Quantum-chemical Study of the Mechanisms of Organic Reactions: VIII. On the Reaction of Ethane-1,2-dithiol with 1,3-Dichlorobut-2-ene in the Hydrazine Hydrate–KOH System

Abstract

A mechanism of the reaction of 1,3-dichlorobut-2-ene with 1,2-ethanedithiol in the hydrazine hydrate–KOH system is proposed on the basis of the results of DFT calculations at the В3LYP/6-311++G(d,p) level of theory. It is shown that this reaction involves several consecutive stages, including the nucleophilic substitution of the chlorine atom on the sp³-carbon atom by a sulfur atom (S_N2 mechanism) to form a monosubstitution product, which is dehydrochlorinated under the action of alkali by the bimolecular mechanism E2 to form an acetylene intermediate. The latter undergoes ring closure via the intramolecular nucleophilic attack of the free thiolate group on the β-carbon atom of the acetylene fragment, yielding the final dithiane derivative.