ANALYTICAL EDITION
152
Vol. 5, No. 3
TABLEI. TYPICAL RESVLTS BY SELECTIVE REDUCTION STANNOUS CHLORIDE REDUCTION SERIBB
1
2
C O ~ P O N BDYES NT
A, ponceau SX B, guinea green B A aunset yellow FCF
B: brilliant blue FCF 3
A orange I B: light green SF yellowish
4
A, amaranth B, fast green FCF
1% DYE
SOLUTION
N SnCh added
cc.
co.
30 30 50 50 100 100
4.5 3.8
Time Min. 3 3 3 3 3 3
Temperature
c.
COMPONENT COMPOWENT COMPONENT A PRESBNTB PRESENT B FOUNDDIFFERPNCB
so- 100 80-100 80-100 80-100 80-100 80-108
%
%
%
91.2 75.2 54.2 25.5 10.3
8.8 24.8 45.8
74.5
3.5
89.7 96.5
11.0 25.8 48.4 74.4 89.8 96.5
%
f2.2
40 110
5.1 1.7
18 hr. 18 hr.
20-25 20-25
75.8 9.5
24.2 90.5
90.5
fl.O f2.6 -0.1 +o. 1 0.0 f1.4 0.0
60
2.0
24 hr.
20-25
19.3
80.7
79.3
-1.4
50 100
1.2
6.0
12 12
80-100 80-100
90.9
9.1 90.9
11.0 91.7
f1.9 +0.8
4.6
2.1 1.8 0.6
stannous chloride are used in the trial reduction. Subsequently, this trial reduction showed that component B used 15.0 cc. of 0.1 N titanous chloride and component A, by difference, needed 10.0 cc. Therefore]2.0 cc. of 1.0 N stannous chloride represented roximately 100 per cent excess. The amounts of stannous %l%ide used, appearing in Table I, were ascertained by such a procedure. In a mixture containing less than 40 to 45 per cent of component B, an additional step was necessary, because (1) estimations of small amounts of triphenylmethane dyes with titanous chloride invariably give high results; and (2) if a larger sample of mixture is taken, the high concentration of the stannic ions formed in the reduction of the azo dye restores the color of component B so rapidly after reduction by titanous chloride that quantitative estimation is uncertain. A known amount. of Component B was therefore added prior to the stannous chloride and subsequently subtracted from the final titration value obtained with titanous chloride.
CONCLUSION The general utility of the set of reducing agents, stannous chloride and titanous chloride, in the evaluation of dye mixtures, has been investigated. Experimental evidence showed
9.1
25.6
that mixtures of azo and triphenylmethane food dyes were satisfactorily analyzed. No doubt there are many dye mixtures whose components differ in ease of reduction in such a manner as to permit evaluation by a similar procedure. The author wishes to thank 0. L. Evenson, of this laboratory, for his helpful suggestions in performing and presenting this work.
LITERATURE CITED (1) Ambler, J. A., Clarke, W. F., Evenson, 0. L., Wales, H., U. 8. Dept. Agr., Bull. 1390, 26 (1925). (2) Evenson, 0. L., a n d Nagel, R. H., IND. END..CHEM.,Anal. Ed., 3, 260 (1931). (3) Holmes, W. C., Am. Dyestuf R e p t r . , 14, 415 (1925).
(4) Kneoht a n d Hibbert, “New Reduction Methods in Volumetric Analysis,” 2nd ed., p. 6, Longmans, 1925. (5) Ibid., p. 7. RECEIVEDNovember 25, 1932. Presented before the Division of Dye Chemistry at the 85th Meeting of the American Chemical Society, Wasbington, D. C., March 26 to 31, 1933. Contribution 10 from the Color Certification Laboratory, Food and Drug Administration, U. S. Department of Agriculture, Washington, D. C.
Volumetric Determination of Nitroglycerol and of Nitroglycerol and Dinitrotoluene in Admixture WALTERW. BECKER,Experiment Station, Hercules Powder Company, Wilmington, Del.
N
ITROGLYCEROL may be conveniently determined is distilled into standard acid. I n the method of Muraour by means of the du Pont nitrometer; the results ( 6 ) the nitroglycerol in acetone solution is treated with obtained, however, are usually slightly low. Certain hydrogen peroxide, sodium hydroxide, and sodium perborate; aromatic nitro compounds, such as dinitrotoluene, do not after standing overnight Devarda’s alloy is added, and the resulting a m m o n i a d i s t i l l e d i n t e r f e r e in this nitrometer into standard acid. Muraour d e t e r m i n a t i o n ; compounds Practically theoretical results f o r nitroglycerol obtained results which closely such as diethyldiphenylurea or diphenylamine, however, do inand for ethylenegh‘ol dinitrate may be obtained checked t h e theoretical. terfere, b e c a u s e they undergo by dissolving the sample in acetic acid, adding Excellent results on the analya n excess of ferrous chloride, hydrochloric acid, sis of nitroglycerol were also n i t r a t i o n in the decomposing boiling, and then titrating the resulting ferric Obtained in this laboratory, but bulb, and cause low results. because of the time r e q u i r e d iron with standard titanous chloride solution, The nitrate groups in nitroglycerol m a y be r e d u c e d by for a determination, the method suitable reagents, and the niusing ammonium thiocyanate as the indicator* was not exactly suited to control trogen determined as ammonia. W h e n present in admixture, 2,4-dinitrotoluene analysis. does not interfere, and may be accurately deD i c k s o n a n d Easterbrook I n t h e method of S i l b e r a a d termined in the residual solution by reduction (2) determined dinitrotoluene (?’) the nitroglycerol i n e t h e r is partially reduced with titanous chloride in the regular way. in admixture with nitroglycerol w i t h sodium e t h y l a t e , then by reducing the latter with W h e n present in small amount, dielhyldiferrous chloride in strong metallic zinc and ironareadded, and the r e s u l t i n g a m m o n i a phenylurea or diphenylamine does not interfere. hydrochloric acid solution, then
May 15,1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
extracting the unchanged dinitrotoluene with ether. Methylsulfuric acid may be used in place of ferrous chloride. Huff and Leitch (4) attempted t o determine nitroglycerol in the presence of aromatic nitro compounds. The nitroglycerol and nitro compound were dissolved in acetic acid, hydrochloric acid was added, and then a known excess of ferrous sulfate. After boiling and evaporating to a small volume, the excess ferrous iron was titrated with standard potassium permanganate solution. Low results were obtained on nitroglycerol alone and in admixture with p-nitrotoluene. Several suggestions for methods of attack were given in their article, however. Their method was tried out in this laboratory, and low results for nitroglycerol were obtained consistently. It was thought that the oxidized iron might be determined accurately without interference from glycerol, traces of nitric oxide, or possibly other substances. Knecht and Hibbert (5) first determined nitric acid by reduction to nitric oxide with ferrous iron, and titrating the resulting ferric iron with a standard solution of titanous chloride. The procedure finally developed was t o dissolve the sample of nitroglycerol in acetic acid, add an excess of ferrous chloride, hydrochloric acid, and boil under a reflux condenser. After cooling, the ferric iron was titrated with standard titanous chloride solution, using ammonium thiocyanate as the indicator. An atmosphere of carbon dioxide was of course maintained in the titration flask during the entire procedure.
PREPARATION AND STANDARDIZATION OF SOLUTIONS A 0.2 iV titanous chloride solution was prepared according to the directions of English (3). For each liter of solution, 150 cc. of 20,per cent titanous chloride and 100 cc. of concentrated hydrochloric acid were used. For control work, a quick and accurate method of standardization is essential. Ferrous ammonium sulfate was used by Knecht and Hibbert ( 5 ) . Thornton and Wood (8) recommend the use of Sibley iron ore. For the analysis of aromatic nitro compounds, Callan and Henderson (1) used titanous sulfate which had been standardized against recrystallized p-nitraniline. English (3) gave a comparison of this standard and ferrous ammonium sulfate. I n the results reported in this article, ferrous ammonium sulfate was used as the ultimate standard. The ferrous iron of the standard may be oxidized by several different methods. Potassium chlorate in hydrochloric acid solution was selected, as the excess oxidizing agent may be easily and completely destroyed by two evaporations to dryness. Knecht and Hibbert (5) suggest the use of a supplementary ferric alum solution for quickly checking the normality of the titanous chloride solution. 0.7 N FERROUS CHLORIDE. For each liter of solution,200 grams of ferrous chloride (FeC12.4Hz0) and 50 cc. of concentrated hydrochloric acid were used. 0.15 N FERRIC ALUM. For each liter of solution, 75 grams of ferric alum and 25 cc. of 95 per cent sulfuric acid were used.
APPARATUS The volumetric solutions were protected from the air, using an arrangement similar to that given by Knecht and Hibbert (t5). Instead of hydrogen, carbon dioxide was used. A special Florence-type titration flask with ground-in condenser was designed for this determination. The capacity of the flask is about 300 cc.; carbon dioxide is admitted by means of a short inlet tube on the shoulder. The groundglass joint is No. 25 $, rendering the condenser and flasks interchangeable. For a titration, the flask is fitted with a narrow one-hole rubber stopper, through which is inserted a short piece of 8-mm. glass tubing.
153
DETERMINATION OF XITROQLYCEROL Weigh 1.8 t o 2.0 grams of nitroglycerol, dissolve in glacial acetic acid, and make up to volume in a 250-cc. volumetric flask. Displace the air in a special titration flask by passing in a current of carbon dioxide for about 5 minutes. By means of an accurate pipet, transfer a 25-cc. aliquot portion of the acetic acid solution to the flask. Add 15 cc. of ferrous chloride solution and 25 cc. of h drochloric acid (1 to 1) in the order named, connect the flasi to the reflux condenser, and boil gently for 5 minutes. A few glass beads may be added to prevent bumping. Increase the current of carbon dioxide, then cautiously immerse the flask in a large beaker of cold water, keeping the index finger over the top of the condenser until the hot vapors are condensed. After cooling to room temperature, disconnect the condenser, insert the one-hole rubber stopper, and titrate with the titanous chloride solution until near the end point. Add 5 cc. of 20 per cent ammonium thiocyanate solution and continue the titration until the red color of ferric thiocyanate just disappears. Determine the small amount of ferric iron in the ferrous chloride solution and traces of interfering impurities in the reagents by running a blank under the same conditions as for a sample, and make the necessary correction. The results obtained on a sample of filtered nitroglycerol and on a sample of ethyleneglycol dinitrate are given in Table I. TABLEI. PURITY OF NITROGLYCEROL AND OF ETHYLENEGLYCOL DINITRATE METHOD
ETHYLENBQLYCOL NITROQLYCH~ROL DINITRATE
%
%
Nitroineter
99.21
99.21
FeCln-TiCla
99.84 99.94 99.88
99.92 99.87 99.86
DETERMINATION OF 2,4-DINITROTOLUENE GLYCEROL IN ADMIXTURE
AND
NITRO-
The determination of dinitrotoluene alone is usually carried out by dissolving the weighed sample in alcohol, acidifying with hydrochloric acid or sulfuric acid, adding a 100 per cent excess of titanous chloride or sulfate, and boiling. After cooling, the excess reducing agent is titrated with a ferric alum solution, using ammonium thiocyanate as the indicator. I n the determination of dinitrotoluene in admixture with nitroglycerol, the latter would interfere if the foregoing procedure were used. It was found, however, that the dinitrotoluene did not interfere in the method developed for the determination of nitroglycerol. Under the conditions of the determination, the 5 minutes’ boiling with ferrous chloride did not reduce the dinitrotoluene. At room temperature, the ferric iron formed by the reduction of the nitroglycerol could be titrated to a sharp end point by the titanous chloride solution, in the presence of the dinitrotoluene. It was also found that the dinitrotoluene could then be determined in the residual solution in the usual way. Dissolve the weighed sample of nitroglycerol PROCEDURE. and dinitrotoluene in acetic acid and make up to volume in a 250-cc. volumetric flask. Transfer a 25-cc. aliquot portion to a titration flask, and proceed exactly as in the determination of nitroglycerol alone, taking care to titrate just to the end point. Add a 100 per cent excess of titanous chloride solution, again connect the flask to the reflux condenser, and boil for 5 minutes. Cool the flask and contents t o room temperature and titrate the excess reducin agent with the ferric alum solution. Run a blanl determination, adding equal quantities of the reagents, and having ascertained the slight loss of titanous chloride on boiling, apply the proper correction in calculating the results.
It will be observed that a few conditions are different from those that prevail in the usual determination of dinitrotoluene, The nitro compound is boiled with titanous chloride in the presence of ferrous chloride and ammonium
ANALYTICAL EDITION
154
thiocyanate. Theindicator was found to have no effect. Ferrous chloride, however, will reduce the nitro compound to a slight extent, unless some ferric iron is present. The amount of ferric iron necessary to prevent reduction of the dinitrotoluene during the nitroglycerol determination does not appear to be critical, as is shown by the results given in Table 11,on two typical laboratory samples. TABLE11. EFFECTOF EXCESSOF FERROUS CHLORIDE ox DETERMINATION OF DINITROTOLUENE AND NITROGLYCEROL IN ADMIXTURE
FeCL ADDED Ce
.
15
NITROQLYCEROL DINITROTOLUENE
%
%
5.03 5 07
6.63 6.59
5
5.06
6.58
15
20.23
2.00
20
20.24
1 98
The results obtained on a sample of dinitrotoluene and on a known mixture of nitroglycerol and dinitrotoluene are given in Table 111. It was found that small amounts of diethyldiphenylurea or diphenylamine did not interfere in the determination of nitroglycerol and dinitrotoluene by the use of the foregoing method.
Vol. 5 , No. 3
TABLE111. DETERMINATION OF NITROGLYCEROL AND DINITROTOLUENE IN ADMIXTURE NITROQLYCEROL FOUND %
..... .....
99.87 99.90
DINITROTOLUENE FOUND % 39.28 99.22 99.36 99.26
ACKNOWLEDGMEKT The author is indebted to W. H. Fravel for certain of the analytical results used in this article.
LITERATURE CITED (1) Callan, T., and Henderson, J. A. R., J . SOC.Chem. Ind., 41, 157-61T (1922). (2) Dickson, W., and Easterbrook, W. C., Analyst, 47, 112-17 (1922). (3) English, F.L., J. IND. ENG.CIimf., 12, 994-97 (1920). (4) Huff, W. J., and Leitch, R. .D., J . Am. Chem. SOC.,44, 2643-45 (1922). (5) Knecht, E., and Hibbert, E., “New Reduction Methods in Volumetric Analysis,” 2nd ed., Longmans, 1925. (6) Muraour, H., Bull. SOC. chim., 45, 1189-92 (1929). (7) Silberaad, O., Phillips, H. A., and Merriman, H . J., J. SOC. Chem. I n d . , 25, 628-30 (1906). (8) Thornton, W. M., Jr., and Wood, A. E., IND. ENG.CHEY., 19, 150-52 (1927).
RECEIVED December 8, 1932.
Indicators for Determining Chromium and Vanadium in Alloy Steels Oxidized Diphenylamine Sulfonic Acid and Oxidized Diphenylamine HOBART H. WILLARD AND PHILENA YOUNG,University of Michigan, Ann Arbor, Mich.
D
grams of the barium salt (obThis paper describes an investigation of the fonic acid is an oxidaproperties of diphenylaminesulfonicacid as un t a i n a b l e from the Eastman Kodak Co., Rochester, N. Y.) in tion-reduction indicator indicatorfor chromium and vanadium in tungsten a liter of water, adding to this which may be used in the pressfeels* Withapreliminaryoxidation Of ence of tungstic acid, but its solution a slight excess of sodium properties under such conditions amine sulfonic acid, the blank correction to be sulfate, and decanting or filtering the solution. have not been thoroughly tested applied when using this indicator is reduced to a PREPARAT1oNoFoXIDrZEDIN(4). It has been used in the very small value. It is suficiently constant with DICATOR. The volume of t h e Of chrome-vanadiumdefinite procedures to give very accurate results o.ol indicator solution specitungsten steels for vanadium (8). Though accurate results were for chromiumOr fied in a given experiment is obtained, the indicator blank A preliminary oxidation ‘of diphenylamine placed in a small beaker, 5 cc. of water, 3 or 4 drops of conwhich had to be applied, because completely eliminates a blank correction for this centrated sulfuric acid, and 3 of reduction of some v a n a d i c indicator used in vanadilim or chromium acid by the indicator, was unor 4 drous of 0.1 N potassium determinat ions. d i c h r o m a t e a r e added, and desirablv large. It was noted in then very dilute ferrous sulfate this pacer that an indicator with no blank correction could be prepared by a preliminary (0.01 to 0.02 N ) is added until the purple color, which appears oxidation, but this is only approximately true. on the addition of the first few drops of ferrous sulfate, just Since diphenylamine and diphenylbenzidine are of no turns to a bluish green. As this purple color begins to disvalue in the presence of tungstic acid (6),i t seemed important appear, the ferrous sulfate should be added in parts of a drop, to study the properties of an indicator not affected by this in order to have no excess present in the oxidized indicator substance. Methods for chromium or vanadium which do solution. This bluish green solution is added to the solution not involve the removal of tungstic acid and the determination to be titrated. I n the experiments described in this paper the of the small amount of vanadium which inevitably accom- oxidized indicator was prepared in separate samples for each panies the precipitate are obviously much more rapid and titration. A stock solution of the oxidized indicator is often more consimple. venient and may be prepared as follows: EXPERIMENTAL One hundred cubic centimeters of 0.01 iM diphenylaminesodium PREPARATION OF INDICATOR. A 0.01 M solution of di- sulfonate and 25 cc. of concentrated d f u r i c acid are diluted to phenylamine sodium sulfonate is prepared by dissolving 3.2 900 CC. in a liter volumetric flask. To this solution 25 CC. of
IPHEXYLAMINE d-
(5
