Pyrolysis of N- p-toluenesulphonylsulphilimines

Abstract

Phenyl alkyl N- p-toluenesulphonylsulphilimines having β-hydrogens when heated to 130°. undergo elimination to give the corresponding olefins and phenyl-N- p-tolylsulphonyl sulphenamide in high yields. The rate of the thermal decomposition of several ethyl aryl N-arenesulphonylsulphilimines in benzene or DMSO solution between 60 and 100° were measured. The reaction obeys the first-order rate equation. The electron-withdrawing substituents on the phenyl group increased the rate, and the electron releasing substituents attached to the trivalent S atom decreased it ( p = +0·90 in benzene and +0·95 in DMSO) while the opposite trend was observed in the effects of the para substituents on the phenyl ring attached to the sulphonyl group ( p = −0·60 in benzene). Large kinetic isotope effects were also observed (k H/k D = 3·03 in benzene and 3·53 in DMSO). Activation enthalpies and entropies were found to be 26·9, 25·7 Kcal/mole and −5·4, −13·3 e.u. in benzene and DMSO respectively. The results indicate that the elimination proceeds through an intramolecular cyclic concerted process. The elimination of aryl alkyl N- p-toluenesulphonylsulphilimines usually proceed much more readily than those of the corresponding sulphoxides and sulphoximines. The relatively facile elimination is interpreted on the basis of the favoured conformation. The orientation in this Ei reaction is also discussed.