GB778132A - Improvements in or relating to the production of complex esters - Google Patents

Abstract

In the production of saturated complex esters or ester blends containing such complex esters, the glycol is added slowly in the glycol esterification stage, the glycol addition being extended over at least 20 per cent of the total reaction time in the glycol esterification stage. The complex esters are defined as esters containing three or more ester groups in linear arrangement and in which there is at least one glycol residue and one dibasic carboxylic acid residue each of which has its functional groups esterified. They may be formed by the esterification in one or more stages of mixtures of dibasic carboxylic acids and glycols with monobasic acids and/or monohydric alcohols. The preferred complex esters are those having the general formula R1OOCR2COOR3OOCR4COOR5 wherein R1 and R5 are residues of aliphatic monohydric alcohols, R2 and R4 are the residues of aliphatic dicarboxylic acids and R3 is the residue of a glycol or polyglycol. The radicals R1 and R5 are preferably fatty alcohol or oxo alcohol residues containing 6 to 20 carbon atoms. The radicals R2 and R4 are preferably residues of acids of the formula HOOC(CH2)nCOOH, where n is less than 20, including oxalic acid, whilst R3 is preferably the residue of a glycol having between 2 and 16 carbon atoms or the residue of a polyalkylene glycol. The complex ester may also be of the type: R6COOR3OOCR2COOR13OOCR7 wherein R2 and R3 are as defined above, R13 has the same definition as R3 and is preferably the same as R3, whilst R6 and R7 are preferably the same and are the residues of aliphatic monocarboxylic acids having 4 to 22 carbon atoms. The preferred complex esters are made by esterifying mixtures of glycols, dicarboxylic acids and monohydric alcohols, the reaction being preferably carried out under reflux at 120-160 DEG C. in the presence of an esterification catalyst such as sulphuric acid, an alkali metal bisulphate, e.g. sodium bisulphate, or an aryl sulphonic acid, and a water entrainer such as a light hydrocarbon fraction forming an aqueous azeotrope. The esterification may be carried out in one stage using stoichiometric amounts of the compounds or in two stages by (a) reaction of equimolar amounts of the dibasic acid and monohydric alcohol to form the alcohol half ester followed by reaction of two moles. of the half ester with 1 mole. of the glycol, or (b) by reacting two moles. of the dicarboxylic acid with one mole. of the glycol to form the glycol half ester which is then esterified with the monohydric alcohol. Preferred dicarboxylic acids are adipic and sebacic acids and mixtures thereof, preferred alcohols are branched chain C8-C9 saturated alcohols, e.g. oxo alcohols, and preferred glycols are polyethylene glycols up to hexaethylene glycol. The slow addition of the glycol in the glycol esterification stage is preferably so prolonged as to take place over the entire reaction time in the glycol esterification stage. It is also preferred to stir the reaction mixture during the addition of the glycol. It is desirable to add an excess, e.g. 20 per cent excess, of monohydric alcohol in the second stage of the esterification. In an example, polyglycol 200 is added gradually to a heated mixture of sebacic acid, sodium bisulphate, and naphtha, and the reactants are heated for a further period after the addition of the polyglycol is complete. The product formed is then reacted with 2-ethylhexanol to form a complex ester. The total reaction time in the glycol esterification stage is 21 hours 20 minutes and the time of the glycol addition is 7 hours 20 minutes. The reaction of the glycol may be carried out in the presence of an excess of sebacic acid in the first stage and the unreacted excess of sebacic acid may then be esterified with the monohydric alcohol in the second stage or in a subsequent stage to give a mixture of complex ester and diester. If desired, the diester component can be stripped off partly or completely, using vacuum or steam distillation or both or the complex ester may be separated from the diester by absorption on silica gel. The diester can be eluted with an aromatic solvent such as benzene leaving the complex ester on the absorbent. The complex ester may then be eluted by a more polar solvent such as acetone. Specifications 659,103, 662,650, 666,697, 687,347 and 756,427, [Group III], are referred to.