The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918
Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.
The Rubia cordifolia (Linn.) was formerly extensively cultivated in India, particularly in the mountainous districts, for the sake of the colouring matters contained in its stem or roots. In the Darjeeling district it occurs as a small climber common all over the hills, at elevations varying from 3000 to 7000 feet, but most abundant between 5000 and 6000 feet, and is found either creeping along the ground or climbing the trunks of trees in large festoons. In Bengal it would seem that the dye of munjeet is extracted mainly from the stem, and only occasionally from the root, as is the case in the North-Western Provinces and elsewhere in India. The munjeet of Bengal is apparently rather the Rubia munjista of Roxburgh than the Rubia cordifolia. This species of Roxburgh is, however, reduced to Rubia cordifolia in Hooker's "Flora of British India". To prepare the dye the wood of the munjeet is first dried, then crushed and pounded, and then generally boiled with water, but sometimes merely left to steep in cold water. The solution obtained is of a deep red, and is used generally to dye coarse cotton fabrics, or the thread which is to be woven into such fabrics. Alum appears to be generally employed as a mordant, although myrobalans also are used in the Darjeeling district, and other astringents in the Maldah district. In the latter district munjeet is used in conjunction with iron salts to produce a deep purple, and in the Darjeeling district is mixed with indigo to form a maroon (McCann, "Dyes and Tans of Bengal"). The red and chocolates of East Indian chintzes were formerly entirely obtained from munjeet. The colours produced from munjeet are bright, but not so durable as those from ordinary madder, the inferiority being due, according to Stenhouse (Pharm. Jahr., 13, 148), to the presence of purpurin and an orange dye munjistin (purpuroxanthin carboxylic acid). Runge, who examined the tinctorial power of munjeet, concluded that it contained twice as much available colouring matter as madder; but later experiments have shown that the colouring power is actually less. Stenhouse found that munjeet garancine has only half the colouring power of garancine made from Naples roots, but that munjeet yields (according to Higgin) from 52-55 per cent, of garancine, whereas madder yields only 30-33 Per cent.
When madder was so much in vogue, munjeet was employed to some extent in this country, because it was considered that a good quality of this material contained as much colouring matter as madder, and could be applied by exactly the same methods.
The important colouring matter of munjeet is purpurin, and no alizarin is present in this root, and it is therefore interesting to note that whereas chay root contains alizarin, and munjeet purpurin, in madder both these substances exist together.
For the analysis of the phenolic constituents of munjeet, a modification of the method of Stenhouse, who first submitted this plant to examination, is to be recommended.
The ground dyestuff is digested with boiling alum solution for five hours, and the deep red extract treated with acid and allowed to cool. The red precipitate is collected, washed, and dried, and then extracted with boiling toluene (carbon disulphide was employed by Stenhouse), by which means the colouring matters pass into solution, and a resinous impurity remains undissolved. The colouring matters are now removed from the toluene by agitation with dilute potassium hydroxide solution, the alkaline liquid is acidified, and the precipitate collected, washed, and dried. In order to separate the constituents of this product it is extracted about ten times with boiling dilute acetic acid, and the dark red residue consisting of purpurin is crystallised from alcohol.
The earlier acetic acid extracts are mixed with hydrochloric acid, and the yellowish-red deposits are crystallised from alcohol. The product consists of orange-coloured leaflets, and is purpuroxanthin carboxylic acid or munjistin, as it was termed by Stenhouse, its discoverer, who first obtained it from munjeet. The properties of this compound have already been given in detail under Madder.
Munjeet has also been examined by Perkin and Hummel, who, in addition to the above constituents, detected the presence of a trace of purpuroxanthin (Chem. Soc. Trans., 1893, 63, 115).
Rubia khasiana
According to Watt ("Dictionary of the Economic Products of India," vol. vi., 571) there exists a variety of the Rubia cordifolia (Linn.) to which he has assigned the name of Rubia khasiana. This form, according also to Watt, is the richest in madder dye principles. It is occasionally met with in Sikkim, but attains its greatest development eastward in the Khasia and Naga Hills. It seems nowhere to be met with to the west of Sikkim. This dyestuff, according to Perkin and Hummel, yields colours similar to those given by Rubia cordifolia and Rubia sikkimensis (Kurz.), but it possesses a somewhat greater colouring power than either (J. Soc. Chem. Ind., 1894, 13, 348).
Rubia sikkimensis. (Kurz.)
This Indian dyestuff is closely allied botanically to Rubia cordifolia (Linn.); the dried root, which has a rough fluted appearance, is covered with a thick powdery layer of a grey pith-like substance, and looks altogether different from the round, smooth, straight roots of Rubia cordifolia. It occurs along with the allied species above mentioned in Sikkim and eastward to the Khasia and Naga Hills, where it is perhaps the most common as it is certainly the largest and most handsome species. Although the root has long been collected and sold in the bazaars at Darjeeling, the plant was not named or even known to exist prior to 1874, having escaped the attention of botanists, who appear to have mistaken it for Rubia cordifolia. The Lepchas of Sikkim do not appear to know that Rubia sikkimensis yields the madder dye, but in the Naga Hills and in Manipur this species alone supplied the brilliant red dye used by the hill tribes (see "Dyes and Tans of India," 154; Special Catalogue of Exhibits by the Government of India, Colonial and Indian Exhibition, 1886).
The examination of this root, by an identical process to that detailed in connection with Munjeet (Rubia cordifolia), has indicated that the phenolic constituents are purpurin, munjistin, and purpuroxanthin. A trace of a red colouring matter approximating to C15H8O6 in formula was also isolated, but the individuality of this compound has not been definitely established.
Dyeing Properties.
The application of Rubia sikkimensis root in dyeing presents no difficulty.
Calico printed with iron and alumina mordants may be dyed without any addition of calcium carbonate or acetate to the bath since there is a sufficiency of lime naturally present in the root. Generally speaking, the colours with the different mordants are similar to those obtained from madder, but the reds and chocolates are much bluer, being devoid of yellow, and the lilacs are decidedly greyer. The colours, however, are very similar to those obtained from Rubia cordifolia, the latter possessing nearly a half more dyeing power.
Comparing the colours on ordinary stripe mordanted calico given by pure purpurin and Rubia sikkimensis, a very marked difference is noticeable; the former gives very yellowish-reds and chocolates, full pinks and purplish lilacs, while the latter yields very bluish-reds and chocolates, bare pinks and greyish lilacs.
The dyeing power of Rubia sikkimensis is equivalent to its containing 0,37 0,5 per cent, purpurin (Perkin and Hummel, Chem. Soc. Trans., 1883, 63, 1157).
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