Theoretical studies on the gas‐phase pyrolysis of acetic anhydride and diacetyl sulphide

Abstract

AbstractThe gas‐phase thermal decomposition of diacetyl compounds, (CH3CO)2X with X = O and S, was investigated theoretically using the semiempirical MO methods MNDO and AM1. The initial decomposition of the diacetyl compounds proceeded through a six‐membered ring transition state involving the keto form with a slightly lower activation enthalpy for diacetyl sulphide (X = S); the process via an enolic form of the transition state was kinetically unfavourable. In the initial decomposition of the diacetyl compounds and in the subsequent pyrolysis of acetic and thioacetic acid, ketene formation was found to be the most preferred path, where the ease of CαX bond cleavage is relatively more important than nucleophilic attack on the β‐hydrogen in determining the overall reactivity. In the methane formation process, the reactivity was entirely dependent on the XH bond strength in CH3COXH where X = S, NH and O.