It is more acidic than phenol or naphthol. It is prepared by nitration of naphthol. A similar reaction uses additional naphthol. Naphthol AS is an organic compound with the formula CH(OH)C(O)NHCH. Naphthol Green B is used in histology to stain collagen. Naphthol AS TR phosphate was used as the substrate and hexazonium paraosaniline as coupler. Naphthol yellow S is an organic compound that is a dye. For example, in Naphthol AS-OL, the aryl substituent on nitrogen is CH-2-OCH. Naphthol Green B is the sodium salt of Naphthol Green Y (C.I. 10005). Naphthol Green B is a coordination complex of iron that is used as a dye.