| abstract |
A process for the preparation of mixed crystals of 1,4-diketopyrrolo 3,4-c!pyrroles, consisting of 1 mol each of two different compounds of formula ##STR1## by heating a corresponding mixture in solid form to the temperature range from 220° to 380° C. n A and B are, for example, each a group of formula ##STR2## wherein R 1 and R 2 are each independently hydrogen, chloro, bromo, C 1 -C 4 alkyl, C 1 -C 6 alkoxy, C 1 -C 6 alkylamino, phenyl or --CN, n G is --O--, --NR 7 --, --N═N-- or --SO 2 --, n R 3 and R 4 are hydrogen, and R 7 is hydrogen, methyl or ethyl. n The mixed crystals and solid solutions obtained are excellently suited for pigmenting high molecular weight material. |