NUCLEOPHILIC SUBSTITUTIONS AT THE PYRIDINE RING - CONFORMATIONAL PREFERENCE OF THE PRODUCTS AND KINETICS OF THE REACTIONS OF 2-CHLORO-3-NITRO-PYRIDINE AND 2-CHLORO-5-NITRO-PYRIDINE WITH ARENETHIOLATES

The reactions of 2-chloro-3-nitropyridine 1 and 2-chloro-5-nitropyridi ne 2 with arenethiolates 3a-i result in arylthio-dechlorination to giv e 2-arylthio-3-nitropyridines 4a-i and 2-arylthio-5-nitropyridines 5a- i. A H-1 NMR study and AM1 calculations of 5a-i have shown that these compounds assume a skew conformation except the 2-(4-nitrophenylthio) derivative 5f which has a twist one. An addition-elimination mechanism is suggested based on second order kinetics and the dependence of rat es on the nature of the nucleophile. It is found that 2 (para-like) re acts faster than 1 (ortho-like). Good correlations are obtained from p lots of log k(2) against Hammett cr constants, pK(a) and log K (thermo dynamic affinity of arenethiolates towards carbon).