Patent GB-623591-A (GB)
Title: Improvements in or relating to mineral lubricating oil compositions
IPC: C10M137/10
Filed: 1947-01-06
Abstract: A lubricating oil composition, particularly a "heavy duty" motor oil for high-speed Diesel engines, comprises a mineral lubricating oil base and a minor proportion, e.g. 0.2 to 2.0 per cent by weight of a metallic salt of an ester of dithiophosphoric acid in which one or two esterifying radicals are derived from a naphthenic acid ester of a polyhydroxylic organic compound, which naphthenic acid ester has in its molecule at least one naphthenate radical and at least one free hydroxyl group.  The metal in the salt may be other than an alkali metal, e.g. barium, calcium, magnesium, aluminium, chromium, manganese, nickel, cobalt or zinc and the lubricating composition may comprise also a minor proportion, e.g. 0.05 to 3.0 per cent by weight of a water-insoluble petroleum sulphonate of a metal other than an alkali metal, e.g. an alkaline earth metal, tin, aluminium, chromium, lead, magnesium, manganese, nickel, cobalt or zinc. One or both esterifying radicals of the dithiophosphate may be derived from a naphthenic acid ester, such as glycollic or glyceryl mononaphthenate, having the general formula (R1COO)x-R-(OH)y, where R1 represents any naphthenic acid residue, R is an organic radical having not less than two carbon atoms, and x and y are integers which may be one or more. The dithiophosphate may have the general formula <FORM:0623591/III/1> where R1, R and x have the significance indicated above, M represents a metal other than an alkali metal having a valency z, and R2 represents any organic radical such as an alkyl, aryl, aralkyl or cycloalkyl group.  Alternatively, the general formula of the dithiophosphate may be <FORM:0623591/III/2> where R1, R, x, M and z have the significance previously assigned and m is a small integer which may be zero in the case where y is one.  One of or both the esterifying radicals of the dithiophosphate may be derived from ethylene glycol mononaphthenate, and in the former case the other esterifying radical may be derived from an alcohol or phenol such as lauryl alcohol, cresol, or octyl-cresol.  The naphthenic acids from which R1 is derived may have average molecular weight of 240 or 320, and R may be an alkylene group represented by (CH2)n, where n is an integer other than one, a di- or polyalkylene ether grouping, e.g. di- or polyalkylene glycol, or an arylene grouping, e.g. a benzene nucleus or a benzyl radical. The polyhydroxylic organic compounds which may be employed for the production of the naphthenic acid ester including the R1 and R groupings are ethylene glycol, propylene glycol, di- and tri-ethylene glycol, glycerol, resorcinol, hydroquinone, and parahydroxybenzoyl alcohol.  The polyhydroxylic organic compounds may include substituent groups such as alkyl, ester, or carboxylic acid groups.  The radical R2 (formula 2) may be an amyl, lauryl, cetyl, phenyl, cresyl, tertiary amyl phenyl, naphthyl, benzyl or cyclohexyl radical.  Alternatively, R2 may be the same as (R1COO)x-R-.  R2 may carry a thioether substituent.  Specific examples of thio-phosphates are di-(ethylene glycol mono-naphthenate) di-thio-phosphate, ethylene glycol mononaphthenate cresyl di-thio-phosphate, glyceryl mono-naphthenate di-thio-phosphate, diethylene glycol mono-naphthenate benzyl di-thiophosphate, propylene glycol mono-naphthenate amyl dithiophosphate, di-(diethylene glycol mononaphthenate) dithiophosphate, and triethylene glycol mononaphthenate octyl cresyl thioether dithiophosphate.  A general method of preparing the dithiophosphates is given and also more detailed examples of the preparation of specific dithiophosphates (see Group IV (b)).  The dithiophosphates described are said to be liquids very readily soluble in either paraffinic or naphthenic mineral lubricating oils, and these solutions are said to be more chemically stable when heated to 160 DEG  C. than the dithiophosphates hitherto used or than ethylene glycol mono-stearate di-thio-phosphate.  Tests are described illustrating the sludge dispersive properties, thermal stability, oxidation resistance and bearing corrosion inhibition properties of motor oils containing the naphthenate dithiophosphates.ALSO:Organic dithiophosphates whose metallic salts are suitable for use as lubricating oil additives (see Group III) consist of esters of dithio-phosphoric acid in which one or two esterifying radicals are derived from a naphthenic acid ester of a polyhydroxylic organic compound, which naphthenic acid ester has in its molecule at least one naphthenate radical and at least one free hydroxyl group.  In an example, crude ethylene glycol mononaphthenate is prepared by refluxing 900 gm. of mixed naphthenic acids (mean mol. wt. 320), 521 gm. of ethylene glycol and 4.5 gm. of p-toluene sulphonic acid catalyst for 4 1/4 hours at 160-180 DEG  C. while CO2 is passed through the mixture and the water given off during the reaction trapped in a separator.  The product is washed with boiling water and dried by heating in a current of CO2. Di-(ethylene glycol mononaphthenate) di-thiophosphate is prepared by heating 198 grams of the crude naphthenate, prepared as above, with 29.5 gm. of P2S5 at 100-120 DEG  C. with vigorous stirring.  The reaction product is dissolved in petroleum ether, the solution filtered and the solvent distilled off under reduced pressure.  The barium salt is prepared by stirring 124 grams of the dithiophosphate with 6 grams of caustic soda dissolved in 50 c.c. of water, diluting the solution of the sodium salt thus formed with water to 1300 c.c., heating to 90 DEG  C. and precipitating the barium thiophosphate by the addition of barium chloride solution.  The product is washed once with boiling water, dissolved in petroleum ether and dried by refluxing under a constant water separator.  The solution is then centrifuged and the solvent distilled off.  In another example, ethylene glycol mononaphthenate cresyl di-thiophosphate is prepared in a similar manner by reacting a mixture of the crude mononaphthenate and cresylic acid with P2S5.  The barium salt is also prepared in the same manner as before.  In a third example, di-(triethylene glycol mononaphthenate) thio-bis-(octyl cresyl) bis-dithiophosphate is similarly prepared by reacting a mixture of the crude naphthenate and octyl cresyl thioether with P2S5.  The nickel salt is prepared by neutralizing the thiophosphate with caustic soda solution, rendering just alkaline to phenolphthalein, and adding an aqueous solution of nickel sulphate.  U.S.A. Specifications 2,151,185 and 2,293,265 are referred to.