Sulfuric Acid → Quinacridone

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Reaction Steps

The oxidation of 6,13-dihydroquinacridone is carried out as described in the Japanese Patent Disclosure JP 54-135821, Example 5. Thus, 10 grams 6,13-dihydroquinacridone are stirred into a mixture of 100 ml dimethyl sulfoxide and 20 grams 33% aqueous potassium hydroxide solution at 110° to 120° and air is then introduced into the vessel at a rate of 90-96 ml/min. for a period of 5 hours. The reaction mixture is cooled and 33% aqueous sulfuric acid is introduced dropwise. The precipitated pigment is filtered and the presscake washed dimethyl sulfoxide-free with water to pH 6 and dried yielding 9.1 grams of a quinacridone pigment. A spectrophotometric analysis shows the product to consist of 0.8% 6,13-dihydroquinacridone, 17.2% of undesirable quinacridonequinone and 78.3% quinacridone. When incorporated into paints or plastics, the pigment shows a dirty red color. Its X-ray diffraction pattern shows the main peaks of known gamma quinacridone and quinacridonequinone.

Provenance & Evidence