# 1911 Encyclopædia Britannica/Naphthylamines

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​NAPHTHYLAMINES, or Aminonaphthalenes, C$_{10}$H$_7$NH$_2$, the naphthalene homologues of aniline, in contrast to which they may be prepared by heating the naphthols with ammonia-zinc chloride.
α-Naphthylamine is prepared by reducing α-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 α-naphthol with sodium acetate, ammonium chloride and acetic acid (A. Calm, Ber., 1882, 15, p. 616); by heating α-naphthol with calcium chloride-ammonia to 270° C.; and by heating pyromucic acid, aniline, zinc chloride and lime to 300° C. (F. Canzonieri and V. Oliveri, Gazz., 1886, 16, p. 493). It crystallizes in colourless needles which melt at 50° C. It possesses a disagreeable faecal odour, sublimes readily, and turns brown on exposure to air. Oxidizing agents (ferric chloride, &c.) give a blue precipitate with solutions of its salts. Chromic acid converts it into α-naphthoquinone. Sodium in boiling amyl alcohol reduces it to aromatic tetrahydro-α-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, (CH$_2$)$_4$(CO$_2$H)$_2$, when oxidized by potassium permanganate. The α-naphthylamine sulphonic 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-sulphonic acid, produced by heating a-naphthylamine and sulphuric 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.
β-Naphthylamine is prepared by heating β-naphthol with zinc chloride-ammonia to 200–210° (V. Merz and W. Weith, Ber., 1880, 13, 1300); or in the form of its acetyl derivative by heating β-naphthol with ammonium acetate to 270–280° C. It forms odourless, colourless plates which melt at 111–112° C. It gives no colour with ferric chloride. When reduced by sodium in boiling amyl alcohol solution it forms alicyclic tetrahydro-β-naphthylamine, which has most of the properties of the aliphatic amines; it is strongly alkaline in reaction, has an ammonia cal odour and cannot be diazotized. On oxidation it yields ortho-carboxy-hydrocinnamic acid, HO$_2$C·C$_6$H$_4$·CH$_2$·CH$_2$·CO$_2$H. Numerous sulphonic acids derived from β-naphthylamine are known, the more important of which are the 2·8 or Badische, the 2·5 or Dahl, the 2·7 or δ, and the 2·6 or Bronner acid. Of these, the δ-acid and Bronner’s acid are of more value technically, since they combine with ortho-tetrazoditolyl to produce fine red dye-stuffs.