Thermodynamics of ionization of 2,4-dinitrophenol in water-dimethylsulfoxide solvents

The ionization constants of 2,4-dinitrophenol were measured in water-dimethylsulphoxide solvent mixtures at five temperatures ranging from 20 to 40°C. The enthalpy and entropy contributions to the ionization process are discussed. The results indicate that in water-rich solvent mixtures the ionization process is controlled by the entropy factor while in the dimethylsulphoxide-rich solvent mixtures it is controlled by the enthalpy factor.