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The mechanisms of the acid-catalyzed decarboxylation of pyrrole-2-carboxylic acid and mesitoic acid have been investigated based on density functional theory calculations at the B3LYP/6-311G (d,p) level. A polarizable continuum model (PCM) has been established in order to evaluate the effects of solvents on these reactions. The results of the calculations indicate that the first step of the acid-catalyzed decarboxylation of the pyrrole-2-carboxylic acid has two possible pathways,that is,the proton of H3O+ attacks either the-carbon atom or the carboxyl oxygen atom. The subsequent process of forming a four-membered ring transition state is the rate-determining step. The activation energies of acid-catalyzed decarboxylation of pyrrole-2-carboxylic acid proceeding via attack at the-carbon atom and the carboxyl oxygen atom are determined to be 194.21 and 210.41 kJ/mol,respectively. The computational results show that both pathways are favored. However,for the reaction of mesitoic acid with H3O+,the reaction barrier for the former pathway is calculated to be 212.15 kJ/mol,whilst the latter pathway has a reaction barrier of 200.45 kJ/mol. Our computational results are consistent with the experimental observations of Mundle and Kluger.
The mechanisms of the acid-catalyzed decarboxylation of pyrrole-2-carboxylic acid and mesitoic acid have been investigated based on density functional theory calculations at the B3LYP / 6-311G (d, p) level. A polarizable continuum model (PCM) has been established in order to evaluate the effects of solvents on these reactions. The results of the analysis that the first step of the acid-catalyzed decarboxylation of the pyrrole-2-carboxylic acid has two possible pathways, that is, the proton of H3O + attacks either the-carbon atom or the carboxyl oxygen atom. The subsequent process of forming a four-membered ring transition state is the rate-determining step. The activation energies of acid-catalyzed decarboxylation of pyrrole-2-carboxylic acid proceeding via attack at the -carbon atom and the carboxyl oxygen atom are determined to be 194.21 and 210.41 kJ / mol, respectively. The computational results show that both pathways are favored. However, for the reaction of mesitoic acid with H3O +, the reaction barrier for the former pathway is calculated to be 212.15 kJ / mol, whilst the latter pathway has a reaction barrier of 200.45 kJ / mol. Our computational results are consistent with the experimental observations of Mundle and Kluger.