Basicity of nitrogen–sulphur(VI) compounds. Part 6. Ionization of NN′-di-and N-mono-substituted sulphamides and dihydro-2,1,3-benzothiadiazoline and benzothiadiazine 2,2-dioxides (cyclic sulphamides)

Abstract

36 Di- and mono- and two tri-substituted sulphamides have been synthesised and their ionization equilibria in base (Schemes 1–3) have been studied. Many of the sulphamides are new materials. The pK_a values obtained for each series have been correlated in Hammett and Taft plots. The Hammett ρ values obtained for the ionization of the proximate hydrogen are ca. 2.3. The Taft ρ* value obtained for ionization of the ‘remoter’ hydrogen is 1.68. The six-membered cyclic sulphamides are more acidic than their acyclic analogues by ca. 2.5 pK_a units and the five-membered cyclic sulphamides are ca. 4 pK_a units more acidic than model open-chain counterparts. Sulphur d-orbital involvement and ring-strain are suggested as possible sources of this ‘acid-strengthening’ effect.