Rhubarb, Chrysophanic acid(CHAPTER I. The Anthraquinone Group.)(Osa artikkelista)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

CHRYSOPHANIC ACID.

Chrysophanic acid, C₁₅H₁₀O₄, as obtained from rhubarb is contaminated with emodin methyl ether which is difficult to remove by fractional crystallisation, and on this account a considerable variation in its melting-point is to be observed in the earlier literature. The difficulty in removing the emodin methyl ether can be overcome according to Oesterle (Arch. Pharm., 1905, 243, 434) by heating the crude substance in benzene solution with aluminium chloride. This demethylates the emodin which can then readily be eliminated by crystallisation and the pure chrysophanic acid isolated in brownish-yellow leaflets, melting-point 196° (Tutin and Clewer, loc. cit.). Chrysophanic acid is insoluble in cold solutions of the alkali carbonates, but dissolves in dilute caustic alkalis with a cherry-red colour, and from this solution the calcium salt is deposited by addition of lime water. Distilled, as already indicated, with zinc-dust it yields, according to Liebermann and Seidler, β-methylanthracene, but according to Jowett and Potter (Chem. Soc. Trans., 1903, 83, 1327), owing to the great similarity which exists between the isomeric methylanthracenes, this cannot be regarded as proven.

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Though chrysophanic acid has long been considered as devoid of tinctorial property, according to Rüpe (loc. cit.) this is incorrect.

By employing mordanted and unmordanted wool the following shades may be obtained:
Aluminium. Red-yellow
Chromium. Dull yellow.
Without Mordant. Citron-yellow.

As already indicated, chrysophanic acid is present in the lichen Parmelia parietina, and among other sources are the Squamaria elegans (Thomson, Annalen, 53, 260), the root of the Rumex obtusifolius (Thann, Annalen, 1858, 107, 324), Rumex ecklonianus (Tutin and Clewer, Chem. Soc. Trans., 1910, 97, 1), Rumex nepalensis (Hesse, Annalen d. Chemie u. Pharmacie, 1896, 291, 306), Cascara sagrada (Leprince, Comptes rend., 1899, 129 60), and in the bark of the Rhamnus frangula (Limousin, J. Pharm. Chim., 1885, 80).

Rhubarb(CHAPTER I. The Anthraquinone Group.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Probably no natural product has been so frequently examined as rhubarb root (Rheum officinale), but only those communications which appear to be of sufficient importance will be dealt with here. Geiger (Annalen, 1823, 8, 47; 1824, 9, 91) isolated from the root a substance, "rhabarberin," which he termed its most important constituent, in the form of small wart-like crystals, and this was later shown by Schlossberger and Dopping (ibid., 1844, 50, 214) to be identical with the chrysophanic acid described by Rochleder and Heldt (Ann. Chem. Pharm., 1843, 48, 12) as present in the wall lichen (Parmelia parietina). W. de la Rue and Miiller by extracting the root (Chem. Soc. Trans., 1857, 10, 298) with benzene and treating the residue with sodium carbonate solution, separated it into two portions, namely, chrysophanic acid, which remains undissolved, and emodin, which passes into solution.

Liebermann and Seidler (Annalen, 212, 36) by distilling chrysophanic acid with zinc-dust obtained methylanthracene, and gave it the constitution of a dihydroxymethylanthraquinone, and whereas emodin consisted ofa trihydroxymethylanthraquinone (Liebermann, Annalen, 183, 176), it appeared that these compounds were related in the same way as purpurin and alizarin. Much more recently Hesse (Annalen, 1899, 309, 32) found that rhubarb contains rhein, and in addition to this isolated rhabarberon, isomeric with emodin, and a third compound containing a methoxy group presumably chrysophanic acid methyl ether.

Eyken (Pharm. Weekblad, 1904, 41, 177), again, besides chrysophanic acid, emodin, and rhein, obtained iso-emodin, evidently identical with Hesse's rhabarberon, whereas Oesterle and Johann (Arch. Pharm., 1910, 248, 476) indicated that Hesse's third compound, containing a methoxy group, was the emodin methyl ether previously isolated by Tutin and Clewer from the Rumex ecklonianus (Meissner). This in reality was first described by Perkin and Hummel as present in the root-bark of the Ventilago madraspatana (Chem. Soc. Trans., 1894, 65, 940), and that of the Polygonum cuspidatum (ibid., 67, 1084). That rhubarb contains glucosides was shown by Tschirch and Heuberger (Arch. Pharm., 1902, 204, 596), and one of these compounds, chrysophanein, a glucoside of chrysophanic acid, has been described by Gilson (Arch. Internat. de Pharmakadynamie et de Therapie, 1905, 487).

The latest and most systematic examination of rhubarb root was carried out by Tutin and Clewer (Chem. Soc. Trans., 1911, 99, 946), who have shown that the iso-emodin of Tschirch and Eyken and the rhabarberon of Hesse consist of aloe-emodin, and moreover, in addition to these a fifth anthraquinone derivative, rheinolic acid, is also present. Rhein, emodin, aloe-emodin, emodin monomethyl ether, and chrysophanic acid exist in the root partly in the form of glucoside, though it was not found possible by these authors to separate the individual constituents of this glucoside mixture. More recently the interesting discovery has been made by Müller (Trans. Chem. Soc., 1911, 96, 967) that alizarin is present in this drug.

Rhubarb root contains also gallic acid, cinnamic acid, and a non-glucosidic resin, to which latter the purgative actions of this drug are mainly due. On the other hand, emodin and chrysophanic acid possess this property in a mild degree.