A process is disclosed wherein 2,5-di(phenylamino) terephthalic acid is half-cyclized by dissolving it in a mixture of polyphosphoric acid and phosphoric acid and heating at 100.degree.-120.degree. C. to form 2-(phenyl)amino-3-carboxy-9(10H)acridone (ACA). The ACA is decarboxylated to form 2-(phenyl)amino-9(10H)acridone, also known as 2-anilinoacridone, by dissolving it in tetramethylene sulfone and heating in the presence of a basic cupric carbonate catalyst.