Polyhalogeno-aromatic compounds. Part XIV. Nucleophilic substitution and peroxy-acid oxidation of pentabromopyridine and some of its NN-dialkylamino- and bis-(NN-dialkylamino)-derivatives

Abstract

Pentabromopyridine was treated with various nucleophiles, such as alkoxides and primary and secondary amines. In the last case, with benzene as the solvent, 2(6)-substitution occurred exclusively, whereas use of ethanol as solvent produced the 4-isomer also. In all other cases a mixture of the 4- and 6-isomer was obtained. Oxidation of pentabromopyridine with peroxytrifluoroacetic acid yielded the corresponding 1-oxide as well as three isomeric tetrabromopyridine 1-oxides by protodebromination. Oxidation of 2-NN-dialkylaminotetrabromopyridines gave hydroxylamines by molecular rearrangement of the intermediate N-oxide, whereas the 4-isomer gave a mixture of 4-nitroso-, 4-nitro-, and 4-amino-tetrabromopyridines by an established mechanism. The nitro-group in tetrabromo-6-nitropyridine was readily replaced with piperidine but not that in the 4-nitro-isomer. Comparisons are drawn between the reactions of polybromo- and the corresponding polychloro-, and, in some cases, polyfluoropyridines, and reasons for differences are advanced. Concurrence of protodebromination and nucleophilic substitution is discussed.