Hydrogen Gas Solubility in the Dimethyl Sulfoxide – Water System: A Further Clue to Solvent Structure in These Media

Abstract

The solubility of hydrogen gas in the dimethyl sulfoxide (DMSO) – water system has been measured as a function of temperature from 25 to 80 °C. A distinct minimum occurs in the solubility, as expressed on the molar scale, in the region 25–35 mol% DMSO at 25 °C. As the temperature is raised towards 80 °C the minimum becomes less pronounced. The maximum deviation from calculated "ideal" behavior is found at 32 ± 5, 35 ± 5, and 32 ± 5 mol% DMSO for 25, 50, and 80 °C, respectively.A maximum is observed for both the partial molal entropy and heat of solution of hydrogen in the same solvent composition region. These results are discussed in terms of a changing entropy and energy of hole formation in the solvent with composition, which in turn is related to DMSO–water interaction in solution.A temperature-dependent equilibrium between DMSO_•2H₂O and DMSO_•3H₂O complexes in solution is proposed in an attempt to correlate the considerable data which have been reported in the literature for the DMSO–water system. The second complex is thought to be present in significant quantity only at temperatures well below 25 °C.