Reactions of hydroxypyridines with 1-chloro-2,4,6-trinitrobenzene - Product structure, kinetics, and tautomerism

Reactions between 1-chloro-2,4,6-trinitrobenzene and 2-hydroxypyridine, 3-hydroxypyridine, and 4-hydroxypyridine are reported. 4-Hydroxypyridine produces the product of attack at the nitrogen atom, while 3-hydroxypyridine reacts at the oxygen atom. 2-Hydroxypyridine reacts as an ambidentate nucleophile, providing a mixture of products arising from attack at both the oxygen and the nitrogen atom. Reactions between X-substituted-3-hydroxypyridines (X = H, 5-Cl, 6-CH3) and 1-chloro-2,4,6-trinitrobenzene provided 3-pyridinyl 2,4,6-trinitrophenyl ethers, analysed by H-1 and C-13 NMR spectra and by X-ray diffraction. Moderate heating of methanolic solutions of 3-pyridinyl 2,4,6-trinitrophenyl ether and of 6-methyl-3-pyridinyl 2,4,6-trinitrophenyl ether caused a methylation reaction of the pyridine nitrogen ring through trinitroanisole, providing 3-hydroxy-1-methylpyridinium picrate and 1,2-dimethyl-5-hydroxypyridinium picrate. Kinetic data are compared and discussed.