 Phenylhydrazine is prepared by oxidizing aniline with sodium nitrite in the presence of hydrogen chloride to form the diazonium salt, which is subsequently reduced using sodium sulfite in the presence of sodium hydroxide to form the final product.Phenylhydrazine was the first hydrazine derivative characterized, reported by Hermann Emil Fischer in 1875.He prepared it by reduction of a phenyl diazonium salt using sulfite salts.