Phenyl and pentafluorophenyl substiuted 1, 3-dio-xolan 2, 4-diones

Abstract

A series of phenyl and pentafluorophenyl substituted 1, 3- dioxolan 2,4-diones (a-hydroxy carboxylic acid anhydrocarboxy— lates) has been prepared by the reaction of phosgene with the copper(II) salt of the appropriate a—-hydroxy carboxylic acid and the potential use of such cyclic compounds as precursors in the synthesis of poly-α-esters investigated. The kinetic behaviour during thermal decomposition of this anhydrocarboxylate series in non-hydroxylic solvents has been studied with particular reference to polymer formation. The reactivity of the anhydrocarboxylates to weak nucleophiles such as alcohols may be adequately explained in terms of the steric and electronic effects associated with both the anhydrocarboxylate and the attacking nucleophile. The solvent in this bimolecular reaction with alcohols exerts a considerable effect on the rate of reaction. The effect of a pentafluorophenyl substituent on the reactivity and polymerisability of the cyclic monomer has been investigated. The results indicate that the effect of a flueroaromatic substituent, unlike many other polymerisations, is to increase the polymerisability of the monomer. The use of tertiary (aprotic) base initiators such as pyridine offers a low temperature synthetic route to poly-a-esters. The ease of polymerisation by this hitherto unexplored method is determined primarily by the size of the substituents on the monomer and the extent to which those substituents may activate the ring to nucleophilic attack. The unusual kinetic behaviour exhibited by this type of reaction is explained in terms of the initial formation of a charge-transfer complex between monomer and initiator and subsequent decomposition to yield a polymerisable species. A number of substituted poly-a-esters have been prepared, including the two optically active forms of the polymer in one case, and some physical properties briefly examined. The primary object of the work, however, was the elucidation of polymerisation mechanisms rather than the preparation of high molecular weight polymer.