Studies in pyrolysis. Part XXV. Acrylic, methacrylic, and crotonic acid, and some derivatives: novel decarbonylation of αβ-unsaturated carboxylic acids

Abstract

Ethyl acrylate and methacrylate break down by competing primary A¹, C², and B² scissions (A¹ predominating); methyl acrylate, methacrylate, and crotonate show competing C² and B² scissions. In addition, ethyl and methyl acrylate yield ethanol and methanol respectively, presumably together with labile methyleneketen by a minor competing B¹ scission. Acrylic, methacrylic, and crotonic acid undergo competing C² and C¹ scissions, together with a minor dehydration to acid anhydride: the novel C¹ scissions produce acetaldehyde, acetone, and propionaldehyde respectively, via the corresponding enol. Acraldehyde, methacraldehyde, and crotonaldehyde undergo C¹ scission, the resulting olefin undergoing some secondary breakdown. All pyrolyses were at ca. 540–500° in the vapour-phase.