Interaction between Sulfur Dioxide and Polar Molecules. II. Systems Containing Ethanol, and Benzene or Hydroquinone

The near ultraviolet absorption for sulfur dioxide in benzene‐ethanol solvent is adequately explained as arising from the superimposed bands for the systems: $$\mathrm{EtOH}+{\mathrm{SO}}_2\mathrm{[open\; phi]}{\displaystyle {lim}^{K_1}}(\mathrm{complex}{)}_1\mathrm{;\hspace{0.17em}\hspace{0.17em}}\mathrm{Benzene}+{\mathrm{SO}}_2\mathrm{[open\; phi]}{\displaystyle {lim}^{K_2}}(\mathrm{complex}{)}_{\text{2,}}$$ if it is assumed that in passing from nonpolar to polar solvents there is no change in K₁, K₂, and in the molar extinction coefficients of the two complexes and of the uncombined sulfur dioxide. Extinction coefficients and equilibrium constants for the benzene complex must be obtained from analysis of solutions with high benzene concentration. It was found that the thermodynamic constants of both complexes, calculated from data for the mixed system, are identical with values obtained for the separate systems with carbon tetrachloride. A similar analysis of the absorption spectra of hydroquinone‐sulfur dioxide‐ethanol solutions gives a value of 14.0±1.0 kcal per mole for the heat of formation of the hydroquinone‐sulfur dioxide complex in ethanol. The heat of decomposition of the solid hydroquinone‐sulfur dioxide clathrate compound was found, by Wynne‐Jones and Anderson, to be 14.2±0.1 kcal. These results demonstrate the importance of lattices in polar solvents.