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Ranjana Bhattacharyya, Sujit Chandra Lahiri

Basicities of Aquo + Alcoholic (Mono-ol) mixtures

Keywords: Aquo-Alcoholic Mixture, basicity, Dielectric Constant, Free Energy of Transfer of Hydrogen Ion, Gibbs Energy of Hydrogen Ion

Gibbs energies of transfer of H⁺ ion [ΔG⁰_t(w→s)(H⁺)] from water (w) to different aquo + alcoholic mixtures (s) were calculated using no extrathermodynamic assumptions. ΔG⁰_t(w→s)(H⁺) values with and without interactions are given.
ΔG⁰_t(w→s)(H⁺) values (without interaction terms) compare well with the selected values of ΔG⁰_t(w→s)(H⁺) in different aquo + alcoholic mixtures recommended by Marcus from compilations of data reported by various workers using different extrathermodynamic assumptions. Suitable conversion was made to bring the data into the range of the TATB scale.
ΔG⁰_t(w→s)(H⁺) values in binary mixtures (without interaction terms) are lower and qualitatively to some extent close to the values reported in the literature at least at low percentages.
The results show that ΔG⁰_solv(H⁺) and ΔG⁰_t(w→s)(H⁺) values are increasingly positive i.e. less basic as the mass% of organic solvents increases and the sequence of basicities are in the order

MeOH + H₂O > EtOH + H₂O > i-PrOH + H₂O > t-butanol + H₂O

i.e. the organic solvent and solvent mixtures are less basic than water contrary to the prevalent conceptions. The main factor appears to be the number of O-atoms with lone-pair of electrons responsible for H⁺ acceptance, H-bonding and other structural modifications of the solvent mixtures. Obviously, the lower the molar mass of the organic solvent, the greater will be the basicity of the solvent and solvent mixtures.

Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0942-9352
Volume: 221, 08/2007
Pages: 1001 - 1016

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