BigPatents India

A process for the preparation of a quinacridone /6, 13-dihydroquinacridone solid solution of the kind such as herein described in the y( or yn crystal form of quinacridone comprising quinacridone of the formula (I): dihydroquinacridone of the formula (II) which comprises preparing a large particle size 6,13-dihydroquinacridone salt, converting the large particle size 6,13-dihydroquinacridone salt to a small particle size 6, 13-dihydroquinacridone salt, wherein said conversion is effected by the addition of an acid, optionally, adding a catalytically effective amount of an aromatic nitro compound if the crystal form is desired, Oxidizing the small particle size 6, 13-dihydroquinacridone salt by the addition of hydrogen peroxide in an amount that the molar ratio is from 1.1 to 5 moles of hydrogen peroxide per mole of the 6, 13-dihydroquinacridone in the presence of an amount from 0.004 to 0.04 times the weight of the 6, 13- dihydroquinacridone; and isolating the y( or y quinacridone /6, 13-dihydroquinacridone solid solution pigment.