NUCLEOPHILIC-SUBSTITUTION AT THE PYRIDINE RING - KINETICS OF THE REACTION OF 2-CHLORO-3,5-DINITROPYRIDINE WITH ARYLTHIOLATES IN METHANOL

The reaction rates of 2-chloro-3,5-dinitropyridine 1 with a series of arylthiolates 2a-h in methanol have been measured at 25 degrees C. The products are the corresponding 2-thioaryl-3,5-dinitropyridine 3a-h. G ood Hammett correlation with rho Value -1.19 was obtained suggesting a n elimination-addition mechanism SNAr and the formation of Meisenheime r-like intermediates. Plot of log k(2) vs. pK(a) values of arylthiols gave straight line with beta = 0.38 indicating that the Ti-bond breaki ng in the pyridine ring is so much advanced over bond making between t he nucleophile and the carbon that bears the chlorine atom. Excellent correlation between log k(2) and log K (carbon basicity of arylthiolat es) was obtained. (C) 1997 John Wiley & Sons. Inc.