Journal of the Chemical Society. Perkin transactions II p. 1129 - 1134 (1988)
Update date:2022-08-03
Topics:
Khan, Mohammad Niyaz
The nucleophilic second-order rate constants for the reactions of N-ethoxycarbonylphthalimide (ECPH) with morpholine, piperazine, 1,4-diazabicyclo<2.2.2>octane, and ethylenediamine exhibit a Bronsted plot of slope (βnuc) 1.2 +/-0.3.The significantly high value of βnuc reveals that the expulsion of the living group from a zwitterionic tetrahedral addition intermediate is the rate-determining step.The reactivity of hydroxylamine is nearly 105-fold larger than that expected from the Bronsted plot of slope (βnuc) 1.2.The hydroxyaminolysis of ECPH reveals general base catalysis.The results obtained on the hydroxyaminolysis of ECPH in the presence of external general base, acetate, reveal that the rate-determining step changes as the buffer concentration is increased and, consequently, it provides evidence for the existence of an intermediate on the reaction co-ordinate.The rate constants for the reactions of monoprotonated 1,4-diazabicyclo<2.2.2>octane and piperazine show positive deviations from the Bronsted plot.
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