碘催化苯乙醛与苄胺合成多取代咪唑的反应机理研究

Investigation the Reaction Mechanism from Phenylacetaldehyde and Benzylamine to Polysubstituted Imidazole Catalyzed by Ι_2

采用密度泛函理论(DFT)中的B3LYP方法,在6-31+G(d)基组水平下,研究了碘催化苯乙醛和苄胺发生氧化环化合成多取代咪唑的微观反应机理.对反应通道上反应物、中间体、过渡态和产物进行了结构优化,对优化后的各化合物在B3LYP/6-311++G(d,p)基组下进行单点能计算和零点能矫正,通过振动频率分析及内禀反应坐标(IRC)计算对过渡态进行了验证,并运用自然键轨道理论(NBO)和分子中的原子理论(AIM)分析了化合物的轨道间相互作用及成键特征.研究结果发现:无碘催化时,苯乙醛和苄胺发生氧化环化合成多取代咪唑,其反应速控步骤活化能为514.32 kJ·mol-1,在碘催化作用下,反应速控步骤活化能为145.94 kJ·mol-1.比较研究结果,说明碘能有效催化该反应的进行,碘的催化性能主要表现在活化苯乙醛乙基上的C—H键.我们还采用连续介质模型(PCM)比较研究了4种溶剂化作用对反应的影响,得到的研究结果与实验相吻合.理论预测了有机溶剂二甲亚砜(DMSO)能有效地提高反应产率.

The reaction mechanism from phenylacetaldehyde and benzylamine to polysubstituted imidazole catalyzed by Ι2was studied by the density functional theory. All of the reactants, intermediates, transition states and product were optimized at B3LYP/6-31+G(d) level. The single point energy and zero point energy correction were calculated for the optimized configuration of each compound at B3LYP/6-311++G(d,p) level. Transition states have been confirmed via vibration analysis and intrinsic reactions coordinate(IRC), and nature bond orbital(NBO) and atoms in molecules(AIM) theories have been used to analysis orbits interaction and bond natures. Our results showed that the activation energy of the rate-determining step was 514.32 kJ·mol-1 without I2-catalyzed, however, the activation energy of the rate-determining step was 145.94 kJ·mol-1with I2-catalyzed. It indicated that I2 catalyst promoted reaction effectively, and the C—H bond of ethyl of phenylacetaldehyde was activated by I2. In addition, polarized continuum model(PCM) method was adopted to discuss the effects of solvation. All calculations were consistent with experiments. It is predicted that the organic solvent dimethyl sulfoxide(DMSO) can effectively improve the reaction yield.