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Anilinolysis of reactive aryl 2,4‐dinitrophenyl carbonates: Kinetics and mechanism
Author(s) -
Castro Enrique A.,
Domecq Claudia,
Santos José G.
Publication year - 2011
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/kin.20544
Subject(s) - chemistry , tetrahedral carbonyl addition compound , reactivity (psychology) , alicyclic compound , amine gas treating , moiety , aryl , dinitrophenyl , kinetics , reaction rate constant , ionic strength , medicinal chemistry , concerted reaction , stereochemistry , nucleophile , polymer chemistry , organic chemistry , aqueous solution , catalysis , medicine , alkyl , alternative medicine , physics , antibody , pathology , quantum mechanics , immunology , biology
The reactions of a series of anilines with phenyl 2,4‐dinitrophenyl ( 1 ), 4‐nitrophenyl 2,4‐dinitrophenyl ( 2 ), and bis(2,4‐dinitrophenyl) ( 3 ) carbonates are subjected to a kinetic investigation in 44 wt% ethanol–water, at 25.0 ± 0.1°C and an ionic strength of 0.2 M. Under amine excess pseudo‐first‐order rate coefficients ( k obs ) are obtained. Plots of k obs against free amine concentration at constant pH are linear, with slopes k N . The Brønsted plots (log k N vs. anilinium p K a ) for the anilinolysis of 1 – 3 are linear, with slope (β) values of 0.52, 0.61, and 0.63, respectively. The values of these slopes and other considerations suggest that these reactions are ruled by a concerted mechanism. For these reactions, the k N values follow the reactivity sequence: 3 > 2 > 1 . Namely, the reactivity increases as the number of nitro groups attached to the nonleaving group increases. Comparison of the reactions of this work with the stepwise pyridinolysis of carbonates 1 – 3 indicates that the zwitterionic tetrahedral intermediate (T ± ) formed in the pyridinolysis reactions is destabilized by the change of its pyridino moiety by an isobasic anilino group. This is attributed to the superior leaving ability from the T ± intermediate of anilines, relative to isobasic pyridines, which destabilize kinetically this intermediate. The k N values for the anilinolysis of carbonates 1 – 3 are similar to those found in the reactions of these carbonates with secondary alicyclic amines. With the kinetic data for the anilinolysis of the title substrates and 4‐methylphenyl and 4‐chlorophenyl 2,4‐dinitrophenyl carbonates, a multiparametric equation is derived for log k N as a function of the p K a of the conjugate acids of anilines and nonleaving groups. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 191–197, 2011