GB594814A - Improvements in the manufacture of mixed esters of poly-hydroxy compounds - Google Patents

Abstract

Mixed aliphatic-aromatic esters of polyhydric alcohols are prepared by heating the complete ester of the alcohol and the more volatile acid with the less volatile acid whereby part of the more volatile acid is replaced, and removing from the reaction zone the liberated acid. The polyhydric alcohols may contain 3-6 hydroxy groups, glycerol, erythritol, pentaerythritol, mannitol and sorbitol being specified. The aliphatic acid component may be a saturated fatty acid such as acetic, propionic or n-butyric, while the aromatic acid is preferably a mononuclear acid such as benzoic, alkyl benzoic, halogen-substituted benzoic or alkyl benzoic, e.g. a chlorbenzoic, or phenyl-acetic. The initial ester and the less volatile acid may be heated in proportions corresponding to the ester required but, preferably, the ester is used in excess, for example 1.5-2.5 times the theoretical. Thus, for glycerol diacetate benzoate, 1.5-2.5 mols. of triacetin and 1 mol. of benzoic acid are used. This reaction begins at about 220 DEG C. and is finally raised to about 280-300 DEG C. An acid catalyst may be present, and a high boiling liquid which may be a solvent for the reactants or form an azeotrope with the liberated acid. Preferably, a still without a column is used, lined with glass or enamel. The initial ester may be made by refluxing the alcohol or an epoxide thereof with the acid or anhydride and, optionally, sulphuric acid or copper sulphate. The mixed esters are plasticisers for cellulose esters and ethers such as the acetate, propionate, acetate-stearate, acetate-butyrate and soluble ethyl celluloses. In an example, triacetin is prepared by adding glycerol to an excess of acetic anhydride boiling under reflux, and distilling under reduced pressure. The residue of triacetin is heated with half the equivalent of benzoic acid to a final temperature of 280 DEG C. and glycerol diacetate benzoate recovered by fractionation. It may be washed and dried in air at about 60 DEG C. under reduced pressure.