DEPROTONATION AND TRANSFER ENERGETICS OF BENZOIC-ACID IN SOME QUASI-ISODIELECTRIC ETHYLENE CARBONATE PLUS WATER MIXTURES

Transfer free energies (DELTAG(t)-degrees), entropies (DELTAS(t)-degre es) and enthalpies (DELTAH(t)-degrees) of benzoic acid (HBz) as well a s deprotonation energetics of the acid have been determined in quasi-i sodielectric aqueous mixtures of 10, 30, 50 and 70 weight (wt) % dipol ar aprotic ethylene carbonate (EC) from solubility measurements of the acid and emf measurements of galvanic cells comprising H-2 and Ag-AgC l electrodes respectively at different temperatures. These values when coupled with the previously determined transfer energetics of H+ base d on the widely used tetraphenylarsonium tetraphenylborate (TATB) refe rence electrolyte assumption, have yielded the transfer energetics of benzoate ion (Bz-). The chemical parts of the transfer energetics, DEL TAX(t, ch)-degrees, are obtained by subtracting the cavity effect as b ased on the scaled particle theory (SPT) for HBz, and the cavity as we ll as Born-type and ion-dipole electrostatic effects for Bz-. Analysis of DELTAG(t, ch)-degrees(HBz)- and DELTAG(t, ch)-degrees(Bz-)-composi tion profiles reveals that while the behaviour of neutral HBz is guide d chiefly by the combined stabilizing effects of dispersion, dipole-in duced dipole, dipole-dipole and the increased basicity of the mixed so lvents, that of Bz- is guided by the opposing effects of stabilizing d ispersion and ion-induced dipole type interactions, and the increased destabilizing effects of dipolar aprotic nature of the cosolvent. TDEL TAS(t, ch)-degrees(i)-composition profiles for HBz and Bz- when examin ed in the light of Kundu et al.'s four-step transfer process reveals t hat addition of cosolvent induces breakdown of three dimensional (3D) water structure due to the possible formation of H-bonded EC-(H2O)x co mplexes and the packing imbalance at higher compositions. The latter p rofiles at three different temperatures, viz.,25, 35 and 45-degrees-C also reflect the expected temperature induced decreased 3D structuredn ess of the solvents at water-rich compositions.