Titration of Aromatic and Aliphatic Amine Picrates in Nonaqueous Solution JOHN R. CLARK and S. M. W A N G M a l t b i e Laboratories, Inc., Newark,
N. J.
C
OSANT, Hall, and Werner (1-4) illustrated in their extensive studies on organic amines too weak to be titrated in aqueous solution that the amines could be successfully titrated in glacial acetic acid with perchloric acid. Sadeau and Branchen (6) first employed the nonaqueous acid-base titration for amine acids successfully. They also employed indicators for their titration. Markunas and Riddick ( 5 ) found most amines could be titrated in acetic acid potentiometrically.
Table I.
Determination of Milliequivalent Weight of Amine Picrates,"
Melting Milliequivalent Weight Sample Point, C. Calculated Found Diinetl.y;aniline picrate 162-163 350 Ethylenediamine dipicrate 232-233 518 Diethanolamine picrate 109-110 332 Aniline picrate 322 165(decomp.) 2-Aminopyridine picrate 2 16-217 324 2,4,6-Collidine Dicrate 155- 156 352 Piperidine picrate 150-152 314 313 a Picrates \yere prepared from commercially available amines by precipitation from alcohol. They were recrystallized from alcohol to obtain a melting point closely corresponding to the accepted value.
These principles were applied to a procedure for the titration of picrates of aromatic or aliphatic amines in glacial acetic acid, using methyl violet as an indicator. Because picrates are in general the most convenient crystalline derivative for the identification of amines in synthetic work, and are easily purified, this method was devised for the determination of the milliequivalent of amines before elemental analysis. REAGENTS
Glacial acetic acid, U.S.P. Methyl violet indicator, 0.2% in chlorobenzene.
Perchloric acid, 0.1S. Mix 8.5 ml. of 72% perchloric acid with 200 ml. of glacial acetic acid and 20 ml. of acetic anhydride. Dilute to 1 liter with glacial acetic acid. Standardize the solution against acid potassium phthalate. PROCEDURE
Dissolve 1to 4 meq. weights of amine picrate in 50 ml. of glacial acetic acid with the aid of gentle heat if necessary. Cool the solution to room temperature and titrate the solution with standardized perchloric acid, using 6 drops of methyl violet indicator, until the disappearance of the purple tinge of the solution. Results arc listed in Table I. SUMMARY
A rapid method was developed for the determination of the milliequivalent weight of amine picrates by direct titration with perchloric acid in glacial acetic acid. By using methyl violet indicator, a reasonably sharp end point was obtained. The yellow coloration of the picrates did not interfere with the end point. This method was found useful for the titration of primary, secondary, and tertiary amines, whether aromatic or aliphatic. LITERATURE CITED (1)
Conant, J. B., and Werner, T. H., J . Am. Chem. Soc., 52, 4 4 3 6 (1930).
Hall, N. F., Zbid., p. 5115. Hall, N. F., and Conant, J. B., Ibid., 49, 3047 (1927). (4) Hall, N. F., and Werner, T. H., Ibid., 50, 2367 (1928). (5) hfarkunas, P. C., and Riddick, J. A., ANAL. CHEM.,23, 3 3 7
(2) (3)
(1951). (6)
Nadeau, G . F., and Branchen, L. B., J. Am. Chem. Soc., 57, 1 3 6 3 (1935).
RECEIVED for review October
16, 1953.
Accepted March 18. 1954.
Colorimetric Determination of Niobium by Molybdenum Blue Method GEORGE NORWITZ and MAURICE CODELL Pitman-Dunn Laboratories, Frankford Arsenal, PhiIade/phia, Pa.
T
HIS laboratory was called upon to develop a method for the
determination of niobium in titanium alloys. I n investigating the problem an attempt was made to determine the niobium by a molybdenum blue method either directly or after a tannin separation of the niobium from the bulk of the titanium. These attempts were unsuccessful owing t o the interference of titanium with the color. However, because of the great current interest in niobium and the lack of good colorimetric methods for niobium, the authors decided to investigate the molybdenum blue color obtained with niobium. The use of the molybdenum blue color for niobium was proposed in 1947 by Davydov, Vaisberg, and Burkser ( I ) , who applied the method to the determination of niobium in steels. Since that time no other paper has appeared on the method. In the procedure proposed by these investigators the sample of steel is dissolved in a mixture of sulfuric, nitric, and hydrofluoric acids,
and the solution is diluted to 50 ml. An aliquot of this solution is diluted so that the normality is approximately 0.5N. Disodium hydrogen phosphate and ammonium molybdate are added and the yellow phosphomolybdate and niobiophosphomolybdste colors are allowed to develop. .4n excess of sulfuric acid is then added to destroy the phosphomolybdate color and the solution is treated with stannous chloride. The molybdenum blue color due to the niobiophosphomolybdate complex is then measured with a colorimeter. At first, attempts to duplicate the results of this procedure were not successful. However, a thorough investigation finally clarified the many factors affecting the method and resulted in the development of an improved procedure. APPARATUS AND R E.AG EYTS
Beckman spectrophotometer, Model B, with four 1-em. matched cells.
1230
1231
V O L U M E 2 6 , NO. 7, J U L Y 1 9 5 4 Standard electric timer. Standard niobium solution (1 ml. contains 0.1 mg. of niobium.) Transfer 0.1000 gram of pure niobium metal to a covered 35-ml. platinum crucible. Add 5 ml. of water, and then add hydrofluoric acid (48'%) and nitric acid dropwise until the sample is dissolved. Wash down the cover lid and remove it. Heat for a few minutes on the hot plate. Cool to room temperature and add 20 ml. of hydrofluoric acid (48%). Wash into a 600-ml. beaker containing about 400 ml. of water. Transfer to a 1-liter volumetric. flask and dilute to the mark. Dilute sulfuric acid, 12.6.V. Dilute hydrofluoric acid ( 1 to 50). .\dd 10 ml. of hydrofluoric acid (48%) to water and dilute to 500 nil. with water. Store in a polyethylene bottle. Disodium hydrogen phosphate solution, 0.06%. .\mmonium molybdate solution, 2%. Dissolve 20 grams of ammonium molybdate, ( SH4)&lo702,4H20, in water and dilute to 1 liter with water. Stannous chloride solution, 25%. Dissolve 125 grams of stannous chloride, SnC12.2H20,in a mixture of 125 ml. of hydrochloric acid and 125 ml. of water. Dilute to 500 ml. with aater. Stannous chloride solution, 0.5%. A4dd10 ml. of hydrochloric acid and 10 ml. of stannous chloride solution (25%) to water and dilute to 500 ml. with water. Make fresh daily.
portions of dilute sulfuric acid (12.65), evaporating to fumes of sulfuric acid, and carrying the solutions through the procedure. EXPERIMENTAL
The results obtained when different amounts of dilute sulfuric acid were used in fuming are shown in Figure 1. Ten milliliters of dilute sulfuric acid comprise about the ideal amount. When too little sulfuric acid is used, the molybdenum blue color is more intense because of the reduction of the phosphomolybdate complex. If too much sulfuric acid is used, the development of the yellow niobiophosphomolybdate color is inhibited. Consequently, the results obtained for the molybdenum blue color are loa.
RECOMMENDED PROCEDURE
Transfer the sample containing up to about 2.5 mg. of niobium t o a 35-m1. platinum crucible and dissolve with an acid mixture of 5ml. of hydrofluoric acid (48%) and 5 ml. of nitric acid. ildd 10 ml. of dilute sulfuric acid (12.6,V) measured with a pipet or buret. Evaporate to fumes of sulfuric acid and fume about a minute. A4110wto cool to room temperature. Add 10 ml. of water and
I00
I
0' 2 M L NozHPO, w
75
Figure 2.
4
I
6 SOLUTION (0.06Y.) 4
I &
Effect of .Amount of Phosphate
t v1
s
50
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0
'K
p" 2 5
0
IO
20
ML DILUTE H,SO,
Figure 1.
30 (12.6N)
40
Effect of Amount of Sulfuric Acid Used in Fuming
5 ml. of dilute hydrofluoric acid (1 to 50). Once the solution has been diluted with water and hydrofluoric acid, it should not be allowed t o stand more than 2 hours. Dilute almost t o the top of the crucible with water and wash the contents of the crucible into a 100-ml. volumetric flask, using a funnel. Cool to room temperature and dilute to the mark. Pipet a IO-ml. aliquot into a 50-ml. volumetric flask. Add by means of a pipet or buret 10 ml. of water, 2 ml. of disodium hydrogen phosphate solution (0.06%), and 5 ml. of ammonium molybdate solution (2%). Allow to stand 15 minutes. Add by means of a pipet 10 ml. of dilute sulfuric acid (12.6N). I n measuring out the dilute sulfuric acid, quickly blow out the contents of the pipet into the volumetric flask. Thirty seconds after the addition of the dilute sulfuric acid add 3 ml. of stannous chloride solution (0.5%) measured with a buret. I n measuring the 30-second interval, use an electric timer. Start the timer the moment the dilute sulfuric acid has been completely blown into the volumetric flask. Swirl and immediately dilute to the 50-ml. mark with water. Within 5 minutes read the color with a spectrophotometer a t '715 mp. The instrument is set a t 100% transmittance with distilled water. Convert the readings to milligrams of niobium by consulting a calibration curve prepared by adding aliquots of standard niobium solution to 10-ml.
The variation of the molybdenum blue color with different amounts of phosphate is shown in Figure 2 . The recommended amount of phosphate is 2 ml. If too little phosphate is present, high results are obtained, probably because the large amount of phosphomolybdate formed is not completely destroyed by the addition of the excess sulfuric acid. A slightly blue color is still obtained even when no phosphate is present. The results obtained when different amounts of molybdate were used are shown in Figure 3. The use of 5 ml. of ammonium molybdate solution is recommended. If too little molybdate is
100
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y
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so
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E
25
0
5 IO M L (NH,),MO,O,;~%O
Figure 3.
I5
20
.SOLUTION ( 2 % )
Effect of Amount of Molybdate
1232
ANALYTICAL CHEMISTRY
present, the color is less intense. If too much molybdate is present, the results will be high. The effect of time on the development of the yellow niobiophosphomolybdate color is shown in Figure 4. Fifteen minutes is satisfactory. If the time is too short, the molybdenum blue color obtained will be less intense. If the solutions are allowed to stand more than 20 minutes, the intensity of the molybdenum blue color will be somewhat greater.
100
g
75
2 t
v) z
2
so
c
z 0 W 75
a
2
W
u
2s
2 t
:so
0
4 z
K
I-
TIME
w 0
2s
-
IN
SECONDS
Figure 6. Effect of Time Interval between Addition of Dilute Sulfuric Acid and Addition of Stannous Chloride
Iz
20
60
40
80
TIME I N MINUTES
Figure 4. Time for the Development of Yellow Niobiophosphomolybdate Color
The results obtained on adding varying amounts of dilute sulfuricacid (12.6N)to destroythephosphomolybdatecolor are shown in Figure 5. Ten milliliters of dilute sulfuric acid seemed best. If too little sulfuric acid is used, the molybdenum blue color is too intense owing to incomplete destruction of the phosphomolybdate color. If too much sulfuric acid is used, the results obtained for the molybdenum blue color will be low. Apparently, too murh acid destroys the niobiophosphomolybdate color.
tion (0.5$70) is required for complete color development. The use of 3 ml. is recommended for the general procedure. If significant amounts of iron are present, the use of 6 ml. is recommended. The stability of the niobium molybdenum blue color is shown in Figure 8. The transmittance should be determined within
100
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1 1
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ir. t
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Figure 7 .
W
0
5 IO ML DILUTE H,SO,
15 112.6N)
I
5 1.5 SOLUTION ( 0 . 5 % )
I IO
Effect of Amount of Stannous Chloride
20
Figure 5. Effect of Amount of Dilute Sulfuric Acid Used in Destroying Phosphomolybdate Color
The effect of the time interval between the addition of the dilute sulfuric acid and the addition of the stannous chloride is shown in Figure 6. The color intensity decreases markedly as this time interval increases. Obviously, this time interval must be carefully controlled. Good calibration curves were obtained at 30-secondJ 1-minute, and 2-minute intervals. A 30-second interval is recommended. This is the time interval used by Davydov, Vaisberg, and Burkser (I). The results obtained with different amounts of stannous chloride are shown in Figure 7. Only 1 ml. of stannous chloride solu-
5 minutes.
After this period of time the color starts to fade slowly. Typical spectrophotometric curves obtained for the niobium molybdenum blue color are shown in Figure 9. Maximum absorption occurs at 715 mg. It is recommended that the color be read a t this wave length. A calibration curve, prepared using the standard niobium solution, deviated only slightly from Beer's law. Good results could be obtained only when the fuming with sulfuric acid was conducted in platinum. When the solutions were fumed in glassware, the results obtained were not satisfactory. The only sure means for accurately adjusting the acidity is to evaporate to fumes of sulfuric acid. Solution of the material in a mixture of sulfuric and hydrofluoric acids, or a mixture of sulfuric, hydrofluoric, and nitric acids without subsequent fuming, is not satisfactory owing to the difficulty of calculating the acid
V O L U M E 2 6 , NO. 7, J U L Y 1 9 5 4 Table I.
1233
Accuracy and Precision of Method
Niobium Added, Mg. 0.10 0.50 1.00
Average Niobium Found, Mg. 0.11 0.50 1.02
2.50
2.47
Standard No. of DeterDeviation, Mg. minations 0.015
4 4
0.021 0.021
4
0.054
4
w
Y
K
30
I
1
60
80
I 20
40 TIME
IN
J
MINUTES
Figure 8. Stability of Niobium Molybdenum Blue Color
loat by volatilization and the acid required t o dissolve the material. The accuracy and precision obtained with the method when standard niobium solution was used are shown in Table I.
ditions described in this paper. However, it has the effect of repressing the development of the niobium molybdenum blue color. Very little arsenic is lost in evaporation of the solution to fumes of sulfuric acid, since arsenic pentafluoride is not readily volatile ( 2 ) . Arsenic(II1) is easily oxidized to arsenic(V) by the nitric acid. More than 0.01 gram of molybdenum or 0.0002 gram of phosphorus interferes by increasing the intensity of the color. Antimony interferes by forming a precipitate on the addition of the phosphate and molybdate. Antimony(II1) reduces the molybdenum to molybdenum blue when the ammonium molybdate solution is added. Antimony(II1) is not readily oxidized to antimony(V) by nitric acid. Cerium interferes by repressing the development of the molybdenum blue color. Bismuth interferes with the method because of the precipitation of insoluble bismuth phosphate. Barium, lead, and strontium interfere because they are precipitated as insoluble sulfates. The precipitated sulfates appear to promote the precipitation of the niobium. Silver, mercury, and selenium interfere by forming plecipitates upon the addition of the stannous chloride. Quantities in excess of 0.005 gram of titanium cause high results when the niobium content is low, and low results when the niobium content is high. The presence of more than 0.03 gram of iron causes erratic results particularly when the niobium content b low. This effect of iron was not remedied by the use of a larger amount of stannous chloride solution (10 ml.). The presence of more than 0.01 gram of tantalum is not recommended because of the danger of hydrolysis.
INTERFERENCES
A complete study was made of possible interferences. It was found that none of the following elements could be present: antimony, arsenic, barium, bismuth, cerium, lead, mercury, selenium, silver, strontium, tungsten, and vanadium. The amounts of other elements that did not interfere with the method are shown in Table 11. Tungsten and vanadium interfere because they form molybdenum blue colors under the same conditions as niobium. Silicon is easily vola6ilieed as the fluoride on fuming with sulfuric acid and does not interfere. If the silicon were not removed, it would produce a molybdenum blue color. Arsenic does not produce a molybdenum blue color under the con-
Table 11. Element Aluminum Beryllium Boron Cadmium Calcium Chromium Cobalt Copper Iron Magnesium Manganese Molybdenum Nickel Phosphorus Potassium Silicon Sodium Tantalum Tin Titanium
Study of Interferences
Added as .41z(604)a. ISH20 BeSol. 4Hz0 HiBOa CdSOi CaCh. 2H.O
KzS04 Naz9103. 9IIzO NanSOi Metallic Ts Metallic Sn HF-HNOa solution of metallic Ti Zinc ZnSOr a Maximum permissible amount.
Figure 9. Spectrophotometric Curves for Niobium Molybdenum Blue Color
Amount in Grama That WGI Not Interfere (in Original 100-MI. Volume) 0.1 0.1
0.1 0.1 0.1 0.1 0.1 0.05 0.03" 0.1 0.1 0.01' 0.1 0.0002" 0.1 0.1 0.1 0.01' 0.1
0.005" 0.1
Such anions as cyanide, thiocyanate, oxalate, citrate, and tartrate did not interfere with the method, as they are destroyed on fuming with sulfuric acid. Any chloride present in the initial solution would be volatilized on fuming with sulfuric acid. However, because stannous chloride solution containinga smallamount of hydrochloric acid is used in the method, the interference of chloride is pertinent. Up t o 0.05 gram of sodium chloride added to the 50-ml. volumetric flask before the addition of the phosphate did not interfere. The presence of about 0.05 to 0.5 gram of sodium chloride caused the color intensity to increase somewhat, although this effect was erratic. More than 0.5 gram of sodium chloride caused low results with the production of greenish tinted solutions. The fluoride used to dissolve the sample is removed by fuming with sulfuric acid. However, since some fluoride is subsequently added to help hold the niobium in solution, the interference of fluoride was investigated. Up to about 0.012 gram of sodium fluoride added to the 50-ml. volumetric flask before the addition
ANALYTICAL CHEMISTRY
1234 of the phosphate caused no interference. More than this amount of fluoride inhibited the development of the niobium molybdenum blue color. Nitrate present in the original solution is driven off on fuming. However, a study was made of the effect of nitrate, since Davydov, Vaisberg, and Burkser in their method for steels developed the color in a solution containing nitric acid. It was found in this laboratory that up to 0.3 gram of sodium nitrate added to the 50-ml. volumetric flask before the addition of the phosphate
caused no interference, if the color were read within 3 minutes. After this interval of time the color faded rapidly. LITERATURE CITED
(1) D a v y d o v , A. L., Vaisberg, Z. M., and Burkser, L. E., Zauodskaya Lab., 13, No. 9. 1038 (1947). (2) Hillebrand, W. F., a n d Lundell, G. E. F., “Applied Inorganic Analysis,” p. 209, S e w York, J o h n Wiley & Sons, 1929. RECEIVED for review December 21, 1953. Accepted April 15, 1954.
Infrared Determination of Biphenyl in Citrus Fruits W. F. NEWHALL, E. J. ELVIN,rnd L. R. KNODEL Florida Citrus Experiment Station, Lake Alfred, Fla.
M
CCH interest has arisen concerning the biphenyl residues remaining in the peel or juice of citrus fruit packed in cartons impregnated with Phenodor X (a mixture of biphenyl, petroleum wax, and odor counteractants) or similar fungistatic preparations containing biphenyl. Several quantitative analytical methods for determining biphenyl in citrus peel and juice have been described. Tomkins and Isherwood ( 4 ) developed a method whereby a sample of biphenyl in orange oil, obtained by steam distillation of minced peel or pulp, was extracted with concentrated sulfuric acid to remove the orange oil. The biphenyl . - mas then determined colorimetrically. The error in this method was reported as 120%. In the biphenyl analysis of fruit developed by Steyn and Rosselet ( S ) , the biphenyl content of steam-distilled oil was calculated from t h e ultraviolet absorption a t 250 mp. A correction for the orange oil present was applied, based on the absorption of the oil at 375 mp, a t which wave length biphenyl does not absorb. Some difficulty has been encountered by other workers in obtaining reproducible results using the method of Steyn and Rosselet. This difficulty is associated with the correction for the orange oil present. A quantitative determination of the biphenyl c o n t e n t of fiberboard Figure 1. Liquid-Liquid cartons i m p r e g n a t e d Extractor with Phenodor X has been developed b y Knodel and El& (2): I n this method biphenyl is extracted from a fiberboard sample with carbon tetrachloride and the absorption peak a t 14.34 microns in the infrared region is measured. The mean per cent error of this method is 1.9%. A quantitative analytical method has been devised for the direct determination of biphenyl in orange oil obtained by steam distillation of minced peel or juice. Use is made of the biphenyl
absorption peak a t 14.34 microns in the infrared. Variations in the optical properties of individual orange oil samples do not affect the accuracy of the results when calculated using a base-line technique. This ability to use orange oil as the solvent greatly simplifies the isolation and determination of biphenyl in fruit. EQUIPMENT
For the analysis, a Beckman Model IR-2 spectrophotometer with rock salt optics is used. It is equipped with a synchronous wave-length drive motor and a chart recorder. The absorption cells used have rock salt windows separated by either a 0.1or 0.4-mm. spacer. (The first analyses were made using a 0.1mm. spacer. However, the standard curvesin Figure 3 show that a 0.4-mm. spacer gives better resolving power, especially for dilute solutions of biphenyl in orange oil, and this spacer is now used for all analyses.) REAGENT
Standard solutions are prepared by dissolving known amounts of pure biphenyl (melting point 68.5’ to 69.5” C.) in technical
Table I. NO.
1 2 3 4 5 6
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
25 26
27 28 29 30 31
Recovery of Biphenyl Using Liquid-Liquid Extractor Biphenyl Added P.p.m. Mg.
Biphenyl Found, BIg.
Recovery,
One Half Whole F r u i t (Approximately 130 Grams) 102 11.9 11.7 90 103 16.6 16.0 123 98 8.2 8.4 65 96 6 . 7 7.0 54 100 6.1 6.1 47 101 7 . 7 7.6 58 93 4.8 5.2 40 98 5.3 42 5.4 96 4.5 36 4.7 99 9.90 77 10.0 103 10.31 10.0 77 95 13.97 114 14.77 90 13.34 114 14,77 91 4.52 4.98 38 97 9.73 ,10.0 77 100 9.99 10.0 77 94 13,81 114 14.77 94 13.80 14.77 114 100 5.00 4 98 38 90 4.46 4.98 38 Valencia Juice (Approximately 1600 Grams) 4.98 4.63 3.1 4.98 4.98 3.1 4.98 5.08 3.1 4.98 4.96 3.1 2.85 2.96 1.8 2.85 2.87 1.8 2.85 2.95 1.8 1.60 1.68 1.0 1 . 6 0 1.60 1.0 1.60 1.65 1.0 1.60 1.54 1.0
Average recovery 98%. Standard deviation +4.24%.
93 100 102 100 104 101 103 105 100 103 96
70
