Acid ionization constants of 4-substituted phenols in methanol + water mixtures
- 1 January 1975
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 71, 1058-1068
- https://doi.org/10.1039/f19757101058
Abstract
The pKa values of 4-t-butylphenol, 4-methylphenol, phenol, 4-bromophenol, 4-formylphenol and 4-nitrophenol in methanol + water mixtures in the 10–90 wt. % methanol composition range have been determined potentiometrically using a combined glass and silver/silver chloride electrode system. The pKa values are in accord with the Hammett ρσ relationship for all solvent compositions with a maximum value of ρ at ca. 60–70 wt. % methanol. The variation of ρ with solvent composition is indirectly attributed to the influence of bulk solvent structure on the free energies of solvation of phenoxide anions. The total medium effects on pKa are considered to be the sum of both electrostatic and nonelectrostatic contributions. Some factors influencing the latter are briefly discussed.Keywords
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