NAPHTHOLS, or HYDROXYNAPHTHALENES, C10H70H  , the naphthalene homologues of the phenols . The hydroxyl group is more reactive than in the phenols, the naphthols being converted into naphthylamines by the action of ammonia, and forming ethers and esters much more readily . a-Naphthol may be prepared by fusing sodium-a-naphthalene sulphonate with caustic soda; by heating a-naphthylamine sulphate with water to 200° C . (English Patent 14301 (1892)); and by heating phenyl isocrotonic acid (R . Fittig and H . Erdmann, Ann . 1885, 227, p . 242): C6H6CH:CH•CH2•CO2H = C1oH70H+H20 . It forms colourless needles which melt at 94° C.; and is readily soluble in alcohol, ether, chloroform, and caustic alkalis . It is volatile in steam . With ferric chloride it gives a dark-blue precipitate of a-dinaphthol, HO•C10Hs•CIOHs•OH . Alkaline potassium permanganate oxidizes it to phenyl-glyoxyl-ortho-carboxylic acid, H02C•CsH4•CO• CO2H .

It is reduced by sodium in boiling amyl alcohol

solution to " aromatic " tetrahydro-a-naphthol (reduction occurring in the ring which does not contain the hydroxyl group) . When heated with hydrazine hydrate at 16o° C. it gives a-naphthyl hydrazine, CIOH7NH•NH2 (L . Hoffmann, Ber., 1898, 31, P . 2909) . Nitric acid converts it into nitro-compounds, which are occasion-ally used for dyeing silk and wool . Martius yellow, C1oH6(NO2)2ONa•H20, the sodium salt of 2.4 dinitro-a-naphthol (for notation see NAPHTHALENE), is prepared by the action of nitric acid on a-naphthol-2.4-disulphonic acid . It forms orange-yellow plates and dyes wool a golden yellow (from an acid bath) . Naphthol yellow S., C1oH4(ONa)(NO2)2SO3Na, prepared by the action of nitric acid on a-naphthol-2.4.7-trisulphonic acid, is an orange-yellow powder which dyes wool and silk yellow (from an acid bath) . Numerous mono-, di- and trisulphonic acids of a-naphthol are employed in the preparation of azo dyes . The most important is Nevile and Winther's acid, C10H6(OH)(SO3H)(1.4), formed when diazotized naphthionic acid (a-naphthylamine-4-sulphonic acid) is boiled with dilute sulphuric acid (Nevile and Winther, Ber., 188o, 13, p . 1949), or when sodium naphthionate is heated with concentrated caustic soda solution under pressure at 240°–260° C . (German patent 46307 (1888)) .

It melts at 17o° C., and is readily soluble in water . With ferric chloride it gives a blue coloration . (3-Naphthol, C10H2OH, prepared by fusing sodium (3-naphthalene sulphonate with caustic soda, crystallizes in plates which melt at 122° C . With ferric chloride it gives a

green colouration, and after a time a white flocculent precipitate of a dinaphthol . With sodium in boiling amyl alcohol solution it gives a mixture of alicyclic and aromatic tetrahydro-(3-naphthols (E . Bamberger, Ber., 1890, 23, p . 197) . When heated with ammonium formate to 15o° C. it forms /3-naphthylamine . With nitrosodimethylaniline hydrochloride it forms Meldola's Blue (dimethylaminonaphthophenoxazonium chloride), C18H15N20C1 (R . Meldola, Ber., 1879, 12, p . 2065) . The $-naphthol sulphonic acids find extensive application in the colour industry .

The most important members are shown in the table: or naphthoquinone-

oximes, C1oH6(OH)(NO) or C1oHs(: NOH) : O .