Daphnetin.(CHAPTER X. α-Pyrone or Coumarin 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.

Daphnetin is present in the form of its glucoside daphnin in the bark of the Daphne alpina (Linn.) and D. mezereum (Linn.).

The concentrated alcoholic extract is digested with boiling water, filtered, and treated with lead acetate solution. The precipitate is removed, basic lead acetate added to the filtrate, the lead compound of the glucoside decomposed with sulphuretted hydrogen, and the solution evaporated (Zwenger, Annalen, 115, 8).

Daphnin, C₁₅H₁₆O₉, 2H₂O, crystallises in prisms, melting at 200°, and dissolves in alkaline solutions with a yellow colour. It is hydrolysed by boiling dilute acids with formation of daphnetin and glucose, _Cl5H₁₆O₉ + H₂O = C₉H₆O₄ + C₆H₁₂O₆.

Daphnetin, C₉H₆O₄, forms pale yellow needles, is soluble in alkalis with a yellow colour, and gives a yellow precipitate with lead acetate solution. On acetylation, a diacetyl-derivative, C₀H₄O₄(C₂H₃₀)₂, is obtained, and by means of ethyl iodide a diethyl ether, C₉H₄O₂(OEt)₂, is produced. When daphnetin diethyl ether is boiled with caustic soda solution, the diethyl ether of daphnetinic acid, is produced in the form of its sodium salt, which when ethylated gives the i derivative.

By oxidising daphnetinic acid triethyl ether triethoxybenzaldehyde is formed, which is readily converted into triethoxybenzoic acid. The silver salt of this acid, when destructively distilled, gives pyrogallol triethyl ether. Daphnetin is accordingly a dihydroxycoumarin, and has the following constitution [KUVA PUUTTUU] (Will and Yung, Ber., 1884, 17, 1081).

It has been synthetically prepared by heating pyrogallol with malic acid in the presence of sulphuric acid (Pechmann, Ber., 17, 933), C₄H₆O₅ + C₉H₃(OH)₃ = C₉H₆O₄ + CO₂ + 2H₂O + H₂, and by the condensation of pyrogallic aldehyde with sodium acetate (Gattermann and Koebner, Ber., 1899, 32, 287) -
C₆H₂(OH)₃. CHO + CH₃. COOH = C₉H₆O₄ + 2H₂O

Daphnetin is a yellow colouring matter, and gives with mordanted woollen cloth the following shades:
Chromium. Olive-yellow.
Aluminium. Pale olive-yellow.
Tin. Very pale yellow.
Iron. Olive-black.
(Perkin and Wilson, Chem. Soc. Trans., 1903, 83, 134).