Dibromanthraquinone, C1,11013,(0,), is formed by the direct action of bromine on anthraquinone at 160° (320° F.) ; it is more conveniently made from tetra-brom-anthracene, one part of which is heated with two parts chromate potash, and 5 to 6 parts colourless nitric acid, sp. gr. 1•42 in a large flask, as the action is very violent at first, and the liquid frequently froths ; the action is emplete as soon as bromine vapours cease to escape. It is mixed ith water, and the pale-yellow mass is collected on a filter, washed, and recrystallized from benzol. The oxidation succeeds as well with glacial acetic and chromic acids. Dibromanthraquinone crystallizes in light yellow needles, and sublimes unaltered in the same form.
Sulpho-compounds.—Anthraquinone heated with sulphuric acid and mercuric nitrate, and the product treated with soda or potash, produces disulpho-anthraquinonic acid.
Anthraquinone, and sulphuric acid (sp. gr. 1. 848), in the proportions of 1 to 3 parts by weight, axe heated in a glass or porcelain re,tort at 260° (500° F.) till the former is completely con verted, as shown by its complete solution in water. The mixture is then left to cool, and diluted with water, and the excess of sulphuric acid is removed by the cautious addition of carbonate lime ; the sulphate is removed by filtration, and the filtrate is treated with carbonate soda or potash, to remove any traces of lime ; the evaporation of clear solution leaves the sulpho-acids of anthra quinone combined with the alkali.
- It has been found that there is no need to convert the anthracene first into anthmquinone ; the same results are attained by converting anthraceue into sulpho-anthracenie acids, and then oxidizing into sulpho-anthraquinonic acids. Anthracene, and sulphuric acid (sp. gr. 1.848), in the proportion of 1 to 1 parts by weight, are heated for about three hours at 109° (212° F.), and the heat is then raised to 149° (300° F.), and maintained till an entirely soluble product is obtained. This is diluted with about three times its weight of water, and to the solution is added, for every 1 lb. anthracene employed, 2-3 lb. manganic dioxide, so that on boiling, the oxidation may be complete. The free sulphuric acid and oxide manganese are removed by milk of lime, which is added till the reaction is alkaline ; carbonate soda Or potash, added to the filtrate, removes the lime, and yields the alkaline salt irr solution. Peroxide lead, chromic acid, nitric acid, or other acids capable of effe,cting the desired oxidation, may be employed. It is necessary, however, if the oxidant be soluble, to remove its excess before carrying out the second part of the process : nitric acid may be driven off by evaporation ; chromic acid, and peroxide lead, may be acted on by a current of sulphuretted hydrogen, or sulphurous acid. According to another plan, anthracene,
I part, and sulphuric acid, 4-6 parts, are boiled for some time, diluted with water, and neutralized with carbonate lime or rttryta, or caustic alkali ; the resulting sulphates of lime or baryta are removed by filtration, and the clear solution is heated at 180°-200° (356°-392° F.) To convert anthracene into chloro-anthracene, and afterwards into sulpho-anthraquinonic acid, the anthracene in fine powder is spread out, in contact with chlorine, on leaden trays, for about twenty-four hours ; this crude dichlor-anthracene may be used at once, or after purification by crystallizing from benzol. One part of it is mixed with 4-5 parts fuming sulphuric acid, and excess of binoxide manganese, and the whole is heated at 112°-149° (231°-300° F.) till it will dissolve in boiling water. Tbe product is diluted with three or four times its bulk of water, and well boiled with excess of binoxide manganese, till the diluted solution does not appear fluorescent ; it is then poured off, and milk of lime is added until the solution is alkaline ; the whole is well boiled and filtered, and the residue on the filter is well washed. The filtrate is concentrated, and carbonate potash or soda is added until all the lime is preCipitated.
Nitro-compounds.—Meister, Lucius and Briining!s method of oxidizing anthrac,ene into authra quinone by nitric acid, with formation of nitro-anthraquinones, is objected to as causing a serious loss ; the fact, however, of this patent (1872, No. 2649) beiug extensively worked in England con. tradicts the existence of any great obstacle, even if a loss can be established ; and it is not improbable that the loss (if any) has been due to impurities and their subsequent elimination, or intermediate reaction due to their presence ; probably the use of nitric acid in such quantities as to produce only mono-nitro-anthraquinone may explain why nitric acid has not been an advan tageous oxidizer. Highly purified anthracene, melting at 207°-210° (405°-410° F.), is heated for some time with a mixture of bichromate potash and dilute nitric acid ; the product is boiled for three hours with six parts by weight of fuming 'nitric acid (sp. gr. 1.50); this yields a yellow solution ; from this, after boiling, and addition of water, is formed a yellowish precipitate, which consists principally of dinitro-anthraquinone. The acid liquor is filtered off, and may be used in the oxidation of a further quantity of anthracene.