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.
It has long been known that clover flowers dye a yellow colour on aluminium mordanted fabrics, and in the past they have been employed to a minor extent for dyeing purposes. Three varieties have been chemically examined, viz. those derived from the Trifolium pratense, the T. incarnatum, and the T. repens.
Trifolium pratense
The flowers known as the "common red clover," according to Power and Salway (Chem. Soc. Trans., 1910, 97, 231), contain in addition to isorhamnetin (quercetin monomethyl ether) and a glucoside of quercetin, melting-point 235°, numerous other phenolic substances, which, judging by their chemical properties, appear to be closely allied to the colouring matters of the flavone group. These are described below.
Pratol, C15H8O2(OH).OCH3, colourless needles, melting-point 253°, readily soluble in hot aqueous sodium carbonate and sodium hydroxide with a pale yellow coloration, yields the acetyl compound, C15H8O2(OC2H3O).OCH3, and is probably a hydroxymethoxyflavone.
A new yellow compound, C18H10O7, thin yellow plates, melting point about 280°, is soluble in alkalis with a yellow colour, and its solution in sulphuric acid exhibits a brilliant green fluorescence. It contains a methoxy group and gives an acetyl compound, C16H6O7(C2H30)4l melting-point 145-147°.
Pratensol, C17H9O2(OH)3, is very readily soluble in alcohol, dissolves in alkali carbonates yielding yellow solutions, and its alcoholic solution gives with ferric chloride a greenish-black coloration. Triacetylpratensol, C17H9O5(C2H3O)3, colourless slender needles, melts at 189°.
A new phenolic substance, C15H7O3(OH)3, colourless needles, melting-point 225°, is soluble in alkali hydroxides, and gives with alcoholic ferric chloride a dark green coloration. The acetyl derivative, silky needles, has melting-point 209°.
The glucoside trifolin, C22H22O11, H2O, pale yellow needles, melts and decomposes at about 260°. It is soluble in alkalis with an intense yellow coloration, and dissolves in sulphuric acid, forming a yellow solution, which rapidly develops a brilliant green fluorescence. When hydrolysed it yields rhamnose and trifolitin, C16H10O6, melting-point about 275°, readily soluble in alcohol,
C22H22O11 = C16H10O6 + C6H12O5
* Both in its melting-point and that of its acetyl derivative there is a marked resemblance between trifolitin and kaempferol.Alkalis dissolve trifolitin with an intense yellow colour, alcoholic ferric chloride gives a dark green coloration, and alcoholic lead acetate an orange-yellow lead salt. It contains no methoxy group, and is unaltered when heated for several hours with 30 per cent, aqueous potassium hydroxide. It does not appear to belong to the flavone group, and differs from the flavone compounds by the fact that it does not give an oxonium salt with sulphuric acid, and only with difficulty a potassium compound by means of alcoholic potassium acetate. It may possibly consist of a tetrahydroxyphenylnaphthoquinone. The acetyl compound when rapidly heated melted at 116°, re-solidified at a higher temperature, and finally melted at 182°.*
The glucoside isotrifolin, C22H22O11, isomeric with trifolin, consists of pale yellow needles, melting-point about 250°, and when hydrolysed yields similarly to the latter trifolitin, C16H10O6, melting-point 275°. Though in general behaviour it is very similar to trifolin, it is much more soluble in alcohol, and does not appear to be identical with this glucoside.
In addition to these compounds the flowers contain salicylic acid, coumaric acid, myricyl alcohol, C31H63OH, heptacosane, C27H56, hentriacontane, C31H64, sitosterol, C27H46O, trifolianol, C21H34O2(OH)2, palmitic, stcaric, linolic, oleic, linolenic, and isolinotenic acids.
Trifolium incarnatum.
A considerable difference is exhibited between the constituents of the "carnation or crimson clover flowers" and those of the T. pratense or "common red clover".
According to Rogerson (Chem. Soc. Trans., 1910, 97, 1006) these flowers contain pratol, C15H8O2(OH)(OCH3), free quercetin, and a glucoside of quercetin, C21H20O12, 3H2O, to which the name incarnatrin is applied. This latter crystallises in yellow prismatic needles, melting-point 242-245°, dissolves in sulphuric acid with formation of a green fluorescent solution, and when hydrolysed yields quercetin and glucose according to the equation
C21H20O12+H2O=C15H10O7+C5H12O6
Incarnatrin is not identical with the quercimeritrin of Perkin (Chem. Soc. Trans., 1909, 95, 2181).
In addition to these substances the flowers yield furfuraldehyde, benzoic and salicylic acids, a trace of p-coumaric acid, incarnatyl alcohol, C34H69OH, hentriacontane, C31H64, a phytosterol, C27H46O, and palmitic, stearic, oleic, linolenic, and isolinolenic acids.
Trifolium repens.
The flowers of the white clover, T. repens, according to Perkin and Phipps (Chem. Soc. Trans., 1904, 85, 58), owe their tinctorial property to quercetin which is present as glucoside.
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