DFT-based study of liquid-phase Beckmann rearrangement mechanism of cyclohexanone oxime
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.
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