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 methods which have been proposed for the analysis of indigo are of a varied character, and the literature upon the subject is extremely voluminous.
These may be classified as follows: methods (a) involving the extraction of impurities with volatile solvents (Schützenberger, Die Farbstoffe, ii., 526); (b) the extraction of indigotin with coal-tar oil (Stein, Die Prüfung der Zeugfarben); with aniline (Honig, Zeitsch. angew. Chem., 1899, 280); with phenol (Brandt, J. Soc. Dyers, 1898, 34); with naphthalene (Schneider, ibid., 1895, 194); with nitrobenzene (Gerland, J. Soc. Chem. Ind., 1897, 108); with acetosulphuric acid (Mohlau and Zimmermann, Zeitsch. farb. text. Chem., 1903, 10, 189); (c) the extraction of indigotin by sublimation (Lee, Chem. News, 1884); (d} the extraction of indigotin by processes of reduction, lime, and ferrous sulphate (Berzelius), stannous chloride and caustic soda (Dana, Jahres. f. prakt. Chem., 26, 398), zinc and caustic soda (Owen, Amer. Chem. J., 10, 178), grape sugar, alcohol and alkali (Fritzsche, Dingl. poly, J., 1842, 86, 306), and hydrosulphite and lime (Rawson, loc. cit.); (e) estimation of nitrogen (Voeller, Zeitsch. angew. Chem., 1891, no).
More important, however, are the methods based upon the titration of a solution of the sulphonated indigo by oxidising agents (/) chlorine water (Berzelius), chloride of lime (Chevreul, "Leçons d. chem. appliq. de la teinture," ii.), potassium chlorate and hydrochloric acid (Bolley, Dingl. poly. J., 119, 114), potassium dichromate and hydrochloric acid (J. pr. Chem., 1851, 18, and Schlumberger, Bull, de la Soc. Mullhouse, 1863, 210, 284), potassium dichromate and oxalic acid (Kinley, Chem. News, 1863, 210, 284), potassium ferricyanide (Ullgren, Annalen, 136, 96), and potassium permanganate (Mohr, Dingl. poly. J., 132, 363), and by reducing agents (g) sodium hydrosulphite (Müller, Ber., 1880, 13, 2283), and titanous chloride (Knecht, J. Soc. Dyers, 1904, 97, and ibid., 1905, 292).
Finally, (ti) colorimetric methods (Dingl. poly. J., 27, 54, and 40, 448); (i) spectrum analysis (Wollf, Zeitsch. anal. Chem., 17, 65, and ibid., 23, 92); and (k) dye trial methods (Chevreul, loc. cit., and Grossmann, J. Soc. Dyers, 1897, 124) have been proposed.
Of these methods of indigo analysisj modifications of Mohr's permanganate process are most generally employed, although others involving the reduction of sulphonated indigo with titanous chloride and sodium hydrosulphite are to some extent in vogue.
The Permanganate Methods.
In order to eliminate the error due to the oxidising action of permanganate upon substances other than indigotin which are present in natural indigo, Rawson, who has been the pioneer in this respect, has devised two processes.
Salting-out Method.
0,5 gram of finely powdered indigo mixed with its own weight of ground glass is sulphonated in a porcelain crucible by means of 20 c.c. of concentrated sulphuric acid at 70° for ¾-1 hour; the product is diluted with water to 500 c.c. and the liquid filtered to remove insoluble impurities. 50 c.c. of this solution are mixed with 50 c.c. of water and 32 grams of common salt, and after standing for i hour the precipitated sodium indigotin sulphonate is collected and freed from certain soluble impurities by washing with about 50 c.c. of salt solution (sp. gr. 1,2). The precipitate is dissolved in hot water, treated with 1 c.c. of sulphuric acid, diluted to 300 c.c., and titrated with a solution of N/50 potassium permanganate. The liquid gradually takes a greenish tint, and the final disappearance of this constitutes the end point of the reaction. According to Rawson, i c.c. of the N/5o permanganate corresponds to 0,0015 f Pure indigotin (J. Soc. Dyers, 1885, 74 and 201; "A Manual of Dyeing," Knecht, Rawson and Löwenthal, 1910, 817). Such a factor, however, according to Bloxam (loc. cit.) gives too high figures even with pure indigotin, and this has been corroborated by Frank and Lloyd (ibid., 1913, 226) who consider 0-00147 as more correct, and with this Rawson (ibid., 1914, 21) is now in agreement.
Barium Chloride Precipitation Process.
0,5 gram of indigo is sulphonated as before, and after diluting with water, but before making up to 500 c.c., 10 c.c. of a 20 per cent solution of barium chloride are added. The barium sulphate formed carries down with it the suspended impurities of the indigo, and the clear liquid can be pipetted off and titrated as before. The results are practically identical with those given by the "salting out" method (Rawson, J. Soc. Chem. Ind., 1899, 251).
Bloxam (ibid. t 1906, 735) notes that the barium precipitate thus produced is always coloured blue, and this is confirmed by Bergtheil and Briggs (ibid., 1906, 729). The latter authors contend that the results given by this modification of Rawson are therefore too low, and consider that this defect is obviated by adding instead of barium chloride freshly precipitated barium sulphate to the indigo mixture.
Grossmann (ibid., 1905, 308) throws down the impurities from the indigo solution with calcium carbonate. Bergtheil and Briggs (loc. cit.) and also Bloxam (loc. cit.) find that some quantity of the colouring matter is also precipitated in this way. Knecht, however, recommends its successful use even in larger quantity (J. Soc. Dyers, 1904, 97, and 1905, 292) in connection with his titanous chloride method; but Bloxam (loc. cit.) points out that such being the case this can only be due to the observance of conditions which are. not stated in Knecht's paper.
Hydrosulphite Method.
This process, devised by Müller (Ber., 1880, 13, 2283), depends upon the fact that sodium hydrosulphite (Na2S2O4) quantitatively reduces pure indigotin sulphonic acids to their corresponding leuco compounds. The solution of the hydrosulphite contained in a stone bottle is covered with a layer of petroleum to prevent oxidation and connected with a supply of hydrogen gas. By means of a siphon, or other convenient arrangement, the liquid can be drawn into a burette. The solution should be equivalent to about 2 c.c. 0,0025 gram of indigotin, and the titrations are performed in an atmosphere of hydrogen or coal gas.
Titanous Chloride Method.
This reagent is much more stable than sodium hydrosulphite, and Knecht (J. Soc. Dyers, 1904, 97, and 1905, 292) was the first to recommend its use for the analysis of indigo. The apparatus employed is similar in character to that required for the hydrosulphite process, and the titration is carried out in an atmosphere of carbon dioxide. If the reduction of the indigotin is effected by the titanium chloride in the presence of mineral acid, no definite end-point can be observed (Knecht), but by the addition of salts of tartaric acid this end-point is rendered quite definite.
In working with natural indigo, Knecht ("Manual of Dyeing"; Knecht, Rawson and Löwenthal, 822) sulphonates 1 gram of indigo with 5 c.c. of 100 per cent, sulphuric acid at 90° for 1 hour. The solution diluted to 300 c.c. is warmed and slowly treated with 12 grams of chalk, cooled, made up to 500 c.c., and 50 c.c. of the clear liquid, to which 25 c.c. of a 20 per cent, solution of Rochelle salt has been added, is titrated whilst boiling with titanium chloride.
On account of the sparing solubility of Rochelle salt, Bloxam (loc. cit.) recommends the use of sodium tartrate, but states that the presence of excess of this or of Rochelle salt (as advocated by Knecht) is to be avoided, or otherwise too high percentages of indigotin are indicated. In the case of pure indigotin (1 gram) sulphonated with 20 c.c. of 100 per cent, sulphuric acid, and made up to 500 c.c. with water, 25 c.c. of this liquid (containing 1 c.c. of acid) requires 4 grams of the sodium tartrate to give quantitative results when titrated with a solution of titanium chloride containing 1 c.c. of concentrated hydrochloric acid per 50 c.c. of solution.
Bloxam (Chem. Soc. Trans., 1905, 87, 975; J. Soc. Chem. Ind., 1906, 25, 735), Orchardson, Wood, and Bloxam (ibid., 1907, 26, 4), and Gaunt, Thomas, and Bloxam (ibid., 1907, 26, 1174) have critically investigated the subject of indigo analysis. Among the methods for preparation of pure indigotin, that involving the crystallisation of crude material from nitrobenzene was discarded as untrustworthy, but the elaborate process of the B.A.S.F. Co. (Brochure, 1900) was found to give a pure substance. On the other hand, sublimation under reduced pressure in Jena flasks immersed in fusible metal at 370-390°, gave, with synthetical indigo of 92 per cent, (approx.) a beautifully crystalline substance, which, after washing with boiling acetic acid, followed by boiling alcohol, was usually chemically pure. The permanganate factor resulting from experiments with these specially purified materials was 1 c.c. of permanganate solution 1/1000 = 0,00222 gram indigotin solution 1/5000, and is in agreement with that previously adopted by the B.A.S.F. Co. Wangerin and Vorlander (Zeitsch. Farben und Textilchemie, 1902, 1, 281) have stated that indigotin suffers loss of strength by oxidation, even when it is sulphonated by 94 per cent, sulphuric acid at 95-100° for half an hour, whereas 8 per cent, fuming acid gives a deterioration of from 2 to 14,2 per cent., according to the time of heating. With the indigotin, however, purified as above, Bloxam showed that heating with 20 per cent, fuming acid for ¾ of an hour at 97° gave no loss, whereas with 30 per cent, acid for 20 minutes at 97°, a deterioration of only 1 per cent, could be observed. In both these cases indigotin tetrasulphonic acid was produced.
The Tetrasulphonate Method.
* Prolonged heating should be here avoided, and it is preferable that the solution of the tetrasulphonate with its subsequent recrystallisation should be effected without unnecessary delay.As a result of these experiments a method for the analysis of indigo based on sulphonation with fuming acid was devised, 1 gram of the indigo, and 2-3 grams of purified sand (powdered glass contains iron, and should not be employed) is treated with 5 c.c. of 25 per cent, fuming sulphuric acid for half an hour in the water oven, and the solution is made up to 500 c.c. with water. 100 c.c. of this solution is treated with 100 c.c. of potassium acetate solution (450 grams per litre) which causes the precipitation of indigotin tetrasulphonate. The mixture is now warmed, and on cooling finally in ice-water,* the salt completely separates in a crystalline condition. This is collected by means of the pump on a Gooch crucible, and washed free from the brown supernatant liquid with a solution containing 90 grams of potassium acetate and 5 c.c. of acetic acid in 600 c.c. of water. The product is dissolved in 200 c.c. of water, and 20 c.c. of this solution, diluted with 80 c.c. of water, is treated with 0-5 c.c. of sulphuric acid, and titrated with permanganate (1/1000). In order to verify the accuracy of this method, Orchardson, Wood, and Bloxam studied the behaviour of indigo brown and indigo gluten, the main impurities of indigo, when submitted to the analytical process, as this subject had not been investigated by previous workers. Indigo brown when sulphonated with 96 per cent, acid gives, when dissolved in water, a dark-brown liquid, which is attacked by permanganate, though not perhaps so readily as the indigotin sulphonic acids, whereas indigo gluten gives similarly a light yellow solution, which is very rapidly oxidised by the reagent. On the other hand, kaempferol or indigotin yellow, treated in the same manner, gave a product which most readily absorbs permanganate, and, indeed, Rawson (J. Soc. Chem. Ind., 1899, 251) had already pointed out its deleterious effect in indigo analyses. Finally, these authors prepared and submitted to analysis by Bloxam's process mixtures containing known quantities of indigotin and one or other of all of these impurities, with the result that the colouring matter was thus estimated with considerable exactness. Bloxam (Chem. Soc. Trans., 1910, 97, 1473), by an adaptation of the pyridine method for the estimation of indirubin (loc. cit.), in which the impurities are eliminated by a process of extraction, has analysed natural indigos, and obtained the same figures as those given by the tetrasulphonate method. Again, by Knecht's titanium chloride method, and employing the modifications above described, this process can also be effectively worked. It is only reasonable to suppose that an analysis based on the selective precipitation of the sulphonated colouring matter is more likely to be efficient than that which presumes the deposition of varied impurities of a diverse chemical character by one specific reagent, and the somewhat lower results given by the tetrasulphonate method, as distinguished from those yielded by the processes previously in use, are in reality due to the almost complete elimination of these impurities from the indigotin sulphonic acid during the analysis. Rawson (loc. cit.) is, however, of opinion that the effect of these impurities on the analytical results has been much overrated; but, on the other hand, no experimental evidence is given in support of this view ("Manual of Dyeing," loc. cit., 8 1 8).
The action of potassium permanganate on solutions of the indigotin sulphonic acids is of interest, because the amount of the reagent necessary for the decolorisation of the liquid varies to some extent with the concentration (Rawson, "A Dictionary of Dyes, Mordants," etc., by Rawson, Gardner, and Laycock, 1901, 187). At the concentrations employed by the B.A.S.F. Co., and adopted by Bloxam (loc. cit.), i gram of indigotin as sulphonic acid requires 0,45 gram of permanganate for decolorisation, whereas the equation
5C16H10O2N2 + 4KMn04 + 6H2SO4
= 10C8H5O2N + 2K2SO4 + 4MnSO4 + 6H2O
implies that 0,4824 gram of the reagent is necessary. Again, for the oxidation under similar conditions of indirubin sulphonic acid considerably less permanganate is required, although the oxidation in this case is of a slower character. Bloxam and Perkin (Chem. Soc. Trans., 1910, 97, 1462) consider, therefore, that the oxidation is of a complex nature, and consists either (a) of two distinct stages in the formation of isatin sulphonic acid, or (b) of two distinct reactions involving the production of two separate substances. According to the first suggestion the isatin sulphonic acid formation would be preceded by that of an intermediate compound (1), whereas by the latter, in addition to isatin sulphonic acid, a dehydroindigotin sulphonic acid (2) may be produced [KUVA PUUTTUU]
In case the first product of the reaction consists entirely of dehydroindigotin sulphonic acid, this must, prior to further oxidation to isatin sulphonic acid, take up two molecules of water with formation of the sulphonic acid of dihydroxyindigotin (3).
In regard to the very small amount of permanganate required for the decolorisation of the indirubin sulphonic acid a similar explanation can be adopted.
Analysis of Indigos Containing Starch.
It has been shown by Thomson (J. Soc. Dyers, 1911, 27, 49) that the indigotin value of samples of indigo adulterated with starch when estimated by the method of sulphonation and titration with permanganate recommended by Rawson and Bloxam give far too low results. Thus an indigo containing starch by Rawson's method gave 18,8 per cent, of indigotin, whereas after removing the starch with 4 per cent, hydrochloric acid, 35,01 per cent, of indigotin was shown to be present. On the other hand, according to this author when hydrochloric acid is employed in this way for the removal of the starch the analytical results are still too low. Frank and Perkin (J. Soc. Chem. Ind., April, 1912) corroborated these experiments in so far that indigos containing starch give low figures when directly analysed, and it seems evident that a destruction of the indigotin occurs during sulphonation, and is to be attributed to the reducing action of the starch degradation products. As a result, however, of numerous experiments, no loss of indigotin could be observed even by long digestion of mixtures of starch and indigo with boiling dilute hydrochloric acid, and after removal of starch in this manner correct figures were always obtained by the employment of Bloxam's tetrasulphonate process.
Testing of Indigo-dyed Woollen Materials.
An important method for ascertaining the quantity of indigo present on such dyed materials has been devised by Green, Gardner, Lloyd and Frank (J. Soc. Dyers and Cols., 1913, 226; 1914, 15). This consists essentially in removing the indigotin from the fibre with boiling pyridine in a modified form of Soxhlet apparatus, and subsequently concentrating the pyridine solution. The main bulk of the indigotin separates as crystals and to complete the precipitation 50 per cent, of alcohol is then added. The product is collected, washed successively with 50 per cent, alcohol, 2 per cent, caustic soda, hot 1 per cent, hydrochloric acid, hot water, alcohol, alcohol and ether, and finally dried and weighed. It should test 100 per cent, by the tetrasulphonate method.
For fuller details the original paper should be consulted.
Ei kommentteja :
Lähetä kommentti