Reaction product of ammonium tetrathiomolybdate with basic nitrogen compounds and lubricants containing same
FIELD OF THE INVENTION 
     This invention relates to a process for preparing lubricating oil additives. It also relates to new lubricating oil compositions containing antioxidant molybdenum compounds. 
     BACKGROUND OF THE INVENTION 
     Molybdenum disulfide has long been known as a desirable additive for use in lubricating oil compositions. However, one of its major detriments is its lack of oil solubility. Molybdenum disulfide is ordinarily finely ground and then dispersed in the lubricating oil composition to impart friction modifying and antiwear properties. Finely ground molybdenum disulfide is not an effective oxidation inhibitor in lubricating oils. 
     As an alternative to finely grinding the molybdenum disulfide, a number of different approaches involving preparing salts of molybdenum compounds have been tried. One type of compound which has been prepared is molybdenum dithiocarbamates. Representative compositions are described in U.S. Pat. No. 3,419,589, which teaches molybdenum (VI) dioxide dialkyldithiocarbamates; U.S. Pat. No. 3,509,051, which teaches sulfurized oxymolybdenum dithiocarbamates; and U.S. Pat. No. 4,098,705, which teaches sulfur containing molybdenum dihydrocarbyl dithiocarbamate compositions. 
     An alternative approach is to form dithiophosphates instead of dithiocarbamates. Representative of this type of molybdenum compound are the compositions described in U.S. Pat. No. 3,494,866, such as oxymolybdenum diisopropylphosphorodithioate. 
     U.S. Pat. No. 3,184,410 describes certain dithiomolybdenyl acetylacetonates for use in lubricating oils. 
     Braithwaite and Greene in Wear, 46 (1978) 405-432 describe various molybdenum-containing compositions for use in motor oils. 
     U.S. Pat. No. 3,349,108 teaches a molybdenum trioxide complex with diethylenetriamine for use as an additive for molten steel. 
     Russian Pat. No. 533,625 teaches lube oil additives prepared from ammonium molybdate and alkenylated polyamines. 
     Another way to incorporate molybdenum compounds in oil is to prepare a colloidal complex of molybdenum disulfide or oxysulfides dispersed using known dispersants. U.S. Pat. No. 3,223,625 describes a procedure in which an acidic aqueous solution of certain molybdenum compounds is prepared and then extracted with a hydrocarbon ether dispersed with an oil soluble dispersant and then freed of the ether. U.S. Pat. No. 3,281,355 teaches the preparation of a dispersion of molybdenum disulfide by preparing a mixture of lubricating oil, dispersant, and a molybdenum compound in water or C 1-4  aliphatic alcohol, contacting this with a sulfide ion generator and then removing the solvent. Dispersants said to be effective in this procedure are petroleum sulfonates, phenates, alkylphenate sulfides, phosphosulfurized olefins and combinations thereof. 
     SUMMARY OF THE INVENTION 
     It has now been found that a lubricating oil additive can be prepared by combining ammonium tetrathiomolybdate and a basic nitrogen-containing composition to form a sulfur and molybdenum-containing complex. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Lubricating oil compositions containing the additive prepared as disclosed herein are effective as either fluid and grease compositions (depending upon the specific additive or additives employed) for inhibiting oxidation, imparting antiwear and extreme properties, and/or modifying the friction properties of the oil which may, when used as a crankcase lubricant, lead to improved mileage. 
     The precise molecular formula of the molybdenum compositions prepared by the process of this invention is not known with certainty; however, they are believed to be compounds in which molybdenum, whose valences are satisfied with atoms of oxygen or sulfur, is either complexed by or the salt of one or more nitrogen atoms of the basic nitrogen containing composition used in the preparation of these additives. 
     The molybdenum compound used to prepare the complexes of this invention is ammonium tetrathiomolybdate, (NH 4 ) 2  MOS 4 . 
     The basic nitrogen compound must have a basic nitrogen content as measured by ASTM D-664 or D-2896. Typical of such compositions are succinimides, carboxylic acid amides, hydrocarbyl monoamines, hydrocarbon polyamines, Mannich bases, phosphonamides, thiophosphonamides, phosphoramides dispersant viscosity index improvers, and mixtures thereof. These basic nitrogen containing compounds are described below (keeping in mind the reservation that each must have at least one basic nitrogen). Any of the nitrogen-containing compositions may be after-treated with e.g., boron using procedures well known in the art so long as the compositions continue to contain basic nitrogen. These after-treatments are particularly applicable to succinimides and Mannich base compositions. 
     The mono and polysuccinimides that can be used to prepare the lubricating oil additives described herein are disclosed in numerous references and are well known in the art. Certain fundamental types of succinimides and the related materials encompassed by the term of art &#34;succinimide&#34; are taught in U.S. Pat. Nos. 3,219,666, 3,172,892, and 3,272,746, the disclosures of which are hereby incorporated by reference. The term succinimide is understood in the art to include many of the amide, imide, and amidine species which are also formed by this reaction. The predominant product is a succinimide and this term has been generally accepted as meaning the product of a reaction of an alkenyl substituted succinic acid or anhydride with a nitrogen containing compound. Preferred succinimides, because of their commercial availability, are those succinimides prepared from a hydrocarbyl succinic anhydride, wherein the hydrocarbyl group contains from about 24 to about 350 carbon atoms, and an ethylene amine, said ethylene amines being especially characterized by ethylene diamine, diethylene triamine, triethylene tetraamine, and tetraethylene pentamine. Particularly preferred are those succinimides prepared from polyisobutenyl succinic anhydride of 70 to 128 carbon atoms and tetraethylene pentaamine or triethylene tetraamine or mixtures thereof. 
     Also included within the term succinimide are the coligomers of a hydrocarbyl succinic acid or anhydride and a poly secondary amine containing at least one tertiary amino nitrogen in addition to two or more secondary amino groups. Ordinarily this composition has between 1,500 and 50,000 average molecular weight. A typical compound would be that prepared by reacting polyisobutenyl succinic anhydride and ethylene dipiperazine. Compositions of this type are disclosed in U.S. Ser. No. 816,063, filed July 15, 1977 the disclosure of which is hereby incorporated by reference. 
     Carboxylic amide compositions are also suitable starting materials for preparing the products of this invention. Typical of such compounds are those disclosed in U.S. Pat. No. 3,405,064, the disclosure of which is hereby incorporated by reference. These compositions are ordinarily prepared by reacting a carboxylic acid or anhydride ester thereof, having at least 12 to about 350 saturated aliphatic carbon atoms in the principal aliphatic chain and, if desired, having sufficient pendant aliphatic groups to render the molecule oil soluble which is with an amine or hydrocarbyl polyamine, such as an ethylene amine, to give a mono or polycarboxylic acid amide. 
     Another class of compounds which are useful in this invention are hydrocarbyl monoamines, hydrocarbyl polyamines, preferably of the type disclosed in U.S. Pat. No. 3,574,576, the disclosure of which is hereby incorporated by reference. The hydrocarbyl, which is preferably alkyl, or olefinic having one or two sites of unsaturation, usually contains from 9 to 350, preferably from 20 to 200 carbon atoms. Preferred amines are those which are derived, e.g., by reacting polyisobutenyl chloride and diethylene triamine, from polyalkylene polyamines such as ethylene diamine, diethylene triamine, tetraethylene pentaamine and the like, or 2-aminoethylpiperazine, 1,3-propylene diamine, 1,2-propylenediamine and the like. 
     Another class of compounds supplying basic nitrogen are the Mannich base compositions. These compositions are prepared from a phenol or alkylphenol, an aldehyde, such as formaldehyde or formaldehyde precursor such a para-formaldehyde, and an amine compound. The amine may be a mono or polyamine and typical compositions are prepared from methylamine, diethylene triamine, or tetraethylene pentaamine and the like. The phenolic material may be sulfurized or unsulfurized. Typical Mannich bases which can be used in this invention are disclosed in U.S. Pat. No. 4,157,309, and U.S. Pat. Nos. 3,649,229, 3,368,972 and 3,539,663, the disclosures of which are hereby incorporated by reference. The last application discloses Mannich bases prepared by reacting an alkylphenol having at least 50 carbon atoms, preferably 50 to 200 carbon atoms with formaldehyde and an alkylene polyamine HN(ANH) n  H where A is a saturated divalent alkyl hydrocarbon of 2 to 6 carbon atoms and n is 1-10 and where the condensation product of said alkylene polyamine may be further reacted with urea or thiourea. The utility of these Mannich bases as starting materials for preparing lubricating oil additives can often by significantly improved by treating the Mannich base using conventional techniques to introduce boron into the composition. 
     Another class of composition useful for preparing the additives of this invention are the phosphoramides and phosphonamides such as those disclosed in U.S. Pat. Nos. 3,909,430 and 3,968,157 the disclosures of which are hereby incorporated by reference. These compositions may be prepared by forming a phosphorus compound having at least one P-N bond. They can be prepared, for example, by reacting phosphorus oxychloride with a hydrocarbyl diol in the presence of a monoamine or by reacting phosphorus oxychloride with a difunctional secondary amine and a mono-functional amine. Thiophosphoramides can be prepared by reacting an unsaturated hydrocarbon compound containing from 2 to 450 or more carbon atoms, such as polyethylene, polyisobutylene, polypropylene, ethylene, 1-hexene, 1,3-hexadiene, isobutylene, 4-methyl-1-pentene, and the like, with phosphorus pentasulfide and nitrogen-containing compound as defined above, particularly an alkylamine, alkyldiamine, alkylpolyamine, or an alkyleneamine, such as ethylene diamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentaamine, and the like. 
     Another class of nitrogen-containing compositions useful in preparing the molybdenum compositions of this invention includes the so-called dispersant viscosity index improvers (VI improvers). These VI improvers are commonly prepared by functionalizing a hydrocarbon polymer, especially a polymer derived from ethylene and/or propylene, and optionally containing additional units from one or more co-monomers such as alicyclic or aliphatic olefins or diolefins. The functionalization may be carried out by a variety of processes which introduce a reactive site or sites which usually has at least one oxygen atom on the polymer. The polymer is then contacted with a nitrogen-containing source to introduce nitrogen-containing functional groups on the polymer backbone. Commonly used nitrogen sources include any basic nitrogen compound, especially those nitrogen-containing compounds and compositions described herein. Preferred nitrogen sources are alkylene amines, alkyl amines, and Mannich bases. 
     Preferred basic nitrogen compounds are for use in this invention succinimides, carboxylic acid amides, and Mannich bases. 
     The compositions of this invention may be prepared by reacting the ammonium tetrathiomolybdate, and basic nitrogen compound, optionally in the presence of an inert diluent. 
     This reaction is preferably carried out at from a temperature slightly above that at which the reaction mixture becomes solid to reflux. The reaction is ordinarily carried out at atmospheric pressure; however, higher or lower pressures may be used, if desired, using methods that are well-known to those skilled in the art. A diluent which does not react with the ammonium tetrathiomolybdate is desirable. Typical diluents are lubricating oil and liquid compounds containing only carbon and hydrogen. The diluent provides a minimum dilution of the reaction mixture to enable the mixture to be efficiently stirred. 
     The lubricating oil compositions containing the additives of this invention can be prepared by admixing, by conventional techniques, the appropriate amount of the molybdenum-containing composition with a lubricating oil. The selection of the particular base oil depends on the contemplated application of the lubricant and the presence of other additives. Generally, the amount of the molybdenum containing additive will vary from 0.05 to 15% by weight and preferably from 0.2 to 10% by weight. 
     The lubricating oil which may be used in this invention includes a wide variety of hydrocarbon oils, such as naphthenic bases, paraffin bases and mixed base oils as well as synthetic oils such as esters and the like. The lubricating oils may be used individually or in combination and generally have a viscosity which ranges from 50 to 5,000 SUS and usually from 100 to 15,000 SUS at 38° C. 
     In many instances it may be advantageous to form concentrates of the molybdenum containing additive within a carrier liquid. These concentrates provide a convenient method of handling and transporting the additives before their subsequent dilution and use. The concentration of the molybdenumcontaining additive within the concentrate may vary from 0.25 to 90% by weight although it is preferred to maintain a concentration between 1 and 50% by weight. The final application of the lubricating oil compositions of this invention may be in marine cylinder lubricants as in crosshead diesel engines, crankcase lubricants as in automobiles and railroads, lubricants for heavy machinery such as steel mills and the like, or as greases for bearings and the like. Whether the lubricant is fluid or a solid will ordinarily depend on whether a thickening agent is present. Typical thickening agents include polyurea acetates, lithium stearate and the like. 
     If desired, other additives may be included in the lubricating oil compositions of this invention. These additives include antioxidants or oxidation inhibitors, dispersants, rust inhibitors, anticorrosion agents and so forth. Also, anti-foam agents stabilizers, anti-stain agents, tackiness agents, anti-chatter agents, dropping point improvers, anti-squawk agents, extreme pressure agents, odor control agents and the like may be included. 
     Certain molybdenum products that can be prepared by the process of invention also find utility in making brake lining materials, in high-temperature structural materials, in iron and steel alloys, in cladding materials, in electroplating solutions, as components for electrical discharge machine electrodes, as fuel additives, in making self-lubricating or wear-resistant structures, as mold release agents, in compositions for phosphatizing steel, in brazing fluxes, in nutrient media for microorganisms, in making electrosensitive recording material, in catalysts for refining coal, oil, shale, tar sands, and the like or as stabilizers or curing agents for natural rubber or polymers.