June, 1926
INDUSTRIAL A,VD ENGIYEERING CHEMISTRY
627
Standardization of Agalma Black 1OB’,’ By Wm. D. Appel, Wallace R. Brode, and I. M. Welch BUREAU OF STANDARDS, WASHINGTON. D.c.
A series of samples of agalma black 10B from foreign and domestic manufacturers has been ecaluated independently by means of titanous chloride titration, spectrophotometric measurements, and practical dyeings. The possibility o j writing specificationsfor and establishing one or more trade standardsfor the dye is discussed.
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HE lack of uniformity in strength, quality, and money value of commercial dyes from different sources is well known to the trade. Inherited from the pre-war industry, this condition has been continued perforce, for the American dye manufacturers have been fully occupied with problenis uf production. With it has continued the multiplicity of names, the appearance of old dyes under new names, and the talk of trade “secrets,”-pre-war practires designed to stimulate business. It may be said with assurance that such practices work no permanent good for the dye industry. Certainly, unscrupulous dealers have profited by them and legitimate industry has suffered corresponding loss. The establishment of trade standards for the more important and better known dyestuffs would not only tend to prevent such loss, but would simplify and clarify the trade for both manufacturer and consumer. This standardization need extend to only a few of the more important technical dyes to be of great benefit to the industry. Thus the first ten dyes in the order of quantity produced in the United States during 1924 made up 65 per cent of the total. The quantity sold amounted to 64 per cent, with a value of 33 per cent of the total.3 I n the accompanying table are given the production and value for 1924 of the more important dyes. The money value of a number of dyes which are made in lesser quantity far exceeds that of other dyes which are made in larger amounts. iluramine, which is number 21 in the order of production, is number 7 in the order of value. Not only the dyes of large production or of high value, but also those produced by a number of different manufacturers should be standardized. The number of American manufacturers of each dye listed is also shown in the table. Some dyes are already reasonably well standardized for strength. Indigo and the vat dyes are sold on a definite strength basis in terms of the dry powder, which is normally a concentrated product. The different manufacturers’ standards of some of the common water-soluble dyes agree reasonably well in strength. Certain dyes, such as the sulfur colors and some of the complex azo dyes, offer peculiar difficulties to standardization because of the variability in constitution or difficulty of test, and much work is required before satisfactory standards for them can be established. Studies of some of the important dyes from the standpoint of commercial standardization are in progress. This paper is the first of three reporting the results of such studies of agalma black 10B. I n it are compared three independent methods for the estimation of the strength of commercial samples of the dye-namely, titanous chloride titration, spectrophotometric analysis, and comparative dyeing. Agalma black 10B ranks fifth in the order of importance of the commercial dyes, nearly 11/3 million pounds with a value of $780,000 having been produced by thirteen manufacturers in the United States in 1924. It dyes wool and silk a greenish black from an acid bath and is the basis of nearly all the A preliminary report of this work was given under this title before the Division of Dye Chemistry a t the 69th Meetrng of the American Chemical Society, Baltimore, Md , April 6 t o 10, 1925. Received Fehruary 26, 1926. Published b y permission of the Director, Natlonal Bureau of Standards. Statistics given in this paper are taken from the Census of Dyes and Other Synthetic Organic Chemicals, 1024, by the U. S. Tarlff Commission.
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black acid dye mixtures on the market. Vegetable fibers are unstained by it. The preparation of agalma black 10B is well known. A neutral solution of H-acid (8-amino-l-naphthol-3,6-disulfonic acid) is added to an equivalent amount of diazotized p-nitroaniline, the mixture containing free mineral acid a t all times. When the acid coupling is complete, diazotized aniline is coupled in alkaline solution to the monoazo dye formed. I n practice, the couplings are hot strictly molecular and red monoazo dyes are also formed and to a greater or lesser extent are present in the finished product. These subsidiary dyes modify the clear green-black shade of dyeings of pure agalma black 10B and intraduce difficulties in the estimation of strength of commercial samples. Their quantitative estimation is the subject of another paper. Materials
Two laboratory preparations of agalina black were used to check the standardization of the titanous chloride solution and for standard spectrophotometric measurements. They were prepared by the method outlined above, using molecular equivalents of the components. One sample was purified by recrystallization, the second sample by recrystallization and then dialysis. The first sample contained 91 per cent of anhydrous dye, 2.2 per cent of moisture, and 6.3 per cent of salt; the second, 99.2 per cent of anhydrous dye and not over 0.2 per cent of salt. Spectrophotometrically the two samples agreed when allowance was made for the difference in strength. The mother liquor of dyeings made from them gave the same spectrophotometric curve as the original solution. The twenty-three commercial samples studied represented about twenty different sources, five of them foreign. They were considered to be representative of the different manufacturers’ and dealers’ stock quality dye. Titanous Chloride Titration
Titanous chloride titrations4 were carried out in the presence of sulfuric acid by the indirect method, the blue-green color of a reduction product with ferric iron giving a satisfactory end point. A sample equivalent to about 350 cc. (300 to 400 cc.) of 0.05 N titanous chloride solution was dissolved in water and diluted to 1000 cc. To a 100-cc. portion of the solution were added 25 cc. of 40 per cent sulfuric acid. The mixture was boiled to expel dissolved air, swept with carbon dioxide, and 50 cc. of the standard titanous chloride solution were added, The mixture was boiled for 5 minutes and then titrated hot (under carbon dioxide) with 0.05 N ferric alum solution to the appearance of a blue-green color. The end point in most cases was sharp. Spectrophotometric Measurements
The spectrophotometric measurements5 were made on the Keuffel Br: Esser color analyzer. The quantity measured 4 Knecht and Hibbert, “New Reduction Method in Volumetric Analysis,” Longmans, Green & Co., 2d ed., 1925; and Calcott and English, THIS J O U R N A L , 16, 1042 (1923). 8 For general information, see “Spectrophotometry,” Report of Progress Committee for 1922-3, J. O p f s c a l Soc A m . , 10, 169 (1925).
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
was the transmittancy-viz. , the transmission a t selected wave lengths of the solution in a given cell relative to that of the solvent in a similar cell. Thicknesses of 5 cm. were used for solvent and solution and the concentration of the latter was 3.33 mg. of pure dye per liter of solution on the basis of the titanous chloride titration. This concentration was obtained by dissolving the required amount (1 to 3.5 grams) of the commercial sample and diluting to a volume of 500 cc., diluting 25 cc. of this solution to 250 cc. and 10 cc. of this to 300 cc. The solvent was an aqueous buffer solution containing 0.01 gram molecule each of sodium acetate and acetic acid per liter and having a pH of 5.0.
Vol. 18, No. 6
temperature was maintained by boiling water in the outer jacket of the dye bath. The requisite amount of the dye solution used for the titanous chloride titration was diluted to 30 cc. and added to the dye bath. Ten cubic centimeters of rinse water, 4 cc. of 10 per cent sodium sulfate solution, 4 CC. of 10 per cent acid sodium sulfate solution, and 12 cc. of rinse water were then added in order. Dyeing was continued for 15 minutes. The dyed fiber was separated from the mother liquor on a wire screen and squeezed in a press between blotting paper. It was then dried in an air bath, conditioned in an atmosphere of 6rj per cent humidity, and bottled. Dyeings were made on the basis of the titanous chloride determinations and also on the spectrophotometric figures. Additional dyeings were made as needed to insure careful evaluations. The relative strengths of these dyeings were judged by visual comparison with dyeings of Sample 13 (Figure 2), a good quality commercial product containing 60 per cent coloring matter, rather than with those of the pure dye. Dyeings of the pure dye were not so satisfactory for judging strength since they were much purer in color than those of the commercial samples. The variations in hue of dyeings from No. 13 were also noted and are given in Figure 2. Comparison of Results
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Wave Length Figure 1-Spectrophotometric Curves for Agalma Black 10B The inside line is the curve for the pure dye 10 mg. per liter, thickness of solution 2 cm. temperature 25' C , in acetate buffer solution, pH 5.0. The curves of the' 23 commercial samples lie within the shaded area, the majority of them within the heavily shaded area.
The negative logarithms of the spectral transmittancies are quantities ordinarily proportional to the amount of dye in solution. Accordingly, if they are plotted against wave length, the area between the curve so obtained and the wavelength axis will be proportional to the amount of dye in solution. Calling this area for a commercial sample and for the pure dye, respectively, A and B, and the weights taken, respectively, C and D, then the percentage purity = A / B x D/C x 100. Wave-length limits of 540 and 670 mp were chosen as boundaries of the area as the measurements on this particular dye are the most reliable within this range. The percentage purity was also calculated from the value of the curve at 620 mp, the wave length of maximum absorption. The average of the two values is the final spectrophotometric value which was used in Figure 2. I n Figure 1 the solid line represents the curve for the pure dye and the shaded area covers the spectrophotometric curves for all twenty-three samples reduced to the same value a t the wave length of maximum absorption. The lightly shaded area is necessitated by a few of the samples only; the majority fall within the heavily shaded area. This composite curve shows the remarkably good agreement among the samples and affords an excellent means of defining the dye type and maximum allowable deviations in color from it. Comparative Dyeing Tests Comparative dyeing tests were made under controlled conditions in the apparatus described elsewhere.6 Four-tenths per cent dyeings on the basis of dye content were made on fine white wool flock. Four grams of wool flock from a large supply previously thoroughly mixed and bottled were placed in the 6 X 23 em. test tube used as a dye bath and wet out by stirring with 100 cc. of boiling water for 5 minutes. The 9
Appel, A m . Dyestuff Rep., 18, 507 (1924).
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The results of these strength determinations are given in Figure 2. I n fifteen out of the twenty-three cases the spectrophotometric and titanous chloride evaluations agree with the dyeing results within the limits of accuracy of the dyeing results, which has been taken as *2 per cent and indicated by the size of the circle. The precision of the spectrophotometric and titanous chloride evaluations is better than this, as is indicated by the size of the circles in the figure. I n three cases the spectrophotometric evaluations agree with the dyeing, hut the titanous chloride titrations are high, indicating the presence of p-nitroaniline or other reducible material.
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Figure 2-Strength
of C o m m e r c i a l S a m p l e s of Agalma Black 10B
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Strength by dyeing test Titanous chloride titration Spectrophotometric method Above the sample number is given the "Shade" of dyeing as compared with Sample 13 D = Duller O K = Same as 13 G = Greener X = Foreign sample R = Redder '
I n three cases the titanous chloride titrations agree with the dyeing results, but the spectrophotometric evaluations are low. I n two instances both titanous chloride titrations and spectrophotometric evaluations are low. The five last-mentioned cases are of especial interest. Although a dye sample may contain less pure dye than the spectrophotometric and titanous chloride evaluations show, it cannot contain more pure dye than they show. Therefore, it is evident that Samples 5, 6, 11, 14, and 17 are abnormal. They cannot contain more true agalma black than is indicated by the spectrophotometer. The first four of these samples
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1926
No. 1 2 3 4 5 6 7 8 9 10
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12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Production a n d Value of S o m e I m p o r t a n t D y e s Produced i n t h e United S t a t e s i n 1924 , SALES Production Quantity Value No. of Units of ' Units of Units of Price NAME Schultz No. mfrs. 100,000 Ibs. 100,000 Ibs. $50,000 per Ib. 3 199.9 78.3 0.22 874 179.8 Indigo, 20% paste 5 42.6 0 . I9 117.3 111.9 720 Sulfur black 37.6 0.38 54.7 49.5 9 462 Direct deep black E W 16.5 3.30 4 858 ... 2.5 Alizarin saphirol B 15.1 0.64 217 12.7 1L.8 13 Agalma black 10B 12.1 1.13 5.4 8 5.4 515 Methyl violet 12.1 1.52 Auramine 4.0 5 3.9 493 ~-. 0.48 11.8 6 12.3 12.4 700 Nigrosine W. S. 10.8 0.38 14.1 14 14.0 Sulfur brown 1.26 9.0 3.6 3 4.1 659 Methylene blue 0.65 9.0 7.7 6.9 9 333 Oxamine black 8.4 0.48 7.7 13 8.8 181 Salicine black U 8.0 0.49 8.3 8.2 476 10 Benzamine brown G 0.33 8.0 12.2 11.6 8 145 Orange I1 7.5 0.84 4.5 5.1 5 304 Chrysophenine G 6 . 8 1.26 2 . 7 2 . 4 5 424 Chicago blue 6B 2.56 6.5 1.3 1.2 8 536 Alkali blue 1.91 6 . 3 1 . 7 1 . 9 4 279 Benzo fast scarlet A.. 9 0.73 . 4.5 4.0 6 363 Benzopurpurine 4B 6 . 8 0.66 4 . 4 4 . 5 8 Direct yellow R 5.7 0.72 3.9 3.3 6 134 Metanil yellow 5.6 1.85 1.5 1.3 4 587 Eosine 5.6 5.5 0.49 5.6 9 33 Chrysoidine 1.70 1.8 5.5 4 1.6 495 Malachite green 5.4 0.51 5.6 10 5.4 284 Bismarck brown 2R 5.4 2.77 5 1.0 1.0 168 Amaranth (food) 0.37 5.1 12 7.0 6.9 337 Benzo blue 2B 4.7 0.89 2.7 2.7 4 257 Sulfoncvanine G 4.7 2.64 0.9 0.9 5 19 Fast light yellow 4.7 0.79 2.9 9 3.0 163 Azo rubine
give dyeings of a very red shade and obviously contain a considerable amount of a red impurity. The B t h sample gives a dull dyeing and is distinctly not the same quality as the remaining samples. It is of interest to note that over half of the samples have a dye content between 55 and 65 per cent, indicating that for most manufacturers the compliance with a definite standard such as 60 per cent would not be difficult. Conclusions It appears that neither the spectrophotometric nor the titanous chloride method is entirely satisfactory for the
629 Per cent total value 11.2 6.1 5.4 2.4
2.2
1.7 1.7 1.7 1.5 1.3 1.3 1.2 1.1 1.1 1.1 1.0 0.9 0.9 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.7
0.7 0.7 0.7
evaluation of commercial samples of agalma black 10B in respect to strength. However, a combination of the two methods seems to give a satisfactory means of specifying a standard commercial type, since where the two methods agree the result is that obtained by the usual dyeing test. Over half of the twenty-three samples examined satisfy this requirement. A standard of 60 per cent purity by titanous chloride and spectrophotometer would necessitate but slight shift in the strength of the standards of a majority of manufacturers.
Preparation of Cyanamide Hydrochloride' By L. A. Pinck and H. C. Hetherington FIXEDNITROGEN &SEARCH
LABORATORY, %'ASHINOTON, D . C.
YANAMIDE, H2CN2, possesses considerable interest as the natural starting point in a large number of organic syntheses, and although at present it has little or no commercial value, it is by no means certain that uses would not soon be found for it were it not for its extremely hygroscopic nature and its tendency to polymerize, even in the solid state and at room temperature. For these reasons the salt cyanamide hydrochloride, H2CN2.2HCIJ which is known to be far less hygroscopic and more stable than cyanamide itself, should be of greater interest. Cyanamide hydrochloride is a white crystalline compound, stable at ordinary temperature when dry but hydrolyzing readily in aqueous solution. It may be heated safely to 7Oo-8O0 C., but decomposes rapidly when heated above 100' C., yielding hydrogen chloride and mellon. Two methods have previously been proposed for the preparation of cyanamide hydrochloride. The earlier2 of these consists in passing dry hydrogen chloride gas into an absolute ether solution of cyanamide. The success of the preparation depends upon the complete absence of moisture, for in the presence of even a very slight amount of water the hydrochloride forms a sticky mass which is difficult to dry and which invariably clogs the gas inlet. The other recorded method3 consists in dissolving cyana-
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Received March 19, 1926.
* Dreschel, J. prakf. Chem., [Z] 11, 315 (1875).
* Hantsch and Vagt, Ann., 314, 366
(1901).
mide in concentrated hydrochloric acid and evaporating the solution in a vacuum desiccator. This method is open to several objections, chief of which is the difficulty of obtaining a dry product, free from uncombined hydrogen chloride. Moreover, there is considerable danger of contamination of the product with urea formed by hydrolysis of cyanamide in the aqueous solution of hydrogen chloride. Since the elimination of water is the principal difficulty in the foregoing methods, it was believed that the preparation might be more satisfactorily carried out in solvents such as ethyl alcohol, methanol, or acetone, which through their miscibility with water would prevent the salt from taking up all the moisture in the system. Qualitative experiments were first made to determine whether or not ethyl alcohol would itself react with the other constituents. That such a reaction might occur was indicated by the reported preparation of alkyl isourea from cyanamide and alcoholic hydrogen ~ h l o r i d e . ~It was found, however, that this reaction is too slow to take place to a measurable extent during the preparation of cyanamide hydrochloride. A somewhat similar behavior was observed in the case of acetone. While no side reactions occurred when cyanamide hydrochloride was prepared in this solvent, a compound corresponding to tri-isopropyl diurea or triacetony1 diurea was formed when a solution of cyanamide 4
Stieglitz and McKee, Bey.. 33, 807 (1900).
