Hydrogen Peroxide → Quinacridone

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A one liter flask equipped with a thermometer, stirrer and condenser is charged with 40 grams 6,13-dihydroquinacridone, 0.3 grams pyrazolylmethylquinacridone, 250 ml methanol and 52.8 grams 50% aqueous sodium hydroxide. The mixture is stirred under a slow flow of nitrogen at 50-55° C. for one hour, generating 6,13-dihydroquinacridone disodium salt. 0.6 grams anthraquinone-2-sulfonic acid sodium salt are added and the mixture is heated to reflux temperature. 73.5 grams of an aqueous 16.9% hydrogen peroxide solution are added into the reaction mixture with a peristaltic pump at a rate of 0.4 ml/minute maintaining reflux under a slow nitrogen flow over 2 hours and 35 minutes. The resulting pigment suspension is further stirred for 1 hour at reflux; then filtered. The presscake is washed with hot water and then dried, yielding 38.9 grams beta quinacridone pigment. This product shows similar good pigment properties and similar color characteristics to the beta quinacridone obtained following the procedure of Example 1.

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