Preparation method of purple red organic pigment

The invention discloses a preparation method of a purplish red organic pigment, which comprises the following steps: adding water and sodium carbonate into a coupling pot, uniformly stirring, adding 5-amino-4-hydroxynaphthalene-2, 7-disulfonic acid in the stirring process, stirring for 0.5-1 hour, then adding 4-chlorobenzoyl chloride, controlling the pH value, and cooling to 5-10 DEG C to obtain a coupling solution; the preparation method comprises the following steps: adding water and 3-amino-4-methoxybenzoylaniline into a reaction pot, adding hydrochloric acid, stirring for 0.5-1 hour, then adding a sodium nitrite solution in a low-temperature environment, and carrying out a constant-temperature diazo reaction for 2-3 hours to obtain a diazo solution; and preparation of the organic pigment: adding the diazonium liquid into the coupling liquid, adjusting the pH value, reacting for 2-3 hours, filtering, rinsing to be neutral, and carrying out filter pressing, washing, drying and crushing to obtain the purplis