Kinetics and mechanisms of hydrolysis of cyclic sulphinamidates. Part 1. Ring opening of 3-phenylperhydro-1,2,3-oxathiazin-2-one

Abstract

The hydrolysis of 3-phenylperhydro-1,2,3-oxathiazin-2-one gives rise to two ionic intermediates depending on the pH: (i) in acidic and slightly alkaline solutions, 3-N-phenylaminopropyl hydrogensulphite ion is sufficiently stable to be characterised by u.v. spectrophotometry; (ii) in strongly alkaline solutions, 3-hydroxypropyl N-phenylsulphinamidate ion, which does not build up in the reaction medium, is formed. Only the first step of the hydrolysis reaction, i.e. the opening of the sulphinamidate ring, is reported here. The rate equation is k_obs=k_Ha_H+k_OH[OH^–]+k_BH[BH⁺]. Two reaction schemes are proposed: (i) in acidic and slightly alkaline media, base-assisted water attack on the N-protonated substrate explains the results obtained from general acid catalysis and isotopic effects; (ii) in strongly alkaline media, the values of the isotope effect and the entropy of activation suggest hydroxide ion attack on the neutral substrate. Both reaction schemes may involve either a concerted or a stepwise (via a tetraco-ordinate intermediate) mechanism. The experimental data do not allow them to be differentiated.