Studies of the protonation in aqueous solution of 1-thia-4,7-diazacyclononane, 1-thia-4,8-diazacyclodecane and 5-thia-2,8-diazanonane

Abstract

The acid–base properties of 1-thia-4,7-diazacyclononane, 1-thia-4,8-diazacyclodecane and of 5-thia-2,8-diazanonane have been investigated in aqueous solution (25 °C, 0.1 mol dm^–3 KNO₃) by pH potentiometry, adiabatic calorimetry and ¹H NMR spectroscopy. The cyclic diamines show a less effective solvation by water in the first protonation step with respect to the open-chain diamine. The presence of an internal hydrogen bond in the first protonation step of 1-thia-4,8-diazacyclodecane is evidenced.