Polyhalogeno-aromatic compounds. Part XVI. The preparation and reactions of polyhalogenophenyl- and polyhalogenopyridyl-hydrazines

Abstract

A series of polyhalogenophenyl- and polyhalogenopyridyl-hydrazines have been prepared, usually from the appropriate perfluoro-, perchloro-, or perbromo-compound and hydrazine hydrate. Treatment with silver oxide or copper sulphate or with a base (sodium hydroxide or hydrazine hydrate) led to replacement of the hydrazinomoiety and, in most cases, also to that of the ortho- or para-halogen atom by hydrogen, yielding the corresponding polyhalogeno-compounds. The loss of the hydrazino-group is due to the established oxidative elimination of such moieties via a diazohydride. The accompanying elimination of the halogen ortho- or para- to the hydrazino-group is interpreted as an HX elimination (X = F, Cl, or Br) from a tautomeric form of the polyhalogenohydrazine. The use of these hydrazines in indole synthesis has been found to be very restrictive.