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).