The decarboxylation of some heterocyclic acetic acids
Decarboxylation rates are reported for 36 heterocyclic acetic acids. Reaction is due to the formally neutral species, i.e., free acid or zwitterion. The question as to which of these is the actual reactant is critically discussed with respect to solvent and substituent effects, the nature of the heterocycle, trends in the activation parameters, and previous work on β-keto- and βγ-unsaturated acids. While no single piece of evidence is decisive, the zwitterionic mechanism is thought to be favoured by the facts taken together even for those compounds in which the proportion of zwitterion is probably very small. Some implications of this conclusion for the dearboxylation of the β-keto-acids are considered.