Preparation of diketopyrrolopyrrole pigments

1) A process for preparing 1,4-diketopyrrolo[3,4-c]pyrrole pigments of the formula (I),

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• where R1 and R2 are identical or different and are each an unsubstituted or substituted isocyclic or heterocyclic aromatic radical, by reaction of a succinic diester with a nitrile of the formula (II)
• R1—CN (II)
• or of the formula (III)
• R2—CN (III)
• or with a mixture of these nitriles, in an organic solvent and in the presence of a strong base, and subsequent hydrolysis of the resultant salt of the diketopyrrolopyrrole pigment, which comprises conducting the reaction, or the hydrolysis, or the reaction and the hydrolysis, in a microreactor.