Syntheses of Key Monomers for Advanced Polymer Materials Using Cyclodextrin as Catalyst

Terephthalic acid was synthesized by the carboxylation of benzoic acid with carbon tetrachloride in aqueous sodium hydroxide solution in the presence of cyclodextrin (CyD) and copper powder as catalyst. By the use of beta-CyD at the initial molar ratio to benzoic acid of 0.5, the carboxylation at 60 degrees C for 7 hours produced terephthalic acid in 75 mol% yield with 87% selectivity. The selective synthesis of 4,4'-biphenyldicarboxylic acid in 70 mol% yield was achieved by the carboxylation of 4-biphenylcarboxylic acid with carbon tetrachloride in the presence of beta-Cyd under similar conditions. The carboxylation of 2-naphthalene carboxylic acid with carbon tetrachloride using beta-Cyd under similar conditions produced 2,6-naphthalenedicarboxylic acid in 67 mol% yield with 84% selectivity. When alpha-CyD and gamma-CyD were used in place of beta-Cyd, both the yields and the selectivities of the dicarboxylic acids were markedly small. In the absence of CyD, carboxylation aid not proceed. Inclusion complex formations between beta-Cyd and aromatic monocarboxylic acids were indicated by the H-1 chemical shifts of the beta-Cyd. The reaction mechanism was discussed on the basis of inclusion complex formation.