The Alcohol Catalytic Mechanism for Schiff Base 1,3-Proton Transfer

In order to explore the catalytic effect of alcohols on the 1,3-proton transfer of 1,1-diphenyl-N-(1-phenylethylidene) methylamine, the reaction potential energy surface was systematically studied at the theoretical level of ωB97-MV / def2-QZVPP // PBE0(D3BJ) / 6-31G**. The results show that the catalytic mechanism of benzyl alcohol can be divided into the acid channel and basic channel, in which the acid channel is the dominant one. In the first step, benzyl alcohol protonated the nitrogen atom of imine to form imine cation and benzyl alcohol anion, and the newly formed benzyl alcohol anion preferentially combined with the proton on C1; in the second step, benzyl alcohol continued to protonize the C3 atom, and the newly formed benzyl alcohol anion combined with the hydrogen on nitrogen, thus completing the whole proton migration process. By means of wave function analysis, it is proved that the stronger the hydrogen bond (O–H···N) is, the lower the free energy barrier is. When alcohols with lower pKa values are used as catalysts, the reaction barrier will be lower.