Substitution at saturated carbon. Part XVII. Substitution of tetraethyltin by mercury(II) carboxylates in methanol

Abstract

Observed second-order rate constants for the S_E2 substitution of tetraethyltin by mercury(II) carboxylates, Hg(OCOR)₂, in methanol increase along the series R = Bu^t < Et < Me < Ph < ClCH₂CH₂ < MeOCH₂ < ClCH₂. From the observed rate constants and the corresponding Hg²⁺–RCO₂^– stability constants, actual rate constants have been calculated for attack of various mercury(II) species on tetraethyltin; it is shown that under the kinetic conditions ca. 60% reaction takes place through the species Hg(OCOR)₂. Rate constants for attack of Hg(OCOR)₃^–, Hg(OCOR)₂, and HgOCOR⁺ are in order 0:1:10², and for substitution by both Hg(OCOR)₂ and HgOCOR⁺ the calculated rate constants yield the above reactivity sequence in R (R = Bu^t < Me < MeOCH₂). It is suggested that substitution of tetraethyltin by the species Hg(OCOR)₂ in methanol takes place by the S_E2(open) mechanism, and not through a cyclic transition state.