Thermal Dimerization of Sodium Crotonate in a Solid State

Abstract

Themal reaction of sodium crotonate in solid state was found to afford exclusively 1hexene-3, 4-dicarboxylic acid[1] in high yield. Sodium crotonate was heated at 300°C in solid state under vacuum for 4 h. The salt was dissolved in water, and the solution was acidified with HCl to recover crude crystals. Recrystallization of the product from water gave [1] (mp 185-486°C) in 84% yield. Hydrogenation of [1] in methanol solution in the presence of Pt-black yielded a product, of which, the melting point agreed with that reported for the meso-hexane-3, 4-dicarboxylic acid [3] (mp 192°C). The structure of [ 1 ] was elucidated by ¹H-NMR and mass spectra of its methyl ester [2]. Refluxing of (2) at 240°C for 20 h, resulted in double bond migration to give dimethyl 2-hexene-3, 4-dicarboxylate consisting of (E)- [5 a] and (Z)- [5 b] forms in yields of 52% and 43%, respectively.