Solutions of HBr in sulpholane

Abstract

Solutions of HBr in C₄H₈SO₂(2,3,4,5-tetrahydrothiophen 1,1-dioxide; sulpholane) are brown in colour, due to the presence of Br₂. Infrared and u.v.investigations have established that equilibrium is set up in the system with C₄H₈SO₂+ 2HBr [graphic omitted] C₄H₈SO + Br₂+ H₂O K= 2.4 × 10^–5 at 20 °C (ΔH=–55 kJ mol^–1 and ΔS=–275 J K^–1 mol^–1). Proton n.m.r. observations of HBr–C₄H₈SO₂ solutions show that protonation of the solvent occurs. The addition of H₂O to such solutions leads to unusual n.m.r. spectra that indicate only slow exchange of H between C₄H₈SO₂H⁺ and H₂O.