The invention discloses a preparation method of P-chlorophenylhydrazine
hydrochloride. The method comprises the following steps: diazotizing chloroaniline taken as a
raw material so as to prepare a corresponding diazonium salt; mixing
anhydrous sodium sulfite with
sodium hydrogen sulfite in a stirring manner, maintaining a pH (Power Of
Hydrogen) value within 6 to 7, controlling a temperature below 40 DEG C, slowly adding the diazonium salt below a liquid surface and reacting at the temperature of 60 DEG C to 90 DEG C according to the
molar ratio of the p-chloroaniline to the
sodium hydrogen sulfite being 1:(1-1):3; maintaining the unchanged pH value in the step 2, slowly adding
hydrochloric acid so as to maintain the pH value within 1 to 3, reacting for 1 to 3 hours at the
reaction temperature of 40 DEG C to 90 DEG C, cooling to a
room temperature, filtering and
drying so as to obtain a reddish P-chlorophenylhydrazine
hydrochloride solid. The pH value of the
reaction system is maintained within 6 to 7 by taking a mixture of the
sodium sulfite and the sodium
hydrogen sulfite as a
reducing agent, so that the phenomenon that the pH value is always regulated by NAOH (
sodium hydroxide) or HCL (
hydrogen chloride) in a reaction process is avoided; and the repeated heating during the reaction process is not required, so that the temperature is convenient to control; and the adding amount of water is reduced, so that the
discharge of
wastewater is greatly reduced, namely, the
wastewater treatment at a later period is avoided. As a result, the cost is lowered.