Two phenols derived from naphthalene with the formula C10H7OH, differing in the position of the –OH group. The most important is naphthalen-2-ol (β-naphthol), with the –OH in the 2-position. It is a white solid (r.d. 1.28; m.p. 123–124°C; b.p. 295°C) used in rubber as an antioxidant. Naphthalen-2-ol will couple with diazonium salts at the 1-position to form red azo compounds, a reaction used in testing for the presence of primary amines (by making the diazonium salt and adding naphthalen-2-ol).