ANTHRACENE, C 14H10, a hydrocarbon obtained from the fraction of the coal-tar distillate boiling between 2 and 400° C. (from the Greek avOpaE, coal). This high boiling fraction is allowed to stand for some days, when it partially solidifies. It is then separated in a centrifugal machine, the more fusible im purities are removed by means of hot water, and the residue is finally hot-pressed. The crude anthracene cake is purified by treatment with the higher pyridine bases, the operation being carried out in large steam-jacketed boilers. The whole mass dis solves on heating, and the anthracene crystallizes out on cooling. The crystallized anthracene is then removed by a centrifugal separator and the process of solution in the pyridine bases is repeated. Finally the anthracene is purified by sublimation.
Many synthetical processes for the preparation of anthracene and its derivatives are known. It is formed by the condensation of acetylene tetrabromide with benzene in the presence of alumin ium chloride :— and similarly from methylene dibromide and benzene, and also when benzyl chloride is heated with aluminium chloride to 200° C. Anthracene crystallizes in colourless monoclinic tables which show a fine blue fluorescence. It melts at 213 ° C. and boils at 351° C. It is insoluble in water, sparingly soluble in alcohol and ether, but readily soluble in hot benzene. It unites with picric acid to form a picrate, C14Hlo • C6H2(NO2)3.OH, which crystallizes in needles, melting at 138° C. On exposure to sunlight a solution of anthracene in benzene or xylene deposits para-anthracene (C14H11)2, which melts at 244° C. and passes back into the ordinary form. Chlorine and bromine form both addition and substitution products with anthracene; the addition product, anthracene dichloride, C14H10C12, being formed when chlorine is passed into a cold solution of anthracene in carbon bisulphide. On treatment with potash, it forms the substitution product, monochlor anthracene, Nitro-anthracenes are not as yet known. The mono-oxyanthracenes (anthrols), or anthraquinone. j3-anthrol and anthranol give the corresponding amino compounds (anthramines) when heated with ammonia.
Numerous sulphonic acids of anthracene are known, a mono sulphonic acid being obtained with dilute sulphuric acid, whilst concentrated sulphuric acid produces mixtures of the anthracene disulphonic acids. By the action of sodium amalgam on an alco holic solution of anthracene, an anthracene dihydride, is obtained, whilst by the use of stronger reducing agents, such as hydriodic acid and amorphous phosphorus, hydrides of composi tion and C14H24 are produced.
Methyl and phenyl anthracenes are known; and /3-methyl an thracene has been identified in tar produced by low-temperature carbonisation. Oxidizing agents convert anthracene into anthra quinone (q.v.) ; the production of this substance by oxidizing anthracene in glacial acetic acid solution, with chromic acid, is the usual method employed for the estimation of anthracene. See E. de B. Barnett, Anthracene and Anthraquinone, 1921.