The conversion of tetrazolyl hydrazones into triazolyl azides via tetrazolyl hydrazidic halides

Abstract

Two series of N-tetrazol-5-yl para-substituted benzhydrazidic halides, the bromides (II) and chlorides (III), have been prepared by halogenation of the corresponding arylidenetetrazol-5-ylhydrazines in acetic acid. The halides (II) and (III) readily form 3-azido-5-aryl-1,2,4-triazoles in aqueous organic media and as well small quantities of N-tetrazol-5-ylbenzhydrazides. The kinetics of these reactions have been studied in 95% aqueous ethanol and correspond to Hammett ρ values of –1·8 (for the bromides) and –0·85 (for the chlorides). These reactions thus proceed through azocarbonium ions (intermediates whose presence was further confirmed by salt effect studies). The sharp difference in the values of ρ for the bromides and chlorides reflect different degrees of cationic character in the respective transition states. Tetrazolyl ring involvement is product-determining, not rate-determining and can be effectively inhibited by allowing the bromides (II) and chlorides (III) to react in aniline, when halogen displacement products (anilides) and not substituted triazolyl azides are formed.