The Curie point pyrolysis and electron impact induced decarboxylation of but-3-ynoic acid and buta-2,3-dienoic acid studied by tandem mass spectrometry

Abstract

It is shown by tandem mass spectrometry that Curie point pyrolysis of but-3-ynoic and buta-2,3-dienoic acid leads to the formation of propyne. This points to a thermodynamically controlled eliminatin of carbon dioxide which for both acids can be rationalized by a combined 1,4- and 1,2-hydrogen shift of the hydroxylic hydrogen atom. The C₃H₄⁺˙ ions, generated upon electron impact induced decarboxylation of the molecular ions of but-3-ynoic and buta-2,3-dienoic acid, have been shown by tandem mass spectrometry to have the allene and propyne structure, respectively. Their formation can be explained by a 1,5-hydrogen shift of the hydroxylic hydrogen atom prior to or during the loss of carbon dioxide from the molecular ions.