NOPR Collection:

Transfer energetics of some ions based on TATB assumption in some quasi-isodielectric ethylene carbonate + water mixtures

1993-01-01T00:00:00Z

Title: Transfer energetics of some ions based on TATB assumption in some quasi-isodielectric ethylene carbonate + water mixtures Authors: Sinha, Subrata; Rudra, Sibaprasad; Kundu, Kiron K Abstract: Single-ion transfer free energies, △G (i), and entropies, △S (i), of some electrolytes from water to quasi-isodielectric aqueous mixtures of 10, 30. 50 and 70 weight per cent ethylene carbonate (EC) have been determined at 35°C, using the widely used tetraphenylarsonium tetraphenylborate [Pb₄AsPh₄B(TATB)] reference electrolyte (RE) assumption, from solubility and emf measurements at five equidistant temperatures ranging from 25° to 45° Analysis of △G (i) values of the ions as well as their chemical effects △G,_ch(i),as obtained after correcting for their cavity effect, estimated by the scaled particle theory (SPT) and the Born as well as ion-dipole type electrostatic effects, estimated by use of simple Born and Kim formulations respectively, reveals that cationophilicity, anionophobicity and/or predominant dispersion interactions of the solvent mixtures are guiding the solvation behaviour of the ions. But the analysis of the corresponding T△S,_ch(i),values in the light of Kundu et al’s four-step transfer process reveals that complex structural changes are guiding the entropic behaviour of these ions in these quasi-isodielectric EC-water mixtures. Page(s): 1-11

Deprotonation and transfer energetics of benzoic acid in some quasi-isodielectric ethylene carbonate + water mixtures.

1993-01-01T00:00:00Z

Title: Deprotonation and transfer energetics of benzoic acid in some quasi-isodielectric ethylene carbonate + water mixtures. Authors: Sinha, Subrata; Kundu, Kiron K Abstract: Transfer free energies (△G), entropies (△S) and enthalpies (△H) of benzoic acid (HBz) as well as deprotonation energetics of the acid have been determined in quasi-isodielectric aqueous mixtures of 10, 30, 50 and 70 weight (wt) % dipolar aprotic ethylene carbonate (EC) from solubility measurements of the acid and emf measurements of galvanic cells comprising H₂ and Ag - AgCl electrodes respectively at different temperatures. These values when coupled with the previously determined transfer energetics of H⁺ based on the widely used tetraphenylarsonium tetraphenylborate (TATB) reference electrolyte assumption, have yielded the transfer energetics of benzoate ion (Bz^-). The chemical parts of the transfer energetics, △X_,ch are obtained by subtracting the cavity effect as based on the scaled particle theory (SPT) for HBz, and the cavity as well as Born-type and ion-dipole electrostatic effects for Bz. Analysis of △G_,ch (HBz)- and △G,_ch (Bz^-)-composition profiles reveals that while the behaviour of neutral HBz is guided chiefly by the combined stabilizing effects of dispersion, dipole-induced dipole, dipole-dipole and the increased basicity of the mixed solvents, that of Bz^- is guided by the opposing effects of stabilizing dispersion and ion-induced dipole type interactions, and the increased destabilizing effects of dipolar aprotic nature of the cosolvent. T△S_,ch (i)-composition profiles for HBz and Bz^- when examined in the light of Kundu et aI's four step transfer process reveals that addition of cosolvent induces breakdown of three dimensional (3D) water structure due to the possible formation of H-bonded EC - (H₂O)_x complexes and the packing imbalance at higher compositions. The latter profiles at three different temperatures, viz., 25, 35 and 45°C also reflect the expected temperature induced decreased 3D structuredness of the solvents at water-rich compositions. Page(s): 12-19

Solvent effects on the ground and excited states proton transfer in 4-methyl- 2, 6-diformylphenol: Aprotic solvents

1993-01-01T00:00:00Z

Title: Solvent effects on the ground and excited states proton transfer in 4-methyl- 2, 6-diformylphenol: Aprotic solvents Authors: Roy, R; Mukherjee, S Abstract: The interaction of 4-methyl-2,6-diformylphenol (MFOH) with tributylamine and trioctylamine in different aprotic solvents has been studied quantitatively by means of electronic absorption and fluoresce spectroscopy with special attention to proton transfer at different temperatures. The acid-base interaction leads to different types of complexes, depending upon the dielectric constant of the solvents. In cyclohexane, dioxane or tetrahydrofuran hydrogen-bonded ion pair is formed, whereas a solvent-separated ion pair is formed in acetonitrile by the addition of amine in the ground state. The large, Stokes-shifted band in the fluorescence spectrum of this compound in the 530 nm region is attributed to the tautomer generated by intramolecular proton transfer in the excited state. In the presence of an amine the sharp band at 445 nm region in cyclohexane, dioxane and tetrahydrofuran has been assigned to the schiff base and the band at 520 nm in acetonitrile to the hydrogen-bonded ion pair. Some thermodynamic data have been evaluated and discussed. Page(s): 20-24

Investigations of transients produced on reactions of OH radicals with azobenzene in aqueous solutions

1993-01-01T00:00:00Z

Title: Investigations of transients produced on reactions of OH radicals with azobenzene in aqueous solutions Authors: Panajkar, M S; Mohan, Hari Abstract: The OH radicals are observed to react with azobenzene with a bimolecular rate constant of 2.0 x 10¹⁰dm³ mol^-1 s^-1. About 40% of (OH radicals add to benzene ring producing a transient band with λ_m_ax= 330nm and ~ 60% add to - N = N - double bond forming a transient band with λ_max = 420 (ε = 10,270 dm³ mol^-1 cm^-1). The OH radicals fail to undergo one electron transfer reaction with azobenzene. Steady state gamma-radiolysis shows the formation of a product absorbing in the 260-280 nm region. Page(s): 25-27