Rhamnus catharticus(CHAPTER VII. Flavonol 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.

The Rhamnus catharticus or Purging Buckthorn, indigenous to Great Britain, is a stiff many-branched shrub growing from five to ten feet high, the fruit of which consists of small berries, resembling when dry black pepper-corns. Formerly it was in great demand as a medicine, but has now fallen into disrepute. The juice of the berries admixed with lime and evaporated to dryness constitutes the pigment known as "sap" or "bladder green". According to Tschirch and Polacco (Arch. Pharm., 1900, 238, 459) the yellow tinctorial constituents yielded by the berries of this plant are quite distinct from those given by the berries of the various species of Rhamnus which constitute the Persian berry proper. Thus in addition to rhamno-emodine they isolated four yellow crystalline substances, rhamnocitrin, β-rhamnocitrin, rhamnochrysin, and rhamnolutin. Rhamnocitrin was considered to consist of the trihydroxy derivative of a dihydroxanthone [KUVA PUUTTUU] rhamnolutin of a tetrahydroxyflavone isomeric with luteolin and fisetin, and rhamnochrysin an oxidation product of rhamnocitrin, whereas β-rhamnocitrin was distinct from rhamnetin and indeed contains no methoxy groups.

Valiaschko and Krasowski (J. Russ. Phys. Chem. Soc., 1908, 40, 1502) and Krasowski (ibid., 1510) criticised this paper of Tschirch and Polacco, and could not isolate the compounds described by these latter authors. On the other hand, quercetin, rhamnetin, and xanthorhamnin, the glucoside of rhamnetin, were found to exist in these berries, and it seemed likely that the rhamnolutin of Tschirch and Polacco was rhamnetin and their rhamnochrysin a mixture of quercetin and emodine.

Oesch and Perkin (Chem. Soc. Trans., 1914, 105, 2350) also isolated rhamnetin from these berries, together with a small amount of quercetin, and considered that the former represents the β-rhamnocitrin of Tschirch and Polacco. The main colouring matter present, however, is kaempferol, C₁₅H₁₀O₆, the trihydroxyflavonol which can be obtained from the flowers of the Delphinium salil and D. consolida, and this is to be regarded as the so-called "rhamnolutin".

A fourth compound, evidently the rhamnocitrin of these latter authors, possessed the formula C₁₆H₁₂O₆, rather than C₁₅H₁₀O₅ which they assigned to it. This crystallised in yellow leaflets, melting-point 221-222°, and its acetyl derivative at 200-201°, and these melting-points are practically the same as those given by Tschirch and Polacco. It contains one methoxy group, by the action of hydriodic acid yields kaempferol, and is evidently a kaempferol monomethyl ether. It bears considerable resemblance to kaempferide, a monomethyl ether of kaempferol present in Galanga root, Alpinia officinarum (Jahresber., 1881, 14, 2385), which, however, melts at 227-229°, and its acetyl derivative at 193-195°, and though there is thus strong probability that the two compounds are not identical, Oesch and Perkin suggest that further work on this point is desirable.