The constituents of rhubarb / by Frank Tutin and Hubert W.B. Clewer.

  • Tutin, Frank.
Date:
1911
Catalogue details

Licence: In copyright

Credit: The constituents of rhubarb / by Frank Tutin and Hubert W.B. Clewer. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    11/29 page 954
    dibenzoyl derivative (m. p. 225°). The product of the benzoylation of emodin, as obtained by the present authors, consisted, however, entirely of tribenzoylemodin (m. p. 186°). Emodin was benzoylated by the Schotten-Baumann method, and the product crystallised from glacial acetic acid. Small, nodular masses, consisting of minute, pale yellow needles, were thus obtained, which melted at 186°: 0'1034 gave 0'2804 CO, and 0'0366 HoO. C = 74'0; H = 3'9. C3gH220g requires C = 74'2; H = 3'8 per cent. Isolation of Rheinolic Acid, The pyridine mother liquors from the emodin were concentrated, and the solution then poured into a quantity of ether. This caused a product to be precipitated, which, on examination, proved to be rhein, together with some amorphous material. The ethereal filtrate was then extracted with an aqueous solution of ammonium carbonate, when, on acidif3ung the alkaline liquid, a reddish- coloured powder was precipitated. This product was collected, and crystallised several times from pyridine, when dark red, lustrous needles were obtained, which, on drying at 130°, lost pyridine, and then melted at 295—297°, previously changing slightly at 290°: 0-1086 gave 0-2613 COg and 0’0329 HoO. C = 65-6; H = 3-4. 0-0748 „ 0-1797 COg „ 0-0244 H.p. C = 65-5; H = 3-6. C]7H]qOq requires C = 65-8; H = 3-2 per cent. This substance is therefore seen to be a new compound, possessing the formula C17HJ0O3, and it is proposed to designate it as rheinolic acid, -with consideration of the fact that it is a carboxylic acid, and also contains at least one hydroxyl group. Rheinolic acid is rather more soluble in the usual solvents than is rhein, and it is also of a much more pronounced red colour than the latter. Its homogeneity was confirmed by converting it into its acetyl derivative, which, after several recrystalUsations, was hydrolysed, when rheinolic acid was regenerated, possessing the same properties as before its acetylation. Acetylrheinolic acid crystallises in rosettes of small, orange-coloured needles, which melt at 236°. It quickly dissolves in cold aqueous sodium carbonate, thus indicating the presence of a carboxyl group. Rheinolic acid is evidently an anthraquinone derivative, as it dissolves in both alkalis and concentrated sulphuric acid with an intense red colour, but differs from rhein, inasmuch as it is not reprecipitated by the addition of water to its dilute solution in the latter solvent. Rheinolic acid is probably related structurally to rhein, but since it differs from the latter by the increment of the
    digitised image 1
    digitised image 2
    digitised image 3