PROCESS FOR PREPARING PIGMENTARY GAMMAQUINACRIDONE BY OXIDATION OF BETA-DIHYDROQUINACRIDONE IN THE PRESENCE OF A NITROGENOUS QUINACRIDONE

摘要

Gamma-quinacridone pigments are known and commonly prepared from beta-dihydroquinacridones using a mild oxidizing agent and an aqueous alkaline reaction medium containing a polar organic solvent. Gamma-quinacridones prepared in this way have valuable pigment properties but for many applications their tinctorial properties need to be improved and this conventionally is done by means of a finishing treatment, normally involving contact with a solvent medium or milling. Such finishing treatments are a disadvantage in that they add to the cost and inconvenience or production. The invention enables production, without carrying out finishing treatments, of gamma-quinacridones having tinctorial properties comparable to those obtained when a finishing treatment is conducted, by carrying out the oxidation of the beta-dihydroquinacridones in the presence of a nitrogenous quinacridone compound of the formula: …CHEM… wherein R1 and R2 are, each independently, hydrogen, fluorine, chlorine, bromine, methyl or methoxy and wherein Z represents a group of one of the formulae II and III below: …CHEM… in which X1 and X2 are, each independently, hydrogen, fluorine, chlorine, bromine, methyl or methoxy, and m is an integer of from 1 to 4, said group(s) Z being substituents for hydrogen on the terminal rings of the quinacridone nucleus.