Thermal dimerization of alkali-metal salts of crotonic acid in the solid state

Abstract

The thermal reaction of sodium crotonate (Na-crotonate) in the solid state gave a nearly quantitative yield of hex-1-ene-3,4-dicarboxylate (1). Potassium crotonate (K-crotonate), on the other hand, afforded three isomeric dimers, i.e.(1), 4-methylpent-2-ene-3,5-dicarboxylate (2), and 2-methylene-3-methylbutane-1,4-dicarboxylate (3). In the case of Na-crotonate, X-ray analysis suggests the formation of a solid solution crystal during dimerization. K-Crotonate yielded predominantly (3) at the early stage of the reaction at 295 °C with formation of a solid solution crystal. At a higher temperature, i.e. 320 °C, (1) and (3) were gradually converted into (2), resulting in the decay of the crystal structure.