Carajura and Chica Red; Bignonia tecoma, Tecomin.(CHAPTER VIII. Pyran Group. Other members of the group.)

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

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

These are rare pigments prepared by the Indians of Central America from species of Bignonia which are very similar in appearance and may contain as a basis the same colouring matter. A red pigment of this character, evidently "Chica red," is referred to in "The Travels and Researches of Baron Humbolt" (Macgilivray, Edinburgh, 1836, p. 229): "Red paint is the ordinary decoration of these tribes. The most common kind is obtained from the seeds of the Bixa orellana and is called annotto, achoute, or roucou. Another more expensive species is extracted from the leaves of the Bignonia chica." According to Crookes ("Dyeing and Calico Printing," 1874, 388) chica is obtained from the leaves of the B. chica which the Indians boil with water, and add some particles of the bark known as "aryane" to the decanted liquid which causes the precipitation of the colouring matter.

An interesting resume of what is known of this subject is given by Holmes (Pharm. J., 1901), who states that preparations very similar to carajura are employed by the South American Indians in Brazil, Bolivia, and Guiana. These include chica from the leaves of B. chica, from "ula" leaves derived from an unknown species of Bignonia in Bolivia, and a pigment prepared from the heartwood of the B. tecoma in Minas (Brazil). The latter, according to Lee (Chem. Soc. Trans., 1901, 284), is prepared by mixing the dust and shavings of this tree with slaked lime and heating the mass with water. From the B. tecoma Lee isolated a considerable amount of a yellow crystalline compound, tecomin, which is referred to later.

Carajura or Crajura was apparently first examined by Virey (Journ. de Pharmacie et Chimie, (3), 5, 154). The sample experimented with, which came from Para, was soluble in alkalis and was precipitated therefrom by acid, and is stated to have been prepared by the Galibis by boiling with water the stem and leaves of an unknown species of Bignonia when the latter in the autumn had acquired a purple colour.

Crookes states (loc. cit.) that chica is soluble in 36 per cent, alcohol, in ether and in alkalis with a vinous red colour, and when heated in a sealed tube with alkali and glucose gives a bluish-red liquid which becomes brown on exposure to air and then yields on acidification an orange-red precipitate.

As the result of an examination of chica red or carajura said to be derived from the leaves of the Bignonia chica, Erdmann (Jahres., 1857, 487) assigned to the colouring matter which he isolated by extraction with alcohol the formula C₈H₈O₃. This substance was soluble in caustic alkali but not in alkali carbonate solutions, and when oxidised with chromic acid gave anisic acid, whereas with nitric acid picric acid was produced.

Perkin (Proc. Chem. Soc., 1914, 30, 212), who examined a sample of "carajura" obtained from Messrs. Wright, Layman, and Umney of London, and which is referred to in the paper of Holmes (loc. cit.), found this to contain a small quantity of the calcium lake of two colouring matters which had either been precipitated on, or intermingled with a substance of the nature of ground bark or peat. After treatment with hot dilute hydrochloric acid, alcohol removes the colouring matters in the form of a resin, and from this, by means of boiling benzene, carajurin is isolated. This compound to which the formula C₁₈H₁₆O₅ has been provisionally assigned separates in ruby needles, melting at 204-206°, is soluble in boiling dilute alkali with a red colour, and is nearly devoid of dyeing properties. With mineral acids it very readily yields oxonium salts, crystallising in bright, orange needles, of which the sulphate, probably C₁₈H₁₆O₅.H₂SO₄.H₂O is the most stable, the hydrobromide and hydrochloride being decomposed at 100°. From the hydrochloride a platinichloride can be prepared. Cold acetic anhydride with a trace of pyridine, after two days, gives an almost colourless acetyl compound, crystallising in needles, whereas bromine gives an immediate precipitate with carajurin in acetic acid, which when boiled with this solvent, separates in orange needles. Hydriodic acid converts carajurin with loss of 2 molecules of methyl iodide and probably also of a molecule of water into a substance provisionally termed carajuretin iodide, bright scarlet needles, stable in the presence of cold water, and from this by means of cold pyridine, carajuretin, C₁₆H₁₂O₅, scarlet needles, melting above 330°, and soluble in alkalis with a reddish- violet colour, is produced. By dry distillation carajurin evolves a trace of aromatic oil, resembling anisaldehyde in odour, and when fused with alkali, p-hydroxybenzoic acid and a colourless substance, melting at 185-187°, as yet unidentified, are obtained. In many respects carajurin resembles the anhydrohydroxybenzopyranol compounds described by Bülow and Wagner (Ber., 1901, 34, 1199).

That portion of the alcoholic extract insoluble in benzene yields to ether carajurone, isolated as a scarlet powder, which readily assumes a beetle-green lustre, and possesses strong dyeing properties. Analysis indicates the presence of more oxygen in this compound than in carajurin. A small amount of a similar, but brighter lake from British Guiana, and obtained from the leaves of a "bushrope," gave a colouring matter dyeing alizarin-like shades. This preparation, considered to be "chica red," appeared to differ in some respects from the "carajura" above described.

Bignonia tecoma.* Tecomin.

* According to Holmes (loc. cit.) the name Bignonia tecoma does not appear in the Kew Index, but only Bignonia tècomoìdes, which is, however, a shrubby species. The Bignonia tecoma is a somewhat common tree in the uplands of Minas, Brazil, which when fully grown is about 30 feet high and in September is covered with brilliant yellow flowers. The natives mix the sawdust and shavings of this tree with slaked lime, heat the mass with water and employ the resulting bath to dye cotton cloth. A paste made of the sawdust mixed with lime is also used to stain lighter coloured woods a deep brown. By exhausting the sawdust with boiling 85 per cent, alcohol and concentrating the extract, Lee (Chem. Soc. Trans., 1901, 79, 284) isolated the colouring matter tecomin, which has been previously referred to. This, which has apparently not been submitted to analysis, forms shining chrome yellow crystals possessing a nacreous lustre, soluble in alkalis with a rose-red coloration.

A further quantity of this compound could be isolated from the alcoholic filtrate, the total amount thus given by the wood being approximately 5 per cent.

The sawdust extracted with alcohol contains a deep brown dye which may now be removed from it by alkalis, and by acidification this is deposited therefrom as an amorphous brown powder. Nothing is at present known as regards the relationship, if such exists, between tecomin and the colouring matter of chica red or carajura.