Patent GB-766770-A (GB)
Title: Process for the preparation of complex esters
IPC: C07C69/34
Filed: 1955-03-10
Abstract: Complex esters are prepared by adding to a reaction zone an esterification catalyst, a volatile hydrocarbon water entrainer, and an organic compound containing at least two esterifiable radicals and, if desired, a diester diluent, continuously circulating the liquid contents of the reaction zone through a heating zone and back to the reaction zone, and adding in controlled amounts a second organic compound containing at least two radicals capable of esterifying the first compound so as to give an esterification product containing two esterifiable radicals, adding to the continuously circulating ester so formed a third organic compound to esterify at least one esterifiable group of the first esterification product, and when the product of the second esterification contains unesterified radicals, adding a fourth organic compound to esterify said unesterified radicals, water being removed by azeotropic distillation to complete each esterification step before a further component is added and continuously circulating the liquid contents of the reaction zone through a heating zone and back to the reaction zone during each esterification step.  The esterifiable radicals are defined as carboxyl radicals and alcoholic hydroxyl radicals.  The first and second organic compounds are generally glycols and dibasic acids and the third and fourth compounds monobasic acid and monohydric alcohols.  By variation of the proportion of the reactants, three types of complex ester may be produced.  (I) Alcohol-Dibasic acid (Glycol-Dibasic acid)x Alcohol; (II) Monobasic acid-Glycol (Dibasic acid-Glycol)x Monobasic acid; and (III) Monobasic acid (Glycol-Dibasic acid)x Alcohol.  Many examples of reactants are given including C2 to C4 glycols, tri-, tetra, and pentamethyleneglycols, di-, tri- and polyethylene glycols, polypropylene glycols, thiodiglycol and 1,2-bis-(2-hydroxyethylmercapto) ethane; C2-C15 dibasic acids, C4-C24 alkenylsuccinic acids, diglycollic acid, thiodiglycollic acid; C2-C17 monobasic acids, alkoxypropionic acids, alkylmercaptopropionic acids, and "oxo" acids; C1-C17 alcohols, glycol ethers, alkylmercaptoalkanols, glycolthioethers and "oxo" alcohols.  Suitable water entrainers are heptane, hexane, toluene and xylene.  Catalysts such as sodium acid sulphate, toluene sulphonic acid and sulphuric acid are also added to the reaction mixture.  The heating zone, through which the reaction mixture is circulated by means of a pump, may be a jacketed reboiler type containing a plurality of tubes through which the reaction mixture passes surrounded by hot oil. During the esterification steps, a mixture of water vapour and entrainer is distilled overhead from the reaction zone, condensed, and the entrainer separated from the water and recirculated to the reaction zone.  When the final esterification step is complete, the system may be placed under reduced pressure and low-boiling constituents removed until the desired viscosity is obtained.  A diester of the dibasic acid and the alcohol may be used as a diluent in the preparation of complex esters and results in reduced formation of diester by-products during the process and gives a product exhibiting improved resistance to low temperature thickening.  The diester may be added to the reaction zone with the initial reactants or to the circulating mixture.  A detailed example describes the preparation of a complex ester from 1 mol. of polyethylene glycol 200, 2 mols. of sebacic acid, and 2 mols. of 2-ethyl hexanol, in the presence of toluene and sodium acid sulphate.  Other runs are described using di-2-ethyl hexyl sebacate as a diluent.  Further examples describe preparations modified by the presence of excess glycol, excess sebacic acid and excess 2-ethyl hexanol.  Preferred reactants for the formation of complex esters are polyethylene glycol 200, adipic, suberic, azelaic and sebacic acids, isooctyl alcohol, 2-ethyl hexanol and other branched chain C4-C10 alcohols.  The products are useful as synthetic lubricants and as constituents of lubricating compositions (see Group III).ALSO:Complex esters, prepared from glycols, dibasic acids, monobasic acids and/or alcohols by a process involving continuous circulation of the reactants from the reaction zone through a heating zone and back to the reaction (see Group IV(b)), are used as components of lubricating compositions.  The esters may be admixed with mineral oils, dibasic acid esters, other complex esters, polymerized hydrocarbons, glycol ethers, glycol ether esters, and formals.  Blends may comprise a major proportion of the complex ester, alone or with other lubricants, and a minor proportion of viscosity index improvers, pour point depressants, detergent inhibitors, antioxidants, rust inhibitors and extreme pressure agents.  Blends of the complex ester and a diester of the dibasic acid and the alcohol are obtained by using the diester as a diluent during the process.  The properties of the product may also be varied by using excess glycol, dibasic acid or alcohol. In examples, complex esters are prepared from polyethylene glycol 200, sebacic acid and 2-ethyl hexanol, with and without the use of di-2-ethyl hexyl sebacate as a diluent.  In other preparations excess of acid and glycol, with or without excess of alcohol, is used.  The properties of the products are indicated. Many other examples of suitable starting materials for the complex esters are specified.