Despite the central importance of monoketones as carbon acids, no intrinsic barriers or intrinsicrate constants for proton transfer to a standard family of bases such as amines have been reported. This paperpresents the results of such determinations for the reaction of 2-acetyl-1-methylpyridinium ion (
1) with secondaryalicyclic amines. They yield log
ko = 0.92 in water and log
ko = 1.70 in 50% DMSO-50% water (v/v) at 20
![](/images/entities/deg.gif)
C. These intrinsic rate constants are lower than for any sterically unhindered carbon acids except fornitroalkanes, reflecting the strong
![](/images/gifchars/pi.gif)
-acceptor character of the CO group as well as the strong solvation of theoxygen in the enolate ion. Rate constants,
![](/isubscribe/journals/jacsat/121/i08/eqn/ja983304ie10001.gif)
, for deprotonation of
1 by OH
- have also been determined inwater and 50% DMSO-50% water, with somewhat different results than those reported by Tobin and
Frey (
J.Am. Chem. Soc. 1996,
118, 12253). The
![](/isubscribe/journals/jacsat/121/i08/eqn/ja983304ie10002.gif)
value in water shows a small positive deviation from acorrelation of such rate constants with the corresponding p
Ka of 17 simple monoketones and aldehydes reportedby Keeffe and Kresge; this deviation as well as the much larger positive deviation for the deprotonation of1-methyl-3-pyridinioacetophenone (
7) and 1-pyridinioacetophenone (
8) can be attributed to electrostatic effectsresulting from transition-state imbalance.