Curie–point pyrolysis of saturated and unsaturated dicarboxylic acids studied by tandem mass spectrometry

Abstract

It is shown by tandem mass spectrometry that Curie-point pyrolysis of saturated α,ω-dicarboxylic acids HOOC(CH₂)_nCOOH (n= 1–6) leads mainly to the formation of intramolecular anhydrides and cyclic ketones. In some cases products are formed which must be due to intermolecular interactions such as acetone formation for n= 1 and hydroxybenzoic acid formation for n= 3. Mechanisms for the formation of these products are presented where 1,5-hydrogen shifts from activated positions to a carbonyl group play a crucial role. The unsaturated dicarboxylic acids HOOC(C₂H₂)COOH and HOOC(C₃H₄)COOH show, in addition to structure dependent dehydration reactions, elimination of carbon dioxide. The latter reaction proceeds in some cases via a 1,5-hydrogen shift from the carbonyl group to the double bond, but also by a 1,4-hydrogen shift from the carboxy-group to the double bond followed by a 1,2-hydrogen shift prior to or during decarboxylation seems to occur as suggested by the products generated.