Process for preparing 1,4-diketo-3,6-diphenylpyrrolo-[3,4-C]-pyrrole

Abstract

A new platelet form of 1,4-diketo-3,6-diphenylpyrrolo-[3,4-C]-pyrrole which is prepared by heating 1,4-diketo-3,6-diphenylpyrrolo-[3,4-C]-pyrrole to elevated temperatures, preferably by recrystallization from an aromatic solvent or mixture of aromatic solvents, which is heated to an elevated temperature, generally a temperature higher than about 220.degree. C., preferably above about 240.degree. C., in the range from about 240.degree. C. to about 280.degree. C., most preferably from about 245.degree. C. to 260.degree. C. The platelets have an average particle size with a diameter of less than 4 .mu.m and a thickness up to 1.5 .mu.m and are distinguished from known crystal forms of 1,4-diketo-3,6-diphenylpyrrolo-[3,4-C]-pyrrole by the X-ray diffraction pattern and differential scanning calorimetry curve. The new platelet form of 1,4-diketo-3,6-diphenylpyrrolo-[3,4-C]-pyrrole can be made from crude 1,4-diketo-3,6-diphenylpyrrolo-[3,4-C]-pyrrole and demonstrates a unique color shade effect and excellent heat resistance when utilized as a pigment. The new platelet form of 1,4-diketo-3,6-diphenylpyrrolo-[3,4-C]-pyrrole is particularly suitable for coloring high molecular weight organic material which can be processed to casted and molded articles and for the pigmentation of lacquers and enamel coating compositions, in particular automotive coating paints.

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