Aromatic substitution. Part 1. Kinetics of reaction of phenyltriethyltin with mercury(II) salts in methanol

Abstract

Reaction of PhSnEt₃ with mercury(II) salts in methanol follows second-order kinetics, first-order in each reactant, and yields only PhHgX and Et₃SnX. It is shown that the reactivity order in the mercury(II) species is HgI₃^– HgI₂ < HgCl₂ < Hg(OAc)₂. Under the investigated conditions, mercury(II) chloride reacts only via the covalent species HgCl₂ and not via species such as HgCl⁺. Comparison with related aliphatic substitutions shows that a phenyl group is cleaved from tin by mercury(II) halides some 4 × 10² times as fast as a methyl group and 1 × 10⁵ times as fast as an ethyl group. Added water mildly accelerates reaction of PhSnEt₃ with HgCl₂, whilst inert salts retard reaction; the activation energy is quite low, and it is suggested that reaction takes place via an intermediate π-complex through a transition state that is not particularly polar.