Structure and mechanism of hydrolysis of diaryl(acylamino)(chloro)-lambda(4)-sulfanes and diaryl(acylamino)sulfonium salts

Aryl (methylaminocarbonylaryl) sulfides were converted by t-BuOCl to diaryl (acylamino)(chloro)-lambda (4)-sulfanes or the corresponding diaryl(acylami no)sulfonium chlorides depending on the substituent of the S-aryl group. H- 1 NMR data showed that chloro-lambda (4)-sulfanes exist only in CDCl3 and D MSO-d(6) solvents, whereas in CD3OD complete ionic dissociation takes place , leading to sulfonium chlorides. Both the chemical shifts of H-1 NMR signa ls and NOE data suggest that chloro-lambda (4)-sulfanes and sulfonium salts having an o-MeO, o-Cl or o-Me substituent on the phenyl ring assume a skew conformation, whereas the aryl ring in compounds without an ortho-substitu ent can rotate practically free about the S-C(1') axis. In o-MeO-substitute d derivatives there exists an equatorial 1,4 type S . . .O close contact. S ulfonium salts with axial 1,5 type S . . .O close contacts involving neighb ouring COOMe, CONHMe, COMe or NO2 groups occur in butterfly conformation, l ike spiro-lambda (4)-sulfanes. There is a correlation between the N-15 chem ical shift of the amide-nitrogen and the elongation of the S-N covalent bon d, by which the interdepending S-N, S-Cl and S . . .O bonds can be characte rized. Effective intermolecular S . . .O interaction was detected between t he sulfonium centre and solvent molecules having a negatively polarized oxy gen atom. The hydrolysis of sulfonium salts yielding sulfoxides was investi gated by a kinetic method in 98:2 (v/v) dioxane-water mixture and in water. On the basis of medium, substituent (rho + 1.03), steric, salt and kinetic isotope effects detailed mechanisms involving a hydroxy-lambda (4)-sulfane intermediate are proposed. The more reactive sulfonium salts with a five-m embered hetero ring are hydrolyzed by water, whereas the sulfonium centre o f the less reactive analogues with a six-membered ring is attacked only by OH- ions.