Theoretical Study on Acid catalyzed hydrolysis of Esters.

Abstract

Hydrolysis mechanism of methylacetate in the acidic conditions was investigated at the MP2/6-311+G(d,p)// MP2/6-31+G(d,p) level of theory. It is necessary to include two waters as reactants to obtain a tetrahedral (TD) intermediate for the AAC2 mechanism that Ingold classified for hydrolysis of methylacetate. The mechanism includes two TS structures, one for formation of the TD intermediate and the other for its decomposition. As activation energies were calculated to be 15.7 and 18.3 kcal mol-1, the second step determines the rate of hydrolysis. The calculated value is close to that observed, ~16 kcal mol-1. It was confirmed that the AAC2 mechanism has a barrier lower by 9.9 kcal mol-1 than that for the AAL2 mechanism. The AAC2 mechanism is also applicable to the acid catalyzed hydrolysis of acetamide