Kinetics of the reaction of 2-chloro-3,5-dinitropyridine withmeta- andpara-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 ΔH‡ versus ΔS‡ gave a good straight line with a 324 °C isokinetic temperature. Good linear relationships were obtained from plots of log k2 against σ values at all temperatures with relatively large negative ρ values (−3.75 to −3.16) indicating the formation of a Meisenheimer σ-complex intermediate. Plots of log k2 against pKa values (β = 0.85) gave good straight lines at 25 °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.