H. N. Po, Z. Shariff, Jeffrey A. Masse
Nov 1, 1991
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Journal
Phosphorus Sulfur and Silicon and The Related Elements
Abstract
Abstract The oxidation and reduction potentials for eight imidazole-2-thiols [imidazole-2-thiol (1a), 1-methyl-(1b), 4,5-dimethyl- (1c), 1,4,5-trimethyl- (1d), 4,5-diphenyl- (1e), benz- (1f), 5-methylbenz- (1g), and 5-nitrobenzimidazole-2-thiol (1h)] have been determined in ethanenitrile-hydrogen chloride solution. Substituent effects on E(ox) are observed and are discussed. The pKa's for thiols 1a, 1b, and 1c have been determined as a function of pH in buffer solutions at five temperatures and constant ionic strength of 0.10 M using ultraviolet spectroscopy. The ΔHo (kJ/mol) and ΔSo (J mol−1 K−1) for imidazole-2-thiol (1a), 1-methylimidazole-2-thiol (1b), and 4,5-dimethylimidazole-2-thiol (1c) are 38.2 and –92.9, 34.1 and –107.5, and 45.2 and –80.3, respectively.