Carboxylic acids in dimethylsulfoxide. A calorimetric study

Abstract

Calorimetric data are presented for the solution and ionization of carboxylic acids in dimethylsulfoxide. The compounds studied include acetic acid and its trifluoro-, dichloro-and monochloro-derivatives, and benzoic acids and its 2-nitro- and 3,5-dinitro-derivatives. Ionization of the substituted acetic acids is increasingly endothermic from CF 3CO 2H (+1.8 kJ mol −1) to CHCl 2CO 2H (+17.6 kJ mol −1), CH 2ClCO 2H (+ 32.2 kJ mol −1), and CH 3CO 2H (+44.8 kJ mol −1). A useful linear correlation is found between the enthalpy and free energy of ionization of the acids. The hydrogen bond energy for the hydrogendiacetate ion is estimated as −115kJ mol −1.