121001-02-3Relevant academic research and scientific papers
Rate and equilibrium studies of the deprotonation of benzylic ketones bearing pyridinium cations
Bunting, John W.,Stefanidis, Dimitrios
, p. 428 - 432 (2007/10/02)
Rates and equilibria for the deprotonation of four benzylic ketones containing pyridinium substituents (1,2,5, and 6) have been investigated in basic aqueous solution (ionic strength 0.1) over the range 15-45 deg C, and thermodynamic and activation parameters have been evaluated.Similar data are also reported for the deprotonation of nitroethane.The kinetic preference for hydroxide ion addition to the carbonyl group in competition with the thermodynamically preferred enolate ion formation, which was previously reported for the 1-methyl-4-phenylacetylpyridinium cation (1) and its 3-phenylacetyl isomer (2), is also found for the 1-(1-methyl-2-oxo-2-phenylethyl)pyridinium cation (6).Rates of equilibration of the 1-(2-oxo-2-phenylethyl)pyridinium cation (5) with its enolate ion conjugate base are too rapid to allow investigation by stopped-flow spectrophotometry.For the hydroxide ion catalyzed deprotonation of each of 1,2,6, and nitroethane, ΔSd is more negative than Δ0.This difference, which represents the entropy of activation for protonation of the conjugate base of each of these carbon acids by water, is approximately constant at Δp = -4.9 +/- 0.5 cal/deg*mol.Key words: carbon acids, kinetic studies, deprotonation, activation parameters, pKa values.
