Thermal dimerization of alkali and alkaline earth acrylate–but-3-enoate and methacrylate–but-3-enoate binary systems in the solid state

Abstract

The solid state thermal reaction of binary salts obtained from a solution of an equimolar mixture of alkali or alkaline earth salts of but-3-enoic acid and methacrylic acid (3-BA–MA), after conversion to the methyl ester, gave mainly dimethyl (E)-hex-1-ene-1,5-dicarboxylate as a novel cross-coupled dimer. The highest conversion (62.2%) to the cross-coupled dimer was obtained using the potassium salts on heating at 230 °C for 2 h. Similarly, the methyl ester of the cross-coupled dimer, dimethyl (E)-pent-1-ene-1,5-dicarboxylate, was obtained from the salts of 3-BA and acrylic acid (AA), however a small amount on an isomeric ester dimethyl (E)-pent-2-ene-1, 5-dicarboxylate was also obtained. The X-ray diffraction patterns of potassium 3-BA–MA and potassium 3-BA–AA indicate the presence of a new phase, different from that of the individual salts. The selective cross-coupled dimerization, without rearrangement of 3-BA to crotonic acid, polymerization and crosslinking, was due to the new crystal phase of the binary salts as well as to the formation of solid solution crystals between the monomeric salts and the dimeric salt.