Preparation method of parafuchsin

The invention belongs to the technical field of dye preparation, and particularly relates to a para-fuchsin preparation method which comprises the following steps: adding 4, 4 '-methylenediphenylamine into aniline, uniformly stirring, then adding nitrobenzene, and continuously stirring to form a mixed solution; adding ferric chloride into the hydrochloric acid solution, uniformly stirring to form a dissolved solution, then adding the dissolved solution into the mixed solution, and uniformly stirring to obtain a reaction solution; carrying out constant-temperature reaction on the reaction liquid for 5-10 hours, adjusting the pH value after the reaction is finished, and carrying out azeotropic treatment to obtain a crude product; washing the crude product in cold water for 10-20 minutes, filtering, airing, stirring in diethyl ether for 5-10 minutes, standing for 20-30 minutes, filtering, and airing to obtain purified para-fuchsin; and adding the purified para-fuchsin into ethanol, uniformly stirring, filtering,