Patent GB-661566-A (GB)
Title: Synthetic lubricants
Filed: 1948-11-30
Abstract: Glycol esters of omega - (alkylmercapto) alkanoic acids useful as lubricants are obtained by esterifying one hydroxyl group of a glycol with one such acid and esterifying the other hydroxyl group with the same acid or another omega-(alkylmercapto) alkanoic acid or an open-chain aliphatic carboxylic acid to give a product of the general formula <FORM:0661566/IV(a)/1> where R and R1, each of which contains 2 to 22 carbon atoms, are the residues of the esterifying acids and where R11 may be a series of saturated aliphatic hydrocarbon radicals linked by oxygen or sulphur or by both oxygen and sulphur provided there are at least two carbon atoms between each carboxyl group and the nearest oxygen or sulphur atom and at least two carbon atoms between each oxygen or sulphur atom in the chain, the whole radical R11 having not more than two sulphur atoms and having a total of from 5 to 80 carbon, oxygen and sulphur atoms, and the glycol and acid being such that the molecular weight of the entire product is at least 300.  The alkyl mercapto group in the acid is affixed to the carbon atom most distant from the carboxylic acid group and the specified sulphur containing acids are ethylmercapto acetic acid, beta-methyl (or ethyl) mercaptopropionic acid, beta-sec.-butyl (or tert.-butyl) mercaptopropionic acid, beta-tert.-octyl (or tert.-dodecyl) mercaptopropionic acid, beta-cetyl mercaptopropionic acid, gamma-octyl (or gamma-dodecyl-) mercaptobutyric acid, gamma-hexadecyl mercaptobutyric acid, w-octyl (or dodecyl-) mercaptoundecanoic acid.  The glycol may be a polyethylene glycol of the formula HO(CH2CH2O)nCH2CH2OH where n is 1 to 26 or a polypropylene glycol of the formula <FORM:0661566/IV(a)/2> where either R1 or R2 is a methyl group and the other is hydrogen and where n is 1 to 19.  The esterification may be effected in the presence of an esterification catalyst.  The properties as a lubricant of the ester obtained from ethylmercaptoacetic acid and polypropylene glycol (mol. weight 400) are given.  The esters may be blended with lubricating oils, especially a mineral lubricating oil, or synthetic oils such as those obtained by the polymerization of olefins or the hydrogenation of coal.  Other known addition agents such as thickeners, pour-depressants, antioxidants and dyes may also be added to the mineral oil composition.  Specifications 401,117 and 401,120 are referred to.  According to the Provisional Specification the radicals R and R1 in the ester product are open-chain aliphatic hydrocarbon radicals, one or both of which contains a sulphur atom.ALSO:Glycol esters of omega - (alkylmercapto) alkanoic acids useful as lubricants are obtained by esterifying one hydroxyl group of a glycol with one such acid and esterifying the other hydroxyl group with the same acid or another omega-(alkylmercapto) alkanoic acid or an open-chain aliphatic carboxylic acid to give a product of the general formula <FORM:0661566/IV (b)/1> where R and R1, each of which contains 2 to 22 carbon atoms, are the residues of the esterifying acids and where R11 is either a saturated aliphatic hydrocarbon radical of 2 to 18 carbon atoms or a series of saturated aliphatic hydrocarbon radicals linked by oxygen or sulphur or by both oxygen and sulphur, provided there are at least two carbon atoms between each carboxyl group and the nearest oxygen or sulphur atom and at least two carbon atoms between each oxygen or sulphur atom in the chain, the whole radical R11 having not more than two sulphur atoms and having a total of from 5 to 80 carbon, oxygen and sulphur atoms and the glycol and acid being such that the molecular weight of the entire product is at least 300.  The alkyl mercapto group in the acid is affixed to the carbon atom most distant from the carboxylic acid group and the specified sulphur-containing acids are ethylmercaptoacetic acid, beta-methyl (or ethyl) mercapto propionic acid, beta-sec.-butyl (or tert.-butyl) mercaptopropionic acid, beta-tert.-octyl (or tert.-dodecyl) mercaptopropionic acid, betacetyl mercaptopropionic acid, gamma-octyl (or gamma-dodecyl) mercaptobutyric acid, gamma-hexadecylmercaptobutyric acid, o -octyl (or dodecyl) mercaptoundecanoic acid.  The glycols include ethylene glycol and any of its paraffinic homologues containing up to 18 carbon atoms, e.g. propylene glycol, butylene glycols, pinacone, trimethylene glycol, tetramethylene glycol, penta- (or deca-) methylene glycol.  Polyethylene glycols of the formula HO(CH2CH2O)nCH2CH2OH, where n is 1 to 26, may be employed and polypropylene glycols of the formula <FORM:0661566/IV (b)/2> where either R1 or R2 is a methyl group and the other is hydrogen and where n is 1 to 19, may also be used.  Glycols containing thioether sulphur atoms, e.g. thioglycol and 1,2-bis-(2-hydroxyethylmercapto)-ethane and bis-[2-(2-hydroxy-ethoxy) ethyl] sulphide may also be used.  The esterification may be carried out in the presence of an esterification catalyst.  A table is given showing the properties of some of the esters when used as lubricants, the esters being obtained by reacting beta-tert.-octyl-mercaptopropionic acid with trimethylene glycol, hexamethylene glycol, triethylene glycol, tetraethylene glycol and thiodiglycol, respectively and by reacting beta-tert.-dodecylmercaptopropionic acid with trimethylene glycol. In each case two mols. of the acid is refluxed in an apparatus provided with a water trap with one mol. of the glycol in the presence of p-toluenesulphonic acid monohydrate and with benzene or naphtha as an entraining fluid. The properties as a lubricant of the ester obtained from ethylmercaptoacetic acid and polypropylene glycol (mol. weight 400) are also given.  The sulphur-containing acids may be prepared by reacting an olefine, e.g. diisobutylene, triisobutylene, propylene, isobutylene and propylene polymers with hydrogen sulphide to form an alkyl mercaptan which is then reacted with acrylonitrile to form the betaalkyl mercaptopropionitrile which is hydrolysed to the beta - alkylmercaptopropionic acid.  Instead of acrylonitrile acrylic acid esters may be used.  The acids may also be prepared by the reaction of halo acids with mercaptans, by the addition of mercaptans to unsaturated acids or by the addition of thioglycollic acid to olefins.  Beta - tert. - octyl- and beta - tert. - dodecyl - mercaptopropionic acids are prepared by adding acrylonitrile to a mixture of benzyltrimethyl ammonium hydroxide and the mercaptan prepared by reacting diisobutylene or triisobutylene with hydrogen sulphide, pouring the product into water, neutralizing with hydrochloric acid, extracting with ether and then heating the extract with alcoholic sodium hydroxide. Specifications 401,117 and 401,120 are referred to.  According to the Provisional Specification the radicals R and R1 in the ester product are open-chain aliphatic hydrocarbon radicals one or both of which contains a sulphur atom.ALSO:A lubricating composition comprises a lubricating oil, which may be a mineral lubricating oil or a synthetic oil such as is obtained by the polymerisation of olefines or the hydrogenation of coal, and a glycol ester of an omega- (alkylmercapto) alkanoic acid (See Group IV (b)) wherein one hydroxyl group of a glycol is esterified with one such acid and the other hydroxyl group is esterified with the same acid or another omega- (alkylmercapto) alkanoic acid or an open chain aliphatic carboxylic acid to give a product of the formula <FORM:0661566/III/1> where R and R\sv each of which contains 2 to 22 carbon atoms are the residues of the esterifying acids and R" is either a saturated aliphatic hydrocarbon radical of 2 to 18 carbon atoms or a series of saturated aliphatic hydrocarbon radicals linked by oxygen or sulphur or by both oxygen and sulphur provided there are at least two carbon atoms between each carboxyl group and the nearest oxygen or sulphur atom and at least two carbon atoms between each oxygen or sulphur atom in the chain, the whole radical R" having not more than 2 sulphur atoms and having a total of from 5 to 80 carbon, oxygen and sulphur atoms, and the glycol and acid being such that the molecular weight of the ester product is at least 300.  The glycol esters are themselves lubricants and may be blended with lubricating oils in proportions ranging from 1 per cent to 10 per cent by weight of the lubricating oil.  Other known addition agents such as thickeners, pour depressants, antioxidants and dyes may be added to the mineral oil composition.  A table is given showing the lubricating properties of a conventionally refined Coastal naphthenic oil containing 6 per cent of the following glycol esters: (1) ester of ethyl mercapto acetic acid with polypropylene glycol (mol. weight 400); (2) ester of beta tert octyl mercapto propionic acid with trimethylene glycol, hexamethylene glycol, triethylene glycol, tetraethylene glycol and thiodiglycol respectively, and (3) the ester of beta tert dodecyl mercapto propionic acid with trimethylene glycol. According to the Provisional Specification the radicals R and R1 in the ester product are open chain aliphatic hydrocarbon radicals one or both of which contains a sulphur atom.