Density functional theory study of the mechanism of the acid-catalyzed decarboxylation of pyrrole-2-carboxylic acid and mesitoic acid  

作　　者：ZHANG XingHui GENG ZhiYuan WANG YongCheng 

机构地区：[1]Gansu Key Laboratory of Polymer Materials,College of Chemistry and Chemical Engineering,Northwest Normal University,Lanzhou 730070,China [2]College of Chemical Engineering,Gansu Lianhe University,Lanzhou 730010,China

出　　处：《Science China Chemistry》2011年第5期762-768,共7页中国科学（化学英文版）

基　　金：supported by the Natural Science Foundation of Gansu Province (0710RJZA114);the Natural Science Foundation of Department of Education, Gansu Province (0801-10, 1013B-01)

摘　　要：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 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.

关 键 词：DECARBOXYLATION pyrrole-2-carboxylic acid ACID-CATALYZED density functional theory 

分 类 号：O643.36[理学—物理化学] O626.13[理学—化学]