NAPHTHALIC GROUP, a division of the Benzoic series of organic compounds. It is chiefly composed of the derivatives of napthtbalin.
Naphthalin or hydride of naplethyl (C„H„ H), or naphtha lene, was first discovered by Garden in coal tar. Faraday determined its composition, and Laurent has particularly investigated its consti tution. It is a very common product of the decomposition of organic bodies by beat, but its most abundant source is coal-tar. Large quan tities of it are produced at all gas-works, and its separation from the tar may be accomplished by the following process :—After exposure to air for some time the tar is redistilled; the first portion of the distillate is set aside, the second portion furnishes much naphthalin if artificially cooled, but the last portion comes over in an almost semi-solid state, and on standing for a short time sets into a solid mass of crystals of naphthalin. Much oily matter is got rid of on submitting the mass to pressure, and the naphtha is finally obtained in a pure state by successive sublimations or recrystallisations from alcohol.
Naphthalin is colourless, has a somewhat tarry odour, and a burning aromatic taste. It crystallises in large, thin, rhombic plates of pearly lustre, and unctuous feel. Exposed to light under a glass covering, it gradually sublimes in magnificent crystals, and altogether presents a very beautiful appearance. It fuses when heated to 174° Fahr., and boils at 428°. Its vapour density is 4.582. It is not very inflammable, and when ignited gives off much smoke. It is very volatile in vapour of water. It is insoluble in cold water, very slightly soluble in hot water, but readily so in alcohol, ether, and the fixed and essential oils. It appears also to be soluble in acetic or oxalic acids, but is not acted upon by caustic potash.
Sulphuric derivatives of Naphthalin.
Sulphonaphthalic acid 2Aq.). Naphthyl-sulphurous acid, hyposulphonaphthalic acid, or naphthyl-dithionic arid. Obtained by acting upon naphthalin with excess of sulphuric acid at a temperature not exceeding 200° Fahr. ; it crystallises on cooling. It is very soluble
in water, alcohol, and oils, but only slightly so in ether. It has an acid, astringent, metallic taste, and at a bigh temperature is decom posed. The sulphonaphthalates are monobasic ; those of the alkalies are readily obtained in crystals. ' By substitution processes, the follow ing compounds of sulphonaphthalic acid are easily produced ; they all form salts with bases, several of the compounds being crystalline :— Disulphonaphthalic acid Thionaphthic acid, or hypo sulphonaphthinic acid. This acid is produced under circumstances similar to those under which sulphonaphthalic acid is obtained, but at a higher temperature ; fuming sulphuric acid also facilitates the reaction. It is dibasic. Both it and its salts crystallise with difficulty.
Sulphonaphthalin C,H + HO, 2 II 0 ). Produced when vapours of anhydrous sulphuric acid are passed into fused naph thalin, the latter being kept in excess. It is a granular body, slightly soluble in water, but more so in alcohol. It is sometimes accompanied by sulphoglutinic acid (hyposulphoglutinic acid).
Nitro-derivativcs of Naphthalin.
Nitronaphthatin (NO,) ). .ATitronaphthalase. Naphthalin is well stirred with five times its weight of cold nitric acid of sp. gr. 1.33. After some days it is found converted into a lemon-yellow mass of nitronaphthalin, insoluble in water, but soluble in hot alcohol or ether, the solutions depositing it in brittle needles on cooling. Heated with lime, it disengages ammonia, and, among other products, yields a substance called by Laurent naphthalase, or, better, naphthasc.
Binitronaphthalin, NO,) ). Nitronoplethalese. Naphthalin added to hot strong nitric acid is converted into the above compound, which crystallises out on cooling in pale yellow needles. It is only slightly soluble in alcohol or ether. Boiled with alcoholic solution of potash, ammonia is disengaged, and nitric acid then precipitates, from the solution, dark brown flocks of nitronaphthalesic acid.