Mechanism and rate constant of proline-catalysed asymmetric aldol reaction of acetone and p-nitrobenzaldehyde in solution medium: Density-functional theory computation

摘要

In search of new ways to improve catalyst design, the current research focused on using quantum mechanical descriptors to investigate the effect of proline as a catalyst for mechanism and rate of asymmetric aldol reaction. A plausible mechanism of reaction between acetone and 4-nitrobenzaldehyde in acetone medium was developed using highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies calculated via density functional theory (DFT) at the 6-31G?/B3LYP level of theory. New mechanistic steps were proposed and found to follow, with expansion, the previously reported iminium-enamine route of typical class 1 aldolase enzymes. From the elementary steps, the first step which involves a bimolecular collision of acetone and proline was considered as the rate-determining step, having the highest activation energy of 59.07?kJ?mol?1. The mechanism was used to develop the rate law from which the overall rate constant was calculated and found to be 4.04 × 10 - 8 d m 3 mol - 1 s - 1 . The new mechanistic insights and the explicit computation of the rate constant further improve the kinetic knowledge of the reaction.