DISCUSSION
Lundell and Hoffman (7) show that 1-nitroso-2-naphthol in acetic acid solution precipitates iron, cobalt, palladium, and gold quantitatively and possibly tin and antimony under certain conditions. Apparently the reagent in sodium hydroxide performs similarly but produces a precipitate much easier to handle. Also, if the cobalt is present in small quantities, the consequent large excess of reagent remains in solution, and precipitation may be easily observed. A further advantage in using this type of precipitation without prior or later removal of iron, nickel, or both, is that, in cases in which the amount of cobalt is less than that of iron or nickel, the desired constituent is separated from the bulk of the material rather than the bulk from the minor constituent. As shown in Table 11, gross amounts of either iron or nickel have no effect on the cobalt recovery. Alloys containing from 0.3 t o 8.5% cobalt were used as standards. With proper sample size, materials containing from 0.01 to 40% cobalt can be run. I n f l u e n c e of Diverse Substances. With nitric acid present, only about 85y0 of t h e cobalt could be recovered i n t h e precipitation step. With copper present in quantities of more t h a n a few per cent only a b o u t half of t h e cobalt could be recovered. With all of t h e available chelating agents t h a t are stable at this p H (3.5) there is yet work t o be done in this area. Gold and palladium, if present, would precipitate under these conditions and would compete for nitroso-R as well. However, gold and palladium are
Table II.
Fe, 70
Determination of Cobalt in Alloys
Nil yo
-
co, %
Spectrographic
Proposed Method
Alloys Prepared for the Analytical Section 1.63 17.6 71.5 74.4 77.0
95.2 80.4 23.9 25.0 20.0
31 32
53.7 43.1
39.6 48.4
126a
b
A
B C D E
3.26 1.82 4.58 0.60
3.04
3.29 1.93 4.56 0.64 3.07
3.29 1.93 4.56 0.56 3.03
3.30 1.93 4.58 0.63 3.11
Synthetic Standards 4.4 5.0
4.754 4.89“
4.76” 4.89“
National Bureau of Standards Samples (NBS value 0.30) 0.30 0.30 0.31 8.55
0.30 0.30 0.30 8.51
0.28 0.30
I (NBS value 8.45) Average of 4 determinations. 3. Xi, 35.89; Mn, 0.414; Cu, 0.092; Cr, 0.054. CNi, 0.107; hIn, 0.219; Cu, 0.099; Cr, 4.14; V, 2.04; hlo, 8.38; W, 1.58.
153
Q
seldom present in quantities large enough to interfere. Chromium and manganese did not interfere in this procedure, although some authors have reported their interference in the 1-nitroso-2-naphthol separation. Vanadium, zirconium, and titanium also have no apparent effect. It is expected that the list of metals which do not interfere can be expanded. LITERATURE CITED
(1) Am. SOC. Testing Materials, Phil-
adelphia, Pa., “ASTM Methods for Chemical Analysis of Metals,” p. 273,
1956. (2) Claassen, A,, Daamen, A., Anal. Chim. Acta 12,547-53 (1955). (3) Clark, L. J., ANAL.CHEM.30, 1153-6 (1958).
(4) Duval, C., “Inorganic Thermo-gravimetric Analysis,” p. 217, Elsevier, Amsterdam, 1953. (5) Evans, B. S., Analyst 62,363 (1937). (6) Heyn, Arno H. A., Brauner, P. A., “Determination of Cobalt by Precipita-
tion from Homogeneous Solutions Using 1-Nitroso-2-naphtho1,” 135th Meeting, ACS, Boston, Mass., April 1959. ( 7 ) .Lundell, G. E. F., Hoffman, J. I., “Outlines of Methods of Chemical Analysis,” p. 119, Wiley, New York, 1938. (8) Lundell, G. E. F., Hoffman, J. I., Bright, H. A., “Chemical Analysis of Iron and Steel,” p. 337, Wiley, New York, 1931. (9) Sandell, E. B , “Colorimetric Determination of Trace Metals,” 3rd ed., pp. 420-2, Interscience, New York, 1959. (10) Snell, F. D., h e l l , C. T., “Colorimetric Methods of Analysis,” Vol. I1 A, p. 290, Van Sostrand, Princeton, N. J., 1959.
RECEIVEDfor review July 22, 1959. Accepted April 22, 1960.
The Sulfur Dioxide Test for Selenious Acid EARLE R. CALEY and CLAYTON
L.
HENDERSON
McPherson Chemical laboratory, The Ohio State University, Columbus, Ohio
b Although the sulfur dioxide test for selenious acid has long been used, the conditions for optimum sensitivity have not been critically studied, nor has proper attention been given to the possibility of interference from selenic acid. Both hydrogen ion concentration and temperature affect i t s sensitivity. The optimum sulfuric acid concentration i s about 5.5M and the optimum temperature i s 80” to 90” C. This test i s unreliable for distinguishing selenious acid from selenic acid, and especially for the detection of small proportions of selenious acid in selenic acid. Hydro-
gen peroxide inhibits the test. It should no longer be used to detect the completeness of oxidation of selenious acid in the preparation of selenic acid by hydrogen peroxide oxidation.
B
showed that sulfur dioxide readily reduces selenious acid to selenium, and this reaction has long been used for the detection and determination of this element. The application considered here is the use of sulfur dioxide t o detect selenious acid in the presence of selenic acid, which has as its basis the incorrect ERZELIUS (2)
statement of Mitscherlich (6) that selenic acid is not reduced by sulfur dioxide. Benger (1) observed that this acid is readily reduced by sulfur dioxide under certain conditions, but i t has been recommended for the qualitative detection of selenious acid as an impurity in selenic acid (3, 6, 7). The purpose of this paper is to show to what extent this reagent is unreliable. EXPERIMENTAL
Selenium dioxide made by t h e oxidation of pure selenium with reagent grade nitric acid mas t h e basis Reagents.
VOL. 32, NO. 8 JULY 1960
975
of t h e standard solutions of selenious a n d selenic acids. The oxide obtained by evaporation \\as sublimed t o yield pure crystals. Standard solutions of selenious acid were prepared by dissolving weighed amounts of the crystals in n-ater and making the solution up to volume in calibrated flasks. The crystals were previously dried a t 110' C. for 24 hours. Selenic acid was prepared from the pure dioxide by the method described by Gilbertson and King (S), but n-ith certain modifications to ensure complete oxidation of the selenious to selenic acid. The amount of 30% hydrogen peroxide 11-as increased by 180 grams, the time of standing before heating t o 36 hours, and the period of refluxing to 14 hours. The extra hydrogen peroxide was added in approximately equal portions after the eleventh, twelfth, thirteenth, arid fourteenth hour of continuous refluxing. After refluxing, thc solution n-as evaporated under reduced pressure until the concentration of the selenic acid was about 40%> which was determined exactly by two independent methods. A comparison of the results also indicated the absence or presence of selenious acid. Procedure. I n t h e first method, weighed samples about 1 ml. in volume were diluted t o 30 ml. and added t o barium nitrate solutions slightly acidified with nitric acid. After digestion for 3 hours t h e precipitated bariumselenate wns filtered off in Jveighed filter crucibles, Ivashed, and dried a t l l O o C. to constant !\-eight. This is an adaDtation of a method for the determin'ation of barium described hy K h i t e (10) and shown by him to yield exact
Table I.
Effect of Sulfuric Acid Concentration
Acid Added, MI.
Total Volume of Soln., MI.
0.05 0.10 0.15 0.20 0.25 0.30 0.40 0.50 0.60
0.60 0.65 0.70 0.75 0.80 0.85 0.95 1.05 1.15
Acid Concn., Reaction Moles/ Time, Liter Sec. 1.5 2.7 3.8 4.8 5.6 6.3 7.5 8.5 9.3
Table II.
Conditions for Precipitation,
Pre-
cipitation of selenium from a selenious acid solution by sulfur dioxide is rapid and complete only when the solution is stronalv acid, hvdrochloric acid being ordinarily used for this. However, it cannot be used for the detection of selenious acid in the presence of selenic acid because chloride ion in high concentration in acid solution reduces selenate ion to selenious ion. Sulfuric acid appears to be the only suitable strong mineral acid, although Rose (8) asserted that the reduction of selenious acid is slow and incomplete when sulfuric acid is used. However, LIiiller (7') recommended sulfuric acid when selenic acid is present, Because the rate of reduction of selenite ion to selenium is largely controlled by hydrogen ion concentration, there seems to be no reason why the reduction should not proceed as well with sulfuric as with hydrochloric acid
Effect of Concentration of Reagent and Acid
Reagent Added, M1.
Total Volume of Soln., M1.
0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 1.30
976 *
73 27 25 20 19 23 29 57 85
results. Selenious acid in low concentration is not precipitated by barium ion in dilute nitric acid solution, as was shown by control tests. I n the second method, the selenium was determined as such in samples of similar size by reduction with sulfur dioxide in strong hydrochloric acid solution according to the procedure rwoinmended by Hillebrand et al. ( 4 ) . The concentration of selenic acid found by t'he two methods was essentially identical. This was taken to indicate that selenious acid was not present in significant proportion. Furt,lier evidence n-as obtained in the course of sonip experiments on the standard solutions which were prepared from it by dilution. To avoid possible action of light on the standard solutions of both selenious and Pelenic acids, the bottles containing them n-ere stored in a cupboard or n-rappctl in a thick cloth while in use. ACS reagent grade sulfurous acid of 67,concentration was used as the source of the sulfur dioxide. Because the concentration of this reagent may change appreciably on exposure, experiments made under any given set of conditions were all run on the same day, and fresh bottles of reagent were frequently used. The other reagents were 95% sulfuric acid and 30% hydrogen peroxide, both used without prior dilution.
ANALYTICAL CHEMISTRY
Concn., Moles/Liter Reagent Acid 0.05 0.10 0.15 0.19 0.22 0.26 0.29 0.31 0.34 0.36
6.3 5.9 5.6 5.4 5.1 4.9 4.7 4.5 4.3 4.1
Reaction Time, Sec. 23 17 12 16 23 30 39 50 61 72
if the concentration of hydrogen ion is euficient, RESULTS AND DISCUSSION
The data in Table I show the results of some of the experiments to determine blie optimum concentration of sulfuric acid for the reduction of selenious acid to selenium by sulfur dioxide. In each experiment 0.50 ml. of 0.010031 selenious acid was mixed with the stated volume of 95% sulfuric acid in a small test tube and brought t80 20' C. in a constant temperature bath. Then 0.05 ml. of 6% sulfurous acid was added and quickly mixed 11y shaking. The time for the first appcarance of a color due to the formation of a colloidal precipitate was measured with a stopwatch. Each figure in the table is the average of sufficient trials to make the probable error of the stated average less than 1 second. The results of corresponding trials with selenious acid solutions of considerably higher or lower concentration \\-ere less sharply defined. With a 0.10051 solution, for example, the times for the appearance of a precipitate were all so short that no clear distinction among the effect of different acid concentrations was possible, and with a 0.001OOilf solution the times were considerably extended and could not be consistently reproduced. The time required for the first appearance of a precipitate is an approximate measure of the sensitivity of the test. Conditions that cause the shortest time of react.ion are also those that make possible the detection of the minimcm amount of selenious acid. The dat'a in Table I1 show the effect of varying the concentration of reagent within a narrow range of high acid concentrat'ion. I n each experiment 0.50 ml. of 0.010031 selenious acid was mixed with 0.30 nil. of 95% sulfuric acid in a test tube and brought to 20' C. in a constant temperature bath. A given volume of 6% sulfurous acid, also a t 20' C., was then added with rapid shaking. The average time for the first appearance of a precipitate was measured as before. These data also indicate that the optimum concentration of sulfuric acid is about 5.5M. This concentration differs considerably from that employed in the procedure recommended by the International Committee on New Analytical Reactions and Reagents of the International Union of Chemistry (9). I n that procedure 1 ml. of selenious acid test solution is treated with 1 ml. of 95% sulfuric acid before the reagent is added in the form of sulfur dioxide gas. With this ratio of test solution to acid the sulfuric acid concentration is about 8.9M, which the results in Tables I and I1 show is not the optimum con-
centration. The data in Table I1 also indicate that Concentration of reagent is a less important factor in the sensitivity of this test than concentration of acid, as an increase in concentration of reagent only leads to longer times of reaction as the concentration of acid falls below 5.5144, Temperature is also important in the sensitivity of this test, as indicated by Table 111. I n each experiment 0.50 ml. of selenious acid of a given concentration was mixed with 0.50 ml. of 95y0 sulfuric acid in a test tube and brought to a given temperature in a constant temperatuie bath. Then 0.10 ml. of 6% sulfurous acid mas added with rapid shaking and the average time for the fiist appeaiance of a precipitate was measurctl. It might be supposed that the use of temperatures near the Foiling point of the solution would considerably iiiciease t h e sensitivity, but no such incrcase occurs, apparently because the effcctiw concentration of the reagent is reduced by the rapid expulsion of sulfur dioxide a t these higher teniperaturcs. I n the procedure recommended by the Inteinational Committee on Kew Analytical Reactions and Reagents of the International Union of Chemistry (9) the solution is saturated B-ith sulfur dioxide gas, boiled for a minute, and then allowed to cool to observe the reaction. For the type of procedure employed in the present experiments the optimum temperature for the test is in the range 80" to 90" C. Table 111.
Effect of Temperature
Selenious Acid
concn,,
hIole/Liter 0.0100 0.00100 0.000100
Fime of Reaction, 8ec. 20°C. 60°C. 8 m 31 100
..
9 20 118
3 13 55
Behavior of Selenic Acid Solutions. The data in Table I V show the results of eyperirnents on the reaction of sclenir acid solutions n i t h 6y0sulfurous acid a t two selected temperatures. The volume of selenic acid solution was 0.50 ml., and both test solution and reagent were a t the same temperature before mixing. To make certain that the positive results observed in these experiments were not due to the presence of a minute proportion of selenious acid in the selenic acid, the noncolloidal precipitates obtained from some of the more concentrated selenic acid solutions were separated by filtration through sintered glass and the filtrates were tested again. Positive results were obtained again even after two such separations. I n these experiments with pure selenic acid solutions the acidity was necessarily low, as shown by the figures in
Table IV. Reaction of Selenic Acid Solutions
Selenic Acid Concn. in Test Soln.,
Reagent Added,
Mole/Liter
111.
Selenic Acid Concn. in Final Soln., MolelLiter
Reaction Time, Sec.
80" c.
20" c.
0.25 2 3 3
the third column of Table IT.'. Because high acid concentration gieatly increases the sensitivity of the reaction between selenious acid and sulfur dioxide, the reaction between selenic acid and sulfur dioxide should also be greatly enhanced by inciease in acid concentration. The data in Table V show the iesults of some experiments in which sulfuric acid was added to selenic acid solutions before the reagent was added. I n each experiment 0.50 ml. of selenic acid solution was mixed with a given volume of 95y0sulfuric acid and treated with 0.10 ml. of 6% sulfurous acid a t a given temperature. Increased acidity obriously has a marked effect. By the use of the same optimums of acidity and temperature as for selenious acid solutions, it is possible to obtain a positive reaction with a 0.010M solution of selenic acid but not with a 0.001OM solution. Though these experiments as a whole indicate that sulfur dioxide is a less sensitive reagent for selenic acid than for selenious acid, the difference is so small that this reagent is not reliable for distinguishing between the two acids or between selenate ion and selenite ion. However, the difference is greater, a t least as determined by the procedure of the present experiments, than is indicated by the dilution limits published by the International Committee on Kew Analytical Reactions and Reagents of the International Union of Chemistry (9).
Effect of Hydrogen Peroxide. Gilbertson and King (5) recommend the sulfur dioxide test for detecting the complet'ion of oxidation of selenious acid by hydrogen peroxide in their method for t'he preparation of selenic acid-in other words, for detecting the presence or absence of a small proportion of selenious acid in a concent'rated solution of selenic acid. The results of the preceding experiments indicate that, a positive test should always be obtained even when no selenious acid is present. However, in preparing selenic acid by this method the authors were usually unable to obtain a positive reaction after either partial or complete oxidation, As it was suspected that hydrogen peroxide might oxidize t'he reagent before it could react, some systematic experiments were made,
Table V. Reaction of Selenic Acid Solutions with Added Sulfuric Acid
Selenic Acid Sulfuric Total Concn. in Acid Acidity, Reaction Test Soln., Added, Moles/ Time, PIIole/Liter MI. Liter Sec. 0.250
0.10b
a
20" C.
0.00 0.05 0.10 0.25 0.00 0.05 0.10 0.25
120 14 11 8
0.2 1.6 2.8 5.5 0.1 1.5 2.7 5.4
..
13 3 3
* 80" C.
Table VI.
Effect of Hydrogen Peroxide on Reduction of 4.OM Selenic Acid with Sulfur Dioxide at 20" C. Reagent Sulfur Dioxide 307, Hydrogen Hydrogen Reaction
Added, 311. 0.10 0.50 1.oo 0.10 0.50 1.00 0.10 0.50 1.00
Concn., Mole/Liter
Peroxide Sdded, M1.
Peroxide Concn., Moles/Liter
Time, Sec.
0.14
0.05 0.05 0.05 0.10 0.10 0.10 0.25 0.25 0.25
0.75 0.47 0.32 1.40 0.88 0.47 2.88 1.96 1.40
..
0.45
0.60
0.13 0.43 0.59 0.11 0.38 0.54
VOL. 32, NO. 8, JULY 1960
2 2 ..
12 9
.. .. ..
917
the results of which are shown in Table VI. I n each experiment 0.50 ml. of 4.OM selenic acid was mixed with a given volume of 30% hydrogen peroxide before a given volume of 6% sulfurous acid was added. I n parallel experiments without hydrogen peroxide, the reaction was so fast that it could not be measured with a stopwatch. The inhibiting effect of the hydrogen peroxide is obvious. Similar experiments with mixtures of selenic and selenious acids of various concentrations showed that hydrogen peroxide always inhibits the reaction, often to such a n extent that the result is negative when the concentration of the selenic acid, the selenious acid, or both, is such that it
should be strongly positive. The data in Table VI also show that when the concentration of hydrogen peroxide is Iow enough, the test will give a positive result even when no selenious acid is present. For the purpose recommended by Gilbertson and King this test is therefore wholly unsuitable. LITERATURE CITED
(1) Benger, E. B., J . Am. Chem. SOC.39,
2171 (1917). (2) Berzelius, J. J., Acad. Handl. Slockholm 39, 13 (1818). (3) Gilbertson, L. I., King, G. B., J . I m . Chem. SOC.5 8 , 180 (1936). (4) Hillebrand, W. F., Lundell, G. E. F., Bright, H. A., Hoffman, J. I., “Applied Inorganic Analysis,” 2nd ed., p. 334, Wiley, New York, 1953.
(5) Mellor, J. W., “Comprehensive Trea-
tise on Inorganic and Theoretical Chem-
istry,” Vol. 10, p. 751, Longmans,
Green, London, 1930.
(6) Mitscherlich, E., Ann. physik. Chem. 9., 629 - - 11827). \ (7) Muller, E.,‘Z. physik. Chem. (Leipzig) 100, 346 (1922). ( 8 ) Rose, H., Ann. physik. Chem. 113, 472
(,1- A-6 -l , ). (9) Wenger, P., Duckert, R., eds., “Reactifs pour l’halyse Qualitative MinBrale Recommand& par la Commission Internationale des Reactions et Reactifs Analytiques Nouveaux de 1’UnionInternationale de Chimie,” 2nd Rapport, p. 52, Basle, 1945. (10) White, H. C., Ph.D. thesis The Ohio State University, Columbus, 6hio, 1950. RECEIVED for review September 23, 1959. Accepted February 29, 1960. Taken from the M.S. thesis submitted by Clayton L. Henderson to The Ohio State University,
1955.
Co I o rimetric Reactio ns of 3,5- Dinitro-0-toI ua mide and Related Compounds with Aliphatic Diamines GRANT N. SMITH AND MARLENE G. SWANK Agriculfural Chemical Research, The Dow Chemical Co., Midland, Mich. )The colorimetric reactions of 3 3 dinitro-o-toluamide and related dinitrobenzamides with aliphatic diamines are described. These reactions can b e used to estimate and distinguish the various dinitro compounds which give a postive test with this reaction. The factors influencing the formation of colored complexes by reaction of 3,5-dinitro-o-toluamide with various diamines and organic solvents are elucidated.
of the color. I n initial investigations @), only the straight-chain primary aliphatic monoamines formed colored complexes with 3,5-dinitro-o-toluamide. The presence of a second functional group such as a hydroxyl or amino group appeared to stabilize the complex. A series of di-, tri-, and polyamines was, therefore, investigated to ascertain if stable complexes could be formed with 3,5-dinitro-o-toluamide. EXPERIMENTAL
T
of 3,5-dinitro-o-toluamide with methylamine in the presence of dimethylformamide has been used as a basis for a colorimetric procedure for the assay of 3,5-dinitro-otoluamide ( 2 , S ) , a drug (Zoalene, registered trade-mark of The Dow Chemical Co.) used to treat coccidiosis in chickens. This reaction has several advantages. The colored complex formed has a yery intense color which permits the detection of microgram quantities of the drug. The complex also exhibits an absorption peak at 550 mpL,a portion of the visible spectrum in which most of the naturally occurring pigments do not exhibit absorption bands. The test is also specific for 3,5-dinitro-o-toluamide in the presence of its possible metabolic degradation products. The one major disadvantage of the reaction is the evanescent properties HE REACTION
978
ANALYTICAL CHEMISTRY
To ascertain the influence of various diamines on the production of color complexes, a solution of 3,5-dinitro-otoluamide in dimethylformamide was mixed with an equal volume of amine solution. The absorbance of the colored solution was then determined in a Cary recording spectrophotometer Model 14 in the region from 350 to 650 mp. All solutions were maintained a t 20” C. and read as soon as possible after the color had been developed. The various factors influencing the intensity and stability of the colored complex were investigated by varying each factor independently. RESULTS A N D DISCUSSION
Influence of Various Diamines on Color Formation. The various amines shown in Table I gave a positive test in t h e color reaction. Of all t h e amines tested, only those compounds containing a primary
amino group produced colored complexes. Most of t h e higher molecular weight polyamino compounds were unsatisfactory for this test because they were solids or had a high visc osity . I n general, the diamines were the most satisfactory reagents for the development of color. I n this series, greater color intensity was obtained with diamines in which the amino groups were attached to the terminal carbons than with compounds in which one amino group was located along the chain. Most of the amines gave complexes
Table I. Comparison of Absorbance Readings for Colored Complex Formed 3,5-Dinitro-o-toluamide, Diwith methylformamide, and Various Amines
Absorbance at 560 Mfi (Corrected for Reagent Blank) 0,565 0.280 0.635 0.515 0.605 0.573 0,545
Amine 1,2-Ethanediamine 1,2-Propanediamine 1,3-Propanediamine 1,3-Butanediamine 1,4-Butanediamine 1,5-Pentanediamine 1,bHexanediamine 3,3 ’-Iminobispropylenediamin le 0.583 Triethylenetetramine 0.493 Methylamine 0.540
