The formation of both these azo-compounds would therefore take place in accordance with the following formula : HN C14H6(NH2)2O2+2NHO2=C11H。 N 0202+2H2O, Dioximidoamidoanthra- N,NO2 O2+4H2O, C1H ̧(NH2)2O2+4NHO,=C1H2| N,NO2 Tetraazoanthraquinon nitrite. The still more violently explosive compound, which hitherto has been only obtained once, is probably (N,NO3) CH N,NOO, Tetraazoanthraquinonnitrate. Generally speaking, the nitrogenous derivatives of aromatic bodies rich in carbon are far more manifold than those of such as are poor in the same element. a-Diazoanthraquinonnitrate, C1H,NO,NO3. If a current of nitrous acid is passed into the solution of the monamid in ethylic ether, the solution is decolourised after some time, and there falls a powder, pale, red, or sulphur yellow, of the composition above mentioned. The solution of the amid in acetic ether is gradually turned brown by nitrous acid without any precipitation. From the solution in chloroform is obtained a brown substance, not adapted for closer examination. This azo-compound dissolves sparingly in water with a reddish colour, which, in contact with caustic potassa, becomes immediately pale brown. It is much more soluble in alcohol and acetic ether; insoluble in ether. If heated with water, nitrogen gas is evolved in abundance, whilst yellow or brown flocks are deposited, and the liquid has an acid reaction due to free nitrous acid. The flocks, after filtration and drying, sublime, when heated in shining flat needles or lamellæ, lemon yellow or gold coloured, which display the reactions of oxyanthraquinon. The meltingpoint is about 2020. The transformation of the diazocompound into the hydroxylate ensues according to the equation C14H,N2O2NO2+H2O=C11H2O2OH+N2+NHO。; 14 2 whilst the azotised product obtained from the diamid is only converted into alizarin on fusion with potassa. The azocompound is moderately permanent, but it gradually gives off nitrous vapours, and, if heated, deflagrates slightly, leaving a carbonaceous residue. Methylanthraquinon, C15H1002. This compound is obtained by the oxidation of methylanthracen in an alcoholic solution, and melts at 162°-163°. It dissolves with moderate readiness in ether, aceton, chloroform, and boiling alcohol; sparingly in glacial acetic acid and benzol. From these solvents it separates in crystals or in minute yellow needles. If heated with zinc powder and soda lye it yields Liebermann's reaction for anthraquinon. If methylanthraquinon dissolved in sulphide of carbon is placed in a sealed tube with bromine and heated for some hours in the water-bath, the result is a finely crystallised bromine compound, which, if fused with caustic potassa at 180°-200°, yields a dye resembling alizarin. It is best obtained from the sulpho-acid. For this purpose methylanthraquinon is heated with five or six parts of fuming sulphuric acid to 250°-270° for several hours; the liquid, before it is quite cold, is poured into water and neutralised with carbonate of baryta or lime; the sparingly soluble baryta or lime salts are repeatedly extracted with boiling water, and the sulphate of baryta or lime is removed by filtration. The solutions of the baryta or lime salts are decomposed with carbonate of potash, and the filtered solution of the potash salt is evaporated to dryness. If the salt thus obtained is melted with excess of potassa at 200°, the mass soon displays the colour phenomena of an ordinary alizarin melt. Acids precipitate the colouring matter in yellowishbrown flocks. It is best purified by sublimation. It sublimes when heated above 200° in red tufts, or it is repeatedly recrystallised from alcohol and aceton, and thus obtained pure. Methylalizarin dissolves in alkalis with a blue violet colour. With salts of lime and baryta, it forms blue precipitates. The melting-point is from 250° to 252°. Methylalizarin dyes cotton mordanted with iron or alumina in shades closely resembling those produced by alizarin. Kundt, in his spectroscopic examinations, was unable to find any essential difference between methylalizarin and common alizarin. It is therefore for the present doubtful whether the methylalizarin did not contain an admixture of ordinary alizarin, which might easily occur during the fusion with potassa by abscission of the methyl group. Sulphanthraquinonic Acids. These acids were first described by Graebe and Liebermann along with Caro, and were obtained by these chemists on heating anthraquinon with sulphuric acid to 260°. They observed subsequently that the sulphanthraquinonic acids can be directly prepared from anthracen by dissolving it in sulphuric acid, and treating the sulphanthracenic acid with oxidising agents such as chromate of potash, nitric acid, or manganese, whereby the sulphanthracenic acid is converted into the sulphanthraquinonic. According to Auerbach, sulphanthraquinonic acid may also be obtained by heating anthracen with sulphuric acid to 212°, when SO, is given off, and the anthracen is oxidised to anthraquinonic acid. The two latter methods have, however, several disadvantages. They require, in the first place, a very pure anthracen, since, if an impure quality is used, the impurities are also converted into sulpho-acids, which can scarcely be separated from the sulphanthraquinonic acid, and which, on further treatment and conversion into alizarin, contaminate this also. In the second place, isomeric sulpho-acids seem to be formed, which, when melted with alkali, do not yield alizarin. Thirdly, even if chemically pure anthracen is employed, the respective preparation of the blue and the red shades of alizarin is not under control, since a mixture of the two sulpho-acids is always produced, and no homogeneous acid can be obtained in this manner on the large scale. The only practical method for obtaining the sulpho-acids is the one first mentioned, with anthraquinon and sulphuric acid, preferably fuming. According to circumstances-i.e. the higher or lower temperature, the larger or smaller proportion of acid, there is formed the mono- or the bisulpho-compound. If 1 part of anthraquinon and 3 parts of concentrated sulphuric acid are heated to about 260° till all anthraquinon has disappeared, and none consequently is separated on the addition of water to a portion taken out, we obtain a mixture of both acids. The one or the other predominates according as the heat has been applied for a longer or shorter time, and has reached a higher or lower degree. It has not yet been found practicable to show whether isomeric sulphoacids are formed during the process. The preparation of the several acids on the small scale is somewhat difficult. The mono-acid is found to predominate if anthraquinon is used in excess, and the mixture is heated to 250°-260°. The bi-acid is obtained on using sulphuric acid in excess and heating to 270°-280°. As both acids are but sparingly soluble in sulphuric acid, the mixture solidifies in both cases when the reaction is complete and it is allowed to cool. A considerable amount of water and a prolonged digestion are required to redissolve the whole. It is therefore advisable to pour the mixture cautiously into water before it is quite cold. From this solution calcium, barium, and lead salts may be obtained by known methods. The barium salts, on account of their sparing solubility in water, are well adapted for the isolation of the acids in experiments on the small scale. For large quantities the lime salts are used for separation from the excess of sulphuric acid. Weith and Bindschädler obtained phthalic acid as a bye-product during the formation of the sulpho-acids. It was produced when anthraquinon, purified by recrystallisation from sulphuric acid, was heated to 270° with 3 to 4 parts of fuming sulphuric acid. In order to place the formation of phthalic acid beyond doubt, they made the experiment with chemically pure anthraquinon, perfectly free from phthalic acid. This was heated for six hours to 270° with 4 parts of fuming sulphuric acid. Sulphurous acid was given off, and there sublimed colourless needles, an inch in length, which, from their melting-point (129°) and other properties, were found to be anhydrous phthalic acid. They dissolved in hot solutions of carbonate of soda, and on addition of acid and agitation with ether pure phthalic acid was obtained, with its characteristic properties. Their amount was 8 to 9 per cent. of the anthraquinon employed. This formation shows that anthraquinon is a keton of phthalic acid, and the latter may have been formed according to the following equation: |