Continuous-Flow Process for the Synthesis of 2‑Ethylphenylhydrazine Hydrochloride

An expeditious process for the synthesis of 2-ethylphenylhydrazine hydrochloride via a continuous-flow reactor from 2-ethylaniline in 94% yield was described. The main steps in this synthesis involved not only the generation of diazonium salt intermediate in situ but also the temperature-programmed reduction by sodium sulfite in the tandem loop reactor. Total residence time was reduced to less than 31 min by increasing the reaction temperature and thereby taking advantage of improved mass and heat transfer of a continuous-flow system. The purification process was simplified by extraction of impurities in situ.