Polyether Catalysis of Ester Aminolysis – A Computational and Experimental Study

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Abstract
Model systems for the reaction of amines with esters were investigated with ab initio methods. Ammonia and methylamine were used as models for primary amines, and formic acid, methyl acetate, phenyl acetate, and p‐nitrophenyl acetate were chosen to represent typical esters. Geometry optimizations were performed for all systems with the HF/6–31G** method, and relative energies were evaluated by using MP2/6–31G** single‐point energies. The lowest barriers are found for the reaction of methylamine with p‐nitrophenyl acetate. Reaction occurs in this case according to a direct displacement pathway, in which all bond formation and breaking occurs in a single step. Complexation of the transition structures by dimethyl ether or dimethoxyethane leads to much the same changes as observed for variation of the leaving group. Based on the ab initio data a force field for the calculation of transition state‐catalyst complexation was developed. This force field as well as ground state complexation energies were employed to predict catalytic activities for a number of polyethers, polyalcohols, and pyrans, which in part, were also investigated experimentally.