2,5-di(methoxyanilino) terephthalic acid polymorphs and quinacridones realized therefrom
2,5-di(p-methoxyanilino)terephthalic acid crystal types I and II are made by controlling the pH during the recovery of the oxidized product of the condensation of dimethylsuccinyl succinate with p-methoxyaniline. The resulting 2,5-di(p-methoxyanilino)-terephthalic acid can be converted into 2,9-dimethoxyquinacridone or a solid solution thereof having controlled characteristics.
1. A method for preparing 2,5-di(p-methoxyanilino)terephthalic acid crystal type II, comprising:
dissolving 2,5-di(p-methoxyanilino)terephthalic acid crystal type I in a solvent with a basic pH; and
precipitating 2,5-di(p-methoxyanilino)terephthalic acid crystal type II by adjusting the pH of the solvent to about 5.5 or lower, wherein:
crystal type I is brown and has an x-ray diffraction pattern that exhibits the strongest peak at d=6.3 angstroms (2θ=13.9 via CuKα); and
crystal type II is violet and has an x-ray diffraction pattern that exhibits the strongest peak at d=16.1 angstroms (2θ=5.5 via CuKα).
2. The method of claim 1 , wherein the basic pH is a pH of about 12.8 or higher.
3. The method of claim 1 , further comprising converting the 2,5-di(p-methoxyanilino)terephthalic acid crystal type II to 2,9-dimethoxyquinacridone.
4. The method of claim 3 , wherein the converting comprises ring closure of the 2,5-di(p-methoxyanilino)terephthalic acid crystal type II.
5. A method for making an ink, coating composition, or pigmented article comprising making 2,9-dimethoxyquinacridone by the process of claim 3 ; and
forming an ink, coating composition, or pigmented article from the 2,9-dimethoxyquinacridone.