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Concerted mechanism of the reactions of 2,4‐dinitrophenyl 4‐cyanobenzoate with secondary alicyclic amines in aqueous ethanol
Author(s) -
Castro Enrique A.,
Hormazabal Andrea,
Santos Jose G.
Publication year - 1998
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1998)30:4<267::aid-kin4>3.0.co;2-q
Subject(s) - alicyclic compound , chemistry , concerted reaction , tetrahedral carbonyl addition compound , amine gas treating , ionic strength , aqueous solution , nucleophile , reaction rate constant , solvent , computational chemistry , kinetics , substrate (aquarium) , medicinal chemistry , organic chemistry , catalysis , physics , quantum mechanics , oceanography , geology
The title reactions are subjected to a kinetic analysis in 44 wt% ethanol‐water, at 25.0°C, ionic strength 0.2 (KCl). With a large excess of amine over the substrate, pseudo‐first‐order rate coefficients ( k obs ) are obtained, which are linearly dependent on the amine concentration. The nucleophilic rate constants ( k N ) are determined from plots of k obs vs. amine concentration. The Brönsted‐type plot obtained with the k N values is linear, with slope β=0.63. The magnitude of this slope suggests that the mechanism is concerted, as opposed to a stepwise process with rate‐determining breakdown of a zwitterionic tetrahedral intermediate ( T ± ), in which the value of β is usually 0.8–1.0. The pyridinolysis of the same substrate in the same solvent is stepwise with the breakdown of T ± as the rate‐determining step. The change to a concerted mechanism for the title reactions is attributed to the superior nucleofugality of the alicyclic amines, compared to the isobasic pyridines, which destabilizes kinetically the “intermediate” T ± in such a way that it does not exist, and the mechanism becomes enforced concerted. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 267–272, 1998.