1911 Encyclopædia Britannica/Naphthalene

NAPHTHALENE, C₁₀H₈, 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, &c., 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, 11, 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 tetracarboxylic 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):—

C6H4	CH2Br	+	Na·C(CO2R)2	→ C6H4	CH2·C(CO2R)2
	CH2Br		Na·C. (CO2R)2		CH2·C. (CO2R)2
					↓
C10H8←C6H4			CH2·CH·CO2H	←C6H4	CH2·C(CO2H)2
			CH2·C. H·CO2H		CH2·C. (CO2H)2

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 α- and β-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 ββ-dinaphthyl, (C₁₀H₇)₂. It forms a crystalline compound with picric acid. It readily forms addition products with chlorine and with hydrogen; the dichloride, C₁₀H₈Cl₂, is obtained as a yellow liquid by acting with hydrochloric acid and potassium chlorate; the solid tetrachloride, C₁₀H₈Cl₄, 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 C₁₀H₁₀ to C₁₀H₂₀. Sodium in boiling ethyl alcohol gives the α-dihydride, C₁₀H₁₀ (E. Bamberger, Ber., 1887, 20, p. 1705); and with boiling amyl alcohol the β-tetrahydride, C₁₀H₁₂ (E. Bamberger, Ber., 1890, 23, p. 1561). The α-tetrahydronaphthalene is formed when naphthalene is heated with phosphonium iodide at 170°–190° (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 ; 1, 4, 5, 8 are α-positions, 2, 3, 6, 7 are β; 1-5 or 4-8 diderivatives are ana, whilst 1-8 or 4-5 are peri (see Chemistry, Organic).

α-Nitronaphthalene, C₁₀H₇·NO₂, 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 dinitronaplithalenes (P. Friedlander, Ber., 1829, 32, p. 3531). When heated with aniline and its salts it yields phenylrosindulin (German patent 67339 (1888)). β-Nitronaphthalene is prepared by acting with ethyl nitrite on an alcoholic solution of 2-nitro-α-naphthylamine in the presence of sulphuric acid (E. Lellmann and A. Remy, Ber., 1886, 19, p. 237), or with freshly prepared potassium cupronitrite on β-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 (α and β) result by acting with sulphuric acid on the hydrocarbon, the α-acid predominating at low temperatures (80° C. and under) and the β-acid at higher temperatures (170°–200° C.). They are crystalline, hygroscopic compounds and are employed for the manufacture of the naphthols. Numerous di- and tri-sulphonic acids are known.

α-Naphthoquinone, C₁₀H₆O₂, resembles benzoquinone, and is formed by the oxidation of many α-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 dihydroxynapthalene. β-Naphthoquinone is formed by oxidizing 2-amino-α-naphthol (from β-napthol-orange by reduction) with ferric chloride. It crystallizes in red needles which melt at 115° C; it has no smell and is non-volatile (cf. phenanthrenequinone). Alizarin black, C₁₀H₄(OH)₂O₂·NaHSO₃, the sodium bisulphite compound of 7·8 dioxy-α-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 α-dinitronaphthalene. A 2·6 naphthoquinone results on oxidizing 2·6 dihydroxynaphthalene with lead peroxide.

α-Naphthoic acid, C₁₀H₇·CO₂H, is formed by hydrolysis of the nitrile, obtained by distilling potassium-α-naphthalene sulphonate with potassium cyanide (V. Merz, Zeit. f. Chemie, 1868, p. 34), or by heating the sulphonate with sodium formate (V. Meyer, Ann., 1870, 156, p. 274). It forms needles which melt at 160° C. β-Naphthoic acid, obtained by boiling β-methylnaphthalene with dilute nitric acid, or by hydrolysis of its nitrile (formed when formyl-β-naphthalide is heated with zinc dust), crystallizes from alcohol in needles which melt at 184° C.