C_6H_2(OH)_3CH_3氧化成羟基苯甲酸反应路径的DFT研究

运用密度泛函(DFT)理论,采用Materials Studio 8.0,用GGA/BP方法研究了C_6H_2(OH)_3CH_3氧化成羟基苯甲酸的反应路径。结果表明,甲基上的氢原子被氧化成羟基以及羟基被氧化为醛基及醛基被氧化成羧基均为放热过程。分子C_6H_2(OH)_3CH_3中甲基氧化成羧基的主路径为三个氢原子氧化反应路径,其路径为C_6H_2(OH)_3CH_3+3O→C6H2(OH)3C(OH)3→C6H2(OH)3COOH+H2O,该路径受限于羟基直接被氧化成羧基过程,需克服130 k J/mol的反应势垒,反应速率常数对数ln(k)为-22.96 s-1;醛基、羟基优先被氧化成羧基的顺序为:-CHO-C(OH)3-HC(OH)2-H2C(OH);提高反应温度、氧气浓度均有利于羟基苯甲酸的生成,适当的催化剂有利于促进整个反应的进行。

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.