Morinda citrifolia
(CHAPTER I. The Anthraquinone Group.)

The Natural Organic Colouring Matters
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
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

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

The roots of Morinda citrifolia (Linn.) and Morinda tinctoria (Roxb.), known as "Morinda Root," are extensively employed in various parts of India under the general trade name of Suranji, more especially for dyeing reds, purples, and chocolates. These plants, the native names for which are Aal, A'l, Ach, or Aich, are to be met with in nearly all the provinces of India, either wild as in the jungles of Bengal, or cultivated in small patches in betelnut plantations, or near the homesteads of the dyers. In Bengal the plant is usually propagated by slips or cuttings, but in other parts it is raised from seed, as well as from cuttings. When the plants have attained a height of from 5-6 feet, that is, as a rule, about the end of the third year, the straight spindle-shaped roots which extend into the ground to the depth of 3 or 4 feet, are dug out and the upper portions of the plant are cut into slips to serve for the propagation of the next crop.

The colouring matter is found principally in the root bark, and is developed in greatest quantity at about the end of three or four years, depending upon the character of the soil. After this time the dyeing principle gradually disappears, and the matured trees, which eventually attain the height of a mango tree, contain hardly a trace of it. The thin roots are most valuable, roots thicker than half an inch being thrown away as worthless. They are or were mainly used for dyeing the thread or yarn from which the coloured borders of the cotton garments worn by the lower classes are woven, but they are also employed for dyeing the coarse cotton fabric called "Kharva," or for dyeing the silk thread which forms the border of the silk fabric known as "Endi cloth". The colours given by A'l range from a reddish-yellow through pink and various shades of red to a dark brown-red. The tint seems to depend primarily upon the age of the root, and upon the proportion of root bark to stem which is employed. The root bark gives the best reds; the dye in the woody part of the root is yellow, and hence when the wood preponderates over the bark the resulting dye is reddish-yellow.

About 1790 some of the powdered root under the name of "aurtch" came into the hands of Dr. Bancroft, who found little or no difficulty in applying it to both wool and cotton. At that time he considered that it might be profitably imported into Europe.

In 1832 Schwartz and Koechlin also examined the root under the names "Nona" and "Hachrout," and reported on its dyeing properties to the Industrial Society of Mulhouse. They referred to the fact that of all the Indian rubiaceæ examined by them, it contained the largest quantity of certain yellow principles of an acid character which not only necessitated the washing of the root with cold water before dyeing, but also made it requisite to add a certain proportion of sodium carbonate to the dye-bath in order to have a perfectly neutral bath. Their conclusion was that since morinda root only possessed one-third the dyeing power of a medium quality of madder, it could never compete with the latter in the European market.

About 1848 some morinda root was submitted for trial to some of the most experienced and skilful calico printers of the Glasgow district, all of whom concurred in declaring it not to be a dye at all.

In 1848 Anderson (Annalen, 71, 216) isolated from the root of the Morinda citrifolia by extraction with alcohol, a crystalline yellow substance which he named Morindin, and to which he assigned the formula C28H30O15. This substance when strongly heated, gave a crystalline sublimate morindon, and Anderson pointed out the great similarity, on the one hand, between morindin and ruberythric acid, and on the other between morindon and alizarin.

Rochleder (Annalen, 1852, 82, 205) gave it as his opinion that morindin and morindon were identical with the ruberythric acid and alizarin derived from madder, and Stokes (Chem. Soc. Trans., 2, [2], 333) by examining the absorption spectra of solutions of alizarin and morindon in sodium carbonate and in ether, came also to the conclusion that these two colouring matters consisted of one and the same substance. Stenhouse (J., 1864, 17, 543) formed a similar opinion, and pointed out that morindin not only gives morindon by heating, but also when digested with boiling dilute mineral acids.

On the other hand, Stein (J., 1866, 19, 645) found that the absorption spectra of alizarin and morindon are not identical, and that ruberythric acid and morindin are distinct substances, although the latter resemble each other in the respect that both are glucosides. The distinction between these compounds was rendered much clearer by the work of Thorpe and Greenall (Chem. Soc. Trans., 1887, 51, 52), and Thorpe and Smith (ibid., 1888, 53, 171), who showed that morindon possesses the formula C15H10O5; on distillation with zinc-dust it gave methylanthracene (melting-point 190-191°), and was evidently a derivative of methylanthraquinone. To morindin, the glucoside, the formula C26H28O14 was assigned.

Somewhat later Perkin and Hummel (Chem. Soc. Trans., 65, 851), during an examination of the Morinda umbellata (Linn.) (v. infra), proved that morindon contains three hydroxyl groups, and that Thorpe and Smith's hydrocarbon was β-methylanthracene.

Oesterle and Tisza (Arch. Pharm., 1907, 245, 534) consider that the true formula of morindin is C27H30O15, and that its hydrolysis with acid can be expressed as follows:
C27H30O15 + 2H2 = 2C6H12O6 + C15H10O5

*Simonsen (private communication in1918) considers this to be incorrect, and that the formula C26H28O14 of Thorpe, Greenall and Smith (cf. Perkin, Chem. Soc. Proc., 1908, 24, 149) correctly represents morindon. See also M. umbellata.The sugar thus formed is not fermented by yeast and yields an osazone melting at 197°.*

Morindin crystallises from 70 percent, alcohol in glistening yellow needles, which melt at 245°, and dissolve in alkaline solutions with a red colour. It does not dye mordanted fabrics.

Nono-acetylmorindin, C27H21O15(COCH3)9 (O. and T.), citron-yellow needles, melts at 236°?

Nono-benzoylmorindin, C27H21O15(CO.C6H5)9 (O. and T.), yellow needles, melts at 186°.

Morindon, the colouring matter of Morinda citrifolia, which is obtained by the hydrolysis of morindin, and also exists as a rule to some extent in the free state in this root, consists of orange-red needles, melting at 271-272°. It is soluble in alkaline liquids, with a blue-violet tint, somewhat bluer than the corresponding alizarin solutions, which, when treated with baryta water, give a cobalt-blue precipitate of the barium derivative. Its solution in sulphuric acid is blue-violet.

Triacetylmorindon, C15H7O5(COCH3)3, crystallises in citron-yellow needles, melting at 242°.

Morindon trimethylether, C15H7O2(OCH3)3, is a yellow crystalline powder, melting at 229°.

The exact constitution of morindon has not yet been determined, but it appears probable that if this compound contains in reality three phenolic hydroxyls, it most likely consists of a methyl anthragallol. If, on the other hand, as is quite probable, morindon contains an alcoholic group, which, according to Robinson and Simonsen, occurs in the isomeric aloe-emodin then its constitution will be represented as alizarin in which one of the three β-positions is occupied by CH2OH. Though such a constitution would appear to harmonise well with the present known properties of morindon, according to Simonsen (private communication) experimental evidence of a CH2OH group in this compound is lacking.

In many respects the Morinda citrofolia resembles chay root and madder, for, in addition to morindin and morindon, it contains a large quantity of chlorogenin, and certain yellow non-tinctorial substances, derivatives of anthraquinone. The preparation of morindon in quantity can be conveniently carried out by extraction with sulphurous acid, according to the details given in the sections on Madder and Chay Root for the isolation of natural alizarin. The non-tinctorial yellow compounds, which are obtained as by-products by this method, have not yet been studied in the case of the Morinda citrofolia, but in the case of the Morinda umbellata have been partially investigated (see below).

From the alcoholic extract of the Morinda citrifolia, Oesterle (Arch. Pharm., 1907, 245, 287) has isolated a small quantity of a substance which has the constitution of a monomethyl ether of a trihydroxymethylanthraquinone. It consists of yellow crystals, melting at 216, soluble in hot alkaline solutions, with a yellowish-red colour. It is not, as this author suggested, identical with the emodin methyl ether which exists in the Ventilago madraspatana (A. G. Perkin, Chem. Soc. Trans., 1907, 2074).

Dyeing Properties.

In Dr. G. Watts' "Dictionary of the Economic Products of India," Dr. J. Murray has written under the head of Morinda, not only a most complete account of the more important species, but full details of the native methods of dyeing with them. These methods of dyeing vary considerably in different parts of India, but they are all similar in general principles, and are practically crude processes of the turkey- red dyeing known in Europe. An extended series of dyeing experiments in connection with morinda root have been carried out by Hummel and Perkin (J. Soc. Chem. Ind., 1894, 1.3, 346), who find that by adopting certain precautions this dyestuff possesses a dyeing power which is greater than madder itself.

To obtain good results it is necessary, as previously indicated by the work of Schwartz and Koechlin (loc. cit.), to neutralise, or better still to remove, the free acid which exists in considerable quantity in the roots. Experiments also with the powdered morinda root which had been allowed to ferment, or had been digested with boiling dilute acid, as in the preparation of "garancine" from madder, showed that these preparations dyed exceedingly well when 1 per cent, of chalk was added to the dye-bath. It was found, for instance, that 7.5 grams of a sample of washed morinda root (equivalent to 10 grams of the unwashed root) had a dyeing power equal to 15 grams madder root of good quality.

The reds and pinks obtained on alumina mordant are yellower than the corresponding madder colours, the chocolate presents a similar difference in tone, and hence again appears fuller than a madder chocolate, whilst the lilac is distinctly redder. Oil-prepared calico mordanted as for turkey- red gives a very bright orange-red or scarlet similar in shade to that given by flavopurpurin, and fast to clearing with soap and stannous chloride. Chromium mordant on similarly prepared calico gives a full rich chocolate, and iron mordant yields colours varying from dull purple to black, according to the intensity of the mordant. On wool and silk, mordanted according to the usual methods, good chocolate-browns are obtained with chromium, orange-reds with alumina, bright orange with tin, and dark purple and black with iron mordant. All the colours referred to are as fast to soap as the corresponding madder colours. With respect to wool and silk in the unmordanted condition, these fibres may be readily dyed both with the washed and unwashed root, more or less rich orange or yellow colours, the brightness of which is enhanced by the addition of a little acetic acid to the dye-bath. These colours, however, which appear to originate from the glucoside morindin itself, are of a sensitive character towards alkalis and of little value.

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