Polyhalogeno-aromatic compounds. Part XXVII. Reactions of polyhalogenopyridines and their N-oxides with benzenethiols, with nitrite, and with trialkyl phosphites, and of pentachloropyridine N-oxide with magnesium

Abstract

Nucleophilic substitution of pentachloro- and of polychlorofluoro-pyridines with benzenethiols leads to 2- and 4-monosubstituted, 2,4-disubstituted, and 2,4,6-trisubstituted pyridines in various proportions according to the reaction conditions. In pentachloropyridine 1-oxide four chlorine atoms are replaced by sodium benzenethiolate at room temperature and all halogens are replaced at 60°. Treatment of these halogenopyridines with sodium nitrite in dimethylformamide provides a simple route to 4-hydroxypolyhalogenopyridines, and similar reactions with trialkyl phosphites furnish the expected dialkyl phosphonates (by a Michaelis–Arbusov reaction) together with dehalogenated pyridines. Attempts to prepare a Grignard reagent from pentachloropyridine 1-oxide failed. Mechanisms are discussed.