Partial molar volumes of sulfur dioxide in organic solvents: formation of charge-transfer complexes

New apparatus for measuring the apparent molar volumes of gases in liquids is described. The apparatus has been used to obtain the limiting partial molar volume of sulfur dioxide in 17 organic solvents. The limiting partial molar volume of sulfur dioxide is found to be significantly smaller in electron-donating solvents that in non-electron-donating solvents, with this difference being interpreted in terms of charge-transfer complex formation. We propose two methods for estimating the standard volume change of the complexation reaction and illustrate the use of these methods by application to the sulfur dioxide + benzene system.