1-Naphthylamine is an aromatic amine. It can be prepared by reducing 1-nitronaphthalene with iron and hydrochloric acid at about 70 °C, the reaction mixture being neutralized with milk of lime, and the naphthylamine steam-distilled. It may also be prepared, in the form of its acetyl derivative, by heating 1-naphthol with sodium acetate, ammonium chloride and acetic acid; by heating 1-naphthol with calcium chloride-ammonia to 270 °C; and by heating pyromucic acid, aniline, zinc chloride and lime to 300 °C. It crystallizes in colorless needles which melt at 50 °C. It possesses a disagreeable odor, sublimes readily, and turns brown on exposure to air. Oxidizing agents, such as ferric chloride, give a blue precipitate with solutions of its salts. Chromic acid converts it into 1-naphthoquinone. Sodium in boiling amyl alcohol reduces it to aromatic tetrahydro-1-naphthylamine, a substance having the properties of an aromatic amine, for it can be diazotized and does not possess an ammoniacal smell. Since it does not form an addition product with bromine, reduction must have taken place in one of the nuclei only, and on account of the aromatic character of the compound it must be in that nucleus which does not contain the amino group. This tetrahydro compound yields adipic acid, (C6O4H10), when oxidized by potassium permanganate. The 1-naphthylamine sulfonic acids are used for the preparation of azo dyes, these dyes possessing the important property of dyeing unmordanted cotton. The most important is naphthionic acid, 1-amino-4-sulfonic acid, produced by heating 1-naphthylamine and sulfuric acid to 170-180 °C with about 3% of crystallized oxalic acid. It forms small needles, very sparingly soluble in water. With diazotized benzidine it gives Congo red.