Coloriasto: 01/2025

29.1.25

Callistephin. Callistephin chloride. Pelargonenin. Pelargonenin chloride.
(CHAPTER VIII. Pyran Group. Derivates of Pelargonidin.)

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.

1. Monosaccharides.

Callistephin.

Callistephin is one of the two pigments isolated by Willstatter and Burdick (Annalen, 1916, 412, 149) from the flowers of purple-red asters (Callistephus chinensis, Nees, syn. Aster chinensis, L.), in which it occurs together with a larger quantity of asterin, a monoglucoside of cyanidin. The petals contain about 7,4 per cent, of their dry weight of the mixed pigments.

Of the several methods used for the isolation of the mixed pigment (asterin and Callistephin) from the flowers, it appears that the use of their lead salts produces the best results. Their value for this purpose was due to the discovery that glacial acetic acid dissolved the lead salts of the colouring matters but not those of the colourless impurities that accompanied them, and further, that by decomposition of the lead salts by propylalcoholic hydrochloric acid the colourless impurities remained insoluble whilst the alcohol retained the pigments in solution. Willstatter and Burdick used glacial acetic acid for the extraction of fresh or dried petals, but state that for the latter it is not so satisfactory, methyl alcohol containing a small percentage of hydrochloric acid being the best solvent. They proceeded in the following manner. The glacial acetic acid extract (8,9 lit. from 3,2 kg. petals) was precipitated, without addition of hydrochloric acid, by twice its volume of ether, and the product (65 gr. syrup, 10 per cent, pure) dissolved in 0,01 per cent. HCl (600 c.c.), filtered from insoluble residue, and the filtrate treated with a solution of lead acetate (12 gr. in 50 c.c. water) which completely precipitated the colouring matter. The product was collected, washed with 0,01 per cent. HCl, and treated whilst moist with glacial acetic acid (600 c.c.), filtered, and the filtrate diluted with twice its volume of ether, whereby the lead salts of the pigments were precipitated (147 gr.). When the product thus obtained was decomposed by treatment with propylalcohol (200 c.c.) containing 25 per cent, methyl alcoholic hydrochloric acid (20 c.c.), filtered, and the filtrate precipitated by addition of ether (600 c.c.), the anthocyan mixture was obtained 70 per cent, pure (6,5 gr.). On repetition of the process the chloride was obtained 85 per cent, pure (4 gr.), in which condition it was pure enough to yield a crystalline picrate, or for the purpose of separating callistephin from asterin. The product obtained as above was fractionated by solution in a mixture of methyl or ethyl alcohol and aqueous hydrochloric acid, allowing the alcohol to evaporate off slowly. From the earlier crops precipitated pure asterin was obtained, whereas from the mother liquors callistephin was isolated by addition of alcohol, then ether, or if sufficient alcohol was already present, by ether only. The precipitate produced was recrystallised from a mixture of alcohol and aqueous hydrochloric acid from which it separated in fine orange-red needles.

Callistephin chloride

Callistephin chloride, C₂₁H₂₁O₁₀Cl, crystallises in hair-fine, orangered needles which in bulk form a bronze-coloured mass; they contain 2-2½ molecules of water of crystallisation, and are hence of the same composition as crystalline pelargonenin chloride.

It is easily soluble in water, giving a yellowish-red solution which on dilution becomes tinged with violet and slowly decolorises owing to pseudo-base formation. In cold or hot alcohol it is easily soluble, the solution being yellow-red, but showing no fluorescence; it gives a red solution in amyl alcohol. The salt is characterised by great solubility in aqueous acid, being very easily soluble in hydrochloric acid up to 7 per cent, and fairly so in 10 per cent. solutions in higher per cent. HCl gelatinise on standing and is easily soluble in 7 per cent, sulphuric acid.

Ferric chloride gives no colour reaction with callistephin chloride; with sodium carbonate, or caustic soda, an acid solution of the salt passes to red-violet or violet-red.

The distribution number of callistephin resembles that for other normal monoglucoside anthocyans, and hydrolysis of callistephin chloride yields pelargonidin chloride (1 mol.) and glucose (1 mol.).

Pelargonenin.

Pelargonenin results from the careful partial hydrolysis of pelargonin (Willstatter and Bolton, Annalen, 1916, 412, 133), and has not as yet been discovered to occur naturally. 7 gr. pelargonin chloride are dissolved in cold concentrated hydrochloric acid (250 c.c.), filtered through glass wool and the solution allowed to stand. The separation of scarlet-red flakes soon commences, and after eighteen hours these are filtered off (ca. 1,6 gr.); the filtrate after the addition of further acid (100 c.c.) is left for three days, by which time some further (2 gr.) brown-red product has separated, which, however, has to be purified from pelargonidin; the residual liquor contains pelargonidin. The crude product is best purified by dissolving in 0,05 per cent. HCl (1,3 gr. in 150 c.c.), shaking twice with amylalcohol (100 c.c. and 75 c.c. respectively) this must be done rapidly to prevent precipitation of the pigment from the aqueous solution; after extraction and separation the amount of acid is increased to 2 per cent. HCl when the pigment separates in flakes. The product thus obtained is recrystallised from warm 2 per cent. HCl, when it is deposited in the form of fine scarlet-red needles.

Pelargonenin chloride

Pelargonenin chloride thus prepared has the composition C₂₁H₂₁O₁₀Cl.2H₂O (? 2½H_2O), loses 1 molecule of water on drying in vacuum desiccator, and the remainder in high vacuum, yielding the anhydrous salt C₂₁H₂₁O₁₀Cl. On hydrolysis each molecule of pelargonenin chloride yields 1 molecule of pelargonidin chloride and 1 molecule of glucose.

The salt is very difficultly soluble in cold water, dilute hydrochloric acid, or dilute sulphuric acid, but is more soluble in warm acids; its solutions in aqueous hydrochloric acid are yellower than corresponding solutions of pelargonidin chloride, but less yellow than those of pelargonin chloride. It is easily soluble in methyl alcohol which contains hydrochloric acid, and fairly so in ethyl alcohol in presence of the same acid; such solutions are intermediate in colour between those of the chlorides of pelargonidin and pelargonin, but they show much stronger fluorescence than those of the latter.

Of the reactions recorded the following may be mentioned. An acid solution on addition of sodium carbonate becomes violet, passing then to violet-blue (pelargonidin gives blue), and the violet-blue is more stable than the blue given by pelargonidin; if the solution of pelargonenin be alcoholic, addition of alkali gives a pure blue colour. Lead acetate added to an alcoholic solution of the salt gives a blue precipitate. Picric acid slowly causes precipitation of a crystalline picrate (needles) when added to a solution just acid with hydrochloric acid; ferric chloride produces no colour reaction.

The differences between callistephin chloride and pelargonenin chloride are well shown by the following data given by Willstatter and Burdick:

	Callistephin Chloride.	Pelargonenin Chloride.
Crystalline form.	Orange-red hair-fine needles.	Scarlet-red needles.
Solubility in H₂O	Easily soluble.	Slightly soluble.
" " HCl	Very easily soluble.	Very difficultly soluble.
Colour of acid solution	Yellow-red in alcohol, no fluorescence.	Yellow-red with bluish tint, strongfluorescence in alcohol.
Reaction with soda	Red-violet - violet-red.	Violet-blue. Concerning the monoglucoside produced from salvinin (he. cit.) in the same manner as pelargonenin is prepared from pelargonin, that is by partial hydrolysis, there is as yet but little known.

Pelargonidin.
(CHAPTER VIII. Pyran Group.)

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Pelargonidin occurs in the form of glucosides in various flowers. It was first isolated from the scarlet Pelargonium zonale (Meteor) hence its name; more recently also from the purple-red summer aster (Callistephus chinensis, Nees, syn. Aster chinensis, L.), the scarlet salvia (Salvia coccinea, L., and Salvia splendent, Sello.), and the rose-coloured corn-flower; whilst Willstatter and Bolton (Annalen, 1916, 412, 136), as the result of qualitative tests, conclude that the scarlet-red gladiolas also owe their colour to a pelargonidin derivative, and that traces are present in other gladiolas and in Zinnia elegans (Jacq.), of which the chief pigments are derivatives of cyanidin. Pelargonidin has also been prepared synthetically by Willstatter and Zechmeister, by the demethylation of the product obtained by the reaction of anisyl magnesium bromide on 3:5:7: trimethox-coumarin (Sitzber. d. K. Preuss. Akad. d. Wiss., 1914, 886).

Pelargonidin forms a crystalline chloride which has the composition C₁₅H₁₁O₅Cl, and the structure [KUVA PUUTTUU]

This yields a hydrate C₁₅H₁₁O₅Cl, H₂O, which does not lose its water of crystallisation on drying in air, vacuum exiccator, or even in high vacuum at 50° C, but does so completely in high vacuum at 105° C. By treatment with hot water, preferably in presence of a trace of sodium bicarbonate, the chloride yields a pseudo-base which crystallises in colourless four-sided prisms; this product when dry has the composition C₁₅H₁₂O₆.

Pelargonidin chloride is readily prepared from any of its naturally occurring glucosides by hydrolysis with hydrochloric acid. This change takes place slowly in the cold if concentrated acid is used, but for the preparation of pelargonidin the glucoside is preferably boiled for three minutes with 20 per cent, hydrochloric acid ('2 gr. glucoside with 15 c.c. acid), the resulting product cooled to 65°C. (if further cooled the substance is contaminated by a by-product mentioned below), the crystalline chloride filtered off, washed with cold 20 per cent, hydrochloric acid and dried.

In this process it has been observed that whilst the pelargonidin chloride separates in brown-yellow leaflets, there is always some 5 per cent, of another product present in the reaction mixture, and this separates in needles. This product closely resembles pelargonidin, both in properties and composition, and can be prepared from it by the action of concentrated hydrochloric acid, but the reverse change has not yet been accomplished. It follows from this that long boiling in the preparation of pelargonidin from its glucosides is disadvantageous.

Pelargonidin chloride crystallises in three forms which are described by Willstatter and Bolton (Annalen, 1915, 408, 42) thus:
(i) Long, not quite rectangular, red tablets somewhat resembling crystals of xanthophyll.
(ii) Short red-brown, usually straight cut, four-sided prisms. These separate from hot dilute acid.
(iii) Sharply formed swallow-tail twin crystals, in form resembling carotin, but yellow-brown by transmitted light when viewed under the microscope. These are obtained by precipitation with concentrated hydrochloric acid.

Pelargonidin chloride is much more soluble in acids than is the cyanidin salt, being described as difficultly soluble in cold dilute hydrochloric or sulphuric acid, though fairly easily soluble when the acids are warm, forming solutions which are orange-red; from the solution in sulphuric acid the sulphate crystallises in needles on cooling. In methyl or ethyl alcohol the chloride is very easily soluble, yielding solutions that have a violet tinge, but show no fluorescence (cf. pelargonin); these solutions are not precipitated by the addition of water (cf. cyanidin). An aqueous acid solution of the chloride when shaken with amyl alcohol gives up all the pigment to the alcoholic layer, and if the red alcoholic solution thus produced is shaken with an aqueous solution of an alkali acetate it becomes violet, whereas if shaken with aqueous sodium carbonate, the colour turns to a fine pure blue and passes completely to the aqueous layer. These changes are the same as those observed with cyanidin chloride.

With reagents, the following are the most important reactions. Lead acetate, when added to an alcoholic solution, produces a blue precipitate; ferric chloride to an aqueous solution gives no characteristic coloration, and to an alcoholic solution only a brown-red tint (difference from cyanidin); Fehling's solution is noticeably reduced if warm.

When heated in a melting-point tube, pelargonidin chloride becomes darker, but does not melt below 350° C.

The chloride dissolves in water without separation of violet flocks (cf. cyanidin), forming a red solution which on warming (in the cold, if very dilute) becomes colourless as a result of the formation of the pseudo-base; if warmed with acids the colour is regained. The distribution number with respect to amyl alcohol is normal for a non-glucoside anthocyan = 100.

Willstatter and Bolton (loc. cit.) state that the absorption spectrum of this salt consists of two bands, one covering the spectrum from yellow to blue, and another in the violet; both have edges that are badly defined. Thus far the presence of a band in the violet has not been observed in any other anthocyan, but they propose to reinvestigate this point photographically. Measurements given are:
Thickness of solution:... 2,5 mm.... 5 mm.... 10 mm.
Band I... 579---569-491---483... 588---576-471... 586---583-
Band II... 448-442 ... 448-... -

The action of caustic potash upon pelargonidin chloride has been studied, and it has been found that whilst 60 per cent. KOH, even at temperatures not above 100° C., yielded the phenolic decomposition product phloroglucinol it required much more concentrated caustic potash and higher temperatures to allow of the isolation of the acid decomposition product (p-hydroxy-benzoic acid). Thus 0,5 gr. of pelargonidin chloride were heated with 10 gr. KOH and 3 gr. water to 220° C., for two to three minutes; the product, after acidification, was extracted with ether and the ethereal extract shaken with sodium bicarbonate which leaves phloroglucinol in the ether from which it was isolated and identified; the aqueous layer yielded p-hydroxy-benzoic acid and a trace of protocatechuic acid. This production of protocatechuic acid resembles its formation from apigenin (Perkin, Chem. Soc. Trans., 1897, 805).

The Ψ Base, C₁₅H₁₂O₆. When pelargonidin chloride is heated with water (0,.5 gr. with 600 c.c.) a pseudo-base is formed. The chloride dissolves, then the solution becomes decolorised the addition of a small quantity of bicarbonate of soda (0,13 gr.) facilitates complete decolorisation and the base can be obtained from this solution by the addition of salt followed by the extraction of the product with ether. It is finally recrystallised from water at 50°C., and in this way the base separates in the form of four-sided prisms.

The base is very easily soluble in alcohol, ether, or hot water, less soluble in cold water, and insoluble in benzol. If a cold aqueous solution be acidified with hydrochloric acid it slowly deposits crystals of the chloride; if the solution is hot, the chloride is very rapidly formed. The base gives a bright yellow coloration on addition of sodium carbonate. No definite melting-point can be observed when the pure substance is heated, the crystals turn red, then very gradually soften till a dark violet oil is produced; melting not taking place below 350°C.

The Natural Pigments.
(CHAPTER VIII. Pyran Group. Anthocyanins and Anthocyanidins.)

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

As previously noted, it is an interesting fact that but very few fundamental compounds form the basis of the comparatively large number of anthocyan pigments that have now been examined. Thus far, all the known colouring matters of this series are derived from pelargonidin, cyanidin, or delphinidin, though from the most recent investigations there appears reason to hope that pigments of different origin may be isolated as the result of further work.

It is a curious coincidence that, before the investigation by Willstatter and Everest of cyanin and cyanidin was completed, it had been decided by them, as the result of preliminary experiments carried out in connection with the corn-flower work, that the pigments of the scarlet pelargonium and the wild larkspur (Delphinium consolida, L.) should be examined next Work had indeed been commenced on them, and thus the three above-mentioned fundamental pigments were the first to be investigated by Willstatter and his collaborators, to whom we owe most of our present knowledge of these colouring matters.

The experimental difficulties to be overcome in the investigation of these pigments were very great until Willstätter and Everest, in their work on the corn-flower pigment, made clear the essential conditions, and further, introduced a rapid test that would distinguish glucoside from non-glucoside pigments.

All the anthocyan colouring matters occur in plants in the form of glucosides, for the available evidence points to their being in nearly every case entirely in that condition. But a few instances have been definitely established in which a small percentage of sugar-free pigment accompanies the glucoside, and in only one exceptional case a considerable proportion of the total colour present was non-glucosidal.

The pigments, at present examined, occur in nature as monoor diglucosides, and the sugars that have been obtained by their hydrolysis are glucose, galactose, and rhamnose; by far the largest portion of the pigments being in combination with glucose only, a smaller number are rhamno-glucosides, whereas, as yet, galactose has only been isolated from one colouring matter of the series.

There are two very interesting abnormal cases of pigments (delphinin and salvianin) in which the natural colouring matter is not merely a complex containing the anthocyanidin combined with the sugar residues, but also with acid components. Thus delphinin, on hydrolysis, yields delphinidin, glucose, and /-oxybenzoic acid, whereas the pigment salvianin gives pelargonidin, glucose, and malonic acid. There is a further point of interest attached to the latter pigment, in that it does not appear to have the two molecules of glucose that it contains present as such, but in a derived form of the composition C₆H₁₀C₅, which is transformed into glucose on hydrolysis.

The three fundamental compounds forming the base of all the anthocyanins to be described below differ from one another only in the number of OH groups present in the molecule.

Pelargonidin, cyanidin, and delphinidin have been shown to have the structures represented by the formulæ (1), (2), and (3) respectively : [KUVA PUUTTUU] and hence are
3:5:7: trihydroxy-2-p-hydroxyphenyl-i: 4: benzopyranol anhydrochloride,
3:5:7: trihydroxy - 2: mp - dihydroxyphenyl -1:4- benzopyranol anhydrochloride, and
3:5:7: trihydroxy -2: mmp-trihydroxyphenyl-i: 4 - benzopyranol anhydrochloride.

Tinctorial Properties.
(CHAPTER VIII. Pyran Group. Anthocyanins and Anthocyanidins.)

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Though there are but few data available concerning the tinctorial properties of the anthocyan pigments, there can be little doubt that they are capable of acting as mordant colours, and it is interesting to find that, more than fifty years ago, the pigment of the black hollyhock was used in Germany particularly in Bavaria both for dyeing and printing. It is stated that the Bavarian Government encouraged the investigation of the chemical nature of this colouring matter, and that the work of Buchner, Eisner, and Kopp was the result (Bull, de la Soc. d'encouragement, 1860, 332; Polyt. Zentr., 1860, 1540). It was observed that an aqueous extract of the black flowers dyed cotton mordanted with iron blue-black shades; the same material mordanted with alum gave violet-blue, whilst with a tin mordant a blue-violet colour resulted. According to Kopp, these colours were more fast to light and air than the colours produced from logwood, but they gradually lose their intensity with age, and are not fast to soap. Recent work has shown that though the natural pigments of this series which are capable of giving dyeings are fast to light, they are all very fugitive to reagents (Willstatter and Mallison, Annalen, 1915, 408, 29).

The colours are taken up well by the fibre, it being stated that excepting in the case of pelargonidin the bath is exhausted even. at low temperatures. The colours are strong even ¼ per cent, dyeings being satisfactory and the tones good though somewhat dull. The best dyeings are given with tin mordant on wool, or on tannined cotton, though in some cases the colours are taken up direct by unmordanted wool.

In regard to their dyeing properties the glucosides of the series react very similarly to the sugar-free pigments, and in this Willstatter and Mallison see evidence that the sugar groupings are not attached to the OH groups of the hydroxy-phenyl ring.

The dyeing properties of some of these pigments are collected together in the table on the next page.

For comparative purposes a bath was made up thus: 0,0025 gr. of the pigment was dissolved in a mixture of 10 c.c. alcohol and 40 c.c. water, the solution being made acid with 5 drops of 10 per cent, sulphuric acid (acetic acid is not used as it is not capable of preventing isomerisation with formation of the pseudo base nor the hydrolytic dissociation of the colour salt). To this bath 1 gr. of wool, or cotton, is added and left therein for one hour1 at a temperature of about 25° C,

Pigment.	Wool - no mordant	Wool - Tin mordant	Tannined cotton
Pelargonidin.	Does not dye.	Purple-red	Red, with bluish tinge.
Cyanidin.	Fine rose.	Blue-violet	Violet
Delphinidin.	Violet	Blue, with violet tinge.	Blue-violet
Myrtillidin.	-	Violet-blue	Violet
Oenidin.	-	Violet-blue	Violet

The dyeings thus produced are fast to light, but not to soap or water. Heating with water causes decolorisation, doubtless due to isomerisation with formation of the pseudo base, as is the case with dilute aqueous solutions of these pigments. Treatment of the dyeings with ammonia causes them to become blue, whereas mineral acids change them to red.

From the above data it will be observed that passing from pelargonidin → cyanidin→ delphinidin, i.e. by the substitution of additional OH groups in the hydroxy-phenyl residue, the colour of the dyeings becomes bluer.

*A. G. Perkin, Chem. Soc. Trans., 1902, 589.
** Willstätter and Mallison, loc. cit.In order to appreciate the alteration in shade produced as the result of the structural change in the molecule on passing from flavonol to anthocyan, the following table is introduced:

Flavonol.*	On Wool (Tin)
Kaempferol	Lemon-yellow.
Quercitin	Strong orange.
Myricetin	Strong orange-red.
Pelargonidin	Purple-red
Cyanidin	Violet
Delphinidin	Blue-violet

It should further be noted that the great increase of the basicity of the oxygen atom of the pyrone ring that occurs in passing from flavonol to anthocyan is presumably the cause of the latter having the power of dyeing on tannin as well as on basic mordants.

The tinctorial properties of certain substitution products of the anthocyans have been studied by Watson (Chem. Soc. Trans., 1915, 1477). He prepared a series of compounds by the interaction of Grignard reagents with flavonol derivatives in which the H atom in the 4 position of the pyran ring is replaced by a variety of groups. The majority of his products are derivatives of cyanidin obtained from quercetin and the variation in the shade and properties of the dyeings produced by change in composition in this series of compounds is of considerable interest. In the table on the next page the most important points in this connection are brought together for comparison. The shades are those given on wool with various mordants.

A point of interest lies in the effect of methylation on the dyeing properties of these colours. It has been mentioned above, that as those anthocyanins of which the tinctorial properties were examined behaved similarly to the sugar-free pigments, Willstatter and Mallison concluded that the sugar groups in these compounds are not attached to the hydroxy-phenyl nucleus. Again, it should be possible, in certain cases, to deduce the position of the methyl groups by the effect of methylation on the tinctorial properties, and Watson refers to this in the case of two products obtained by him, and included in the above table. The great difference, both in shade and fastness to reagents, observed between the trimethyl ether prepared direct from quercetin-trimethyl ether by means of magnesium-ethyl iodide, and the triethyl ether obtained by partial de-ethylation (with aluminium chloride or sulphuric acid) of the product of the reaction of magnesium-ethyl iodide on quercetin-penta-ethyl ether is very interesting, and cannot be considered as being due to mere replacement of methyl by ethyl. It appears necessary, as Watson points out, to assume that it is caused by the attachment of alkyl to different OH groups in these two compounds (nos. 4 and 5 in above table). [KUVA PUUTTUU]

In the natural anthocyan pigments methylation causes the shade of the dyeings on wool (tin mordant) to be shifted towards the red; thus Willstatter and Mallison record that delphinidin gives blue (with violet tinge), whilst its monomethyl ether (myrtillidin) gives violetblue, and its dimethyl ether (oenidin) a blue-violet colour. Further, they state that these methyl derivatives have weaker dyeing properties than the free delphinidin, and, moreover, that in these cases the dyebath is not exhausted. This latter effect is also noticed in the case of pelargonidin where there is only one OH group in the hydroxypheny) residue.

Everest has pointed out (loc. cit.) that as flavone derivatives (as distinct from flavonols) are fairly widely distributed in the plant world, and that flavonols also occur in which the OH groups in the oxyphenyl nucleus are in the meta-position to one another, e.g. morin, and that as these, on acid reduction, yield red pigments resembling known anthocyans, it is probable that further investigation may lead to the isolation of natural anthocyans related to them in the same way that the known pigments of the series are to quercetin, etc. Up to the present no such bodies have been discovered, but, on the other hand, Watson has prepared (loc. cit.) a small number of products that are related to them in just the same way as his other compounds are related to the known anthocyans. His startingpoints were morin, luteolin, and apigenin, from which, by the use of methyl- or ethyl-magnesium iodide, he obtained compounds represented by the formulæ (1), (2), and (3) respectively. The results of his examination of their dyeing properties are recorded beside their formulæ, and those of the corresponding derivative of cyanidin (4) added for comparison.

The use of anthocyanin pigments as indicators has been suggested by various authors, e.g. Watson (Amer. J. Pharm., 1913, 85, 246), extract of blueberry pigment; Walbum (Biochem. Zeit, 1913, 48, 291), red cabbage pigment; but it should be noted that the colour change of many of these pigments, e.g. cyanin, is very seriously affected by neutral salts if present in any considerable quantity.

27.1.25

Anthocyan Pigments
Introduction
CHAPTER VIII. Pyran Group. Anthocyanins and Anthocyanidins.

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

The red, blue, and purple pigments of this group being the cause of some of nature's most beautiful and vivid colour effects, it is not at all surprising that at quite an early date chemists began to attempt the investigation of these pigments. Despite this, it is only within the last few years that anything definite concerning the chemistry of this group has become known.

The term Anthocyan appears to have been introduced by Marquart (Die Farben der Blüten, Bonn, 1835) to designate the blue pigments present in flowers. Later there arose the belief that the red and purple flower pigments were all merely different forms of the same blue anthocyan or, as Fremy and Cloëz styled it, cyanin - and that the variation of colour was merely due to the nature of the cell sap; this resulted in the name anthocyan being indiscriminately applied to all of them. The present use of the term anthocyan to designate a large class of naturally occurring plant pigments gradually became general as from time to time evidence accumulated to show that the red, purple, and blue pigments differed considerably among themselves.

As early as 1836, Hope, in a paper read before the Royal Society of Edinburgh (March 21; cf. J. f. prakt. Chem., (10), 269 (1837)), concluded, as the result of experiments on a large number of different kinds of flowers, that the pigments, or chromules, present were formed from faintly coloured chromogens, by a variety of changes. Of these chromogens, according to Hope, there were two types, one called by him Erythrogen, which by the action of acids yielded red pigments, and a second, named by him Xanthogen, which with alkalis gave rise to yellow pigments. He concluded that, in orange, red, purple, and blue flowers both were present, whereas in yellow and white flowers only xanthogen was found. From his examination of leaves, he concluded that chlorophyll was accompanied by xanthogen, but that, excepting in cases where reddening was obvious e.g. autumn leaves no erythrogen was present.

In the following year, Berzelius (Annalen, 1837, 21, 262) published the results of experiments on the pigments present in some berries, as cherry, black-currant, and in autumn leaves, e.g. red-currant, and of his attempts to purify and isolate them. For the red-leaf pigments he suggested the name Erythrophyll (leaf red), but pointed out that there might be objections to this term, as the pigments of flowers and berries appeared to belong to the same class, an indication of the expansion of the term anthocyan to cover other than flower pigments.

In his attempts to prepare the pure pigments, Berzelius made use of the precipitation, by means of lead acetate, of the insoluble lead salts of these pigments, and of their regeneration by means of sulphuretted hydrogen. Berzelius did not obtain any pure pigments, but the above-mentioned method, either as used by him, or with such small modifications as the decomposition of the lead salt by means of hydrochloric acid instead of with sulphuretted hydrogen, has been employed by a large number of later workers, though by this means only Grafe (1906) and Willstätter (1916) have succeeded in obtaining crystalline products. Berzelius was not of the opinion that all these pigments could be considered as the same blue substance changed by variation in the cell sap.

The next work of interest was that of Morot (Annales des Sc. nat., (3), 13, 1 60 (1849-1850)) who attempted to prepare the blue pigment of the cornflower by repeated precipitation of its aqueous solutions by means of alcohol. He did not thus obtain a pure product, but the method is of interest in that, improved by the use of modern apparatus, it constitutes the first step of the process whereby Willstätter and Everest isolated the pure corn-flower pigment. Impurities containing nitrogen were present in Morot's products, and in the presence of nitrogen he saw a possible connection between this pigment and chlorophyll, but it should be noted that he was doubtful whether this nitrogen was really a constituent of the pigment. He described the decolorisation on standing in solution which is characteristic not only of this, but also of nearly all anthocyans. That this decolorisation observed by Morot occurred in other cases was proved by the work of Fremy and Cloëz (Journ. de Ph. et de Chim., (3), 25, 249), who, moreover, by allowing such a decolorised solution to evaporate in the air, whereby the colour returned as the solution became concentrated, showed that the pigment was not destroyed by this change. They, however, looked upon the decolorisation as the result of a reduction of the pigment. These workers used the cornflower, violet, and iris for their experiments on blue pigments, and for those on red ones, the dahlia, rose, and peony. In each instance they attempted to purify the pigment by use of the lead salt, as described by Berzelius, but in no case, however, did they obtain a pure product.

Fremy and Cloëz discussed the general ideas then current regarding the plant pigments, and pointed out the uselessness of assuming, as so many.workers about that time did, that a relationship existed between chlorophyll and the blue and yellow pigments, for, as pure chlorophyll had not then been obtained, and the flower pigments were almost uninvestigated, no reliable conclusions could be drawn. They suggested that all anthocyans were one and the same substance which they called cyanin and that the colour variations were due to the properties of the particular plant sap. They distinguished three flower pigments: (1) Cyanin (red or blue); (2) Xanthins (yellow, insoluble in water); (3) Xantheïns (yellow, soluble in water). Here a clear distinction is made between the carotin derivatives, corresponding to (2), and the flavone and flavonol derivatives, to (3), both of which occur as yellow flower pigments. These authors considered that (1) and (3) were in no way related to each other, for although they almost invariably found (3) occurring in flowers containing (1), they never observed a blue flower turn yellow, nor a yellow flower turn blue.

Filhol (Comptes rend., 39, 194; J. pr. Chem., 1854, 63, 78) investigated qualitatively a large number of flowers and confirmed previous workers' observations that yellow pigments - for which he retained the name Xanthogen - were present, not only in yellow and white, but also in red, purple, and blue flowers. He concluded that, with some few exceptions, all the red, purple, and blue pigments were derived from the same anthocyan. He examined the decolorisation of anthocyans in solution, and finding that the addition of acid caused the reappearance of colour, concluded that the decolorisation could not be the result of a reduction, as suggested by Fremy and Cloëz. In his opinion this was due to the mixing of the pigments with other contents of plant cells, from which they were kept apart in the living plant.

Martens in 1855 (cf. Jahres., 1855, 657) attacked the problem from another point of view, attempting to elucidate the mode of formation of the anthocyans in plants. He further confirmed the presence of the yellow pigments, for which he used the name Xanthein of Fremy and Cloëz in flowers containing anthocyan, and as the result of his work was led to put forward the hypothesis that both yellow and red pigments have their origin in a faintly yellow substance produced in the sap of all plants, which by oxidation, particularly under the influence of alkalis and light, produces the different yellow pigments, from which by further action of light and oxygen, the red pigments are formed. It is interesting to note that the relationship thus suggested by Martens as existing between the yellow pigments and the anthocyans is that which has been revived in more recent years by Wheldale; Keeble, Armstrong and Jones, and others (see below).

In 1859 Morren put forward the suggestion that the blue flower pigments (anthocyans) were the alkali salts of acids which in the free state are red, and for which he used the name Erythrophyll (cf. Berzelius). His conception of the blue pigments has been confirmed by recent work, but not so that regarding the red colouring matters.

A number of workers have, at different times, attempted to prepare pure anthocyan pigments by making use of their lead salts (cf. Berzelius); thus Glénard (Comptes rend., 47, 268; Jahres., 1858, 476), working with red wine, and using ethereal hydrochloric acid for the decomposition of his lead salt, obtained a pigment which he called Oenolin, and for which he put forward the nitrogen-free formula C₂₀H₁₆O₁₀. His preparation was, however, by no means pure. Senier (cf. Jahres., 1878, 970), using Rosa gallica, and decomposing the lead compound, suspended in alcohol, either by sulphuric acid or sulphuretted hydrogen, prepared a pigment, for the lead salt of which he gave the formula C₂₁H₂₉O₃₀Pb₂. Heise (cf. Chem. Zentr., 1889, 2, 953) by similar means prepared two pigments (A and B) from red wine, using sulphuretted hydrogen for decomposing the lead salts, and suggested that Glénard's compound was a mixture of these. His examination, however, was not complete. Glan (Dissertation, Erlangen, 1892), examining the pigment of the deep-red hollyhock, also obtained two products, and in 1894, Heise (cf. Chem. Zentr., 1894, 2, 846) further prepared two pigments (A and B) from the bilberry (in this case using ethereal hydrochloric acid to decompose the lead salt), and obtaining them in a fairly pure, but amorphous condition, showed that the one (B) was a glucoside of the other (A). He gave analyses and formulæ, but these have proved to be incorrect, though the relative amount of glucose which he found to be present in his glucoside (B) has proved to be approximately accurate.

The result of this work of Heise and Glan was to produce a general tendency to consider that the anthocyan pigments were present in plants both as glucosides and non-glucosides, the former predominating somewhat. Molisch, in 1905, decided in favour of their being glucosides, but Grafe, who carried out a continuation of Molisch's work on a preparative scale, reverted to the earlier ideas. The results of recent work have definitely proved that in all investigated cases these pigments occur as glucosides possibly accompanied in a few instances (cf. Annalen, 1916, 412, 195) by a small percentage of sugarfree pigment, the non-glucosides isolated by the above workers being almost entirely the result of hydrolysis during their preparation.

In 1895 Weigert published (Jahrber. der k. k. 6nol. and pomol., Lehranstalt inKlosterneuburg, 1894-1895) a classification of the anthocyan pigments, thereby completely dispelling the one pigment idea that had so often been brought forward. As already stated, the views of earlier workers upon this point differed considerably; thus Berzelius was of the opinion that more than one anthocyan pigment existed, whereas Fremy and Cloë'z considered that all red, violet, and blue flowers contained the same blue pigment (cyanin), its colour having been changed by the conditions prevailing in the various cell saps. Filhol, as also Wigand (Bot. Ztg., 1862, 123), likewise asserted that all red and blue flower colours were produced by different forms of one and the same anthocyan, and Hausen (Die Farbstoffe der Bliiten und Früchten, Würzburg, 1884, p. 8) went still further, being of the opinion that not only all red colours in flowers, but also those in fruits, were due to one and the same pigment. Wiesner (Bot. Ztg., 1862, 392), however, cast considerable doubt upon the identity of all these compounds.

Weigert, as a result of the comparison of the behaviour of the anthocyan pigments with various reagents, in particular with regard to the colour of their lead salts, and the colour changes that took place on addition of acid or alkali, distinguished two classes of these compounds, the first Wine-red group such as gave blue or bluegreen lead salts, and whose acidified solution, on addition of alkali became blue or blue-green; and a second the Beetroot-red group which gave red lead salts, and whose acid solution showed no change of colour, or slight change to violet-red, on being made alkaline. The crude anthocyan pigments are, however, so varied in their reactions, that this simple classification of Weigert by no means covers all cases, for even by comparison only of the colour changes on acidification or on being made alkaline, and by formation of the lead compounds, quite a number of sub-groups can be observed.

Overton (Pring. Jahrber. f. wiss. Bot., 1899, 33, 222) also came to the conclusion that a considerable number of different anthocyan pigments existed.

In all the above-mentioned work, either qualitative results only were aimed at, or the preparations were amorphous and lacked the essential characteristics of chemically pure products. From these observations, however, it had become clear that in the anthocyans a large class of new pigments were awaiting chemical investigation, and moreover, in the light of the work of Heise and Glan, it was evident that at least certain of these must be looked upon as belonging to a class of nitrogen-free glucosides. This view was expressed by Molisch in 1905.

In 1903 two papers were published by Griffiths (Ber., 36, 3959; and Chem. News, 88, 249) which, had they been followed up, might have had considerably greater influence on this field of work than has been the case. He describes the preparation for the first time of an anthocyan in a crystalline condition. His work was carried out with geranium and verbena flowers, but the pigment obtained from the latter contained nitrogen and sulphur and was doubtless impure; that from the geranium contained neither of these elements, and was the only one analysed. His method of preparation consisted in extracting the petals with 90 per cent, alcohol, and after filtration evaporating in vacua. The residue thus obtained was extracted with absolute alcohol, filtered, and the filtrate again evaporated in vacuo, when the pigment separated in crystalline form. He did not attempt to decide whether the pigment was a glucoside or not. The description of his experiments is very superficial and imperfect; thus, for example, the fact that a fresh 90 per cent, alcoholic extract of geranium petals has a fine scarlet colour, but passes in a few minutes to a practically colourless solution, which, however, regains its original colour as evaporation takes place, is not even mentioned.

Very different in character from these papers of Griffiths is the beautifully clear and descriptive publication of the botanist Molisch (Bot. Ztg., 1905, 145), and a greater incentive to research upon these pigments than lies in this paper one cannot easily imagine. Molisch, after giving a summary of the literature dealing with the then very doubtful appearance of solid anthocyan pigments in plants, described how, on examination of a number of anthocyan-containing flowers and leaves, he found that these pigments existed not only in solution in the cell sap, but were, in many cases, present also in the solid state, sometimes as small spheres, sometimes as definitely crystalline formations. Of some of the more well-defined cases he gave illustrations. Having described the appearance of anthocyan crystals in the living plant, he followed up these observations with a description of his attempts to obtain crystals of these pigments outside the plant. In this in several cases (pelargonium, rose, Anemone fulgens) he was successful, and gave illustrations of the resultant microscopic crystals. Having thus established the fact that some of these pigments readily crystallise, he pointed out that it should not be difficult to prepare them in sufficiently large quantities for chemical examination. In a very slightly modified form, the method whereby Molisch obtained his crystals is so simple and certain, that it is worth describing. One or two petals of the flower are laid upon a piece of glass, slightly larger than a microscope slide and upon which are one or two drops of 75 per cent, acetic acid, the cell structure is then broken down by rolling a glass rod over them, leaving the petals flattened on the glass with the cell sap beside or upon them. Two or three more drops of 75 per cent, acetic acid are then placed on the petals, and a microscope slide pressed down upon them. The whole is then placed under a clockglass (to ensure slow evaporation), and after some twelve to twentyfour hours crystals begin to appear, either round the edge of the slide, or round or on the petals. Scarlet pelargonium gives the best results and very rarely fails; in some cases, using these flowers, clusters of crystals may be obtained so large that they are readily discernible by means of the naked eye.

As mentioned above, Grafe was moved by the work of Molisch to attempt the chemical investigation of some of these pigments. He published three papers (Sitzber. k. Akad. d. Wiss., Vienna, 1906, 975; 10+0. 1033; and 1911, 75); in the first he described experiments with red cabbage leaves and rose petals, from neither of which could he obtain any crystalline pigment; from the blueblack berries of Ligustrum vulgare he obtained a crystalline product, but was unable to obtain any agreement in his analyses of it, and finally, with the flowers of the hollyhock (Althaea rosea), he obtained two pigments, one crystalline, the other amorphous, of which he gave analyses. In each case he used the lead compound for the preparation of his pigment, and decomposed this by means of sulphuretted hydrogen. After separation of the hollyhock pigment in this manner, he further purified it by means of alcohol and ether.

To the crystalline compound he gave the formula C₁₄H₁₆O₆, the amorphous product C₂₀H₃₀O₁₃; he considered the latter to be a glucoside, as from it he obtained glucose by hydrolysis, but apparently did not examine the non-glucoside pigment produced by this reaction. In his second paper he continued his investigation of the hollyhock pigment, and discussed the formation of anthocyans in the plant. The third paper of the series contains an account of his further attempts to prepare the pigment of the red cabbage in a crystalline form. Despite the fact that Molisch had failed to obtain crystals by his method, Grafe attempted to produce them by using the same process on a larger scale. Failing in his attempts, he tried dialysis previously used in other cases by Portheim and Scholl (Ber. deut. Bot. Ges., 1908, 26a, 480) as a means of purification, but again failed to obtain any crystalline product. Grafe then turned his attention to the pigment of the scarlet pelargonium, which had so readily yielded crystals. He was successful in obtaining this pigment in a fine crystalline condition (microphotographs of the crystals were given) by carrying out Molisch's experiment on a large scale, employing the lead salt method, or dialysis. Besides the crystalline pigment, Grafe obtained, as with the hollyhock, an amorphous compound, and in this case also considered the latter to be a glucoside, whereas the former was sugar-free. The crystalline compound he described as very unstable and deliquescent; as this is not true of the pure pigment his crystals must have contained impurities for it he gave the formula C₁₈H₂₅O₁₃. To the amorphous substance he gave the formula C₂₄H₄₄O₂₀, and from it by hydrolysis obtained glucose; here again he does not appear to have examined the resulting non-glucoside pigment. Of the crystalline substance he obtained 10 grams, together with 15 grams of the amorphous compound, from some 28 kilograms of fresh petals, which would point to a slight preponderance only of the glucoside in the petals if no hydrolysis took place during its isolation.

Having thus overcome the experimental difficulties involved, and having for the first time obtained considerable quantities of an anthocyan in crystalline condition, it is to be regretted that Grafe drew such incorrect conclusions from his results. Doubtless he had in mind those of Heise and Glan, that both glucoside and non-glucoside pigments were present in the plants they examined, for, on finding that his amorphous product reduced Fehling's solution, but that his crystalline substance did not, he concluded that the former only was a glucoside, and convinced himself of this by its hydrolysis whereby he obtained glucose. Recent work has proved that Grafe's amorphous product must have been an impure specimen of the glucoside containing reducing sugars, whereas the crystalline substance was the glucoside in a practically pure condition; the possibility that such glucosides when pure do not appreciably reduce Fehling's solution never appears to have occurred to Grafe, and as a result he never seems to have attempted to hydrolyse his crystalline pigments. He concluded that his work, together with that of Heise and Glan, proved the co-existence, in the cases examined, of glucoside and non-glucoside in these plants. This conclusion has, however, been proved erroneous by the work of Willstätter and Everest, who have shown that only the glucoside there exists, accompanied in a few instances by a small percentage of sugar-free pigments.

* This oxidation may, or may not, be accompanied by polymerisation.During the years covered by this series of papers by Grafe, a considerable amount of work had been published by botanists, dealing with the formation of the anthocyans in plants. Miss Wheldale, as the result of much botanical work, came to the conclusion that the anthocyans are derived from colourless or faintly coloured chromogens (probably flavone or xanthone derivatives) by oxidation, most probably as the result of the action of peroxidases. She considered that the chromogens were produced by hydrolysis of glucosides that existed in the plant, this reaction being reversible. An essential feature of her theory is that the oxidation of the chromogen, with production of anthocyan, can only take place after the hydrolysis of the glucoside. To represent these changes she proposed the following scheme:
Glucoside + H₂O → Chromogen + sugar,
then,
Oxidation of chromogen* → Anthocyan pigment.

As chemical evidence of the latter part of these changes, Nierenstein and Wheldale (Ber., 1911, 44, 3487) and Nierenstein (Ber., 1912, 45, 499) brought forward products obtained by the oxidation of quercetin and chrysin respectively with chromic acid, which they described as "Anthocyan-like" products. The reactions from which they drew this conclusion were, however, by no means sufficient to show that any relationship exists between these compounds and the anthocyans. In this connection it is necessary to mention the observation of Perkin (Chem. Soc. Trans., 1913, 650), that gossypetin by oxidation in alkaline solution yields a substance (gossypeton) which is coloured deep blue by alkalis and red by acids. He pointed out the bearing of this observation upon the theory of Miss Wheldale. The fact, however, that this pigment is somewhat stable to alkalis is not in agreement with the properties of such anthocyans as have as yet been investigated, and indeed Perkin expresses doubt as to its existence as such in the cotton flower itself.

Keeble, Armstrong, and Jones (Proc. Roy. Soc., B., 1912, 85, 215; B., 1913, 86, 308, and 318; B., 1913, 87, 113; and Keeble and Armstrong, Jour. Genetics, 1913, 2, 277) have published a number of interesting papers upon the formation of anthocyans, and the hypothesis which they support is very similar to that of Miss Wheldale, but they part company with that author in regard to the process necessary subsequent to hydrolysis of the glucosides, for they maintain that the oxidation must be preceded by reduction of the non-glucosidal flavone or flavonol derivative.

In these experiments Keeble, Armstrong, and Jones came very near to the discovery of the true relationship that exists between the anthocyans and the flavones, for, in the light of later work described below, it is obvious that by some misfortune their reductions were carried too far (cf. Everest, Proc. Royal Soc., 1914* B., 87, 449).

In 1913 Willstätter and Everest (Annalen, 401, 189) published an account of investigations upon the anthocyan pigments, and in particular of the pigment of the corn-flower, and in this communication the first of a series by Willstätter and his collaborators some important conclusions were arrived at. It was proved that the blue form of corn-flower pigment was a potassium salt, the free compound being violet in colour, whereas the red form was not this latter, as had always been assumed by previous workers, but an oxonium salt in which the pigment was combined with an equivalent of some mineral or plant acid. The anthocyans were found to be most stable when in the form of these oxonium salts. It was also definitely proved that the decolorisation in solution, so often mentioned by other workers, was not due to reduction.

Having obtained the corn-flower pigment pure and crystalline in the form of its chloride, they proved that it was a disaccharide, since on hydrolysis 2 molecules of glucose were split off from each molecule of pigment; the sugar-free pigment was obtained in a finely crystalline condition. Microphotographs of the crystals were given. The pure glucoside does not reduce Fehling's solution.

By careful oxidation of cyanidin with hydrogen peroxide, a yellow crystalline product was obtained which in its reactions closely resembled a flavonol colouring matter.

To prevent confusion these authors proposed the terms anthocyanins and anthocyanidins for the glucoside and non-glucoside pigments respectively, and in agreement with this assigned to the glucoside present in the corn-flower the name introduced by Fremy and Cloëz cyanin, whereas to the sugar-free pigment obtained by hydrolysis of cyanin the name cyanidin was given.

Willstätter and Everest introduced a method whereby they were able to distinguish between glucoside pigments of the anthocyan series and the corresponding sugar-free pigments. This depends upon the difference that exists between these classes of pigment in their distribution between amyl alcohol and aqueous acid. It has been very carefully studied by Willstätter and his collaborators in the course of their later work, and by but very slight modification it has been possible to utilise it in many cases to determine, with very considerable certainty, whether a given anthocyan pigment is a mono- or disaccharide, or a sugar-free pigment; and indeed in certain instances (e.g. chrysanthemum pigments) to separate mixtures of mono-, di-, and non-glucosides by its means, and show clearly the presence of all three. There are, however, limitations to its use for these purposes, dependent upon circumstances that are dealt with below.

Under suitable conditions of acid concentration Willstätter and Everest used dilute sulphuric acid ca. N-2N; whereas in later work Willstätter and Zollinger use 0.5 per cent, hydrochloric, or sulphuric acid. The disaccharide anthocyans (with few exceptions) are almost quantitatively retained by the aqueous layer in the form of their oxonium salts when a solution of the pigment in aqueous acid is shaken with amyl alcohol; the monosaccharide derivatives, however, pass partially into the amyl alcohol layer the percentage of the total pigment taken up by the alcohol being to a certain extent characteristic of the individual pigment. This may be quantitatively removed again by repeated washing with dilute aqueous acid, whereas, when sugar-free pigments are subjected to this test, the amyl alcohol layer takes the pigments quantitatively from the aqueous layer, and they cannot be removed from the amyl alcohol by washing with aqueous acid.

Willstätter and Zollinger have given the name "Distribution Number" (Verteilungszahl) to the percentage of the total pigment present which is taken up into the amyl alcohol layer when the above test is carried out under certain conditions. These numbers are of considerable use in characterising a pure pigment of this series.

For the purpose of estimating the "Distribution Number" of an anthocyan, 0.01 gr. of the pigment is dissolved in 50 c.c. of 0.5 per cent, hydrochloric acid. In the original description of this method (Annalen, 1916, 412, 208) this is erroneously stated as 0.05 per cent. HCl, but the various references in the context, p. 208 and p. 209, make it obvious that 0.5 per cent, is meant. It is stated also that a more dilute acid allows of some isomerisation, whilst in more concentrated acids the pigments are less soluble (hence the choice of 0.5 per cent). The solution is shaken twice with amyl alcohol (free from pyridine), using 50 c.c. amyl alcohol for each shaking. The small quantity of acid that passes to the alcoholic layer is sufficient to prevent isomerisation of the pigment in that layer.

The amyl alcoholic extracts are then quantitatively estimated by comparison (colorimetrically) with standard solutions of the pure pigment in amyl alcohol also containing a small quantity of acid to prevent isomerisation. As -the anthocyan pigments are not very soluble either in aqueous acid or in amyl alcohol, it is necessary to work with dilute solutions so that both layers shall remain unsaturated.

By these means Willstätter and Zollinger have obtained the following values:

Pigment	Type	Distribution Number (Mean).
Malvin chloride	Diglucoside	1.6
Cyanin "	"	1.8
Salvinin "	"	ca.1-2
Keracyaninen "	Rhamno-glucoside	6.8
Prunicyanin "	"	9.7
Ampelopsin "	Mono-glucoside	9.8
Oenin "	"	10.4
Myrtillin "	"	10.8
Salvianin "	? Complex anhydro-di-glucoside	ca.50
Salvin "	? Anhydro-diglucoside	57
Cyanidin "	Non-glucoside	100.0
Oenidin "	"	100.0

At one time it appeared as if diglucoside anthocyans had a number ca. 1-2, the monoglucosides ca. 10-11, and the nonglucosides 100, but the above table shows that this does not hold good now that further pigments have been investigated.

The discovery by Willstätter and Zollinger that certain diglucoside anthocyans have distribution numbers of the same order as those of the monoglucosides, prevents the full use of this test in the direction in which they were developing it viz. to characterise the three types of anthocyan pigments: non-glucosides, mono-, and disaccharides. Indeed, except in such cases where it is known that disaccharide pigments which have numbers similar to those of the monosaccharides are absent, it remains much in the position where Willstätter and Everest left it; i.e. that sugar-containing pigments either do not pass to the amyl alcohol layer, or, if they do so to some extent, they may be completely removed again by frequent shaking with fresh aqueous acid, whereas the sugar-free pigments pass quantitatively to the alcoholic layer and cannot be removed from it by such treatment.

With this method there are a few peculiarities that concern the sugars attached to the pigments, and which appear to show that these are of considerable importance in deciding the distribution number of these pigments.

Comparison of the values given in the table above, for disaccharide pigments, and of the products of their hydrolysis, shows that those which are rhamno-glucosides yield numbers that approximate to those of the monosaccharides,

Another very interesting case is that met with in the colouring matters of the salvia (scarlet). Here the flower pigment "Salvianin" appears to be rather more complex than most anthocyans (in this it resembles delphinin) in that on hydrolysis it yields pelargonidin, 2 molecules of glucose, and also malonic acid (proportion not yet determined), but by partial hydrolysis a compound "Salvin" is obtainable which appears to have the formula C₂₇H₂₆O₁₃, i.e. that of a pelargonidin diglucoside less 2 molecules of water, whilst a third pigment "Salvinin -" a true diglucoside of pelargonidin - is also obtained by partial hydrolysis of the original salvianin. Now, whilst salvinin, which is isomeric with pelargonin, behaves as a normal disaccharide anthocyan, i.e. gives a low distribution number, both salvianin - the original flower pigment - and salvin give extraordinarily high numbers, the former well over fifty, the latter almost exactly fifty. Willstätter ascribes these abnormal numbers to the diminution in the number of OH groups present in the sugar molecules attached to the pigment as is indicated by analysis, and by peculiarities observed during the carrying out of quantitative hydrolyses of these pigments.

By means of the test described above it has been shown that in almost every case investigated the anthocyan pigments are present in plants solely as glucosides; in a few instances, however, sugar-free pigments appear to be present to a small extent also. Thus in black grapes (North Italian or hot-house grown) Willstätter and Zollinger (Annalen, 1916, 412, 206) found that the sugar-free pigment, oenidin, was present, but to the extent only of a few per cent, of the total pigment. In this respect a very interesting exception was met with by them in specimens of "Black Alicante" grapes, which were gathered at the Kgl. Gartner-lehranstalt, Berlin-Dahlem, towards the end of November, and which had light brown-violet berries; in these they found (by colorimetric estimation) as much as 12 per cent, of the colour present as the non-glucoside pigment.

In 1914 Miss Wheldale (Biochem. Jour., 1914, 8, 204) published further work from which she concluded that the fact that she failed to obtain a crystalline pigment, and that her product had no melting-point, was evidence of the high molecular weights of the anthocyan pigments. By comparison with the case of cyanidin chloride, the melting-point evidence collapses at once, and it appears as though the non-crystalline condition of her pigment was either due to the presence of a small quantity of impurity, or that she did not ascertain the conditions for its necessary crystallisation.

That luteolin and morin give red pigments on reduction in acid alcoholic solution by means of sodium amalgam has been known for many years (cf. Rüpe, "Die Chemie der natürlichen Farbstoffe," vol. i., pp. 77 and 85). Watson and Sen (Chem. Soc. Trans., 1914, 389) obtained a red pigment from quercetin in like manner, whilst R. Combes (Comptes rend., 1913, 1002) produced a red pigment, identical with that which he had obtained from the red leaves of Ampdopsis hederacea, by reducing in the same way the yellow pigment obtained from the green leaves of the same plant. A further paper of Combes (Comptes rend., 1913, 1454) described the reverse change, viz. from red to yellow by means of oxidation with hydrogen peroxide. In each case he obtained crystalline compounds and compared their melting-points; he did not, however, give analyses, nor state whether he worked with glucosides or not.

That a series of red pigments whose properties coincide in every way with those of the anthocyanidins may be produced by reduction of the flavonol derivatives by various methods, the best of which appears to be treatment of the pigment dissolved in a mixture of five volumes absolute alcohol and one volume concentrated hydrochloric acid, with magnesium, has been confirmed by Everest (Proc. Roy. Soc., 1914, B., 87, 444), who, moreover, in the same paper described the production, by the same means, of anthocyanins from the glucoside flavonol derivatives present in various flowers, thus showing the direct formation of red glucoside pigments from the yellow flavonol glucosides without intermediate hydrolysis. This important observation makes the hypothesis of Miss Wheldale and others, in which hydrolysis of the flavonol glucoside is an essential factor, unnecessary, and moreover shows that reduction, not oxidation, is necessary for the passage from flavonol to anthocyan.

The results obtained, coupled with those of Willstätter and Everest in their investigation of the corn-flower pigment, led Everest to suggest a scheme to represent the passage from a typical flavonol to the corresponding anthocyan, and to put forward a structural formula for the anthocyans (see below). The correctness of these has been confirmed by the more recent work upon the natural pigments carried out by Willstätter and his collaborators.

The γ-Pyran, or Benzobyranol Group - Introduction
CHAPTER VIII. Pyran Group.

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

The groups [KUVIA PUUTTUU] are of considerable interest in connection with both the artificial and naturally occurring colouring matters. They form the basis of a number of synthetic colours that have been in commercial use for many years, of which the following may be cited as typical instances: [KUVIA PUUTTUU] Pyronin G, Eosin A., Tetramethylrosamine, Rhodamine B., Coerulein - whilst related to these, but of less value, are such products as the succineins and sacchareins.

The result of recent researches upon naturally occurring colouring matters has been that a large number of substances, the anthocyans, colours of great beauty and widely distributed in nature, are now known to be derivatives of the benzopyranol complex; indeed all the products of this group as yet investigated are derived from the following nucleus [KUVA PUUTTUU] by the introduction of further hydroxyl groups.

Interest in this type of compound is increased by the fact that compounds related to the anthocyans have been synthetically prepared which have rather more useful tinctorial properties than those possessed by the natural colours, and it is not impossible that the number of commercially useful derivatives in which the y-pyran nucleus is present may be further increased by work that may follow upon the recent researches in this field.

26.1.25

African Marigold - Tagetes patula
(CHAPTER VII. Flavonol Group.)
(Osa artikkelista)

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Quercetagetin was isolated from the flowers of the African marigold, Tagetes patula, by Latour and Magnier de la Source (Bull. Soc. Chim., 1877, (ii.), 28, 337), who state that it also occurs in other varieties of the same plant. In appearance and general properties it is described as resembling quercetin, the colouring matter of quercitron bark, and from this fact, together with its origin, the name quercetagetin is evidently derived. On the other hand, according to these authors, its crystalline form, solubility in 60 per cent, alcohol, and the numbers obtained on analysis indicated that it was distinct from quercetin C₂₇H₂₀O₁₂, and it was considered to possess the formula C₂₇H₂₂O₁₃ (anhydrous) or C₂₇H₂₂O₁₃, 4H₂O (air-dried). A preliminary re-examination of this colouring matter was made by Perkin in 1902 (Chem. Soc. Proc., 18, 75), and it has more recently been studied in greater detail by the same author (Chem. Soc. Trans., 1913, 103, 209). To isolate the colouring matter, which is largely present in the flowers as glucoside, a concentrated alcoholic extract is diluted with water which precipitates a viscous impurity, and this is removed by means of ether. The clear liquid treated when boiling with addition of a little hydrochloric acid deposits after cooling but a small bulk of the colouring matter, and repeated extraction of the solution with ether is necessary for its economical isolation. The crude product thus obtained can be crystallised from dilute alcohol, but for complete purification it is necessary to prepare the acetyl derivative, and after re-crystallisation to hydrolyse this in the usual manner.

[---]

Quercetagetin readily dyes mordanted fabrics shades of a generally similar character to those given by other well-known flavonol colouring matters.
Chromium. Dull olive-yellow.
Aluminium. Yellow-orange.
Tin. Brown.
Iron. Brownish-black.

A trace of a more sparingly soluble colouring matter is present in the flowers and represents about 1 per cent, of the crude quercetagetin referred to above. It crystallises from alcohol in somewhat indefinite groups of minute needles and dissolves in alkaline solutions with an orange colour passing to green on dilution with water. Though similar in appearance to rhamnetin (quercetin monomethyl ether) it does not contain a methoxy group.

Dyeing Properties of the Flowers.

Employing mordanted woollen cloth, the following shades are produced:
Chromium. Yellowish-Brown.
Aluminium. Pale dull yellow.
Tin. Deep yellow-orange.
Iron. Brownish-black.

These possess a somewhat redder character than those given by quercitron bark, and are similar to, though not so red as those from patent bark. As quercetagetin mainly occurs in the flowers as glucoside, their tinctorial effect is evidently due to this latter.

11.1.25

Cotton Flowers
(CHAPTER VII. Flavonol Group.)
(Osa artikkelista)

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Among the various portions of the cotton plant which have been industrially employed must be included the flowers which constitute one of the numerous Indian dyestuffs. According to Watt ("Dictionary of the Economic Products of India") they are thus used in the Manipur district. Gossypetin was first isolated in small quantity from the flowers of the ordinary Indian cotton plant, G. herbaceum (Perkin, Chem. Soc. Trans., 1899, 75, 826), and has been more completely studied at a later period (ibid., 1913, 103, 650). For its preparation a concentrated alcoholic extract of the flowers is treated with hot water and the mixture digested when boiling with addition of hydrochloric acid for three hours. After removal of tar by filtration the hot liquid on cooling deposits a brownish-yellow powder, which contains a mixture of quercetin and gossypetin. These colouring matters are separated by a fractional crystallisation of their mixed acetyl derivatives from acetic anhydride, acetylgossypetin being in these circumstances the least soluble. The acetyl compound is finally hydrolysed by sulphuric acid in the presence of acetic acid in the ordinary manner.

[---]

Gossypitone, C₁₅H₈O₈, the name assigned to this substance, consists of microscopic needles of a dull red colour, which are difficultly soluble in the usual solvents. It dissolves in dilute alkalis with a pure blue coloration and its solution in concentrated sulphuric acid is dull brown. Sodium hydrogen sulphite solution reconverts it into gossypetin. Gossypitone possesses strong dyeing properties, and gives the following shades on mordanted woollen cloth:
Chromium. Dull-brown.
Aluminium. Orange-brown.
Tin. Orange-red.
Iron. Deep olive.

* This compound, more recently synthesised by Neirenstein (Chem. Soc. Trans., 1915, 107, 872), is described as melting at 354-355°, and its hexamethyl ether at 145-147°.These, it is interesting to note, are identical with those given in these circumstances by gossypetin itself, and it is accordingly evident that during the dyeing operation oxidation of the latter to gossypitone takes place. Until a definite knowledge of the tetrahydroxybenzene nucleus in gossypetin has been obtained the position of the hydroxyl groups in this portion of the molecule can only be conjectured. Existing as it does side by side with quercetin it seems natural to consider that gossypetin is a hydroxyquercetin. Again, should gossypitone be a p-quinone, the constitution of gossypetin will be the same as that which Neirenstein and Wheldale have suggested (Her., 1911, 48, 3487) for the flavonol described earlier (1) which they obtained from quercetone, but the descriptions of the two compounds are not in agreement.*

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Quercimeritrin, C₂₁H₂₀O₁₂, 3H₂O, melting-point 247-249°, consists of small, glistening, bright yellow plates, insoluble in cold and fairly readily soluble in boiling water. Its alkaline solutions possess a deep yellow tint; with aqueous lead acetate it gives a bright red precipitate, and with ferric chloride an olive-green coloration. Octa-acetylquercimeritrin, needles, C₂₁H₁₂O₁₀(C₂H₃O)₈, melting-point 214-216°, is sparingly soluble in alcohol, whereas monopotassium quercimeritrin, a yellow powder, can be obtained by means of alcoholic potassium acetate. By hydrolysis with dilute sulphuric acid quercimeritrin yields quercetin and glucose according to the following equation: C₂₁H₂₀O₁₂ + H₂O = C₁₅H₁₀O₇ + C₆H₁₂O₆ and is thus analogous to quercitrin which in this manner is converted into quercetin and rhamnose.

On wool mordanted with aluminium, tin, chromium, and iron, quercimeritrin gives the following shades:
Aluminium. Orange-yellow.
Tin. Bright orange.
Chromium. Reddish-brown.
Iron. Olive-brown.
and these results are interesting, because with the exception of the iron mordanted pattern, which is of a rather browner character, the colours thus produced closely resemble those which are given by quercetin itself when dyed in a similar manner. They are widely different from those given by rutin and quercitrin, and mainly as a result of this property there can be little doubt that quercimeritrin is to be represented by one of the two following formulæ: [KUVA PUUTTUU]

Quercimeritrin is also present in the flowers of the Primus emarginata? (Finnemore, Pharm. Jour., 1910, (iv.), 31, 604).

[---]

Acetyl-gossypitrin, C₂₁H₁₁O₁₃(C₂H₃O)₉, colourless needles, melting-point 226-228°, is almost insoluble in alcohol.

When hydrolysed with dilute sulphuric acid gossypitrin yields gossypetin and dextrose according to the equation C₂₁H₂₀O₁₃ + H₂O = C₁₅H₁₀O₈ + C₆H₁₂O₆

The shades given by this glucoside on mordanted wool are as follows:
Chromium. Reddish-brown.
Aluminium. Dull yellow.
Tin. Bright orange.
Iron. Dark olive-brown.

Gossypitrin reacts, like gossypetin itself, with benzoquinone, and yields in this way a quinone to which the name Gossypitrone, C₂₁H₁₈O₁₃, has been assigned. This consists of maroon coloured needles, which possess no definite melting-point, although fusion of the product occurs about 255-259°. By the action of warm dilute sulphurous acid solution it is reconverted into gossypitrin, and the same change appears to occur in the dyeing process, for the shades produced are identical with those yielded by this latter glucoside. It is considered probable that the sugar group of gossypitrin is attached to its tetrahydroxybenzene nucleus, though until the exact nature of this has been decided, its position is necessarily uncertain.

Isoquercitrin, C₂₁H₂₀O₁₂, 2H₂O, crystallises from dilute alcohol in pale yellow needles, melting at 217-219°. It is sparingly soluble in water, and dissolves in alkaline solutions with a deep yellow tint, but its most interesting property is the fact that with aqueous lead acetate solution it gives a bright yellow precipitate entirely distinct from the deep red deposit which is produced in this manner from the isomeric quercimeritrin.

Again, though more readily susceptible to hydrolysis than the latter glucoside, it yields identical products: C₂₁H₂₀O₁₂+H₂O=C₁₅H₁₀O₇+C₆H₁₂O₆

Dyeing experiments with isoquercitrin give shades entirely distinct from those given by quercimeritrin, and these, although slightly paler, resemble those yielded by quercitrin.
Chromium. Brownish-yellow.
Aluminium. Golden-yellow.
Tin. Lemon-yellow.
Iron. Brownish-olive.

The properties of this substance indicate that its sugar group is riot attached as in quercimeritrin to the phloroglucinol nucleus of quercetin. Indeed it is probably constituted similarly to quercitrin (loc. cit.), which, however, contains a rhamnose in the place of the glucose residue. Three formulæ are possible for isoquercitrin, which may be briefly expressed by the statement that the position of the sugar residue in respect to the quercetin group is at one or other of the points in the following which are marked with an asterisk: [KUVA PUUTTUU]

The aqueous extract of the Egyptian cotton flowers employed in this investigation gave by hydrolysis with acid []86 per cent, of crude colouring matter, and in this approximately 10 per cent, of gossypetin was present. Dyeing experiments with the flowers in the usual way gave the following shades:
Chromium. Reddish-brown.
Aluminium. Green-yellow.
Tin. Orange-brown.
Iron. Olive-brown.
and these though duller were somewhat similar in character to those given by quercimeritrin. In comparison with the shades similarly produced from other natural dyes, they most nearly resemble those of the so-called "Patent Bark," a preparation of quercitron bark in which quercetin and no quercitrin is present.

Among the types of cotton flowers there are (a) red, (b) pink, (c) yellow, and (d) white flowered plants. In the offspring of a cross between (a) and (c) there occurs in the second and subsequent generations red and yellow plants which breed pure, whereas in the off-spring of a cross between (a) and (d) all four forms occur which breed pure. As a supplementary investigation to that of the Egyptian flowers the petals derived from such pure plants occurring among the offspring of one or other of these crosses have been examined (Perkin, Chem. Soc. Trans., 1916, 109, 145), (cp. Leake, Proc. Roy. Soc., 1911, (B), 83, 147).

The types were as follows: red flowered, G. arboreum (Linn.); pink, G. sanguineum (Harsk); yellow and white, two varieties of G. neglectum (Tod), usually now treated as one species but originally described as G. neglectum and G. rossrum. As a result it has been found that the red flowers of G. arboreum contain isoquercitrin, quercimeritrin and gossypitrin in this case being absent, whereas in the yellow flowers of G. neglectum, gossypitrin and isoquerdtrin were present, and quercimeritrin appeared to be absent. On the other hand, the white flowers of G. neglectum and the pink flowers of G. sanguineum gave but traces of colouring matter too small for complete identification, though the respective products obtained resembled in their properties apigenin and quercetin. An examination of the ordinary Indian cotton flower, G. herbaceum, available only in small amount, gave the same results as the G. neglectum.

Gossypetin is also present in the flowers of the Hibiscus sabdariffa or "red sorrel" of the West Indies, a small shrub which is widely cultivated throughout the hotter parts of India and Ceylon (Perkin, Chem. Soc. Trans., 1909, 95, 1855). The stems yield the "Rozelle hemp" of commerce, and this is obtained by retting the twigs as soon as the plant is in flower. The yellow flowers are just capable of dyeing yellow but are not used at all in India for this purpose; on the other hand, the red calyces are employed for dyeing in an obscure degree in two remote parts of the country (Burkill, Agricultural Ledger, Calcutta, 1908, No. 2, 13).

5.1.25

Other Sources of Myricetin.
(CHAPTER VII. Flavonol Group.)

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Other Sources of Myricetin.
(CHAPTER VII. Flavonol Group.)

Sicilian sumach, the leaves of the Rhus coriaria (Linn.), contain myricetin, probably as glucoside (Perkin and Allen, ibid.) 69, 1299). The colouring matter also exists in Venetian sumach, R. colinus, and this is interesting, because the wood of this tree constitutes "young fustic" and contains fisetin. Among other plants myricetin has been isolated from the Myrica gale (Linn.), the leaves of Pistacia lentiscus (Linn.), the leaves of the logwood tree, Haematoxylon campechianum (Linn.), and it is found in conjunction with quercetin in the leaves of the Coriaria myrtifolia (Linn.) and the R. metopium (Linn.).

Everest (Royal Soc. Proc.,1918, B., 90, 251 (has shown that in all probability myricetin as a glucoside accompanies the anthocyanin pigment Violanin; a glucoside of [KUVA PUUTTUU] in the flowers of the purple-black viola (Sutton's "Black Knight"), an observation which is of considerable interest in connection with the relationship which exists between the flavonols and anthocyans.

2.1.25

Myrica nagi
(CHAPTER VII. Flavonol Group.)

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Myrica nagi (Thunb.). This is an evergreen tree belonging to the Myricaceæ met with in the sub-tropical Himalaya from the Ravi eastwards, also in the Khasia mountains, the Malay Islands, China, and Japan. It is the box-myrtle or yangma of China, and is synonymous with M. sapida (Wall.), M. rubra (Sieb. and Zucc.) and M. integrifolia (Roxb.). The bark is occasionally used as a tanning agent, and is said to have been exported from the North-West Provinces to other parts of India to the extent of about 50 tons per annum. In Bombay it is met with under the name of kaiphal, and in Japan as shibuki.

Myricetin, C₁₅H₁₀O₈, H₂O, the colouring matter, can be isolated from an aqueous extract of the plant by a similar method to that which is serviceable for the preparation of fisetin (see Young Fustic), but is more readily obtained in quantity from the Japanese commercial "shibuki" extract (Perkin and Hummel, Chem. Soc. Trans., 1896, 69, 1287; and Perkin, ibid., 1902, 81, 204).

The extract is treated with ten times its weight of hot water to remove tannin, and when cold the clear liquid is decanted off, the residue washed twice in a similar manner, and well drained. The product is extracted with boiling alcohol, and the solution evaporated until crystals commence to separate. On cooling these are collected (the filtrate A being reserved) and washed first with strong and then with dilute alcohol. A complete purification is best effected by converting the colouring matter into its acetyl derivative, and when pure hydrolysing this in the usual manner. Myricetin crystallises in yellow needles, melting at about 357°, and closely resembles quercetin in appearance. Dilute potassium hydroxide solution dissolves myricetin with a green coloration, which, on standing in air, becomes first blue, then violet, and eventually brown coloured. Alcoholic lead acetate gives an orange-red precipitate, and ferric chloride a brown-black coloration.

[---]

Myricetin dyes mordanted woollen cloth the following shades, which are practically identical with those given by quercetin:
Chromium. Red-brown.
Aluminium. Brown-orange.
Tin. Bright red-orange.
Iron. Olive-black.

[---]

Myricitrin, C₂₁H₂₂O₁₃, H₂O, or rather C₂₁H₂₀O₁₂, 2H₂O, the glucoside, is present in the alcoholic filtrate A, from the crude myricetin, from which it separates on standing. The crystals are collected, washed first with alcohol, then with dilute alcohol, crystallised from water, from alcohol, and finally from water. Myricitrin forms pale yellow, almost colourless leaflets, melting at 199-200°, and is soluble in alkalis with a pale yellow tint. Aqueous lead acetate gives an orange-yellow precipitate, and alcoholic ferric chloride a deep greenishblack coloration. In appearance it cannot be distinguished from quercitrin, and the shades given by the two substances on mordanted woollen cloth are practically identical.
Chromium. Full brown-yellow.
Aluminium. Full golden-yellow.
Tin. Lemon-yellow.
Iron. Brown-olive.

When hydrolysed with dilute sulphuric acid myricitrin yields rhamnose and myricetin, according to the equation C₂₁H₂₀O₁₂+H₂O=C₁₅H₁₀O₆+C₆H₁₂O₅, and is analogous to quercitrin which in a similar manner gives rhamnose and quercetin. In addition to myricetin the M. nagi contains a trace of a glucoside of second colouring matter, which is probably quercetin.

The dyeing properties of myrica bark are generally similar to those of other yellow mordant dyestuffs. On wool with chromium mordant it gives a deep olive-yellow, and with aluminium a dull yellow, similar to the colours obtained from quercitron bark, but much fuller; with tin mordant it gives a bright red-orange, redder in hue than that given by quercitron bark; with iron mordant it gives a dark greenish-olive like that obtained from quercitron bark, but again fuller.

On cotton with aluminium and iron mordants it dyes colours which are more similar to those obtained from old fustic than from quercitron bark. Some specimens of myrica bark are exceedingly rich in colouring matter, and a sample examined by Hummel and Perkin (J. Soc. Chem. Ind., 1895, 14, 458) possessed much stronger dyeing power than old fustic.

According to Satow (J. Ind. Eng. Chem., 1915, 7, 113) (Abst. Chem. Soc., 1911, 149), the colouring matter of the M. rubra has the formula C₁₅H₁₀O₈, and is identical in some of its properties with myricetin. By fusion with sodium polysulphide and sulphur a product is obtained which dyes cotton a deep sepia colour, though if copper sulphate, manganese sulphate, or ferrous sulphate is added to the fused mass, substances possessing a bluish or bluish-grey colour are produced. By fusing myricetin with sulphur alone a brown-yellow compound is obtained. A yellow dye may also be obtained by nitrating myricetin sulphonic acid.

1.1.25

Jak-wood
(CHAPTER VII. Flavonol Group.)
(Osa artikkelista)

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

Jak-wood, or Jack-wood, is derived from the Artocarpus integrifolia (Linn.) which belongs to the Urticaceæ, and is cultivated throughout India, Burmah, and Ceylon, except in the north. It is largely used for carpentry, furniture, etc., and is stated to be imported to Europe for this purpose. The rasped wood is used by the natives of India and Java as a yellow dye in conjunction with alum, for the robes of the Burmese priests, also for dyeing silk and for general purposes.

An aqueous solution of the wood possesses the characteristic property that when it is treated with alkali and gently warmed, the yellow solution at first obtained assumes a beautiful blue tint.

Jack-wood (Perkin and Cope, Chem. Soc. Trans., 1895, 67, 937) is very similar to old fustic, and its dyeing properties are due to morin (see Old Fustic). Unlike old fustic, however, it contains no maclurin, but there is present a second substance, cyanomaclurin, which is devoid of tinctorial property. These compounds can be isolated from jack-wood by methods which are almost identical with those which have been applied to fustic itself, and their separation may be effected by means of lead acetate as this precipitates only the morin.

[---]

Jack-wood dyes shades very similar to those given by old fustic; that is, olive-yellow with chromium, dull yellow with aluminium, and a brighter yellow with tin mordant. On the other hand, the sample examined by Perkin and Cope possessed only about one-third of the dyeing power of old fustic.