithia-5-thiaalphamethylstyryl-1, 3,4 thiadiazole; 2-mercapto-5-octyldithio-1,3,4-thiadiazole and 2-mercapto-5-dodecyldithio-1,3,4-thiadiazole and mixtures thereof. An especially desirable ratio of the above copper corrosion inhibitors, when two are mixed together is from 1:20 to 20:1, preferably from 1:10 to 10:1.

A small but effective amount of terephthalic acid is the preferred lead corrosion inhibitor herein. The terephthalic acid may be prepared in accordance with conventional techniques and apparatus. For example, para-xylene may be oxidized to terephthalic acid at increased temperature and pressure in the presence of acetic acid, a bormine promoter and a heavy metal catalyst, i.e., cobalt, manganese, etc. A second method of preparing terephthalic acid comprises reacting benzene and potassium carbonate over a cadmium catalyst at increased temperature and pressure. Generally, the terephthalic acid is incorporated into lubricating oils at a concentration of from about 0.001 to about 1 weight percent, especially from about 0.01 to about 0.05 weight percent.

The invention will now be described with reference to several non-limiting examples. In Examples I to X, there is described the preparation of certain preferred boramid compounds which are useful as extreme pressure, anti-wear and friction-reducing additives in the lubricating compositions herein. A method of preparing preferred copper corrosion inhibitors is disclosed in Examples XI and XII.

The lead corrosion inhibitor (terephthalic acid) may be prepared in accordance with conventional techniques and equipment and therefore is not exemplified. The superiority of the foregoing compounds, when added in combination to a lubricating oil in accordance with the invention, is established by the comparison of Examples XIV to XVIII.

The invention will be further described with reference to the following non-limiting Examples.

A boramid compound is prepared by adding 20 grams of boric acid, 95 grams of Armak Ethomeen C/12 [bis(2-hydroxyethyl)cocoamine] and 250 ml of toluene to a single-necked one liter round-bottom flask. The toluene acts as a solvent and as an azeotrope for water produced during the reaction. It should be noted that boric acid is not soluble in toluene or Ethomeen C/12. The flask is placed in a heating mantle and fitted with a Dean-Stark trap that is topped with a condenser. The mixture thus formed is, then, heated until it begins to reflux. Next, the mantle is adjusted to give a moderate reflux rate. The reaction mixture is refluxed for one hour, or until the stoichiometric amount of water (12 ml) collects in the Dean-Stark trap and all of the boric acid has dissolved, after which the toluene is distilled from the reaction product. The reaction product (103 grams) is designated boramid C/12 and has a clear golden color. Boramid C/12 is a fluid liquid while hot but sets into a soft viscous material when cooled to room temperature. The compound is readily soluble in hydrocarbon solvents and water.

A boramid compound is prepared by following the procedure of Example I with the following substitution:

Armak Ethomeen T/12 [bis(2-hydroxyethyl)tallowamine] is substituted for the Armak Ethomeen C/12. Substantially the same results are obtained, however, the resulting compound is designated boramid T/12.

A boramid compound is prepared by mixing 20 grams of boric acid, 95 grams of Armak Ethomeen 18/12 [bis(2-hydroxyethyl)octadecylamine] and, as a solvent, 250 ml of toluene in a single-necked one liter round-bottomed flask. The flask is placed in a heating mantle and fitted with a Dean-Stark trap and water cooled condenser. The mixture is heated under reflux for one hour, during which 12 ml of water collects in the Dean-Stark trap. The toluene is then distilled from the reaction product. The compound is designated boramid 18/12 and is readily soluble in hydrocarbon solvents and water.

The procedure of Example III is followed to prepare a boramid compound with the following exception: N,N-diethanol-n-methylamine (46.3 grams) is substituted for the Armak Ethomeen 18/12. The reaction product thus produced is a liquid product with the consistency of honey when hot and becomes a waxy semi-solid when cooled to room temperature.

Boric acid (20 grams), N,N-diethanol-N-phenylamine (46.3 grams) and 250 mls of toluene are mixed in a one liter single-necked flask to prepare a boramid compound. The flask is equipped with a heating mantle, Dean-Stark trap and water-cooled condenser. The mixture is heated under reflux until the reaction is completed (12 ml of water collects), approximately one hour, and the toluene is distilled from the reaction mixture. The product thus prepared is suitable for use as an extreme pressure, antiwear and friction reducing additive for lubrication compositions.

A metal derivative of boramid C/12 is prepared by mixing 54 grams of the product of Example I (boramid C/12), 400 ml of toluene, 24.6 grams of nickel acetate and 150 ml of methanol in a single-necked, one liter round bottom flask which is equipped with a heating mantle and water-cooled condenser. The mixture is refluxed for four hours. Next, water, toluene, methanol and acetic acid are distilled from the reaction product. The product (59 grams) contained 7.8 weight percent nickel as determined by emission spectroscopy and the resulting product is a fluid green liquid when hot, which turns into a solid upon cooling to room temperature. The product is readily soluble in hydrocarbon solvents and water.

A metal boramid is prepared by following the procedure of Example II with the following exception: the boramid T/12 (54 grams), 400 ml of toluene, 24 grams of nickel acetate and 150 mls of methanol are mixed in a single-necked, one liter round bottom flask, equipped with a heating mantle, Dean-Stark trap and water-cooled condenser. The mixture is refluxed for four hours and the toluene, water and acetic acid are distilled from the reaction product.

A zinc derivative of boramid C/12 is prepared by mixing 54 grams of the reaction product of Example 1 (boramid C/12) with 400 ml of toluene, 19.1 grams of zinc acetate and 50 ml of methanol in a single-necked, one liter round bottom flask, equipped with a heating mantle and water-cooled condenser. The mixture is refluxed for four hours and the toluene, methanol, water and acetic acid are distilled. The resulting product is suitable for use as an extreme pressure, anti-wear, friction reducing additive for lubricating compositions.

A metal boramid is prepared by following the procedure of Example VII with the following exception: zinc acetate is substituted for the nickel acetate to produce zinc-boramid T/12.

It is to be noted that transition metals having an atomic number between 21 and 30, and Group IVA metals of the Periodic Table may be substituted for the nickel and zinc metals herein to prepare corresponding metal boramids.

Dodecylamino di(phenylethylate) hydrogen borate is prepared by adding 34.85 pounds of deodecylamine (1 equivalent) and 41.0 pounds of styrene oxide (2 equivalents) to a 17 gallon round bottomed flask equipped with a water cooled condenser and containing 3 gallons of toluene and 1 liter of water. The reaction is exothermic and begins immediately upon addition of the above reactants. Additional heat is applied and the reaction mixture is refluxed for a total of 24 hours, however, as little as 2 hours may result in complete reaction. The reaction is cooled to room temperature, 10.49 pounds of boric acid (1 equivalent) is added and the flask is equipped with a Dean-Stark trap. Heat is again applied and the reaction mixture refluxed until water stops collecting in the trap. Toluene is, then, distilled from the reaction product at a temperature of 400.degree. F. or less. About 6 liters of water collect in the Dean-Stark trap. The reaction produces approximately 75 pounds of product and is designated as H-boramid-CDS.

A copper corrosion inhibitor comprising 1,3,4-thiodiazole-2,5-bis(dodecyldisulfide) is prepared by chlorinating 284 grams of n-dodecyl mercaptan in 0.6 liter of carbon tetrachloride with 1.47 moles of chlorine over a two hour period at a temperature of about 23.degree. F. to about 32.degree. F. Next, sulfenyl chloride which forms as a reaction product is stripped with nitrogen to remove hydrogen chloride, and the resultant compound is added to 86 grams of a 2,5-dimercapto-1,3,4-thiadiazole slurry. The mixture is heated at 86.degree. F. for 11/2 hours and the resultant compound (1,3,4-thiadiazole-2,5-bis(dodecyldisulfide) is recovered by washing with water and sodium bicarbonate and vacuum stripping to remove carbon tetrachloride.

The procedure of Example XI is followed to prepare 1,3,4-thioadiazole-2,5-bis(octyldisulfide) with the following exception: octyl mercaptan is substituted for the dodecylmercaptan.

The extreme pressure, anti-wear and friction reducing additives boramid C/12 produced in Example I and boramid T/12 produced in Example II are sequentially mixed with SAE 10 W/40 motor oil.sup.(a) containing 0.15 weight percent of phosphorus and 0.17 weight percent of calcium.

The additive and/or lubricant composition is tested in accordance with the procedure disclosed in ASTM D3233-73 (Reapproved 1978) using a Falex lubricant tester. The test, in accordance with the above ASTM designation, is performed by applying resistance to a revolving metal journal. A rachet mechanism movably attached to two V-Blocks applies resistance by steadily increasing pressure on the journal. The metal journal and V-Blocks (steel) are submerged in the lubricant composition to be tested. The results are indicated in Table 1 below.

It should be noted that the other boramid compounds herein, including the metal derivatives thereof, may be substituted for the boramid C/12 and boramid T/12 compounds above with substantially the same results.

A lubricant composition containing H-boramid-CDS, 1,3,4-thiadiazole-2,5-bis(octyldisulfide) and terephthalic acid is tested for copper and lead corrosion inhibition properties using a single-cylinder Labeco CLR Test Engine equipped with sintered copper (65 wt.%)/lead (35 wt.%) connecting rod bearings, in accordance with the procedure of Federal Test Method Standard No. 791B, Method 3405.2. The lubricant composition used is a standard SAE 30 motor oil containing the additives and concentrations disclosed in Table 3.

The copper lead corrosion tests are conducted in accordance with the test conditions of Table 2 below:

The test is conducted by charging 3.5 pints of the test lubricant to the engine sump. Test duration consists of 40 hours operation at the prescribed test conditions of Table 2 above. When the prescribed gallery oil temperature is reached, the test time begins. Interim oil adjustments are made at the end of 10, 20 and 30 hours of test operation. A copper/lead bearing weight loss of about 40 mg or lower is considered acceptable. All of the tests are conducted using SAE 30 motor oil containing the additives and/or compounds, including concentrations in Table 3 below.

As can readily be determined from the above Examples, the lubricant additives herein impart extreme pressure, anti-wear friction reducing and copper and lead corrosion inhibition properties to lubricant compositions when used in accordance with the disclosure herein. Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.