Oxidation process for preparing quinacridone pigments
AssigneeCiba Specialty Chemicals Corporation
InventorFridolin Babler
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Abstract
The present invention relates to a process of preparing quinacridone pigments in their specific crystal forms by oxidizing a premilled 6,13-dihydroquinacridone corresponding to the quinacridone pigment in a basic, aqueous reaction medium utilizing hydrogen peroxide as the oxidizing agent. The inventive process is an environmentally friendly process which yields a polymorphically homogeneous product in excellent yield.
Claims31
A process for preparing a quinacridone of the formula I ##STR3## wherein X and Y are independently 1 or 2 substituents selected from the group consisting of H, F, Cl, C.sub.1 -C.sub.3 alkyl and C.sub.1 -C.sub.3 alkoxy, by the oxidation of a corresponding 6,13-dihydroquinacridone of the formula II ##STR4## which comprises (a) premilling a 6,13-dihydroquinacridone of formula II to subpigmentary size;
- (b) oxidizing the premilled 6,13-dihydroquinacridone to the corresponding quinacridone in a basic, aqueous reaction medium with hydrogen peroxide in the presence of a catalyst;
- and
- (c) isolating the quinacridone of formula I.
Dependencies are inferred from the claim text.