Mechanisms of decarboxylation of ortho-substituted benzoic acids

The rotational transition state in the isomerization of the syn- to anti-conformer for the parent and substituted benzoic acids has been characterized and the decarboxylation mechanism for these acids has been determined. A previously unreported intermediate in the salicylic acid decarboxylation pathway has been observed, demonstrating that there is a change in the reaction mechanism when the orthogroup participates in the development of the transition state. The intermediate, in a shallow well, has a keto-like structure. While salicylic acid reacts through the keto-like intermediate, other substituted benzoic acids, including 2-aminobenzoic acid, follow the previously reported direct mechanism. (c) 2006 Elsevier B.V. All rights reserved.