A DFT study on the reaction pathway for the oxidation of C₆H₂(OH)₃CH₃ to hydroxyl benzoic acid

The reaction pathways for the oxidation of C₆H₂(OH)₃CH₃ oxidizing into hydroxyl benzoic acid were investigated by using density functional theory (DFT) method at the GGA/BP levels with Materials Studio 8.0 program. The results illustrated that the reactions for the oxidation of hydrogen on the methyl into hydroxyl, the hydroxyl to aldehyde, and then the aldehyde to carboxylic are all exothermic. As the main path, the oxidation of C₆H₂(OH)₃CH₃ to hydroxyl benzoic acid follows:C₆H₂(OH)₃CH₃+3O → C₆H₂(OH)₃C(OH)₃ → C₆H₂(OH)₃COOH+H₂O; as the controlling step, the conversion of hydroxyl to carboxyl exhibits a high energy barrier (130 kJ/mol) and a low reaction rate (ln(k)=-22.96 s^-1). The oxidation of hydroxyl and aldehyde to carboxylic acid follows the sequence of -CHO > -C(OH)₃ > -HC(OH)₂ > -H₂C(OH). An increase in the temperature and oxygen concentration is beneficial to the formation of hydroxyl benzoic acid, whereas appropriate catalyst can promote the whole reaction process.