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.
The Gentiana lutea (Linn.), from which the gentian root is derived, chiefly occurs in mountainous districts, especially in Switzerland and the Tyrol. There is present in the root of this and other species of gentiana a bitter principle which is said to possess valuable tonic virtues, and on this account some quantity of the material is imported into this country for medicinal purposes.
Gentisin, the colouring matter of gentian root, was first isolated by Henry and Caventou (J. Pharm. Chim., 1821, 178), and was shown by Baumert (Annalen, 62, 106) to possess the formula C14H10O6. Hlasiwetz and Habermann (ibid., 175, 63; 180, 343), somewhat later, found that gentisin contains two hydroxyl groups, and that, when fused with potassium hydrate, phlorglucinol and gentisic acid (hydroquinone carboxylic acid) are produced from it. By the action of hydrochloric acid on gentisin, methyl chloride was evolved, a probable indication of the presence of a methoxy group. To prepare gentisin (Baumert, loc. cit.}, the root is well washed with water, then extracted with alcohol, and the extract evaporated to a small bulk. The residue is washed with water to remove the bitter principle, and then with ether to extract plant wax. For purification, the crude colouring matter is repeatedly crystallised from alcohol; 10 kilos, of the root yield about 4 grams of the substance. Gentisin crystallises in yellow needles, is sparingly soluble in alcohol, and dissolves in alkaline solutions with a yellow colour.
Gentisein, C13H8O5, 2H2O. When gentisin is digested with boiling hydriodic acid, it is converted into gentisein with evolution of i molecule of methyl iodide. Gentisein consists of straw-yellow needles, melting at 315°, and gives with sodium amalgam a bloodred coloration, whereas gentisin, by a similar method, yields a deep green coloured liquid (v. Kostanecki, Monatsh., 12, 205). By the action of acetic anhydride, gentisein is converted into the triacetyl derivative, C13H5O5(C2H3O)3, needles, melting-point 226° (v. Kostanecki, loc. cit.}; but on methylation with methyl iodide, a dimethyl ether, C13H5O2(OH)OCH3)2, yellow needles, melting-point 167°, is produced (v. Kostanecki and Schmidt, Monatsh., 12, 318).
Partial methylation converts gentisein into gentisin, and it is thus certain that the latter consists of gentisein monomethyl ether. v. Kostanecki and Tambor (Monatsh., 15, 1) obtained gentisein by distilling a mixture of phloroglucinol and hydroquinone carboxylic acid with acetic anhydride and its constitution is therefore represented as 1:3:7 trihydroxyxanthone. By a study of disazobenzene-gentisin, C14H8O5(C6H5N2)2, scarlet-red needles, melting-point 251-252° (Perkin, Chem. Soc. Trans., 73, 1028), which gives the diacetyl derivative,
C14H6O5(C2H30)2(C6H5N2)2,
orange-red needles, melting-point 218-220°, it has been shown that gentisin itself possesses the constitution. As gentisin yields by means of methyl iodide only a monomethyl ether, the original methoxy group cannot be in the position (1). On the other hand, if gentisin is represented by the formula (2) [KUVAT PUUTTUVAT], the azobenzene groups would enter the positions 4 and 2, and from such a compound an acetyl derivative cannot be obtained in the ordinary manner (compare disazobenzene phloroglucinol).
Gentisin is a feeble dyestuff, and gives on wool mordanted with chromium, aluminium, and tin, respectively, pale green-yellow, pale bright yellow, and very pale cream-coloured shades (Perkin and Hummel, Chem. Soc. Trans., 1896, 69, 1290).
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