S. Sinha et Kk. Kundu, DEPROTONATION AND TRANSFER ENERGETICS OF BENZOIC-ACID IN SOME QUASI-ISODIELECTRIC ETHYLENE CARBONATE PLUS WATER MIXTURES, Indian journal of chemistry. Sect. A: Inorganic, physical, theoretical & analytical, 32(1), 1993, pp. 12-19
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.