METHOD FOR PRODUCING IMIDE ALKYLATED DERIVATIVE OF DIKETOPYRROLOPYRROLE PIGMENT

PROBLEM TO BE SOLVED: To provide a method for producing a high-purity imide alkylated derivative of a diketopyrrolopyrrole pigment in a high yield.SOLUTION: The method for producing an imide alkylated derivative includes: a process (1) of reacting cyclic imides with a diketopyrrolopyrrole pigment in the presence of sulfuric acid to introduce a cyclic imide alkyl group represented by formula (I) to the diketopyrrolopyrrole pigment; a process (2) of putting the reaction mixture obtained in the process (1) into water to precipitate a reaction product and filtering the precipitate; and a process (3) of washing the precipitate obtained in the process (2) with water until the ionic conductance of a washing liquid becomes 1,000 μS/cm. In the process (1), a temperature range of the reaction liquid when reacting the pigment with the cyclic imides is -2 to 10°C, and a reaction time is 2.0-6.0 hours. In the formula (I), R is a 1-6C alkylene group; and X is an arylene group which may be substituted by a halogen atom, arylsulfonyl group, acyl group or -(C=O)-CH-(C=O)-.