Kinetics of the reaction of 2-chloro-3,5-dinitropyridine with meta- and para-substituted anilines in methanol

The kinetics of the reaction of 2-chloro-3,5-dinitropyridine (1) with meta- and para-substituted anilines (2a-j) to give 2-anilino-3,5-dinitropyridine derivatives (3a-j) were studied in methanol at different temperatures. IR studies of the products (3a-j) indicated the presence of hydrogen bonding between N-H and an o-nitro group, and UV spectra showed a red shift resulting from the interaction between an amino group and aza and nitro groups. A plot of Delta H double dagger: versus Delta S double dagger gave a good straight line with a 324 degrees C isokinetic temperature. Good linear relationships were obtained from plots of log k(2) against sigma values at all temperatures with relatively large negative rho values (-3.75 to -3.16) indicating the formation of a Meisenheimer sigma-complex intermediate, Plots of log k(2) against pK(a) values (beta = 0.85) gave good straight lines at 25 degrees C, except for 2f (4-COCH3), indicating that the reactions involve a significant bond formation in the transition state. An SNAr mechanism is suggested to proceed via two stages, with the first being rate determining. Copyright (C) 2000 John Wiley & Sons, Ltd.