Anilinolysis of reactive aryl 2,4-dinitrophenyl carbonates: Kinetics and mechanism

✍ Scribed by Enrique A. Castro; Claudia Domecq; José G. Santos

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 108 KB
• Volume: 43
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20544

✦ Synopsis

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 pK 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 pK a of the conjugate acids of anilines and nonleaving groups.