Protodemercuration of organomercuric chlorides. II. Heterocyclic mercuric chlorides

Abstract

The kinetics of protodemercuration, or displacement of the HgCl group by hydrogen, have been measured for 2- and 3-furyl, 2-thienyl, and 2-selenophenylmercuric chlorides. The reactions of these compounds with aqueous alcoholic hydrochloric acid were first order in hydrogen ion, first order in RHgC1, and zero order in chloride ion, when the latter was present at concentrations less than 0.1M. At 70°, the relative rates were: 3-furyl, 1; 2-furyl, 27; 2-thienyl, 11; 2-seleno- phenyl, 25. At higher chloride concentrations, the rate increases; this is discussed in terms of formation of complex anions of the type RHgCl₃^2- and in terms of H⁺Cl^- ion pair attack. The dominant influence of entropy effects in the case of furan compounds emphasizes the danger of trying to account for observed relative rates in terms of π-electron effects alone.