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Nitroalizarin, C1H5(NO2)(OH)2O2•

Perkin obtained this compound from diacetylalizarin, C1H(C2H2O)2O4, by the action of nitric acid. Rosenstiehl gives the following method for its preparation. Large flasks are coated internally with alizarin paste, which is allowed to dry, and they are then filled with the fumes of hyponitrous acid. After a few minutes the flasks are rinsed out with water and the insoluble part treated with soda. The soda salt of nitroalizarin dissolves in pure water, but is very sparingly soluble in presence of excess of alkali. Nitroalizarin is also obtained if we dissolve alizarin in glacial acetic acid and add nitrite of potassa. The nitro-compound is further obtained by treating alizarin dissolved in alcohol with nitrous acid; but in both these cases the yield is unsatisfactory, as a part of the alizarin is destroyed. Free nitroalizarin crystallises from chloroform in orange-red scales with a green reflection. It is capable of sublimation, but a large portion is destroyed. The compound which it forms with metallic oxides is more permanent than the corresponding alizarin derivatives. With iron mordants it gives a dark-red violet, but with aluminous mordants a fine orange-red.

On reduction, this compound yields, according to Perkin, amidoalizarin, but according to Rosenstiehl it forms two colouring matters which have not been closely examined.

This compound is obtained by heating alizarin with anhydrous acetic acid at 160° C. From alcohol it is obtained as an amorphous powder.

crystallises in golden yellow scales, and, like diacetylalizarin, is easily decomposed by alkalis.

This compound was obtained by Schützenberger, on heating iodide of ethyl with sodium alizarin.

C1H(NaO),O,+2 CH,. I=C1H(O. C2H),O,+2NaI.

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Iodide of ethyl and alizarate of sodium are heated in closed tubes to 120°. It is a clear yellow liquid, insoluble in water, but soluble in alkalis.

Bibenzoylalizarin, C11H6(OC,H,O),O2.

According to Schützenberger, this is obtained by heating chlorbenzoyl with alizarin in sealed tubes to 190° C. It is yellow, insoluble in water, soluble in alcohol, out of which it crystallises. In the cold it is insoluble in alkalis and ammonia. If heated with alkalis, it is decomposed into alizarin and benzoic acid.

Sulphalizarinic Acid.

Alizarin dissolves in sulphuric acid at moderate temperatures, but is precipitated unchanged on the addition of water. But if the temperature is raised, nothing is precipitated on the addition of water, the alizarin having been converted into a sulpho-acid. The acid is best precipitated from the solution with carbonate of lead, and the precipitate is decomposed with sulphuretted hydrogen, when the free acid is obtained in solution. With baryta and sugar of lead it yields a reddish-violet precipitate. In water the acid dissolves in every proportion with a yellow colour, and in potash-lye with a beautiful red. If it is melted with potash, which requires great care to avoid over-heating, the melt takes a violet colour. If supersaturated with acid, we obtain a precipitate which partly disappears on washing.

The residue remaining on the filter yields, on sublimation, a small quantity of a sublimate consisting of yellowish crystals, which dissolve in alkali with a violet colour. Trihydroxylanthraquinon is certainly formed in this process.

Very similar to this sulphalizarinic acid is the sulpho-acid obtained on heating anthracen to 240°-250° with sulphuric acid. If this acid is shaken with ether, the ethereal liquid drawn off and shaken with alkali, the latter takes a blueviolet colour. If the crude sulpho-acid is neutralised with lime for purification, the sulpho-compound of lime separated from the gypsum by filtration, and the solution decomposed with carbonate of soda, we obtain a deep-red solution of a sulpho-compound of soda, whilst the precipitated carbonate of lime is coloured a deep violet-blue. On melting the red sulpho-salt of soda with alkali, we obtain a violet solution, from which acids precipitate only a very little flocculent matter. If the melt is not precipitated till it has grown cold, we obtain more flocks, which, however, chiefly dissolve on washing. Perhaps the sulphuric acid has an oxidising effect upon the anthracen, so that sulphoalizarinic acid is formed directly. The transformation may be represented by the following equations :—

According to the formula of anthraquinon now universally assumed as correct, 10 isomeric bioxyanthraquinons are possible, of which nine are known, although not with sufficient accuracy. These are anthraflavic acid, isoanthraflavic acid, anthraxanthic acid, alizarin, quinizarin, chrysazin,

frangulic acid, xanthopurpurin, and isalizarin.

Concerning the structure and the position of the hydroxyls, little is known; and only in two, alizarin and quinizarin, can its position be given with certainty. Some of these isomers are true colouring-matters, that is, they dye mordanted tissues, whilst others do not. If we compare these bioxyanthraquinons with the mono- and trioxyanthraquinons, we find a very interesting agreement. The two monoxyanthraquinons known to us, oxyanthraquinon and erythryoxyanthraquinon, are not dyes; alizarin and quinizarin, probably also xanthopurpurin, are dyes, and the trioxyanthraquinons hitherto known are all dyes. Concerning alizarin and quinizarin, we know with certainty that both the hydroxyls are contained in one benzol-ring; in the trioxyquinons, two hydroxyls are always present in one benzol-ring. Hence the remarkable circumstance seems to appear, that an oxyanthraquinon derivative is only then a dye when at least two hydroxyls are contained in one benzol nucleus. Hence, xanthopurpurin may perhaps be the anthraquinon derivative corresponding to resorcin, whilst in all the other isomers the hydroxyls are distributed in both the benzol-rings.

Quinizarin, C1H ̧O1(1·4).

This substance was first obtained by Grimm according to Baeyer's method, the action of anhydrous phthalic acid upon phenols, i.e. in this case by heating a mixture of hydroquinon, phthalic acid, and sulphuric acid. If the melt is heated to 130°-140° C., two bodies are formed-a phthalein similar to phenol-phthalein, and a red colouring-matter isomeric with alizarin. In order to isolate the latter body, quinizarin in a state of purity, the crude melt is extracted, first with boiling water, and then with absolute alcohol, the latter extract being then precipitated with water Or the melt is treated with benzin (boiling-point 110°-120°), which

dissolves quinizarin readily, and phthalein but sparingly. It is purified by crystallisation from alcohol and ether. Not merely hydroquinon, but all the substances which produce it, when heated with sulphuric acid, yield quinizarin. Such, e.g., is the behaviour of quinic acid, which, if heated with sulphuric acid, yields a-bisulphohydroquinonic acid: further, the thiochronate of potassa, from which Graebe's B-bisulphohydroquinonic acid is first formed. The sulpho-acids themselves yield this compound; but it is remarkable that the two isomeric bisulpho-acids produce exactly the same quinizarin. If we assume that on the displacement of the two sulphogroups phthalein takes their place, we must conclude from this behaviour that one of the two isomeric bisulpho-acids, on heating with sulphuric acid, is converted into the other.

Quinizarin crystallises from ether in orange leaflets, but from benzin and alcohol in deep-red needles. From the alcoholic solution it is precipitated in yellowish-red flocks on dilution with water, which, if heated to 100°-110°, become darkred and crystalline. The solutions in ether and sulphuric acid are distinguished by a greenish-yellow fluorescence. The ethereal solution appears brownish-yellow by transmitted light; the sulphuric solution has a peculiar violet colour, which, on dilution, passes into a pale onion-red. A similar fluorescence is displayed by the munjistin obtained by Stenhouse from rubia munjith, a compound which possibly stands in the same relation to quinizarin as does purpurin to alizarin.

When heated, quinizarin sublimes in paler or darker needles and plumose crystals resembling alizarin, whilst a shining carbon is left behind. The melting-point of the sublimed body is from 1940-195°; that of the crystals obtained from alcohol 192°-193°.

With alkalis quinizarin yields blue solutions, with a faint violet cast; the ammoniacal solution displays a violet colour. It is most distinctly produced by the alkaline carbonates.