Lotus arabicus(CHAPTER V. The Flavone 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 L. arabicus (Linn.) is a leguminous plant, indigenous to Egypt and Northern Africa, and in the young condition is extremely poisonous. It has been investigated by Dunstan and Henry (Phil. Trans., 1901, 194, 515).

Lotusin, the active principle, can be isolated by extracting the dried plant with methyl alcohol. The extract is evaporated, the residue treated with water to remove chlorophyll and resin, and from the aqueous solution tannin and other impurities are precipitated by means of lead acetate. The nitrate, on evaporation, leaves a syrupy residue, from which crystals of lotusin slowly separate. In the pure condition lotusin, C₂₈H₃₁NO₁₆, forms yellow needles, and when hydrolysed by digestion with hydrochloric acid, or by means of an enzyme lotase, also found in the plant, yields dextrose, lotoflavin, and hydrocyanic acid, according to the following equation:
C₂₈H₃₁O₁₆N + 2H₂O = 2C₆H₁₂O₆ + C₁₅H₁₀O₆ + HCN

When warmed with alcoholic potash (20 per cent.) lotusin is gradually decomposed with production of ammonia and lotusinic acid:
C₂₈H₃₁O₁₆N + 2H₂O = C₂₈H₃₂O₁₈ + NH₃ (Lotusinic acid.)

This compound is monobasic, gives yellow crystalline salts, and is hydrolysed by dilute hydrochloric acid with formation of lotoflavin dextrose and heptogluconic acid:
C₂₈H₃₂O₁₈ + 2H2 = C₁₅H₁₀O₆; + C₆H₁₂O₆ + C₇H₁₄O₈

Lotoflavin, C₁₅H₁₀O₆, crystallises in yellow needles, soluble in alkaline solutions with a yellow colour. By fusion with alkali, phloroglucinol and β-resorcylic acid are produced.

With acetic anhydride lotoflavin gives a tetra-acetyl compound, C₁₅H₆O₆(C₂H₃O)₄, colourless needles, melting-point 176-178°, and when methylated by means of methyl iodide the trimethyl ether, C₁₅H₇O₃(OCH₃)₃, is obtained. This latter compound exists in two forms, viz. the a-form yellow rosettes, melting-point 125°, and the -form glistening needles, melting-point 175°, which are mutually convertible. Both varieties give by means of acetic anhydride the same monoacetyl-lotoflavin trimethyl ether, C₁₅H₆O₃(C₂H₃O)(OCH₃)₃, yellow needles, melting-point 147°.

According to Dunstan and Henry, lotoflavin is probably a tetrahydroxyflavone, possessing the formula [KUVA PUUTTUU]

The hydrolysis of the cyanogenetic glucoside lotusin, with formation of maltose, lotoflavin and hydrocyanic acid, may be expressed by the equation
C₂₈H₃₁NO₁₆ + H₂O = C₁₂H₂₂O₁₁ + C₁₅H₁₀O₆ + HCN

The following constitutions are respectively assigned to lotusin (1) and lotusinic acid (2): [KUVA]