Structural–Thermodynamic Characteristics of Maleic Acid in Water–Organic Solvents

Results are presented from investigating the structure of maleic acid, processes of gas-phase protonation, and acid–base equilibria with the participation of maleic acid in water–ethanol and water–dimethylsulfoxide solutions. The рK values of maleic acid dissociation in water–ethanol and water–dimethylsulfoxide solvents are determined. It is established that the рK values grow along with the content of the nonaqueous component in a water–organic mixture. Analysis of the solvation contributions from all reagents participating in the acid dissociation of maleic acid in water–ethanol and water–dimethylsulfoxide solvents reveals that the main contribution to the increase in рK1 and рK2 comes from the desolvation of anions.