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.