MECHANISTIC ASPECTS OF CYCLIC SULPHONIUM SALT FORMATION AND HYDROLYSIS OF 1,n-HALO(ALKYLTHIO) ALKANES

Abstract

Cyclization rate constants for various 1,n-halo(alkylthio)alkanes X[sbnd](CH₂) _n [sbnd]S[sbnd]R with n=4 and n=5 were determined in CH₃CN, CH₂CI₂, C₆H₁₄, CDCI₃ and H₂O/CH₃CN (9:1) at T=25°C. The rate of formation of the five- and six-membered cyclic sulphonium salts depends on the halogen atom (I>Br>Cl), the number of methylene groups between sulphur and halogen (n=4>n=5), on the alkyl group R and on the solvent. In aqueous CH₃CN hydrolysis becomes competetive. The hydrolysis rate constants of several 1,n-halo(alkylthio)alkanes with n>3 were determined in water at T=25 and 60°C and compared to those of some alkyl halides and the mustard derivative 1-chloro-2-methylthioethane. Hydrolysis of the chloro compounds is slower than of the bromo and iodo analogoues and depends on the number of methylene groups (n) between halogen and sulphur.