Patent GB-699440-A (GB)
Title: Synthetic esters suitable as lubricants
Filed: 1948-12-29
Abstract: Diesters suitable for use as lubricants are obtained by reacting together under esterification conditions a saturated thioether sulphur-containing dicarboxylic acid which has been prepared by the additive reaction of a monobasic mercapto aliphatic acid and a diolefin, or of an unsaturated dicarboxylic acid and a mercaptan, or of a mercapto monobasic aliphatic acid and an unsaturated monocarboxylic acid, with a saturated aliphatic monohydric alcohol or alcohols which may or may not contain ether oxygen and/or thioether sulphur linkages, the total number of carbon atoms in the alcohol residues of the resulting diester being between 16 and 40 in the case of a hydrocarbon alcohol, and the total number of carbon, oxygen, and/or sulphur atoms in the alcohol residues being together between 8 and 40 in the case of alcohols containing ether and/or thioether atoms, and wherein the starting materials are so chosen as to give a product of molecular weight of at least 300.  The invention is particularly directed to the production of ester products of the general formula R1OOC.R.COOR11 where R is an organic group which consists of one or more saturated hydrocarbon radicals containing at least two carbon atoms linked to at least one thioether sulphur atom, the total number of carbon and sulphur atoms in the group being from 5 to 85 and the number of sulphur atoms being not greater than 2.  In this group there is at least one carbon atom between the carbon atom in each carboxyl group and the nearest thioether sulphur atom and at least two carbon atoms between any two sulphur atoms.  The hydrocarbon radicals in group R may be aliphatic, cycloaliphatic, aromatic, or aliphaticaromatic and may be straight chain or branched. R1 and R11 are organic groups, like or unlike, and either consist of saturated aliphatic hydrocarbon radicals containing a total in the two groups together of 16 to 40 carbon atoms or they may be groups each consisting of a series of saturated C2 or higher hydrocarbon radicals interlinked by 1 to 5 ether oxygen and/or thioether sulphur atoms (not more than two sulphur atoms) the total number of carbon, oxygen and sulphur atoms in the two groups together being from 8 to 40.  When R1 and R11 contain oxygen or sulphur atoms there should be at least two carbon atoms between any two such non-carbon atoms and at least two carbon atoms between the carbon atom of the carboxyl group and the nearest atom of oxygen or sulphur in the alcohol residue whilst the hydrocarbon group at the end of a chain may contain one or more carbon atoms.  Several monohydric alcohols which may be used in esterifying the dibasic acids are specified and these include methyl-, 2-ethylhexyl-, and cetyl alcohols, mono ethers of ethylene and diethylene glycol and of propylene, dipropylene and tripropylene glycols, and substituted mercapto alcohols such as beta - n - butylmercaptoethanol, beta - tert. - octyl mercaptoethanol, beta-n-dodecylmercaptoethanol, n - butylmercapto - b  - ethoxy - ethanol, and tert.-octyl mercapto-g -propoxy propanol.  Primary alcohols, especially C8 to C14 alcohols, obtained from the Oxo synthesis, e.g. from di-isobutylene and C7 olefins, are also suitable.  The esterification is preferably carried out with the use of an esterification catalyst such as p-toluene sulphonic acid and a water entraining agent, e.g. naphtha, benzene, or toluene.  The properties as lubricants of the following esters are tabulated: (1) thiodipropionic acid (which is obtained by reacting mercaptopropionic acid and acrylic acid) esterified with 2-ethylhexyl alcohol, C8 Oxo alcohol, C9 Oxo alcohol, C10 Oxo alcohol, butyl carbitol, and beta-(tert.-octylmercapto-ethanol respectively; (2) the adduct of 2 mols. thioglycollic acid and 1 mol. isoprene, cyclopentadiene or vinyl cyclohexene respectively esterified with n-decyl alcohol; (3) the adduct of 1 mol. thioglycollic acid and undecylenic acid esterified with butyl carbitol, and ethylene glycol monobutyl ether respectively; (4) the adduct of 1 mol. thioglycollic and 1 mol. oleic acid esterified with C8 Oxo alcohol; (5) the adduct of 1 mol. maleic acid and 1 mol. n-dodecyl mercaptan esterified with n-decanol, C8 Oxo alcohol, and tripropyleneglycol monoisopropyl ether respectively; and (6) the adduct of 1 mol. itaconic acid and 1 mol. n-dodecyl mercaptan esterified with C8 Oxo alcohol and butyl carbitol respectively.  It is stated that the adducts may be formed by bubbling air through a mixture of the mercapto acid and diolefin or by refluxing the unsaturated dicarboxylic acid with the mercaptan in the presence of an acid catalyst such as SnCl4.  Specification 653,337 is referred to.ALSO:A lubricating composition comprises a mineral lubricating oil and a synthetic diester lubricant prepared by esterifying a saturated thioether sulphur-containing dicarboxylic acid which has been prepared by the additive reaction of a monobasic mercapto aliphatic acid and a diolefin, or of an unsaturated dicarboxylic acid and a mercaptan, or of a mercapto monobasic aliphatic acid and an unsaturated monocarboxylic acid, with a saturated aliphatic monohydric alcohol or alcohols which may or may not contain ether oxygen and/or thioether sulphur linkages, the total number of carbon atoms in the alcohol residues of the resulting diester being between 16 and 40 in the case of a hydrocarbon alcohol, and the total number of carbon, oxygen, and/or sulphur atoms in the alcohol residues being together between 8 and 40 in the case of alcohols containing ether and/or thioether atoms, and wherein the starting materials are so chosen as to give a product of molecular weight at least 300 (see Group IV(b)).  Specification 653,337, [Group IV(b)], is referred to.