Use of reaction products of trialkyl phosphites with elemental sulfur and process for making same

Abstract: Dialkyl and trialkyl phosphites are reacted with sulfur to form a first product useful as a lube oil additive. The first product may be further reacted with an amine, olefin, or alkylene oxide to form a lube oil product which may be reacted with phosphorus trioxide to form another lube oil additive.

Description: This invention relates to processes for making reaction products of trialkyl phosphites with elemental sulfur, and use of any of these products in lubricating oil formations. US Patent 3,984,448 discloses the use of metal oxides, such as those of copper, calcium, barium, magnesium, zinc, cadmium, 0,0-dialkylphosphorus acid esters to produce dialkyl thiophosphates. US Patent 4,242,511 discloses the reaction of 0,S-dialkylthiophosphoric acid esters by subjecting a thiophosphate to partial dealkylation in forming the salt of the dealkylated product by treatment with an amine. Although dithiophosphate products are known lubricant additives, their preparation involves processes resulting in noxious, undesirable by-products such as hydrogen sulfide and chloride-containing waste streams. FR-A-1,312,167 and GB-1,015,201 disclose a process in which trimethyl and triaryl phosphites are reacted with elemental sulfur. According to one aspect of the present invention there is provided a process for making a reaction product suitable for use as an additive in lubricating oils which process comprises reacting in the absence of catalyst a trialkyl phosphite with elemental sulfur in a mole ratio of sulfur to phosphite of between 0.8 and 1.2 at a temperature from 75° to 100°C. Useful trialkyl phosphites include oleyl, 2-ethyl hexyl, 1,3-dimethylbutyl, tridecyl, isodecyl, octyl and butyl, and mixed phosphites of the above radicals. According to a further aspect, this invention provides the use of a reaction product, prepared by reacting in the absence of catalyst a trialkyl phosphite having the formula (R₁O)₂ POR₂ wherein R₁ and R₂ are defined in claims 1 or 2 with elemental sulfur in a mole ratio of sulfur to phosphite of between 0.8 and 1.2 at a temperature from 75°C to 100°C, as an antiwear additive in lubricating oils. If desirable, an unreactive organic solvent can be utilized. Preferably the organic solvent is selected from benzene, toluene, xylene, and mixed alkyl and aromatic petroleum distillates. The pulverulent sulfur should conveniently have a mean particle size of less than one millimeter, preferably less than 0.01 millimeters, as this enables the reaction to be shortened. The reaction is carried out, preferably under a blanket of material such as nitrogen or other non-reactive gas. At the end of the reaction period the reaction mixture is allowed to cool to room temperature. The desired product is then stripped under vacuum to remove solvent and volatile byproducts and can be subsequently filtered or decanted from the reaction vessel. The resulting reaction products of this invention are used with lubricating oils or greases to the extent of from 0.1% to 10% by weight of the total composition. Furthermore, other additives, such as detergents, antioxidants, antiwear agents and the like may be present. These can include phenates, sulfonates, succinimides, zinc dialkyl dithiophosphates, polymers, calcium and magnesium salts of phenates and sulfonates, including overbased salts of the same, and the like. The lubricants contemplated for use with the esters herein disclosed include mineral and synthetic hydrocarbon oils of lubricating viscosity, mixtures of mineral oils and synthetic oils and greases from any of these, including the mixtures. The synthetic hydrocarbon oils include long-chain alkanes such as cetanes and olefin polymers such as oligomers of hexane, octene, decene, and dodecene, etc. These vicinal diols are especially effective in synthetic oils formulated using mixtures of synthetic hydrocarbon olefin oligomers and lesser amounts of hydrocarbyl carboxylate ester fluids. The other synthetic oils, which can be used alone with the compounds of this invention, or which can be mixed with a mineral or synthetic hydrocaron oil, include (1) fully esterified ester oils, with no free hydroxyls, such as pentaerythritol esters of monocarboxylic acids having 2 to 20 carbon atoms, trimethylolpropane esters of monocarboxylic acids having 2 to 20 carbon atoms, (2) polyacetals and (3) siloxane fluids. Especially useful among the synthetic esters are those made from polycarboxylic acids and monohydric alcohols. More preferred are the ester fluids made by fully esterifying pentaerythritol, or mixtures thereof with di- and tripentaerythritol, with an aliphatic monocarboxylic acid contianing from 1 to 20 carbon atoms, or mixtures of such acids. A wide variety of thickening agents can be used in the greases of this invention. Included among the thickening agents are alkali and alkaline earth metal soaps of fatty acids and fatty materials having from 12 to 30 carbon atoms per molecule. The metals are typified by sodium, lithium, calcium and barium. Fatty materials are illustrated by stearic acid, hydroxystearic acid, stearin, cottonseed oil acids, oleic acid, palmitic acid, myristic acid and hydrogenated fish oils. Other thickening agents include salt and salt-soap complexes as calcium stearate-acetate (U.S. Patent No. 2,197,263), barium stearate acetate (U.S. Patent No. 2,564,561), calcium stearate-caprylate-acetate complexes (U.S. Patent No. 2,999,065), calcium caprylate-acetate (U.S. Patent No. 2,999,066), and calcium salts and soaps of low-, intermediate-and high-molecular weight acids and of nut oil acids. Another group of thickening agents comprises substituted ureas, phthalocyanines, indanthrene, pigments such as perylimides, pyromellitdiimides, and ammeline. The preferred thickening gelling agents employed in the grease compositions are essentially hydrophobic clays. Such thickening agents can be prepared from clays which are initially hydrophilic in character, but which have been converted into a hydrophobic condition by the introduction of long chain hydrocarbon radicals onto the surface of the clay particles prior to their use as a component of a grease composition, as, for example, by being subjected to a preliminary treatment with an organic cationic surface active agent, such as an onium compound. Typical onium compounds are tetraalkylammonium chlorides, such as dimethyl dioctadecyl ammonium choloride, dimethyl dibenzyl ammonium chloride and mixtures thereof. This method of conversion, being well known to those skilled in the art, is believed to require no further discussion, and does not form a part of the present invention. More specifically, the clays which are useful as starting materials in forming the thickening agents to be employed in the grease compositions, can comprise the naturally occurring chemically unmodified clays. These clays are crystalline complex silicates, the exact composition of which is not subject to precise description, since they vary widely from one natural source to another. These clays can be described as complex inorganic silicates such as aluminum silicates, magnesium silicates, barium silicates, and the like, containing, in addition to the silicate lattice, varying amounts of cation-exchangeable groups such as sodium. Hydrophilic clays which are particularly useful for conversion to desired thickening agents include montmorillonite clays, such as bentonite, attapulgite, hectorite, illite, saponite, sepiolite, biotite, vermiculite, zeolite clays, and the like. The thickening agent is employed in an amount from about 0.5 to about 30, and preferably from 3 percent to 15 percent by weight of the total grease composition. Having described the invention in general aspects, the following examples are offered as specific illustrations. Parts are by weight. EXAMPLE 1 A one-liter flask was charged with 209.3 grams of tris-2-ethylhexylphosphite and 16 grams of sulfur under a nitrogen atmosphere. The initial reaction elevated the temperature to 109°C. When the temperature started to decline, heat was applied to maintain 100°C for eight hours. The product when analyzed was determined to contain 6.7 percent of phosphorus and 7.5 percent of sulfur. EXAMPLE 2 In accordance with the procedure of Example 1 a product was made from 208 grams of tri-isopropyl phosphite and 32 grams of sulfur. Analysis of the product showed 6.57 percent of phosphorus and 11.6 percent of sulfur. FOUR BALL WEAR TEST SCAR DIAMETER (mm) 1/2 Inch Balls, 52100 Steel, 60 Kg., 30 Minutes, 1.5% Additive Temperature, (°F) °C 1000 RPM 2000 RPM 93°C (200°F) 149°C (300°F) 93°C (200°F) 149°C (300°F) Base Stock 1.02 1.92 4.12 3.85 Example 1 0.57 0.75 0.82 0.87 Example 2 0.65 0.50 0.70 0.70 The product of Example 1 was combined at 0.6 weight percent into a fully formulated hydraulic oil and compared to the same formulation using 0.7 weight percent of commercial zinc dithiophosphate in the Vickers V1O4C pump Wear Test (ASTM D2882). The results were as follows and demonstrated the antiwear performance of the products herein disclosed. Formulation Containing ASTM D28882 Wear, Milligrams Zinc dithiophosphate 27 Example 1 Product 22

Claims: A process for making a reaction product suitable for use as an additive in lubricating oils which process comprises reacting, in the absence of catalyst, a trialkyl phosphite having the formula (R₁O)₂ POR₂ wherein R₁ represents a C₄ to C₁₈ alkyl and R₂ represents a C₄ to C₁₈ alkyl which may be the same as or different from R₁ with elemental sulfur in a mole ratio of sulfur to phosphite of between 0.8 and 1.2 at a temperature from 75° to 100°C. A process according to claim 1 wherein the trialkyl phosphite comprises one or more substituents which may be the same or different selected from oleyl, 2-ethyl hexyl, 1, 3-dimethyl butyl, tridecyl, isodecyl, octyl or butyl. The use of a reaction product, prepared by reacting in the absence of catalyst a trialkyl phosphite having the formula (R₁O)₂ POR₂ wherein R₁ and R₂ are defined in claims 1 or 2 with elemental sulfur in a mole ratio of sulfur to phosphite of between 0.8 and 1.2 at a temperature from 75°C to 100°C, as an antiwear additive in lubricating oils.

Inventors: CARDIS ANGELINE BAIRD, CARDIS, ANGELINE BAIRD
Applicants: MOBIL OIL CORP, MOBIL OIL CORPORATION
Application year: 1987
Main classification: C10M159
IPC codes: C07F9, C10M137