pKa values of 3-thioxo-1,2-dithiole-4- and -5-carboxylic acids and of 3-oxo-1,2-dithiole-4- and -5-carboxylic acids in aqueous solution at 298 K
| Autor: | M. Chollet, J. L. Burgot |
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| Rok vydání: | 1998 |
| Předmět: | |
| Zdroj: | Journal of the Chemical Society, Perkin Transactions 2. :387-392 |
| ISSN: | 1364-5471 0300-9580 |
| DOI: | 10.1039/a704826b |
| Popis: | The pKa values in aqueous solution of some 3-thioxo-1,2-dithiole-5-, 3-oxo-1,2-dithiole-5-, 3-thioxo-1,2-dithiole-4- and 3-oxo-1,2-dithiole-4-carboxylic acids have been determined both by UV–VIS spectrophotometry and by potentiometry at 298 K. The 3-thioxo-1,2-dithiole- and 3-oxo-1,2-dithiole-5-carboxylic acids exhibit very low pKa values of the order of 1.20. The 1,2-dithiole-3-thione- and 1,2-dithiole-3-one-4-carboxylic acids exhibit pKa values in the range 1.8–3.2. The pKa values of 5-alkyl-4-carboxylic acids are 0.6 pH units lower than those of the corresponding unsubstituted dithiolone and dithiolethione acids. Thermodynamic ionization parameters determined by thermometric titrimetry show that: (i) for the 5-carboxylic acids, the strength is the result of an entropic effect; (ii) for the 4-carboxylic acids, the unexpected pKa values are essentially of enthalpic origin. |
| Databáze: | OpenAIRE |
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