Synonyms: 1,1'-Naphthol-4,4'-phthalein(6CI);Phthalide, 3,3-bis(4-hydroxy-1-naphthyl)- (8CI);1-Naphtholphthalein;3,3-Bis(4-hydroxy-1-naphthyl)-1,3-dihydroisobenzofuran-1-one;3,3-Bis(4-hydroxy-1-naphthyl)phthalide;Di-p-a-Naphtholphthalide;Naphtholphthalein blue;p-a-Naphtholphthalein;a-Naphtholphthalein;