500
ANALYTICAL CHEMISTRY
which was stored in the dark during the study. Excess magnesium was used to complex completely tthe dye which was present. The vertical dotted line represents the wave length of 520 mM which was used in determining the concentration curves. 16
Complex I
-
I
Reagent V
Table 1. Determination of Magnesium i n Water
0
VI
5
Ill
VI1
10
9983
12.7 12.7
12.7
12.6
9984
13 7
13 0
14 5
996
16 0 16. J
16.3
15.5
9986
1.5 3
12.4
14.1
4.9
4.9
2 5
2.9
10009
10010
I
Gravimetric Analysis (Av.), Mg, P.P.M.
Rlg, p.p.rn.
Days
I1
Colorimetric Bnalysis Average AIg, p.p.m.
Sample No.
1.i j
I.i.5 3 2 4.5 2 3
2 .i
Geological Survey Department, Institute of Science and Technology, Water Analysis Laboratories, University of Arkansas. The results obtained by the new method agreed with those from the gravimetric procedure within the usual error encountered in water analysis and the precision was excellent. The data obtained from both the gravimetric and colorimetric analyses are presented in Table I. It is hoped that the method can be extended to include a calcium determination either by difference or by using the calcium sulfate precipitate directly. It is also proposed that the method be adapted for the determination of magnesium in soils and plants and other materials having small magnesium content,
I I I
I I
LITERATURE CITED
This series of curves shows a considerable change in the dye curve a t longer wave lengths as the aging progresses. The variation in the absorption curves with time indicates a probable structural change of the dye in solution. The variation in the absorption curves of the magnesium complex solution could probably be attributed to the structural variation taking place in the dye solution during the aging process. Further studies have shown that with the dye in excess, the variation of the absorption curve of the magnesium complex prepared from dye aged up to 5 days is negligible a t the xave length of 520 mp. APPLICATION TO WATER SAMPLES
Analyses of water samples by the proposed method were compared to gravimetric determinations as reported by the U. S.
(1) Caley, E. R., and Elving, P. F., IXD.ENQ.CBEM.,ANAL.ED., 10,264 (1938). (2) Diehl, H., Goetz, C. A., and Hach, C. C., J . Am. Waterworks Assoc., 42,40 (1950). (3) Harvey, C. O., Analyst, 61,817 (1936). (4) Hoffman, J. I., Bur. Standards J. Research, 9, 487 (1932). (5) Hoffman, W. S., J. Bid. Chem., 118,37 (1937).
(6) Ludwig, E. E., and Johnson, C. R., IND.ENG.CHEM.,ANAL.
ED.,14,895 (1942). (7) Mellon, M. G . , “Analytical Absorption Spectroscopy,” p. 309, New York, John Wiley & Sons, 1950. (8) Schwarzenbach, G . , and Biederman, W., Helv. Chim. Bcta, 31, 678 (1948). (9) Snell, F. D., “Colorimetric Methods of Analysis,” 2nd ed., p. 470, New York, D. Van Nostrand Co., 1936. (10) Theil, A., and Van Hengel, E., Ber., 71B, 1157 (1938). (11) Thrun, W. E., IND. ENQ.CHEM.,ANAL.ED.,4, 426 (1932). (12) Vosburgh, W. C., and Cooper, G. R., J. Am. Chem. SOC.,63, 437 (1941). RECEIVED for review August 18, 1952. Accepted October 24, 1952.
Volumetric Determination of Tellurium in Organic Compounds F. H. KRUSE’, R. W. SANFTNERZ, AND J. F. SUTTLE Department of Chemistry, University of New Mexico, Albuquerque, N . M . v PREVIOUS volumetric determinations of tellurium, the element ‘.was present in alloys or in inorganic compounds. This paper describes a volumetric method which can be applied to organotellurium compounds where rather vigorous conditions are required to decompose the organic constituent. The sample is digested in perchloric acid and then titrated with potassium dichromate using sodium diphenylamine sulfonate indicator in the back-titration with ferrous ion. Though numerous volumetric methods for the determination of tellurium have been developed, those applicable to the types of 1 2
Present address, University of California, Los Angelea, Calif. Present address, University of Illinois, Urbana, Ill.
organotellurium compounds studied in this laboratory proved too tedious or unsatisfactory. Lenher (8) has written a review of the analytical methods, volumetric and gravimetric, available up to 1926. Volumetric methods using potassium dichromate (9, 1 4 , potassium permanganate ( 7 ) ,and ceric sulfate (IS)for the oxidation of tellurium from an oxidation state of I V to VI have been reported, as well as iodometric (4, 6),instrumental (1, 6), and gravimetric (9, 3, 10) methods employing elemental tellurium. Only the gravimetric methods by Drew (2) and by Tsao (12) have been specifically developed for organotellurium compounds, although solution of the elemental tellurium and titration of the
V O L U M E 25, NO. 3, M A R C H 1 9 5 3 solution have been suggested by the work of others. It was thought that digestion of the sample, followed by titration, would be more rapid and possibly more accurate than the three-step method involving precipitation of tellurium, subsequent solution, and titration.
Table I.
Normality of Standard Te Solutions
(hblank on all reagents used showed no detectable reducing agents) S o HClOa digestion
Solution digested with HClOd 0.1854 0.1854 0.1861 Av. 0.1856
0.1850 0.1858
0.1864 .it..
0 . 1833 -
The compounds studied are of the type ROC6H4TeX3 and ROC6H4Te-TeC'6H40R,where X is chloride or bromide and R is methyl, ethyl, propyl, or butyl. The tellurium-carbon bond is relatively sta},le, and it was found that digestion with coneentrated sulfuric acid or a mixture of nitric and sulfuric acids gave inconsistent results possibly indicating incomplete decomposition of the organic material. High concentration of halide ions is undesirable due to the volatility of tellurium tetrahalides, and thus hydrochloric acid is not used in the digestion. The more poxverful oxidizing agent, perchloric acid, when employed as suggested by Smith (ii), proved to be a satisfactory digestion medium. The sample is initially digested with concentrated nitric acid and then further decomposed with perchloric acid. rifter dilution, the sample is titrated with standard potassium dichromate solution according to the method of Lenher and Wakefield (9L using sodium diphenylamine SUIionat? indicator (24). 3TcO2
+
IXr207
+ 8HC1 --+
+
3H2Te04 2KC1
50 1 Table 111. Deviation in Analysis of a Series of Individual Samples Of p-(n-Butoxy)phenY1 (Theoretical % Te, 33.30) Crude Sample (Once Recrystallized) % Te A 33.57 -0.06 29.7Ga 33.56 7 33.85 +o. 22 33.61 -0.02 .... 44.29b 33.78 +O. 15 34.78b .... 33.55 -0.08 33.50 -0.13 Av. 33.63 (om = 0.05)e Analytical Sample (Twice Recrystallized from CClr) % Te A 33.66 +o. 15 +O 03 33.54 -0.09 33.42 33.43 -0.08 Av. 33.51 (urn = + O o 0 6 ) C a LOW result due t o the sample having been evaporated t o dryness. tiobHigh result due t o the sample not being digested t o a water white solu-
*
E
um =
s,d/n
,,Student,, deviations =
d2 nZ
Part, are not too restrictive, and a number of samples may be analyzed rapidly and conveniently using no special equipment Or
REAGENTS
The potassium dichromate, ferrous ammonium sulfate, and sodium diphenylamine sulfonate solutions were prepared in the usual manner, Analytical grade nitric acid was employed. Baker's Analyzed C.P. perchloric acid (70%) was used for the digestions.
+ 2CrC13+ HzO
PROCEDURE
The limitations of this procedure, though somewhat narrow in
The sample, containing 0.075 to 0.25 gram of tellurium, is weighed into a 400 ml. beaker. Ten milliliters of concentrated nitric acid are added, and the mixture is warmed until solution of the sample is effected' and a Table 11. Analysis of Organotelluriurn Compounds pale-colored mixture is obtained. It (The average of a t least three samples is given) must not be permitted to go to dryness. Te c1 Br To the cooled mixture is added 10 ml. Theory, Found, Theory, Found, Theory, Found, of 1:l nitric acid and 10 ml. of 70% Compound % % A 7% % % % perchloric acid, and the heating is continued carefully in an adequate hood p-hIethoxypheny1 tellurium trichloride" 37.41 37.96 i0.55 until strong fumes of perchloric acid and Bis-p-(methoxy)phenyl ditellua colorless solution are obtained. It is ride b 54.36 54.33 -0.03 important that the final volume be less p-Ethoxyphenyl tellurium trichloride 35.93 35.60 -0.33 than 10 m]. and that the solution be p-Ethoxyphenyl tellurium triwater white. The cooled solution is dibromide 26.12 25.73 -0.39 luted to 200 m]., and sufficient 0.1 N Bis-p-(ethoxy)phenyl ditelluride 51.30 51.40 +O. 10 p-Propoxyphenyl tellurium tripotassium dichromate is added to prochloride 34.57 34.91 +0.34 28.95 28.37 vide an excess of a t least 5 m]. The p-(n-Propoxy)phenyl tellurium solution is stirred and is allowed to stand tribromide 25.39 25.06 -0.33 47.80 47.48 p-(n-Propoxy)phenyl ditellua t room temperature for a t least 30 ride0 48.56 48.40 -0.16 minutes. Standing a greater length of p-(n-Butoxy)phenyl tellurium trichloride 33.30 33.51 4-0.21 27.83 27.10 time is not harmful. Excess 0.1 N ferrous p-(n-Butoxy)phenyl tellurium ammonium sulfate is then added, and tribromide 24.70 24.07 -0.63 46.47 46.13 the mixture is back-titrated with the Bis-(n-butoxy)phenyl ditellu0.1 hr potassium dichromate solution usrided 46.10 45.90 -0.20 4-Ethoxy-3-methylphenyl teling 1: 1 phosphoric acid as stabilizer and lurium trichloride 34.57 33.35 -0.22 28.95 28.75 four drops of 0.01 M sodium diphenyl4-Ethoxy-3-methylphenyl diamine sulfonate as indicator, both added telluride6 48.56 48.75 iO.19 2-Ethoxy-5-methylphenyl teljust before the back-titration. The lurium trichloride 34.57 35.08 +0.51 28.95 27.90 potassium dichromate used corresponds 3,4-Dimethoxyphenyl tellurium to a change of oxidation number in the 34.37 34.11 -0.26 28.80 28.36 trichloride Bis-(3,4-dimethoxy)phenyl ditellurium from IV to VI. telluride
48.20
48.22
f0.02
Morgan and Kellett (IO) report, theory: C = 24.6,H = 2.05,C1 = 31.2, T e = 37.4; found: C = 24.5, H = 2.20,C1 = 31.4,T e = 37.7. b Morgan and Kellett report, theory: C = 35.8,H = 3.0,T e = 54.4; found: C = 35.6,H = 3.0, T e = 54.2 Carbon and hydrogen, theory: C = 41.14, H = 4.19; found: C = 41.10,H = 4.10. d Carbon and hydrogen, theory: C = 43.38,H = 4.70; found: C = 43.69,H = 4.59. e Carbon and hydrogen, theory: C = 41.14,H = 4.22; found: C = 40.97, H = 4.94. a
DISCUSSION
Lenher and Wakefield (9) claim the degree of acidity is important to this method, and 2% hydrochloric acid solution is desirable during the titration.
ANALYTICAL CHEMISTRY
502
The acidity provided by the digestion mixture appears to be quite satisfactory in the above method. The tellurium oxide, oxychloride, and tellurous acid do not have sufficient vapor pressure to allow loss of tellurium during the digestion. Care should be taken that the digestion does not proceed to dryness, the perchloric acid digestion mixture becomes colorless, the entire procedure is carried out within a 24 hour period, the phosphoric acid and indicator are added just prior to the backtitration with the potassium dichromate, and the sample is completely dissolved before the perchloric acid is added. The excess ferrous ion is easily observed due to a color change in the sohtion. RESULTS
Table I summarizes the results obtained on blanks and on titration of tellurite stock solution, prepared according to DeMeio ( 1 ) with, and without, perchloric acid digestion. A number of organotellurium compounds were analyzed and the results are summarized in Table 11. The anisyl compounds were previously analyzed gravimetrically by Morgan and Kellett (IO). Halogen analysis, carried out in this laboratory, as well as some carbon and hydrogen analyses are included for comparison. To indicate the usual deviation in a series of samples of a given com-
pound, the results of the analysis of p-(n-butoxy)phenyl tellurium trichloride are included in Table 111. ACKNOWLEDGMENT
The authors gratefully wish to acknowledge partial support of the above work by the Office of Naval Research. LITERATURE CITED (1) (2) (3) (4) (5)
DeMeio, R. H., ANAL.CHEM.,20, 488 (1948). Drew, H. D. K., J. Chem. SOC., 1934, 1796. Drew, H. D. K., and Porter, C. R., Ibid., 1929, 2091. Evans, B. S.,Analyst, 63, 874 (1938). Johnson, R. A. and Frederickson, D. R., ANAL.CHEM.,24, 866
(1952). (6) Johnson, R. A, and Kwan, F. P., Ibid., 23, 651 (1951). (7) Lang, R., 2. anal. chem., 128, 484 (1948). ( 8 ) Lenher, V., Proe. Am. Phil. Soc., 65, 33 (1926). (9) Lenher, V., and Wakefield, H. F., J . Am. Chem. SOC., 45, 1423 (1923). (10) Morgan, G. T., and Kellett, R. E., J . Chem. SOC., 1926, 1084. (11) Smith, G. F., “Mixed Perchloric, Sulfuric and Phosphoric Acids.” Columbus. Ohio. G. F. Smith Chemical Co.. 1942. (12) Tsao, E. T., Chem. I n d . ( C h i n a ) , 10, KO. 2, 15 (1935); C . A . , 30, 2135’ (1936). (13) Willard, H. H., and Young, P. J., J . Am. Chem. SOC., 52, 553 (1930). (14) Willis, U. F., Analyst, 66, 414 (1941).
RECEIVED for review March 17, 1052. Accepted October 17, 1952
Precipitation in Homogeneous Solution Separation and Determination of Lead PHILIP J. ELVINGI AND WALTER C. ZOOI
