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.
Under the name of Brazilwood certain varieties of the so-called "soluble" red woods are known, the term "soluble" being employed to distinguish them from the dyestuffs of the barwood class, which only with difficulty yield their colouring matters to boiling water. These soluble red woods give with aluminium mordanted fabrics a bright-red shade, which in each case is derived from one and the same colouring matter, and all are botanically allied, in that they consist of the wood of various species of Caesalpinia. About nine varieties have been employed as dyestuffs, of which the following are the best known.
Fernambuco or Pernambuco wood is considered to be the richest in colouring matter, and is the product of the Caesalpinia crista, a tree which is abundant in Jamaica and Brazil.
The true Brazilwood is derived from the Caesalpinia braziliensis, and is said to contain only one-half the colouring matter which is present in the Fernambuco variety. It is obtained exclusively from Brazil.
Sappanwood is obtained from the Caesalpinia sappan, a tree which is common to the warmer regions of Asia. The so-called Limawood is a variety of sappan, and the dyewood imported from the Philippine Islands is an inferior quality of this product.
Peachwood is the product of the Caesalpinia echinata, which occurs in Central America and the northern parts of South America.
These woods, which are very hard, and of a deep red colour, come into the market in the form of billets varying in weight from a few pounds up to a hundredweight. If freshly cut the internal colour of the wood is seen to be light yellow, but this soon changes to deep red in contact with air.
Some varieties of these woods were employed for dyeing purposes in India long before the discovery of America, and it is stated that when South America was discovered by the Spaniards, in 1500, the northerly portion of the country was named Brazil (from braza, fiery red), because this red dyewood was found there in such immense quantities.
Owing to the fugitive character of the colours yielded by Brazilwood it is now only employed to a somewhat limited extent.
Brazilin, C16H14O5, the colouring principle of Brazilwood, was first isolated in a crystalline condition by Chevreul (Ann. Chim. Phys., (1), 66, 225); but was not further examined until 1864, when Bolley (Schweiz. poly. Zeitsch., ix., 267) assigned to it the formula C22H20O7. Subsequently Kopp (Ber., 6, 446) proposed the formula C22H18O7, but it was left to Liebermann and Burg (Ber., 9, 1883) to determine the exact composition of this substance, and their formula, C16H14O5, is in use at the present time. To prepare brazilin from the wood itself, it is best to employ the commercial extract. This is stirred up with a considerable quantity of sand, the product extracted with cold ether, the ethereal liquid evaporated to a small bulk, treated with a little water, and allowed to stand for some days. Crystals slowly separate, and these are purified by crystallisation from a little water.
This method is, however, tedious, and the usual source of brazilin consists of the crude crystalline crusts of this substance which are frequently deposited from Brazilwood liquor, an intermediate product in the manufacture of Brazilwood extract. The crude substance is best purified by two or three crystallisations from water, to which a little sulphurous acid has been added (Gilbody and W. H. Perkin, and Yates, Chem. Soc. Trans., 1901, 79, 1396). Brazilin crystallises in two forms, either as colourless needles containing 1½H2O, or as colourless prisms with 1H2O. It is readily soluble in alcohol and water, and dissolves in a dilute solution of sodium carbonate with a beautiful carmine-red colour.
Tetraacetylbrazilin, C16H10O5(C2H3O)4, colourless needles, melting-point 149-151° (Liebermann and Burg); triacetylbrazilin, Cl6H11O5(C2H3O)3, needles, melting-point 105-106° (Buchka and Erck, Ber., 18, 1139); brombrazilin, C16H13BrO5, brown-red leaflets (Buchka and Erck); dibrombrazilin, C16H12Br2O5, leaflets (Schall and Dralle, Ber., 23, 1550); tetraacetylbrombrazilin, C16H9BrO5(C2H3O)4, needles, melting-point 203-204° (Buchka, Annalen, 17, 685); tetraacetyldibrombrazilin, C16H8Br2O5(C2H3O)4, melting-point 185° (Schall and Dralle); tribrombrazilin, C16H11Br3O5 (Schall and Dralle); dichlorbrazilin, C16H12C12O5 (Liebermann and Burg); and tetrabrombrazilin, C16H10Br4O5, fine red needles (Buchka and Erck), have been prepared.
When brazilin is methylated with methyl iodide in the usual manner, it gives brazilin trimethyl ether (Schall and Dralle, Ber., 20, 3365; Herzig, Monatsh., 14, 56; and Schall, Ber., 27, 525), C16H11O2(OCH3)3, prisms, melting-point 138-139°, which on acetylation yields acetylbrazilin trimethyl ether, C16H10O2(OCH3)3(C2H3O), melting-point 171-173° (Herzig, Monatsh., 15, 140; Schall, Ber., 27, 326).
According to Gilbody, W. H. Perkin and Yates (Chem. Soc. Trans., 79, 1403), large quantities of the trimethyl ether are conveniently prepared as follows: 143 grams of brazilin dissolved in the smallest possible quantity of methyl alcohol are treated with 35 grams of sodium in methyl alcohol and methyl iodide (250 grams) and the mixture is heated fifty hours to 60-65° in absence of air. A second method, employed also by v. Kostanecki and Lampe (Ber., 35, 1669), consists in methylating brazilin with excess of dimethyl sulphate and alkali.
The difficulty experienced in fully methylating brazilin is evidence of the presence of an alcoholic group; but the tetramethyl ether, C16H10O(OCH3)4, melting-point 137-139°, has been prepared by Schall by treating the sodium compound of the trimethyl derivative suspended in benzene with methyl iodide at 120° (compare also Herzig, loc. cit.). From this substance the following derivatives have been prepared:
Brombrazilin tetramethyl ether, C16H9BrO.(OCH3)4, prisms, melting-point 180-181° (Schall and Dralle, Ber., 21, 3014), and dibrombrazilin tetramethyl ether, C16H8Br2O.(OCH3)4, melting-point 215° (Schall and Dralle, Ber., 23, 1432).
When brazilin is submitted to dry distillation, it gives resorcin (Kopp, loc. cit.), and by fusing it with potassium hydroxide Liebermann and Burg obtained resorcin, and Herzig (Monatsh., 27, 739) protocatechuic acid. With nitric acid brazilin yields trinitroresorcinol (Reim, Ber., 4, 334).
When brazilin, the colouring principle, is oxidised under suitable conditions, it is converted into brazilein, the true colouring matter, C16H14O3+O=C18H12O5+H2O, and for this purpose the action of air on an alkaline brazilin solution, alcoholic iodine (Liebermann and Burg), potassium nitrite and acetic acid (Schall and Dralle), nitric acid in the presence of ether (Buchka and Erck), and sodium iodate (Mayer, Zentr., 1904, i., 228) have been employed. It can, however, be more economically prepared from Brazilwood extract in the following, manner (Hummel and A. G. Perkin, Chem. Soc. Trans., 1882, 41, 367):
To an aqueous solution of the extract of the wood an excess of ammonia is added, and air is aspirated through the liquid. A precipitate of the impure ammonium salt of brazilein gradually separates, and this is collected, dissolved in hot water, and treated with dilute acetic acid (sp.gr. 1.04). A brown viscous precipitate of the crude colouring matter is thus obtained, which is extracted with hot dilute acetic acid, and the extract evaporated on the waterbath. Crystals of brazilein separate, which are collected and washed with acetic acid.
Brazilein consists of minute plates possessing a strong metallic lustre, and by transmitted light a reddish-brown colour. It is very sparingly soluble in all the usual solvents, and cannot be recrystallised in the ordinary manner. It is in reality the colouring matter of Brazilwood, and possesses strong tinctorial property. Alkaline solutions dissolve it with a deep-red coloration, which on standing in air passes gradually to brown.
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The commercial preparations of Brazilwood known as Brazilwood extract and Brazilwood liquor, are prepared by boiling the ground fresh wood with water, and evaporating the decoction thus obtained to various degrees of consistency without access of air, or as rapidly and at as low a temperature as possible, e.g. in vacuum pans.
Dyeing Properties.
Before dyeing the logs, as imported, are rasped to a coarse powder, and this is then usually moistened with water and allowed to ferment for some weeks. This operation is performed in order to increase the colouring power of the wood, and there can be little doubt that a considerable quantity of the brazilin present is thereby oxidised to the colouring matter brazilein. It has been considered by some that the fresh wood contains in reality a glucoside of brazilin, which, under the influence of fermentation, is hydrolysed, but no evidence has been forthcoming in support of this suggestion.
Although still used in calico printing and in wool dyeing, Brazilwood and its allies have lost their importance, chiefly because of the fugitive character of the colours they yield. In calico printing sappan liquor is employed for producing steam reds and pinks, the mordant used being aluminium acetate or stannic oxalate, separately or combined, together with some oxidising agent, e.g. potassium chlorate or a copper salt. It also enters into the composition of steam chocolates and certain steam colours in conjunction with other dyewood extracts. These woods have also been much used in the past along with garancine in dyeing the reds, chocolates, and other colours of cheap prints.
In wool dyeing these woods have been applied for the purpose of dyeing reds and various shades of claret and brown, the wool being previously mordanted with alum and cream of tartar or oxalic acid, or with potassium dichromate, in which case other dyewoods, e.g. logwood and old fustic, are applied in addition. The colours produced by this method are now only used to a limited extent.
In cotton dyeing, peachwood-red was formerly obtained by first preparing the cotton with tannin matter, then mordanting with a stannic salt, and finally dyeing with peachwood, sappan-wood, etc. Browns were obtained by the use of logwood in addition, with or without a final passage through a ferric salt solution (nitrate of iron). These colours are now replaced by others obtained from coal tar.
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