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Naphthalene

NAPHTHALENE, CioH 8 , a hydrocarbon discovered in the " carbolic " and " heavy oil " fractions of the coal-tar distillate (see COAL-TAR) in 1819 by A. Garden. It is a product of the action of heat on many organic compounds, being formed when the vapours of ether, camphor, acetic acid, ethylene, acetylene, etc., are passed through a red-hot tube (M. Berthelot, Jahresb., 1851), or when petroleum is led through a red-hot tube packed with charcoal (A. Letny, Ber., 1878, n, p. 1210). It may be synthesized by passing the vapour of phenyl butylene bromide over heated soda lime (B. Aronheim, Ann., 1874, 171, p. 219); and by the action of ortho-xylylene bromide on sodium ethane tetracarbexylic ester, the resulting tetra-hydronaphthalene tetracarboxylic ester being hydrolysed and heated, when it yields hydronaphthalene dicarboxylic acid, the silver, salt of which decomposes on distillation into naphthalene and other products (A. v. Baeyer and W. H. Perkin, junr., Ber., 1884, 17, P- 451):

, Na-C(CO 2 R)i " CH S -CH-CO,H r ^CH 2 -C(COH), lH4 <CH 2 .C(C0 2 H), 1 " Nape," the back of the neck, is of doubtful origin; it may be a variant of " knap," a knob or protuberance.

It is a colourless solid, which melts at 80 C., and boils at 218 C. It crystallizes in the monoclinic system; it is to be noted that a- and /3-naphthol assume almost identical forms, so that these three compounds have been called isomorphous. It is insoluble in water, but is readily soluble in alcohol, and ether. It has a characteristic smell, and is very volatile, distilling readily in a current of steam. It acts as a weak antiseptic. It is used for enriching coal gas, as a vermin killer, in the manufacture of certain azo dyes, and in the preparation of phthalic acid (q.v.). When passed through a red-hot tube packed with carbon it yields j3/3-dinaphthyl, (CioH 7 ) 2 . It forms a crystalline compound with picric acid. It readily forms addition products with chlorine and with hydrogen; the dichloride, CioH 8 Cl 2 , is obtained as a yellow liquid by acting with hydrochloric acid and potassium chlorate; the solid tetrachloride, CK> H 8 CU, results when chlorine is passed into naphthalene dissolved in chloroform. Numerous hydrides are known; heated with red phosphorus and hydriodic acid the hydrocarbon yields mixtures of hydrides of composition CioHio to CioH 20 . Sodium in boiling ethyl alcohol gives the a-dihydride, Ci Hi (E. Bamberger, Ber., 1887, 20, p. 1705); and with boiling amyl alcohol the /3-tetrahydride, Ci Hi 2 (E. Bamberger, Ber., 1890, 23, p. 1561). The a- tetrahydronaphthalene is formed when naphthalene is heated with phosphonium iodide at i7o-i9O (A. v. Baeyer). Structurally naphthalene may be represented as a fusion of two benzene nuclei, the hydrogen atoms being numbered as in the inset formula i, 4, 5, 8 are o-positions, 2, 3, 6, 7 are /3; 1-5 or 4-8 diderivatives are ana, whilst 1-8 or 4-5 are peri (see CHEMISTRY, ORGANIC).

a-Nitronaphthalene, CioH 7 'NO 2 , is formed by the direct nitration of naphthalene. For its commercial preparation see O. Witt, Die chemische Industrie, 1887, 10, p. 215. It crystallizes in yellow needles, which melt at 61 C., and are readily soluble in alcohol. By the action of nitro-sulphuric acid it is converted into a mixture of 1-5 and 1-8 dinitronaphthalenes (P. Friedlander, Ber., 1809,32, P- 353 ') When heated with aniline and its salts it yields phenylrosmdulin (German patent 67339 ( 1888 ))- 0-Nitronaphthalene is prepared by acting with ethyl nitrite on an alcoholic solution of 2-nitro-o-naphthylamine in the presence of sulphuric acid (E. Lell' mann and A. Remy, Ber., 1886, 19, p. 237), or with freshly prepared potassium cupronitrite on ^-naphthalene diazonium sulphate (A. Hantzsch, Ber., 1900, 33, p. 2553). It crystallizes in small yellow needles which melt at 78 C. and are volatile in steam.

Sulphonic Acids. Two monosulphonic acids (o and /3) result by acting with sulphuric acid on the hydrocarbon, the a-acid predominating at low temperatures (80 C. and under) and the /3-acid at higher temperatures (i7o-2OO C.). They are crystalline, hygroscopic compounds and are employed for the manufacture of the naphthols. Numerous di- and /ri-sulphonic acids are known.

a- Naphthoquinone, CioHeOa, resembles benzoquinone, and is formed by the oxidation of many o-derivatives of naphthalene with^chromic acid. It crystallizes in yellow needles which melt at 125 C. It sublimes readily, is volatile in steam and reduces to the corresponding dihydroxynaphthalene. /3 Naphthoquinone is formed by oxidizing 2-amino-a-naphthol (from/S-naphthol-orangebyreduction) withferric chloride. It crystallizes in red needles, which melt at 115 C; it has no smell and is non-volatile (cf. phenan- NAPHTHOLS, or HYDROXYNAPHTHALENES, Ci H 7 OH, 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): C 6 H 6 CH:CH-CH 2 -CO2H = CioH 7 OH+H 2 0. 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, HOCioHe-CioHe-OH. Alkaline potassium permanganate oxidizes it to phenyl-glyoxyl-ortho-carboxylic acid, HC^C-CeHvCO- CO 2 H. 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 160 C. it gives a-naphthyl hydrazine, CioH 7 NH-NH2(L. Hoffmann, Ber., 1898, 31, p. 2909). Nitric acid converts it into nitro-compounds, which are occasionally used for dyeing silk and wool.

Marlius yellow, CioH^NC^ONa-HzO, the sodium salt of 2-4 dinitro-o-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., CioH 4 (ONa)(NO2) 2 SO 3 Na, 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 o-naphthol are employed in the preparation of azo dyes. The most important is Nevile and Winther's acid, CioH c (OH)(SO3H)(i-4), formed when diazotized naphthionic acid (a-naphthylamine-4-sulphonic acid) is boiled with dilute sulphuric acid (Nevile and Winther, Ber., 1880, 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 170 C., and is readily soluble in water. With ferric chloride it gives a blue coloration.

fi-Naphthol, CioH 7 OH, prepared by fusing sodium j3- 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-jS-naphthols (E. Bamberger, Ber., 1890, 23, p. 197). When heated with ammonium formate to 150 C. it forms /3-naphthylamine. With nitrosodimethylaniline hydrochloride it forms Meldola's Blue ( dimethylaminonaphthophenoxazonium chloride), CisHis^OCl (R. Meldola, Ber., 1879, 12, p. 2065).

The |8-naphthol sulphonic acids find extensive application in the colour industry. The most important members are shown in the table :

the sodium bisulphite compound of 7-8 dioxy-a- naphthoquinone, is a dyestuff used for printing on cotton in the presence of a chromium mordant. The naphthoquinone is prepared by the action of zinc and concentrated sulphuric acid on o- dinitronaphthalene. A 2-6 naphthoquinone results on oxidizing 2-6 dihydroxynaphthalene with lead peroxide.

a-Naphthoic acid, CioHT-COsH, is formed by hydro. lysis of the nitrile, obtained by distilling potassiumo-naphthalene sulphonate with potassium cyanide (V. Merz, Zeit. f. Chemie, 1868, p. 34), or by heating the sulphonate withsodiumformate (V.Meyer, Ann. ,1870, 156, p. 274). It forms needles which melt at 160 C. ft-Naphthoic acid, obtained by boiling j3- methylnaphthalene with dilute nitric acid, or by hydrolysis of its nitrile (formed when formyl-/3-naphthalide is heated with zinc dust), crystallizes from alcohol in melt at 184 C.

FORMULA.

METHOD OF PREPARATION.

REMARKS.

2-oxy-8-sulphonic (Baeyer's acid)

From /3-naphthol and concentrated sulphuric acid at 5 o-6o C.

Sodium salt soluble in strong alcohol.

2-oxy-6-sulphonic (Schaffer's acid)

From /3-naphthol and concentrated sulphuric at 100 C.

Sodium salt insoluble in alcohol.

2-oxy-7-sulphonic (F-acid)

By fusion of naphthalene 2-7- disulphonic acid with caustic soda at 200 "-250 C.

Very soluble in water and alcohol.

2-oxy-3'6-disulphonic (R-acid)

Both R- and G-acid from /3- naphthol and concentrated sulphuric acid at ioonoC.

The sodium salts separated by crystallization. R-salt insoluble in alcohol ; G-salt soluble.

2-oxy-6-8-disulphonic (G-acid)

2-oxy-3-6-8-trisulphonic From /3-naphthol and fuming sulphuric acid at l4O-l6oC.

Alkaline solutions show green fluorescence.

needles which I Nitrosonaphthols or naphthoquinone-oximes, CioH 6 (OH)(NO) or I CioH(:NOH):O. Two are known, namely 4-nitroso-a-naphthol or a-naphthoquinone-oxime, formed by the action of nitrous acid on o-naphthol or of hydroxylamine hydrochloride on a-naphthoquinone (H. Goldschmidt and H. Schmidt, Ber., 1884, 17 p. 2064); and 2-nitroso-a-naphthol (/3-naphthoquinone-oxime), formed by the action of hydroxylamine hydrochloride on /3-naphthoquinone, NAPHTHYLAMINES, or AMINONAPHTHALENES, C 10 HvNH 2 , the naphthalene homologues of aniline, in contrast to which they may be prepared by heating the naphthols with ammoniazinc chloride.

a-Naphthylamine is prepared by reducing a-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 a-naphthol with sodium acetate, ammonium chloride and acetic acid (A. Calm, Ber., 1882, 15, p. 6 1 6); by heating a-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, etc.) give a blue precipitate with solutions of its salts. Chromic acid converts it into a-naphthoquinone. Sodium in boiling amyl alcohol reduces it to aromatic tetrahydro-a- 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, (CI^MCC^HJj, when oxidized by potassium permanganate. The a-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, i-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.

0-Naphl/iylamine is prepared by heating /3-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 /3-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-/3- naphthylamine, which has most of the properties of the aliphatic amines; it is strongly alkaline in reaction, has an ammoniacal odour and cannot be diazotized. On oxidation it yields ortho-carboxy-hydrocinnamic acid, I^C-CeHcCI^-CHa-COsH. Numerous sulphonic acids derived from /3-naphthylamine are known, the more important of which are the 2-8 or Badische, the 2-5 or Dahl, the 2-7 or 5, and the 2-6 or Bronner acid. Of these, the5-acid and Brenner's acid are of more value technically, since they combine with ortho-tctrazoditolyl to produce fine red dye-stuffs.

Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)

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