Patent ID: 8557990

Claim:
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).