Experimental and Theoretical Studies of Oxalic Acid Dissociation in Water-Ethanol Solvents

The first and second dissociation constants of oxalic acid were determined using potentiometric and spectrophotometric methods. Measurements were made in water-ethanol solvents of chemical composition in percentage weight of 0, 16.3, and 80. The temperatures ranged from 298K to 318K. The dissociation free enthalpy changes, enthalpy changes and entropy changes were determined and discussed. Furthermore, DFT was used at B3PW91/LanL2DZ level to compute molecular descriptors as EHOMO, ELUMO, energy gap -E and the charge on the oxygen of the hydroxyl group. Those parameters were then used to establish a QSPR model that furnishes pKa1 and pKa2 values. Experimental and theoretical results were in good agreement.