The chloropyridines

Abstract

The synthesis and some chemical properties are described of 2,4,5‐trichloropyridine, the only chloropyridine which has as yet not been mentioned in the literature. Six other chloropyridines, which have only been prepared once previously, have been examined more closely. It has been shown that a compound, which Königs, Mields and Gurlt obtained by heating 4‐nitraminopyridine with hydrochloric acid, is not 3,4‐dichloropyridine as stated by these investigators, but 4‐amino‐3,5‐dichloropyridine. 3,4‐Dichloropyridine has been prepared from 4‐hydroxypyridine via the well known 4‐chloro‐3‐nitropyridine. Further it appeared that a solid, m.p. 74°‐75°, which Sell and Dootson obtained by chlorination of pyridine and which they assumed to be 2,3,4,6‐tetrachloropyridine, must have been a mixture of chlorinated pyridines. We have synthesised 2,3,4,6‐tetrachloropyridine from 2,4‐dihydroxypyridine via 2,4‐dichloro‐3‐nitropyridine and from 4‐amino‐2,6‐dichloropyridine. The structure has been established of twenty five compounds discussed in connection with the chloropyridines mentioned above. Finally, the melting points and boiling points of the nineteen chloropyridines have been determined or verified. Copyright © 1950 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim