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 pKa 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 pKa units and the five-membered cyclic sulphamides are ca. 4 pKa 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.