NAPHTHALENE DERIVATIVES Homologues.--The methyl, ethyl and other alkyl derivatives of naphthalene used to be of little importance, but they are now being investigated as low-temperature lubricating oils. a-Methyl naphthalene is a liquid which boils at C f3-methylnaphtha lene is a solid, melting at 32° C. Both are present in coal-tar, which also contains at least four dimethylnaphthalenes.
Chloronaphthalenes.—During the classical researches of Arm strong and Wynne on the constitution of naphthalene derivatives, the mono-, di- and tri-chloronaphthalenes (all of which—and there are 26—were prepared) were of the greatest scientific importance, in that any naphthalene compound of unknown configuration could be converted into the corresponding chloro- derivative, and its constitution thus established. Only a-chloronaphthalene and :4-dichloronaphthalene can, however, be produced cheaply; the former is manufactured by passing chlorine into boiling naphthalene in presence of ferric chloride, and is an oil, boiling at 263° C; its chlorine atom is more reactive than that in chloro benzene. I :4-Dichloronaphthalene, melting point 68° C, is pre pared by heating naphthalene with thionyl chloride at 140-160° C.
Naphthalene Chlorides.—Another type of chlorinated naphtha lene is known in which the halogen atoms are associated with the carbon atoms of the nucleus without replacing the hydrogen atoms. These "additive" compounds, as they are called, are of little technical value, but their formation serves to show the unsaturated nature of the naphthalene nucleus. Napthalene di chloride, is a yellow oil formed when the hydrocarbon is treated with potassium chlorate and hydrochloric acid. When heated to 50° C hydrogen chloride is eliminated, leaving a-chloro naphthalene. Naphthalene tetrachloride, formed when chlorine is passed into a chloroform solution of the hydrocarbon, melts at C.
Nitronaphthalenes.— a-Nitronaphthalene, C1oH7•NO2, prepared by the action of strong nitric acid on naphthalene, is readily solu ble in benzene, ether and hot alcohol from which it crystallizes in yellow needles, melting point 61° C. It is not volatile in steam. Its technical importance is mainly due to the fact that on vigor ous reduction it gives a-naphthylamine (see below). /3-Nitronaph thalene is commercially unimportant because of its relative in accessibility. The most convenient method of preparation is that
of Vesely and Dvorak (1922), who obtained it in 28% yield by decomposing diazotized j3-naphthylamine sulphate with copper bronze in presence of potassium nitrite. It crystallizes from dilute alcohol in yellow needles, melting point 79° C; unlike the a-com pound, it is volatile in steam.
On further nitration with nitric acid in presence of sulphuric acid,a-nitronaphthalene yields a mixture of 1:5- and i :8-dinitro naphthalenes, the former after purification melting at 216° C, and the latter at 17o° C. A mixture of the same two components is obtained on dinitrating naphthalene itself. This crude mixture, when heated with sulphur and fuming sulphuric acid, or when dis solved in sulphuric acid and electrolysed at 13o° C, furnishes naphthazarin, the bisulphite compound of which is the important black mordant dyestuff Naphthazarin S. For many years naphtha zarin was assumed to be 5 :6-dihydroxy-a-naphthoquinone, I., because of its similarity to alizarin (q.v.). In 1925, however, it was proved to possess the constitution II. Several tri- and tetra-nitronaphthalenes have been described ; some of them find a limited use in the manufacture of explosives.
Naphthoquinones.—Six different naphthoquinones, are theoretically possible, three homonucleal, i.e., with the :CO groups in the same ring, and three heteronucleal (in different rings). Of these, only the 1:4-, the 1 :2- and the 2:6-, together with a derivative of the 2:3-, have been prepared. :4-Naphtho quinone (I.), obtained in yellow plates by the oxidation of various a-derivatives of naphthalene with chromic acid, resembles benzoquinone in that it has a characteristic odour and is volatile in steam. A hydroxy-derivative of this quinone, juglone, affords a very delicate test of nickel, since in I% alcoholic solution it gives a distinct violet colour with o•ooi% of Ni. :2-Naphtho quinone (II.), obtained by oxidizing 2-amino.a-naphthol with ferric chloride, differs from the r :4-quinone in being, like phenan thraquinone, odourless and non-volatile in steam. 2 :6-Naphtho quinonc (III.), too, is non-volatile and odourless, but similar to benzoquinone in chemical properties; it is formed by the oxida tion of the corresponding dihydroxynaphthalene with lead peroxide in benzene solution. The I :2- and 2 :6-quinones are red.