Journal of Organic Chemistry p. 653 - 655 (1984)
Update date:2022-08-11
Topics:
Venkatasubban, K. S.
Schowen, Richard L.
Substituted phenols serve as general-acid catalysts of leaving-group departure from the adduct of methoxide ion with m-NO2C6H4N(CH3)COCF3 in methanol at 25 deg C.Sufficiently high concentrations of general acid convert methoxide addition to the rate-limiting step, allowing determination of rate constants for methoxide addition to substrate carbonyl (ka = 300 M-1 s-1), for overall solvent-assisted leaving-group departure (ke = kake'/k-a = 5.9 M-1 s-1) and for overall general-acid-catalyzed leaving-group departure (kBH = kakBH'/k-a = 2400 +/- 1200 M-2 s-1 for five substituted phenols with pKa's from 12.7 to 14.6).Thus the Broensted α ca. 0.It is suggested that the general acid is a spectator at spontaneous expulsion of the leaving group, producing catalysis by fast subsequent trapping of CH3NAr-.The Jencks clock shows the tetrahedral intermediate to have a minimum characteristic lifetime of 1-10 ns.
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