GB654511A - Improvements in or relating to esters of beta-hydroxy carboxylic acids and method ofpreparing same - Google Patents

Abstract

Esters of beta-hydroxy carboxylic acids are made by reacting, in the presence of an acid esterification catalyst, an alcohol with a linear polyester derived from a saturated aliphatic beta-lactone and containing a plurality of connected units <FORM:0654511/IV (b)/1> wherein each R is hydrogen or an alkyl radical, and n is a whole number greater than 1. Alcohols may be saturated or unsaturated, aliphatic or aromatic, primary, secondary or tertiary or mono- or poly-hydroxy, with many of each of these types being specified. Preferred alcohols are monohydric alcohols containing 1-4 carbon atoms per molecule and polyhydric alcohols containing 2-4 hydroxy groups. Sulphuric, phosphoric, hydrochloric and para-toluene sulphonic acid are specified catalysts in amounts of, e.g. 0.1-5 per cent, particularly 0.5 per cent, by weight of reactants. The reaction is effected preferably at refluxing temperatures, generally 50-150 DEG C., for 16-50 hours. Methods for preparing the polyester starting materials from beta-lactones are given. Thus the lactones may be polymerized with acid or alkaline catalysts, many of which are specified, including sulphuric acid, aluminium chloride and potassium hydroxide or carbonate either with or without an inert diluent. If polymerization is effected in the presence of water products of structure, e.g. when beta propiolactone is used, <FORM:0654511/IV (b)/2> are obtained although under anhydrous conditions a molecule of water is eliminated to give products of structure <FORM:0654511/IV (b)/3> Polyesters are also obtained by reacting, e.g., propiolactone, preferably in excess, with an alkali metal salt of a carboxylic acid, with alkali metal halides, or with alkanols in the presence of an acid or alkaline catalyst to give products respectively of formul <FORM:0654511/IV (b)/4> and <FORM:0654511/IV (b)/5> where R1COO is acyloxy, X is halogen, R2 is alkyl and n is a whole number greater than 1 which depends on reaction conditions such as relative proportions of reactants and time of reaction. The first two of the above reactions are effected in a polar solvent. In illustrations, beta-propiolactone is treated with (a) a small quantity of concentrated sulphuric acid at 60-80 DEG C. to give a mixture of compounds corresponding to both formul indicated under polymerization above, where n is 10; (b) an equimolar and 1/10 th molar quantity of sodium acetate in water to give products of formula indicated above, where R1 is methyl and n is 2 or higher; (c) with a small quantity of ferric chloride in refluxing benzene solution; and in (d) and (e) beta-propiolactone and beta-isovalerolactone are polymerized by heating at 130-150 DEG C. and about 50 DEG C. for about 2 and 3 hours respectively to give viscous products of formul corresponding to those obtained in (a) above. In the reaction of the invention a small quantity of by-product corresponding to the radical occurring at the left-hand side of the above formul will be obtained, e.g. acrylic acid ester from the <FORM:0654511/IV (b)/6> group, an acetic ester from the <FORM:0654511/IV (b)/7> group, and beta-chloropropionic acid ester from an end group X, when X is Cl. The starting polyesters may be obtained as by-products in many reactions of beta-lactones and in the preparation of the latter. Hydracrylate esters may be reduced to 1,3-propylene glycols. In examples: (1) an ester obtained as in (b) above is refluxed for 16 hours in methanol containing concentrated sulphuric acid, neutralized with calcium carbonate, filtered, and methyl hydracrylate obtained by vacuum fractionation of the filtrate; (2) ester obtained by process (d) above is refluxed for 36 hours in ethyl alcohol containing concentrated sulphuric acid and ethyl hydracrylate isolated by the process of (1), it being stated that the alcohols of (1) and (2) may be substituted by n-butyl, isoamyl, allyl, n-octyl, 2-ethylhexyl, cyclohexyl and benzyl alcohols; in (3) the ester made by process (e) above is treated by the process of (2) to give ethyl-beta, beta-dimethyl hydracrylate. Specification 649,028, as open to inspection under Sect. 91, is referred to.