Nucleophilic substitution at sulphonyl sulphur. Part 3(1,2). Hydrolysis of substituted Tiophene-2-sulphonyl chlorides catalysed by silver nitrate and silver nitrite salts

Hydrolysis reactions of substituted thiophene-2-sulphonyl chlorides (5-methyl, 5-H, 5-chloro, 5-nitro)catalysed by silver nitrate and silver nitrite salts have been studied in water at 25°C. Salt effects by potassium nitrate,sodium perchlotate and mercuric bromide have also been investigated.For the catalysis effected with silver nitrate, the pseudo-first order rate constants depend on the firstpower of silver ion concentration,while nitrate anion is not involved in the transition state.The corresponding curved Hammett plot suggests a transition state with a partially developed sulphonylium character.With silver nitrite, the rate dependence on both silver and nitrite ion concentrations would indicate tha silver is involved in the transition state as well as nitrite. Also, in this case the curved Hammett plot obtained suggests a partial positive charge on the sulphur atom in the transition state. A comparison with uncatalysed hydrolysis reactions would support a previous interpretation that thiophene-2-sulphonyl chlorides hydrolize by an Sn" mechanism which can shift toward an Sn1 or an SAN process depending on the ring substituent.