Vapour pressure and calorimetric data for the solution of sulfur dioxide in aprotic solvents

Vapour–liquid equilibrium data for dilute sulfur dioxide solutions in sixteen solvents were derived from total vapour pressure measurements at 25 °C. The SO 2 enthalpies of solution at infinite dilution ΔH 0 were determined at 25 °C by direct calorimetry. The solvents used belong to the aprotic class. The ΔH 0 values (kcal mol −1 ) are for the non-polar solvents, isooctane (−3.5), cyclohexane (−3.5), n-heptane (−3.8), benzene (−5.8), and for the polar solvents, 1,2-dichloroethane (−5.5), nitromethane (−6.2), nitrobenzene (−6.3), acetonitrile (−6.7), ethyl acetate (−7.1), sulfolane (−7.3), propylene carbonate (−7.5), trimethyl phosphate (−8.9), tetrahydrofuran (−9.4), dimethylformamide (−10.9), pyridine (−11.6), dimethylsulfoxide (−13.0). Out of three correlation methods which we tested to account for our data in non-polar solvents, the Hildebrand solubility parameter treatment gives the best results. The SO 2 enthalpies of solution, ΔH 0 , in the polar solvents are discussed in terms of solvent basicity. There is a good correlation between the ΔH 0 values, which relate to the basicity of the bulk solvent, and the solvent 'donor number' which is a molecular basicity parameter.