Effect of temperature on the protonation constants of some aromatic, heterocyclic nitrogen bases and the anion of 8-hydroxyquinoline
- 1 January 1982
- 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. 78 (6) , 1961-1970
- https://doi.org/10.1039/f19827801961
Abstract
Concentration-based association constants for the heterocyclic nitrogen atoms of 4,4′-bipyridyl (4,4′-bipy), 8-hydroxyquinoline (oxine), 8-aminoquinoline (amquin), pyridine (py) and the 2-(aminomethyl)pyridinium cation (2-ampy) with hydrogen ion have been determined in aqueous solution at various temperatures between 278 K and at least 373 K from spectrophotometric data. All the reactions are isoelectric and the constants decrease with increasing temperature. In two cases (oxine and 2-ampy) non-linear plots of pKa against T–1 were obtained. The reaction of base with oxine to yield the oxinate anion is also isoelectric but a non-linear plot of pKb against T–1 was obtained. The published, high-temperature pKa values and associated thermodynamic quantities for 1,10-phenanthroline, some of its derivatives and 2,2′-bipyridyl have been re-evaluated using more realistic experimental errors.Keywords
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