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US 5,286,863 AGranted
Oxidation process for preparing quinacridone pigments
AssigneeCiba-Geigy Corporation
InventorsFridolin Babler, Edward E. Jaffe
Life of this patent
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Abstract
A process for preparing quinacridone pigments comprising oxidizing 6,13-dihydroquinacridone or derivatives thereof at elevated temperatures in the presence of a base, dimethyl sulfoxide medium and a quinone catalyst, drowning the resulting pigment solution to precipitate the quinacridone pigment and isolating the desired quinacridone product.
Claims20
A process for preparing an unsubstituted or substituted quinacridone pigment or a solid solution of quinacridone pigments, which comprises the steps of:
- (a) oxidizing a precursor of the quinacridone pigment or solid solution by introducing a gas containing at least 2 percent by weight of molecular oxygen, above or below the surface of a solution, at a temperature from 50.degree. C. to 90.degree. C., said solution consisting essentially of the precursor, dimethyl sulfoxide, an alkali metal hydroxide, water and a catalytically effective amount of a quinone catalyst, the precursor being a 6,13-dihydroquinacridone with the same substitution as said quinacridone pigment or a mixture of 6,13-dihydroquinacridones with the same substitution as the quinacridone pigments in said solid solution, said dimethyl sulfoxide being present in an amount ranging from 3 to 20 times the weight of the precursor, said water being present in a concentration of 0.2 to 3.0 parts per part, by weight, of the precursor, and the molar ratio of the precursor to said alkali metal hydroxide being 1:1.9 to 1:7;
- (b) precipitating said quinacridone pigment or said solid solution from a solution resulting from step (a) by drowning in a C.sub.1 -C.sub.4 alkanol in the presence or absence of a particle growth inhibitor;
- and
- (c) isolating said quinacridone pigment or said solid solution.
1 more element
A process for preparing a solid solution of quinacridone pigments, which comprises the steps of:
- (a) separately preparing a pigment salt solution of at least two different quinacridone pigments, each of the pigment salt solutions being prepared by oxidizing a precursor by introducing a gas containing at least 2 percent by weight of molecular oxygen, above or below the surface of a solution, at a temperature of from 50.degree. C. to 90.degree. C., said solution consisting essentially of dimethyl sulfoxide, the precursor, an alkali metal hydroxide, water and a catalytically effective amount of a quinone catalyst, the precursor being a 6,13-dihydroquinacridone with the same substitution as the different quinacridone pigments, said dimethyl sulfoxide being present in an amount ranging from 3 to 20 times the weight of the precursor, said water being present in a concentration of 0.2 to 3.0 parts per part, by weight, of the precursor, and the molar ratio of the precursor to said alkali metal hydroxide being 1:1.9 to 1:7;
- (b) mixing the separately prepared pigment salt solutions;
- (c) precipitating said solid solution by drowning the mixed pigment salt solutions in a C.sub.1 -C.sub.4 alkanol in the presence or absence of a particle growth inhibitor;
- and
- (c) isolating said solid solution.
2 more elements
Dependencies are inferred from the claim text.