Goa Powder(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.

Goa powder, also known as araroba or crude chrysarobin, is a substance found in the trunk of the Andira araroba, a tree growing in Bahia, Brazil. It is scraped out of the cavities, and consists of an umber-brown powder, usually admixed with woody fragments, from which it is freed by sifting. It is employed in medicine in the form of an ointment for parasitic affections of the skin.

Goa powder was first examined in 1875 by Attfield (Pharra. J., (111), 5, 721), who considered it to consist largely of chrysophanic acid.

Liebermann and Seidler (Ber., 11, 1603) also detected the presence of chrysophanic acid in this drug, but showed that the main constituent is chrysarobin C₃₀H₂₆O₇, from which chrysophanic acid can be obtained by oxidation. Hesse (Annalen, 1899, 309, 32) as the result of his examination considered that chrysophanic acid is not present in Goa powder, but that the latter consists of two parts of chrysarobin C₁₅H₁₂O₃ and one part of chrysarobin methyl ether. Chrysarobin he found to be isomeric with chrysophan-hydranthrone, into which it was converted by the action of hydrochloric or hydriodic acids, but on acetylating this latter the reverse change takes place, triacetyl -chrysarobin being formed. Jowett and Potter (Chem. Soc. Trans., 1902, 81, 1575) considered, however, that chrysarobin and the chrysophan-hydranthrone of Liebermann and Seidler are identical, and that moreover the other constituents of Goa powder were dichrysarobin C₃₀H₂₄O₇, dichry sarobin methyl ether C₃₀H₂₃O₇CH₃, and a substance C₁₇H₁₄O₄. For dichrysarobin which yielded the same oxidation and reduction products as chrysarobin, the following constitution was suggested by these authors: [KUVA PUUTTUU]

Oesterle and Johann in 1910 (Arch. Pharm., 248, 476) obtained emodin methyl ether from chrysarobin, and suggested that the dichrysarobin of Jowett and Potter was not a pure compound.

Finally, Tutin and Clewer (Chem. Soc. Trans., 1912, 101, 290), by a very exhaustive examination of Goa powder, have determined the exact nature of the substances it contains. According to these authors, the commercial product is somewhat variable as to the relative proportion of the substances present, some samples being devoid of certain constituents which are present in others. Those invariably present, however, are chrysophanic acid, emodin methyl ether, the anthranols of these compounds, and the methyl ether of dehydroemodinanthranol, C₁₆H₁₂O₄. One sample, again, contained free emodin, and in two others a new compound, ararobinol, C₂₃H₁₆O₃, was found to exist. The chrysarobin of Jowett and Potter was a mixture of chrysophanol-anthranol and emodinanthranol, and their dichrysarobin, of chrysophanol-anthranol and the monomethyl ether of dehydroemodinanthranol.

Ararobinol, C₂₃H₁₆O₅, crystallises in yellow flattened crystals which decompose about 225°, and possess no definite melting-point. It is insoluble in 1.5 per cent, aqueous potassium hydroxide, but dissolves in a 10 per cent, solution of the alkali to form a yellow liquid. Very characteristic is its reaction with sulphuric acid with which it at first acquires an orange colour. On shaking, the liquid gradually becomes blue and this subsequently passes through green, to a dull grey tint.

Oxidised with chromic acid, ararobinol gives chrysophanol, and when reduced with hydriodic acid dihydro-ararobinol, C₂₃H₁₈O₅, greenish-yellow plates, is produced. Triacetyl-ararobinol,
C₂₃H₁₃O₅(C₂H₃₀)₃,
nearly colourless flattened prisms, decomposes at 225°.

Dehydro-emodinanthranol monomethyl ether, C₁₆H₁₂O₄, forms pale yellow needles, which melt and decompose at 265°. It oxidises with greater difficulty than the anthranols, and probably differs from the monomethyl ether of emodin-anthranol by two atoms of hydrogen. Its constitution, according to Tutin and Clewer, can be represented as follows: [KUVA PUUTTUU]

Hydriodic acid converts it into emodin-anthranol, melting-point 255°, and by oxidation with chromic acid, emodin monomethyl ether is produced.