Solvent-solute interactions in dimethylsulfoxide

Abstract

The osmotic and activity coefficients of six non-electrolytes and ten electrolytes in dimethylsulfoxide have been measured by the depression of the freezing temperature. A cryoscopic constant of (4.40 ± 0.01) K kg mol −1 has been determined for the solvent. The behavior of non-electrolytes both as to solubility and osmotic coefficients is intermediate between that in water and in ethylene carbonate. Ethylene carbonate and dimethylsulfoxide are both polar aprotic solvents but the smaller size of the latter apparently allows it to solvate both electrolytes and non-electrolytes more effectively. Solvent size is apparently more important than dielectric constant or dipole moment in determining the properties of solutions. The osmotic and activity coefficient of salts decrease in the sequence: Li + > NA + > K + > Cs + > NH + 4 > (C 2 H 5 ) 4 N + . The ammonium ion is apparently not solvated by DMSO through hydrogen bonding.