| Autor: |
Bunting, John W., Kanter, James P., Nelander, Raymond, Wu, Zhennan |
| Zdroj: |
Canadian Journal of Chemistry; August 1995, Vol. 73 Issue: 8 p1305-1311, 7p |
| Abstrakt: |
The acidity and keto–enol tautomerism of a series of symmetrical β-diketones (RCOCH2COR (1): R = methyl (a), phenyl (b), 3-pyridinyl (c), 4-pyridinyl (d), 3-(N-methyl)pyridinio (e), and 4-(N-methyl)pyridinio (f)) and two series of unsymmetrical β-diketones (RCOCH2COCH3(7a–7f) and RCOCH2COC6H5(8a–8f)) have been investigated in aqueous solution at 25 °C and ionic strength 0.1. Values of were measured spectrophotometrically, and the acidities of the enols were obtained from the analysis of the pH dependence of the buffer catalysis for the general acid-catalyzed protonation of the enolateconjugate bases. These data in turn allowed the calculation of the acidities of the keto tautomers and the equilibrium constants for enolization (KE = [Enol]/[Keto]). In general, KEis greater for the symmetrical ketones(1) than for the corresponding R-substituted unsymmetrical ketones (7and 8). KEis much more sensitive to the nature of the R substituent in these three series of β-diketones than in the corresponding series of β-keto esters and amides. Correlations between for 8and 7combined with the known acidities of the corresponding β-keto esters and amides provide the first accurate estimates of the acidities of dimethyl malonate (pKa = 13.0)and malonamide (pKa = 12.5) in aqueous solution. Keywords: acidity, tautomerism, β-diketones. |
| Databáze: |
Supplemental Index |
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