Abstract:

Protonic acid catalyzed rearrangement and hydrolysis mechanisms of cyclohexanone oxime were studied based on density functional theory (DFT) at the B3LYP-D3/6-31G(d) level with the SMD implicit solvent model. The dominant factors for the rearrangement reaction were determined by frontier molecular orbitals and electrostatic potential surfaces, and Gibbs free energies of transition states and intermediates were obtained by frequency calculation to identify the rate-determining steps. The rearrangement reaction is irreversible, while the hydrolysis is reversible. Cyclohexanone oxime undergoes bimolecular rearrangement first and follows by reverse hydrolysis. At low temperature, a small amount of water has little effect on the reaction, and it is proposed that the bimolecular rearrangement-hydrolysis reaction pathway of cyclohexanone oxime is most likely to occur. The electrostatic effects govern the electrophilic reaction of cyclohexanone oxime with proton, and local ambiphilicity/nucleophilicity controls the reaction of protonated cyclohexanone oxime with water or cyclohexanone oxime in acetonitrile solvent. This study elucidates the liquid-phase Beckmann rearrangement mechanism of cyclohexanone oxime in depth and provides a theoretical basis for the design of solid catalysts to avoid side reactions.

Key words: cyclohexanone oxime, Beckmann rearrangement, catalysis, chemical reaction, reaction mechanism

摘要：

为了研究质子酸催化的环己酮肟液相贝克曼重排反应机理，使用密度泛函理论中的B3LYP-D3/6-31G（d）方法研究了反应中的过渡态内禀反应坐标，并使用SMD隐式溶剂模型模拟了液相环境。利用前线分子轨道和表面静电势确定了反应的主导因素，通过频率计算获得了过渡态和中间体的Gibbs自由能，确定了速率控制步骤。重排反应不可逆，而水解可逆，环己酮肟先进行双分子重排，然后进行反向水解。低温下，少量水对反应影响较小，提出了环己酮肟最有可能发生双分子重排-水解反应路径。在乙腈溶剂中，静电效应是环己酮肟与质子发生亲电反应的主导因素，局部亲电/亲核性是质子化环己酮肟与水或环己酮肟发生亲核反应的主导因素。本研究有助于深入理解环己酮肟液相贝克曼重排过程，并为避免发生副反应的固体催化剂设计提供理论基础。

关键词: 环己酮肟, 贝克曼重排, 催化, 化学反应, 反应机理