Bulletin of the Chemical Society of Japan p. 922 - 927 (2014)
Update date:2022-08-11
Topics:
Kim, Ha-Ram
Yoon, Jung Hwan
Kim, Min-Young
Um, Ik-Hwan
Second-order rate constants for reactions of 2-chloro-4-nitrophenyl X-substituted-benzoates 1a-1j with a series of cyclic secondary amines in MeCN have been measured. Comparison of the kinetic results with those reported previously for the corresponding reactions carried out in H2O containing 20 mol % DMSO has revealed that amines are less reactive in MeCN. The Bronsted-type plot for the aminolysis of 2-chloro-4-nitrophenyl benzoate (1f) in MeCN is linear with βnuc= 0.64, which is in contrast to the curved Bronsted-type plot reported for the reaction performed in the H2O-DMSO misxture. The Hammett plot for the reactions of 1a-1j with piperidine consists of two intersecting straight lines while the Yukawa-Tsuno plot exhibits an excellent linear correlation with ρX= 1.22 and r = 0.60, indicating that the nonlinear Hammett plot is not due to a change in rate-determining step but is caused by stabilization of substrates possessing an electron-donating substituent through resonance interactions between the substituent and the carbonyl functionality. It has been concluded that medium change from the H2O-DMSO mixture to MeCN forces the aminolysis of 1a-1j to proceed through a concerted mechanism by destabilizing the zwitterionic tetrahedral intermediate (T±).
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