Patent GB-786767-A (GB)
Title: Process for preparing complex ester synthetic lubricants
IPC: C07C69/34
Filed: 1955-04-26
Abstract: A synthetic lubricating composition is obtained by reacting together under ester-interchanging conditions a glycol, a dicarboxylic acid, and either a diester of a dicarboxylic acid and a monohydric alcohol, or a diester of a glycol and a saturated monocarboxylic acid to produce a composition containing a complex ester.  The complex ester products obtained may be glycol centred esters of the type: alcohol - dibasic acid - (glycol - dibasic acid)x alcohol or dibasic acid centred complex esters of the type: monobasic acid - glycol - (di - basic acid - glycol)x - monobasic acid, wherein x is a number greater than zero, preferably 1 to 6.  The product is generally a blend of a complex ester and a simple ester and the preferred products are blends containing from about 3 to 90 per cent of a complex ester of the formula ROOCR1COOR11OOCR1COOR with about 10 to 97 per cent of a simple diester of the type ROOCR1COOR, wherein R is a monovalent aliphatic radical containing 1 to 12 carbon atoms, R1 is a divalent aliphatic radical containing 0 to 20 carbon atoms, preferably 6 to 8 carbon atoms and R11 is a divalent radical consisting of a saturated straight or branched chain aliphatic hydrocarbon group containing 2 to 24 carbon atoms or is a divalent radical consisting of a series of saturated aliphatic hydrocarbon radicals interlinked by oxygen and/or sulphur atoms provided that there are at least 2 carbon atoms between each carboxyl group and the nearest oxygen or sulphur atom and at least two carbon atoms between each oxygen and/or sulphur atom and provided further that the total number of carbon, oxygen and sulphur atoms in the radical is from 5 to 80 and the number of sulphur atoms is not greater than 2.  Such products are obtained by reacting together a diester R1(COOR)2, a glycol R11(OH)2 and a dibasic acid R1(COOH)2 under ester interchanging conditions. Several alcohols which may be used to form the dicarboxylic acid diester used as starting material are specified representative examples being methanol, 2-ethyl butyl alcohol, 2-ethyl hexyl alcohol, oleyl alcohol, alkylene glycol mono-alkyl ethers and thioethers, e.g. ethylene glycol mono-n-butyl ether, b -tert.-octylmercaptoethanol, diethylene glycol mono-2-ethyl hexyl ether; propylene glycol mono-butyl thioether, alkylmercaptoalkoxy alcohols, e.g. tert.-octylmercaptopropoxy propanol and monoalkyl ethers of propylene-, di-propylene- and tripropylene-glycols, the preferred alcohols being branched chain alkyl alcohols having from 4 to 12 carbon atoms and particularly oxo alcohols derived from diisobutylene and C7 olefins. Several monocarboxylic acids which may be used to form the glycol diesters are also specified, representative examples being acetic acid, stearic acid, oxo acids, and alkoxycarboxylic acids, and alkyl mercapto carboxylic acids, e.g. b -tert.-octylmercaptopropionic acid, the preferred acids being those of the formula R111COOH, wherein R111 is a C1-C18 alkyl group. Specified dibasic acids are oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, brassylic, pentadecanedicarboxylic, tetracosane-dicarboxylic, C4-C24 alkenylsuccinic, diglycollic, and thiodiglycollic acids, 2-methyl adipic acid, 2-methyl azelaic acid and a ,a 1-diethyl adipic acid. Several glycols which may be used are also specified including alkylene glycols, polyethylene glycols, and polypropylene glycols and glycols containing sulphur and/or oxygen atoms in the chain, e.g. thiodiglycol, 1,2-bis-(2-hydroxyethylmercapto) ethane and bis-2-(2-hydroxyethoxy) ethyl sulphide.  The ester interchange reaction is preferably carried out in the presence of an acid or basic esterification catalyst such as sodium bisulphate, sulphuric acid, toluene sulphonic acid, calcium oxide, lithium oxide, an alkali metal alcoholate, e.g. sodium or potassium alcoholate, or a metal salt such as calcium sebacate or zinc stearate.  A small amount of an oxidation inhibitor, e.g. phenothiazine, may also be present and the reaction may be carried out in an inert reaction medium, e.g. a water-entrainer such as naphtha, benzene, hexane, or heptane.  The process may be carried out by heating under reduced pressure, e.g. at a temperature of about 220 DEG  to 270 DEG  C. Any diester formed may be removed from the product by extraction or distillation.  An example is given for the production of a blend of complex ester and diester (di-2-ethyl-hexyl sebacate) by heating a mixture of di-2-ethyl hexyl sebacate, tetraethylene glycol, and sebacic acid in the presence of heptane, sodium bisulphate and phenothiazine.  A comparative example is also given for the preparation of a complex ester-diester mixture by conventional esterification of a mixture of 2-ethylhexanol, sebacic acid and tetraethylene glycol in the presence of heptane, sodium bisulphate and phenothiazine.  The lubricant products of the invention may be blended with other lubricants or lubricant additives (see Group III).ALSO:A synthetic lubricating composition, comprising a complex ester with or without diester, and which has been obtained by reacting together under ester interchanging conditions a glycol, a dicarboxylic acid, and either a diester of a dicarboxylic acid and a monohydric alcohol or a diester of a glycol and a saturated monocarboxylic acid (see Group IV (b)), may be blended with either a mineral or synthetic lubricating composition or may be used as a base for the preparation of lubricating grease compositions.  They may also be blended with conventional lubricant additives, e.g. oxidation inhibitors such as phenothiazine, extreme pressure agents such as tricresyl phosphate, viscosity index improvers such as polybutenes, polymerized acrylate and methacrylate esters, and pour point depressants such as polymerized fumarate and maleate esters and copolymers of such esters with other polymerizable compounds, e.g. vinyl acetate.  The complex ester products may be glycol centred esters of the type alcohol-dibasic acid-(glycol-dibasic acid)x-alcohol or dibasic acid centred esters of the type: monobasic acid - glycol - (dibasic acid - glycol)x - monobasic acid wherein x is a number greater than zero, preferably 1 to 6.  Several alcohols, glycols, monocarboxylic acids, and dicarboxylic acids which may be used in the production of the complex ester product, are specified including ether- and thioether-alcohols, glycols and acids.  The preferred alcohols are branched chain C4-C12 alkyl alcohols, e.g. the oxo alcohols derived from diisobutylene and C7 olefins, preferred glycols are alkylene and polyalkylene glycol having from 2 to 18 carbon atoms, preferred dibasic acids are straight chain aliphatic dicarboxylic acids having a chain of from 2 to 10 CH2 groups and preferred monocarboxylic acids are saturated fatty acids containing from 2 to 19 carbon atoms.  In an example a blend of complex ester and diester (di-2-ethylhexyl sebacate) is obtained by heating a mixture of di-2-ethyl hexyl sebacate, tetraethylene glycol and sebacic acid and the properties of this blend as a lubricant are tabulated and compared with the lubricant properties of a complex ester-diester blend obtained by conventional esterification of a mixture of 2-ethyl hexanol, sebacic acid and tetraethylene glycol.