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Subsidiary Dyes in Commercial Agalma Black 1OB'.' Spectrophotometric Method-for Their Identification and Quantitative Estimation By Wallace R. Brode NATIONAL BUREAU OF STANDARDS, WASHINGTON, D. C.
ARIATIONS in quality of commercial dyes are largely azotized p-nitroaniline. I n Figure 1 are given the absorption dependent on variations in the amounts of subsidiary spectrum curves of these compounds and of agalma black dyes normally formed in their manufacture and present 10B, the latter being the standard curve as determined by in the finished product. Spectrophotometric measurements previous work on this dye.4 All these compounds were prepared in the laboratory of solutions of such dyes do not give satisfactory estimates of these i m p ~ r i t i e s , ~whereas )~ further work s h o w that and purified by repeated salting from solution. The strength spectrophotometric measurements of the exhaust liquors of these dyes was determined by titration with titanous obtained from standard dyeings made under suitable con- chloride in the usual manner. A study of the dyeing properties and color reactions of ditions give this information. The determination of the presence and amount of sub- these dyes has shown that either 2-p-nitrobenzeneazosidiary dyestuffs in agalma black 10B is important from the l-amino-8-naphthol-3,6-disulfonicacid (acid coupling) or could be idenstandpoint of defining certain standards for this dye. This l-amino-8-naphthol-3,6-disulfo-7-azobenzene t i f i e d i n t h e presence of paper-deals with the identia g a l m a black 10B. The f i c a t i o n and quantitative identification of 2-p-nitroestimation of the subsidiary spectrophotometric method has been developed b e n z e n e a z0 - 1- a m i n o -8dyes which are formed in for the quantitative determination of impurities naphthol-3.6-disulfo-7-a z o the preparation of the dye in agalma black 10B. p-nitrobenzene in the presagalma black IOB. It was The absorption spectra in the visible have been deence of agalma black 10B necessary in the course of termined for agalma black 10B, acid fuchsin (l-aminocould be determined only if this work to prepare and 8-naphthol - 3,6-disulfo - 7 - azobenzene), 2 - p - nitrobenthe amount was large and study these subsidiary dyes zeneazo-l-amino-8-naphthol-3,6-disulfo-7 azo-p-nitrothen by difference in titraand to study their color benzene, and for 2-p-nitrobenzeneazo-l-amino-8tion and the general slope reactions and dyeing propnaphthol-3,6-disulfonicacid. of the shorter wave-length erties, both as s e p a r a t e Data have been obtained relating to the mechanism side of the absorption band. dyes and as mixtures with and reactions of mixed dyeings. agalma black 10B. As a 2-p-Nitrobenzeneazo 1 Amino 8 Naphthol-3,6result of this study a method Disulfonic Acid is proposed for the identiThis acid was prepared from recrystallized p-nitroaniline fieation of these dyes in the presence of agalma black 1013. acid. Molecular quanI n the commercial preparation of agalma black 10B and l-amino-8-naphthol-3,6-disulfonic (Colour Index No. 246: Schultz No. 217) (2-p-nitroben- tities of the two intermediates were used and care was taken zeneazo-l-amino-8-naphthol-3,6-disulfo-7-azobenzene) one to insure the absence of any free diazonium salt a t the end molecular portion of diazotized p-nitroaniline is coupled of the reaction. The coupling was carried out in an acid solution and the resulting mixture allowed to stand for with one molecular portion of l-arnino-S-naphthol-3,6-disulfonic acid in mineral acid solution and, after coupling 24 hours. It was then made alkaline and salted out, taken is complete, the red precipitate is made alkaline with sodium up in solution, and the solution made acid and the dye carbonate, when the whole passes into solution with a blue salted out again. This dye is the only one of the four that color. One molecular portion of diazotized aniline is then were studied which gave a marked color change in going added to this alkaline solution and after the coupling is from acid to alkaline solutions or the reverse. It was red complete the dye is salted out, filtered, washed, and dried. in acid and blue in alkaline solutions. This blue was obtained only by the use of strong alkali-i. e., in a 10 per The filtrate from this dye is almost invariably red. Assuming the l-amino-8-naphthol-3,6-disulfonic acid used cent sodium hydroxide solution. Weaker solutions gave a to be pure,S the impurities which might be present in the purple rather than a blue, as did also solutions of sodium finished dye are (1) l-amino-8-naphthol-3,6-disulfo-7-azo-carbonate. The sodium carbonate solutions faded in a day benzene, which is formed when an excess of 1-amino-8-naph- or two, but the deep blue, more strongly alkaline solution thol-3,B-disulfonic acid is used or there is an incomplete of the dye in sodium hydroxide, although it faded very coupling of the two intermediates; ( 2 ) 2-p-nitrobenzeneazo- slowly, maintained its blue color while the purple carbonate l-amino-S-naphthol-3,6-disulfonicacid, which would be color faded t o a light orange. This color change is probably formed in case a deficiency of aniline were used; and ( 3 ) due to the presence of the nitro group, for the 1-amino-S2- p -nitrobenzeneazo- 1-amino-8-naphthol-3,6-disulfo-7-azo-p-naphthol-3,6-disulfo-7-azobenzenedye, which is quite similar nitrobenzene, which would be formed by an excess of di- except for the nitro group, does not give such color reactions. The absorption spectrum curves for these alkaline and acid 1 Received February 26, 1926. * Published by permission of the Director, National Bureau of Stand- solutions are given in Figure 2. A 0.4 per cent dyeing made under the standard conditions ards. 8 Appel and Brode, THIS JOURNAL, 16, 797 (1924). as employed in this work4 did not exhaust completely, there Appel, Brode, and Welch, I b i d . , 18, 627 (1926). being about 2 per cent of the dye still in solution, indicating 8 A study is now being made of the dyes derived from certain known poor affinity between the dye and wool. The same was true impurities which are sometimes found in commercial H-acid, the results of with a more concentrated dyeing. For example, in the case which will be presented in a later paper.
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of a 16 per cent dyeing, 30 per cent of the dye still remained in the solution. The 0.4 per cent dyeing was a bluish red, somewhat bluer than the corresponding 1-amino-8-naphthol3,6-disulfo-7-azobenzene dyeing. The 16 per cent dyeing was a dark red-brown. l-Amino-8-Naphthol-3,6-Disulfo-7-Azobenzene
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for this dye than for agalma black 10B, or in other words, it took a smaller amount of this dye to satisfy completely the absorptive powers of the wool. The 0.4 per cent dyeing was a bluish red of a slightly redder shade than the nitro dye. The 16 per cent dyeing was a dark brown. Figure 3 gives the absorption spectrum curves for this dye in acid, and weak and strong alkaline solutions.
This dye was prepared by coupling molecular portions 2-p-Nitrobenzeneazo-1-Amino-8-Naphthol-3,6of diazotized aniline and l-amino-8-naphthol-3,6-disulfonic Disulfo - 7-Azo-p-Nitrobenzene acid in an alkaline solution. The temperature was kept This dye was prepared in the usual manner, the 2-pbelow 4" C. a t all times, and after coupling the solution was allowed to stand for 24 hours before filtering. The nitrobenzeneazo-l-amino-8-naphthol-3,6-disulfonicacid dye solution was then saturated with salt, the dye filtered off, being first prepared as previously described and then this redissolved, and again filtered, salted out, filtered, and dried. compound coupled with another molecular portion of diazotized p-nitroaniline in an alkaline solution. During this latter coupling the temperature was maintained below 5' C., and the whole mixture was allowed to stand 24 hours before salting out and filtering. It was then redissolved and again salted out of solution for further purification. The dye gives a greenish blue solution in water, is precipif tated out of solution by acids, and gives a slightly darker blue solution in weak alkalies, but strong alkalies will also precipitate it out of solution. Complete exhaustion was obtained in a 0.4 per cent dyeing and only 4 per cent remained in a 16 per cent dyeing. The 0.4 per cent dyeing had a considerably greener shade than the standard agalma black 10B dyeings of the same strength. The identification of a small amount of this dye in agalma black 10B is not possible spectrophotometrically, because its shade and color reactions are very similar to this dye; however, for the same 200, ! reasons small amounts of this dye are not objectionable. 400 420 440 460 500 520 580 600 620 6 r 0 660 '10 760 WAVE L E N G T H It would also be impossible to apply the dyeing method Figure 1-Absorption Spectra of of concentrating the impurity, because wool has an even (1) !-Amino-8-naphthol-3,6-disulfo-7-azobenzene.(21 2-$-Nitrobengreater affinity for it than for agalma black 10B. If this zeneazo-l-amino-5-naphthol-3,6-d~sulfonic acid (3) 2-$ Nitrobenzeneazo1-amino -8- naphthol-3,6-disulfo-7-azo-p-nitrobenzene(4) Agalmd black impurity is present in any large amount i t may be detected 10B The cell thickness in all cases was 5 cm and the solvent distilled water Concn , cg per liter (1) 0 5 0 : (2) 0 5 4 , (J) 0 61; (4) 0 33. by the shift in the peak of the band and the rise in the band on the shorter wave-length side. The strength of the dye was then determined by titration Because the dye is precipitated by acids and strong alwith titanous chloride. The neutral and acid solutions kalies only the absorption curve in a neutral solution is of the dye are red and the alkaline a pale orange, the latter given (Figure 1). being quite stable as compared with the color of the 2-pnitrobenzeneazo-1-smino-8-naphthol-3,6-disulfonicacid dye. I n dilute alkali or carbonate solution the dye gives a curve somewhat similar to that of the nitro dye, but there is a decided difference In the color as obtained in strong alkaline solutions. The fact that these two possible red impurities in agalma black 10B give absorption curves in a neutral or slightly acid solution which are almost identical, both in height and wave length, for equal concentration would make their identification in the presence of each other quite difficult were it not for the distinctly different color reaction in alkaline solutions. The occurrence of these two impurities together in the ordinary course of the manufacture of agalma black 10B, although possible, is not generally found, and no cases of this sort were observed in any of the If 2-p-nitrobenzeneazo-l-amino-8samples investigated. naphthol-3,6-disulfonic acid was detected in a sample of agalma black 10B, i t would be necessary to make the par- Figure 2-Absorption S ectra of 2-p-Nitrobenzene-l-Amino-ENaphtKol-3.6-Disulfonic A d d tially exhausted solution alkaline to determine the amount per cent HC1 solution. (2) In 1 per cent NaOH solution. of the 2-p-nitrobenzeneazo-l-amino-8-naphthol-3,6-disul- (3)(1)n! In10 1per cent NaOH solution. Concn., 0.54 cg. per liter: cell thickfonic acid dye present and from these data the amount, ness, cm. if any, of l-amino-8-naphthol-3,6-disulfo-7-azobenzenecould Agalma Black 10B be determined. I n its dyeing properties l-arnino-8-naphthol-3,6-disulfo-7- The agalma black 10B (2-p-nitrobenzeneazo-l-amino-8azobenzene was similar to the nitro dye and did not give naphthol-3,6-disulfo-7-azobenzene)used in this investigation, an exhausted solution even on a 0.4 per cent dyeing, about other than the commercial samples, was prepared in the 2 per cent of the dye still remaining in solution. I n the case laboratory from purified intermediates and salted out a of a 16 per cent dyeing about 25 per cent of the dye remained number of times to remove possible impurities. It gave i n solution, indicating that the wool had much less affinity no color change in alkaline solutions and took on only a
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Having determined a suitable strength of solution to use, slight green tinge in acid solution, the latter being due to some extent to the colloidal form of the dye as it soon pre- a series of concentrated dyeings was made on a number of commercial samples to obtain representative impurities. cipitated out when allowed to stand. Its 0.4 per cent dyeing matched the standard dyeings used Among the samples used for these experiments were Nos. 6, in the previous work on this dye and completely exhausted 7 , 10, 14, 20, 21, and 22 as shown in Figure 2 in the previous the dye solution. The 16 per cent dyeing did not exhaust paper in this series4 The dyeings agreed with the previous quite so well as the di-p-nitro dye, but left behind about estimations of the colors; that is, those previously given as 10 per cent of the dye originally in solution. I n Figure 1 being strongly red on a 0.4 per cent dyeing gave dark red is given the absorption curve of agalma black 10B in distilled solutions, those which were designated as 0. K. gave red water solution, which corresponds with the standard curve solutions with a purple tinge and were not as dark as the previously determined. RR or RRR solutions, while those which were rated as G gave blue and bluish green solutions. This method gives a much easier means than the visible comparison of dyeings for the estimation of the shade of the dye, as it increases the impurity color content in relation to the agalma black 10B content. Representative curves of these dyes are given in Figures 5, 6, 7 , and 8. I n addition there is also shown in each of these graphs the standard curve for agalma black 10B, reduced to a proportionate height. By a method of differences the third or impurity curve is determined. Identification and Estimation of Amount of Subsidiary Dye
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Spectra of l-Amino-8-Naphthol-3,6-DIsulfo7-Azobenzene (1) In 1 per cent HCl solution. (2) In 1 per cent NaOH solution. (3) In 10 per cent NaOH solution. Concn., 0.50 cg. per liter; cell thickness, 5 cm. Figure 3-Absorption
Dyeing Properties of Commercial Agalma Black 10B
It is well known that the mother liquors from strong dyeings made with commercial samples of agalma black 10B are often dark red because of the red impurities present in the dye. A spectrophotometric study of such liquors revealed the fact that there was a certain equilibrium between the amount of impurity and agalma black 10B that was adsorbed. An increase in the ratio of the impurity present to the amount of agalma black 10B caused an increase in the amount of agalma black 10B remaining in the dye solution after the dyeing had been made. This increase in the amount of agalma black 10B in the dye liquors was caused by a rather small increase in the amount of impurity present. Partly, but, as will be shown later, not solely, for this reason, it was impossible to use the relative heights of the two absorption bands to determine the amounts of impurity present in the original solution. A series of dyeings of commercial samples of agalma black 1OB varying in strength from 10 to 20 per cent was made in order to determine what particular strength of dyeing would leave the greatest ratio of impurity to true agalma black 10B in the mother liquors. The results are given graphically in Figure 4. Dyeings stronger than 16 per cent left an increasing proportion of agalma black 10B to impurity in the mother liquors and dyeings weaker than 15 per cent gave too great an exhaustion of the bath for the present purposes. The average amount of impurity remaining in most commercial samples after concentration by dyeing is not enough to give a 0.04 per cent dyeing. The actual reaction in the foregoing process of dyeing is not a concentration of the impurity, as the amount of impurity in the solution is much less than in the original dye. The point is, however, that the concentration of the impurity in relation to other material, and especially agalma black 10B, is greatly increased.
When these solutions containing the red impurities were treated with alkali, no blue color developed but there was a light greenish or brown tinge which by comparison with dyeings made with pure agalma black IOB and l-amino-8naphthol-3,6-disulfo-7-azobenzene,and agalma black 10B sulf o n i c and 2-p-nitrobenzeneazo-l-amino-8-naphthol-3,6-di acid was found to be due to the presence of a small amount of agalma black 10B along with the l-amino-8-naphtho1-3,6disulfo-7-azobenzene. I n no case was a blue color obtained by making alkaline the red solutions from commercial samples, and the only case in which a blue color was obtained was where the 2-p-nitrobenzeneazo-l-amino-8-naphthol-3,6disulfonic acid was actuallv l
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is therefore assumed that 1 l l ! l l l l t h e i m p u r i t y , as far as studied a t least. consists almost, if not entirely, of Ij i I a m i n o-8-naphthol -3,6-diI sulfo-7-azobenzene. This 1 fact is also confirmed by the position of the absorp- 2 tion band of the impurity, 51 although this alone could .% '*I not be used as proof because 3 of t h e r a t h e r i n d i r e c t method of its determination and the large possibility for error in the exact location of the Deak of the band. "." I 10 11 14 18 10 D As seen in Figure 1, the Per cent dyeing absorption band Of the Figure &Amount of Agalma amino-8-naphthol-3,6-di- Black IOB ( I ) a n d A m o u n t of s u 1f o - 7 - a z o b e n z e n e dye g:k:fJFif ~ ~ D $ ~ s h o w s n o a b s o r p t i o n a t mercial S a m p l e Containing APproximately 1.75 Per c e n t Subsidiary about 620 mU so that it mag Dye be assumed that the height of the absorption band of the mother liquor of the commercial sample a t 620 is due solely to the quantity of agalma black 10B present. On the basis of this assumption the standard agalma black 10B curve is drawn in, reduced of course to a height corresponding to the height of the curve a t 620, and the difference between these two curves is plotted on the same ordinate, thus giving a third or impurity curve. From the height of this impurity curve whose maximum I
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Figure 5-Absorption Spectra of (1) Mother liquor from a 16 per cent dyeing of a commercial sample of agalma black 10B whose shade was rated as R by dyeing tests at a strength of 0.4 per cent. (2) Agnlma black 10B spectrum. (3) Impurity spectrum.
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Figure 6-Absorption Spectra of (1) Mother liquor from 9 16 per cent dyeing of a commercial sample of agalma black 10R whose shade was rated as R R R by dyeing tests. (2) Agalma black 10B spectrum. (3) Impurity spectrum.
may vary slightly from 530 mp because of its method of de- would give the effect of both of them, and then making the termination, one may determine the amount of l-amino-8- solution strongly alkaline and determining the height of naphthol-3,6-disulfo-7-azobenzenepresent in the dye liquor. the band at 600 mp, which is the maximum of 2-p-nitrobenThis value does not represent the amount present in the zeneazo-l-amino-8-naphthol-3,6-disulfonicacid. From Figure 3 the amount of this dye could be calculated, and from original dye but is a function of this amount. The amount originally present in the dye solution can be this result and the results obtained from the curve in acid determined by reference to Figure 9, which gives the curve solution, the amount of l-amino-&naphthol-3,6-disulfo-7representing the relation between the amount in the original azobenzene could be determined. dye and the amount in the partially exhausted dye 'solution. This curve was obtained by making dyeings with pure Effect of Filtration of Partially Exhausted Dye Solutions agalma black 10B containing known amounts of l-amino-8Although it is a comparatively easy matter to make a naphthol-3,6-disulfo-7-azobenzenewhich were varied from standard dyeing such as a 0.4 per cent dyeing, in which the 0.1 per cent to 10 per cent of added impurity. To check dye solution is completely exhausted, it is much more diffithese results further dyeings were made on commercial cult to make saturated dyeings in which there is more dye samples containing a previously determined rather small in solution than can possibly be adsorbed by the fiber and amount of impurity, to which were added more knowri get anything like the close agreement in results that is obamounts of l-amino-8-naphthol-3,6-disulfo-7-aeobenzene.tainable in exhaustive dyeings. I n the course of these Plotting the values obtained from the impurity curves in experiments i t was found that filtration of the acid dye each of these dyeings gave this curve from which the im- solution after the dyeing, tended to remove the agalma purity present may readily be determined.
Figure 7-Absorption Spectra of Mother liquor from a 16 per cent dyeing of a commercial sample of agalma black 10B whose shade was rated as O . K . by dyeing tests. (2) Agalma black spectrum. (3) Impurity spectrum. (1)
Figure 8-Absorption Spectra of (1) Mother liquor from a 16 per cent dyeing of a commercial sample of agalma black 10B whose shade was rated as G by dyeing tests. (2) Agalma black spectrum. (3) Impurity spectrJm. (4) (Note apparent yellow impurity.)
Since both 1-amino-8-naphthol-3,6-disulfo-7-azobenzene black 10B, with the removal a t the same time of only a and the 2-p-nitrobenzeneazo-l-amino-8-naphthol-3,6-disul- slight amount of impurity from the solution. fonic acid give peaks very near to each other and at pracThis effect is clearly shown in Figure 10, in which the tically the same absorption coefficient for equal concentrations concentrations in centigrams of both the impurity and the in solution, it is nearly impossible to determine these in a agalma black 10B are plotted against the number of times mixed solution of the two. This can be done, however, by the solution has been filtered and may be explained by the determining the height of the band in acid solution which larger colloidal proportions of the agalma black 10B and the
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greater solubility and lower molecular weight of the impurity. This can be demonstrated by placing a drop of mixed solution of the two dyes on a piece of filter paper, in which the blue spreads out in a ring and beyond the rather sharply defined edge of this ring the red spreads for a considerable distance. Because of this fact it is impossible to dram any safe conclusions from the relative heights of the two absorption bands in the solutions, but it is possible to determine with
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The solution was then allowed to stand in a rack for 20 minutes and then filtered. The hot solution on cooling became slightly opaque owing to the precipitation of a certain amount of agalma black 10B which had been in solution while hot, so that after standing 20 minutes the solution was filtered a second time. Both filterings were done on a h-0. 558 S & S folded filter 18.5 cm. in diameter. The solution was then ready for spectrophotometric examination and usually had to be diluted in order to obtain observations a t the maxima of the two peaks. In general, this dilution was about 40 cc. in 100, but in cases where the amount of impurity was great it might be necessary to dilute as low as 10 parts in 100. This dilution was made with calibrated pipets and volumetric flasks. The absorption spectrum was determined spectrophotometrically with the use of a 5-cm. absorption cell. From the curves obtained, the height of the impurity curve for 100 per cent concentration was determined and from this, as previously described, the actual amount of l-amino-8-naphthol-3,6-disulfo7-azobenzene present determined.
In general, the amount of impurity present in commercial agalma black 10B varies from 1 to 2.5 per cent. A sample containing 1.5 per cent or less of l-amino-8-naphthol-3,6disulfo-7-azobenzene may be considered as an acceptable dye, whereas dyes containing much more than 2.5 per cent will give red shades on dyeing and where such shades are objectionable these dyes do not give acceptable results. The fact that the addition of a small amount of impurity causes considerable decrease in the amount of agalma black 10B adsorbed, in the case of a saturated dyeing, would indicate that the amount of dye a given amount of wool adsorbs does not necessarily determine the order of dyeing when two dyes are present together, but would rather support a theory of saturation or equilibrium reactions. This is Per cent l-amino-S-naphthol-3.6-disulfo-7-azobenzene present in sample of agalma black 10B Figure 9-Relation between A m o u n t of 1-AminoR-Naphthol-3 6-Disulfo-7-Azobenzene h e s e n t in Original Sample a n d i n Solution after a 16 Per c e n t Dyeing
considerable accuracy the height of the impurity band. Hence the following determinations were made, not on the relative heights of the bands, but on the direct height of t,he impurit,y band. It is therefore necessary t o maintain the condition of dyeing with some accuracy and use definite volume relations at all times. Experimental
The dyeings were made in a standard dye bath developed at the Bureau of Standards6 on specially prepared wool flock so as to secure uniform adsorption of the dye. The following directions were followed on all these standard dyeings and gave results which could easily be duplicated within the allowable errors of the method: Five grams of wool flock were placed in a large test tube (6 X 25 cm.), which served as the dye-bath container, to which were added 100 cc. of boiling distilled water. The test tube was adjusted to the stirrer and heated in a boiling water bath for 5 minutes. To this was now added the dye dissolved in 35 cc. of hot water, and the dye container was washed out with 40 cc. of hot water, which was also added to the dye solution. The amount of dye used in these runs for a 16 per cent dyeing was 0.8000 gram of pure dye or the equivalent amount of crude dye as determined by a titanous chlotide titration. This was then stirred for 1 minute and then 5 cc. of sodium sulfate (10 per cent solution) and 5 cc. of sodium acid sulfate (10 per cent solution) added and the container washed with 15 cc. of hot water and this also added. The whole was then stirred continuously for 30 minutes on a boiling water bath. Although by previous experiments it had been shown that dyeing for 15 minutes was ample to insure complete adsorption, these experiments were carried out for 30 minutes t o insure uniform results. 8
Appel, A m . Dycstuf Re#., 13, 507 (1924).
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Times filtered Figure 10-Effect of Filtration o n A m o u n t s of Agalma Elack 10B ( 1 ) a n d l - A m i n o - 8 Naphthol 3,6 Disulfo-7 Azobenzene (2) Present i n Mother Liquor of a Partially Exh a u s t e d D l e Solution
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further shown by the fact that there is no definite amount of dye that the wool adsorbs, but that it is dependent upon the concentration in the solution from which the dyeing takes place. Such condition as a definite saturation point may exist in certain simple dyes in which the possible modes of adhesion t o the wool are few, but in complex azo dyes such as agalma black 1OB and l-amino-8-naphthol-3,6-disulfo-7azobenzene there appears no definite point but rather an equilibrium, which is dependent on the concentration of the dye in the solution.
