Vapour–liquid equilibrium data for dilute sulfur dioxide solutions in sixteen solvents were derived from total vapour pressure measurements at 25 °C. The SO2 enthalpies of solution at infinite dilution ΔH0 were determined at 25 °C by direct calorimetry. The solvents used belong to the aprotic class. The ΔH0 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 SO2 enthalpies of solution, ΔH0, in the polar solvents are discussed in terms of solvent basicity. There is a good correlation between the ΔH0 values, which relate to the basicity of the bulk solvent, and the solvent 'donor number' which is a molecular basicity parameter.

The activity coefficients of several solutes in dilute binary solutions of nonelectrolytes were determined at 20 °C from vapour–liquid equilibria in a novel static equilibration apparatus, by gas-chromatographic analysis of the equilibrium vapor phase. The solutes were nitromethane, nitroethane, 1-nitropropane, 2-nitropropane, acetonitrile, propionitrile, ethyl acetate, and n-butyl acetate in n-heptane and in benzene as solvents, and also carbon tetrachloride as solute in each of the above-listed polar compounds as the solvent.The modifications by Weimer and Prausnitz and by Blanks and Prausnitz to the Scatchard–Hildebrand equation in order to accommodate binary mixtures containing a polar component were tested by using the values found in the present work for the limiting activity coefficients of these solutes. In addition, it was found that the ratio of the dipole – induced dipole interaction parameter for polar solutes in the two nonpolar solvents was nearly constant.Three methods for evaluating the dispersion contribution to the solubility parameter of a polar compound were considered.

ETELA MILANOVA and ROBERT L. BENOIT. Can J. Chem. 55,2807Chem. 55, (1977.Complex formation between sulfur dioxide and iodide ions in acetonitrile (AN) has been studied by vapour pressure measurements. The enthalpy changes AH0 for 1:l association reactions between SOz and halide (X-) ions in AN and between SO2 and C1-in dimethylsulfoxide (DMSO) have been determined at 25°C by calorimetry. The AH0 values (kcal mol-') are respectively -4.1 (Cl-), -3.4 (Br-), -3.0 (I-) in AN and -0.7 (Cl-) in DMSO. In contrast to previous literature data there is a linear relationship between these AH0 and reported AGO values for the formation of the S0,X-complexes in AN. The difference between the AH0 values for SOZC1-in the solvents AN and DMSO is accounted for by the more exothermic enthalpy of solution of SO, in DMSO which is the more basic solvent, and by the expected minor difference in the enthalpies of transfer of C1-and S02C1 -from AN to DMSO, both dipolar aprotic solvents. Some of the problems connected with the stability order of the S0,Xcomplexes are discussed in relation to solvent effects and properties of X-.ETELA MILANOVA et ROBERT L. BENOIT. Can. J. Chem. 55,2807(1977.

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