1408
ANALYTICAL CHEMISTRY
iridium is in an oxidation state of f4, and that some change other than oxidation is the cause of the color formation. The fact that identical purple solutions can be formed by treatment of iridium(1V) chloride (or chloro complex), or of hydrous iridium dioxide, b y such a wide variety of acids mikes it seem improbable that the color is due to any specific complex of iridium(1V) with the anion of the acid. The existence of large aggregates is indicated by the fact that the colored material exhibits some Tyndall effect, and passes through collodion membranes only very slowly. It is possible that some kind of polymer might form through iridium-oxygen bridges, in a manner similar to the formation of chromium-oxygen bridges when solutions of chromic salts are aged or boiled, with a resulting color change from violet to green (IO). Further studies of the color reaction are contemplated. LITERATURE CITED
Ayres, G. H., ANAL.CHEM.,21, 652 (1949). Ayres, G. H., and Wells, W. N., Ibid., 22, 317 (1950). Beamish, F. E., and Russell, J. J., IND. ENQ.CHEM.,ANAL.ED., 8, 141 (1936). Bouvet, P., Ann. pharm. franc., 5 , 2 9 3 (1947). Chugaev, L. A., Ann. inst. pkzline, 7,.205 (1929). Fish, F. H., Noell, J. R., and Kemp, B. H., Virginia J. Sei., 1, 125 (1940). Friend, J. N., “Textbook of Inorganic Chemistry,” Vol. IX, Part 1, p. 249, London, Charles Griffin and Co., 1920. Gilchrist, Raleigh, and Wichers, Edward, J . Am. Chem. Soc., 57,2565 (1935). Hahn, F. L., Mikrochemie,8 , 7 7 (1930). Hall, H. T., and Eyring, Henry, J. Am. Chem. Soc., 72, 782 (1950).
Hiskey, C. F., ANAL.CHEM.,21, 1440 (1949). Hopkins, B. S., “Chapters in the Chemistry of the Less Familiar Elements, Chap. 21, p. 10, Champaign, Ill., Stipes Publishing Co., 1940. Howe, J. L., and Mercer, F. N., J. Am. Chem. Soc., 47, 2926 (1925). ’
Khlopin, V. G., Ann. inst. platine, 4, 324 (1926). Lecoq de Boisbaudran, Compt. rend., 96, 1336, 1406, 1551 (1853). Maynard, J. L., Barber, H. H., and Sneed, M. C., J . Chem. Education, 16, 77 (1939).
Mellor, J. W., “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. XV, p. 755, New York, Longmans, Green and Co., 1936. Miller, C. C., J. Chem. Soc., 1941, 756. Miller, C. C., and Lowe, A. J., Ibid., 1940, 1263. Noyes, A. A., and Bray, W. C., “System of Qualitative Analysis for the Rare Elements,” pp. 377-9, New York, Macmillan Co., 1927. Ogburn, S. C., Jr., J . A m . Chem. Soc., 48, 2493 (1926). Sandell, E. B., “Colorimetric Determination of Traces of Metals,” p. 259, New York, Interscience Publishers, 1944. Scott’s “Standard Methods of Chemical Analysis,” Furman, N. H., editor, 5th ed., Vol. 1 , New York, D. Van Nostrand Co., 1939.
Thompson, S. O., Beamish, F. E., and Scott, M., IND.ENQ. CHEM.,ANAL.ED.,9, 420 (1937). Whitmore, W. F., and Schneider, H., Mikrochemie, 17, 279, 302 (1935).
Willard, H. H., Merritt, L. L., and Dean, J. A., “Instrumental Methods of Analysis,” p. 7, New York, D. Van Nostrand Co., 1945.
RECEIVED April 7, 1950. Condensed from a thesis submitted by Quentin Quick to the faculty of the Graduate School of the University of Texas in partial fulfillment of the requirements for the degree of master of arts, May 1950.
Infrared Determination of Ortho and Meta isomers in p-Cresol Freezing Points of Pure Cresols 0. E. KNAPP AND H. S . MOE, The Sherwin-Williams Company, Chicago, Ill., AND
R. B. BERNSTEIN, Illinois Institute of Technology, Chicago, Ill. An infrared spectrophotometric procedure for the determination of low wncentrations of 0- and m-cresol in p-cresol is described. The absorption bands at 13.37 and 12.92~characteristic of the ortho and meta isomers are used for the determination, With a 0.027-mm. absorption cell, the accuracy of the analyses was ‘0.3% 0- and *0.5% m-cresol. A n acwunt of the method of preparation and purification of the three isomers is given. ‘Freezing-point data far the pure compounds are given.
-.
D
ETERMINATION of the concentrations of 0- and m-cresol in samples of impure pcresol is of practical interest, as is a detailed development of a suitable instrumental procedure, inasmuch as no precise chemical method is known. A rapid infrared spectrophotometric method suitable for use in the low range of concentrations has been developed, based on the early infrared studies of the cresols by Whiffen and Thompson (3). These authors indicated the possibility of infrared analysis of mixtures of isomeric cresols. The present paper outlines the details of a practical procedure for the determination of isomeric impurities in pcresol. Special consideration is given to the problem of obtaining pure standards, which has not been adequately stressed in previous reports on cresol analysis. Reliable data on the freezing points of the individual pure cresols were sought. Obviously, the freezing point of pure p
cresol was of particular interest; therefore, all values reported were obtained while observing the best conventions, including a carefully standardized precision-type thermometer. Seeding was found to be essential and was employed in every cafe. It was necessary to guard against contamination of samples by moisture. For this reason, all transfeix were conducted under a bell jar in an atmosphere of dry nitrogen. The presence of water in cresols, even in small quantities, produces a significant lowering of the freezing point. For example, with gcresol containing approximately 3y0 o-cresol, an increment of 0.1% in water content produced a freezing point depression of 0.37’ C., over the range 0.05 to 0.8% water. Standards containing not over 0.1% water were deemed to be satisfactory. Water determinations were made according to the Karl Fischer method,
1409
V O L U M E 22, N O . 11, N O V E M B E R 1 9 5 0 Table I. Mixture 1
Wt. Cresol,
G.
1.13
2
1.18
3
1.28
4
1.21
5
0.95
6
1.07
7
1.14
8
1.26
9
1.00
13
1.00 1.02 1.02 1.03
14
1.02
10 11 12
1.05 15 0.99 16 Av. Deviation
absorption bands rhosen for the analysis were those suggested b j Whiffen and Thompson (3) which appeared a t 13.37 and 1 2 . 9 2 ~for 0- and m-cresol, respectively. These were the bands used by Friedel et al. ( I ) in the analysis of mixtures of phenols and cresols and presumably those used by Woolfolk et al. (4)in their study of complex mixtures containing cresols. In the present work the base line chosen to represent 100% transmission was the absorption curve for a standard solution of pure p-cresol in cyclohexane. A series of synthetic mixtures was prepared to cover the desired range of concentrations. The infrared absorption spectrum for each solution was obtained over the range from 12 to 1 4 ~ .A blank determination on the cyclohexane showed no interference in this region. Figure 1 shows a recorded transmission curve. On the recorded chart, 1 cm. corresponds to about 0.01 microvolt output from the thermocouple. The zero transmission base line is not shown. The following was adopted as a standard working procedure for the analysis of all samples of mixed cresols:
Summary of Analytical Data
A, ?& Ortho Ortho Calcd. Taken 0.002 0.3 0.0 0.002 0.3 3.05 0.023 3.0 0.024 3.1 1.45 0.010 1.2 0.010 1.2 0.013 1.55 0.023 2.9 3.05 0.023 2.9 8.95 0.058 9.35 0.055 8.85 4.9 0.034 4.9 0.040 5.7 0.034 4.9 0.036 5.15 0.11 1.5 1.4 0.11 1.5 3.2 0.025 3.0 0.025 3.0 0.029 3.5 11.1 0.071 10.9 0.073 11.2 0.072 11.0 0.060 9.2 9.4 0,031 4.65 5.7 0.096 14.9 14.4 0.041 6.1 5.7 0.042 6.2 0.040 6.0 5.4 0.041 6.15 0.060 8.7 8.3 12.4 0,082 12.7
A%,
Ortho +0.3 +0.3 -0.1 0'.0 -0.3 ,-0.3 +0.1 -0.2 -0.2 f0.4 -0.1 0.0 +0.8 0.0 +0.2 +0.1 +0.1 -0.2 .-0.2 +0.3 -0.2 +O.l -0.1 -0.2 -1.0 -0.5 +0.4 +0.5 +0.6
+0.7 +0.4 f0.3
A, hfeta 0.012 0.010 0,006 0.010 0.000 0 002 0.000
0.011 0.006 0.000 0,000 0.031 0,029 0.032 0,033 0.015 0.015 0.007 0.008 0.007 0.017 0.018 0.021 0,036 0 049 0,043 0,019 0.021 0.030 0 ..030 0.023 0.045 I
Yo IvletaCalcd. 3.1 2 6 1.5 2.45 0.0 0.45
A%,
Taken N e t s 2.05 +1 0 +O 6 1 75 - 0 . 2 +o 7 0.45 - 0 . 5 0.0 -0.5
0.0
2.6 1.45 0.0
1.75 0.0
+0.8 -0.3 0.0
8.4 7.85 8.65 8.95
8.45
-0
3.8 3.8 1.6 1.86 1.6 4.9 5.2
3.55
0.0
1.5
5.6
6.1
0.0
1
-0.6 +0.2 +0.5 +0.2 +0.2 +0.1 +0.3 +0.1 -0.7 -0.4 +0.5
10.5 13.9 12.2 5.36 5.9 8.5
11.9 15.2 12.6 5.3 8.0
4-0.5 fO.3
6.35 13.2
5.7 11.9
i-0.7 +1.3 t0.5
-1.4 -1.3 -0.4 +0.1
Approximately 1 gram of total cresol was weighed out into a tared weighing bottle of a p p r o x i m a t e l y 15-ml. capacity. Cyclohexane (10 ml.) was then pipetted directly into the weighing bottle. After stirring thoroughly, a portion of the solution was transferred to a small glass-stoppered ('$) bottle for storage. The percentage of 0- and m-cresol in the sample is given by the following expressions, obtained from calibration data:
+0.6
8,s
10.3
STANDARDS
p-Cresol. PREPARATION 1. Nitration-grade toluene was sulfonated with concentrated sulfuric acid and the resulting toluenesulfonic acid mixture, in the form of the sodium salt, was subjected to alkali fusion. The crude product obtained was purified by a succession of distillations and recrystallizations. The preparation in its final form had a freezing point of 34.3" C. and a water content of 0.05%. PREPARATION 2. p-Toluidine was diazotized and allowed to undergo a modified Sandmeyer reaction. The crude product was separated, treated with barium carbonate, and then purified by fractional distillation. This greparation had a freezing point of 33.3' C. and a water content of 0.09%. PREPARATION 2A. p-Cresol (preparation 2) was recrystallized four times. The crystallization yield was about 50%. The freezing point of this preparation was 34.0" C. and the water content was 0.06%. (The highest freezing point reached as a result of repeated recrystallizations and fractionations was 34.6' C.) o-Cresol. Paragon (hlatheson Company) o-cresol (practical, freezing point 30.0" C.) was recrystallized three times. The remaining crystals were distilled a t atmospheric pressure, and the intermediate cut was retained. The freezing point of the refined product was 30.7" C., and the water content was 0.08%. m-Cresol. Paragon (Matheson Company) m-cresol (practical, freezing int 9.3" C.) was recrystallized three times in a water bath h e I c t 7" to 8' C. The remaining crystals were distilled a t atmospheric pressure, and an intermediate cut was taken. The freezing point of the tefined product was 11.3" C., and the water content was 0.10%. Cyclohexane. Paragon (Matheson Company) cyclohexane was used without further purification as the solvent for the infrared studies. APPARATUS AND PROCEDURE
A Perkin-Elmer Model 12C spectrophotometer with sodium chloride optics was employed. The thickness of the matched absorption cells was 0.027 mm., determined by the method of interference fringes ( 9 ) . A continuous slit drive was used; the average slit width was about 0.25 mm. This rather low slit width was used for better resolution of the ortho and meta bands. The
% ortho yo meta
A / W X 100 (1) A / W X 100 (2) where the A's re resent, respectively, the absorbancies of the 1 3 . 3 7 ~(ortho) a n 8 1 2 . 9 2 ~(meta) bands, and W is the weight of the sample in grams. = 1.53 X = 2.90 X
i I CM
T
P, PRA
cI
12.92 v META
13.37 y
\I
\\
I1
ORTHO
A
B C
-
-
100 */e
P-CRESOL X 2 (100 /'e BASE L I N E ) 4 . 9 % O R T H O - , 8 5 % META-CRESOL 14.9% ORTHO-,12.6 e/' META-CRESOL
A L L S O L U T I O N S APPROXIMATELY 0 . 8 M T O T A L CRESOL IN CYCLOHEXANE PARA
Figure 1.
Infrared Transmission Curve for Cresol Solu'tions
Table I summarizes the data for sixteen synthetic mixtures. The columns give, successively, the weight of total cresol taken, the average absorbancy of the ortho band taken from several successive wave-length scans, the calculated percentage of o-cresol, the actual percentage of ortho- taken, and the difference between
1410
ANALYTICAL CHEMISTRY
calculated and known percent:tges of ortho-; the remaining columns give the corresponding data for the meta isomer. Where several observed values are given for a particular mixture, they represent the results of repeated determinations made at other times over a period of several weeks. ‘DISCUSSION
The largest source of error in the determination is the uncertainty in absorbancy due to the noise-to-signal ratio. The noise lev61 was variable but generally amounted, to about *l mm. (0.001 microvolt) or less 0 1 1 t,he recorder chart, corresponding t o approximately 0.5% of the total deflection. For o-cresol a t 5% roncentration, this corresponds to *0.40/;,error; for m-cresol a t t.he same Concentration, the anticipated error would be +O.S%. The average deviation of all the results is *0.3y0 ortho and *0.57, meta. These values are somewhat more favorable than the calculated errors, probably because two or more successive wave-length scans were always averaged for each determination. Samples of purified p-cresol prepared in the different ways previously outlined were compared on the basis of their spectra in the region 12 t o 1 4 ~ ; these were found to he indistinguishable a t concentrations of about 1 M.
The results of this study show that an accuracy of approximately *0.3% for o- and t 0 . 5 7 , for m-cresol is possible in the low conrentration region with the infrared spectrophotometric method described. With the use of absorption cells of greater thickness and a split-beam type spectrophotometer, a considerable improvement in precision should be attainable. Unfortunately, these were not available. The present method does not appear suitable as an analytical technique when the purity of the p-cresol is above 99%. Preliminary experiments have indicated that the freezing point depression offers a more sensitive analytical method for t o t d impurities in the region from 0 to 2% impurity. LITERATURE CITED (1) Friedei, R. A., Pierce, L., and McGovern, J. J., A 4 ~ a C ~~ .M .22,. 418 (1950). ( 2 ) Sutherlapd, G. B., and Willis, N. A . , Trans. Faraday SOC., 41, 181 (1945). (3) Whiffen, D. H., and Thompson, H. N‘,, J, Chem. Soc., 1945, 268. (4) Wootfolk, E. O., Orchin, M., and Dull, M. F., IND. ENG.CHEM., 42, 552 (1950).
RECEIVEDMay 1 , 1950.
High Frequency Titrations Mercurimetric Determination of Chloride W. J. BLAEDEL AND €1. V. MALMSTADT University of Wisconsin, Madison, Wis. Chloride may be determined in acidic solution by direct titration with 0.01 kf mercuric nitrate using the high frequency titrimeter with a precision corresponding to ahout 0.03 ml. of mercuric nitrate. The end point agrees well with the equivalence point over a considerable range of conditions, allowing a simpler procedure than is possible when chemical indicators are used to establish the end point. For this titration, the high frequency titrimeter appears superior to the potentiometric or conductometric methods for establishing the end point.
C
HLORIDE may be determined volumetl’ically by titration
with standard mercuric nitrate according to the reaction : H g + + 2C1- +HgCIS (1) .Is stated by Kolthoff and Sandell ( J ) , this determination is of considerable practical importance because it allows direct determination of chloride in acid medium even at great dilutions. Jn:ismuch as there do not exist many such metho.ds, it seems worth while to attempt improvement of the mercurimetric procedure. Any of several substances may be used a? indicators for the rnercurimetric titration of chloride. Perhaps the most careful investigation of the procedure is that by Roberts (6), in which 1,5tliphenylcarbohydrazide is used a6 an indicator. The difficulty with thiE indicator (and with others) is that the end point is considerably different from the equivalence point and that large blanks are therefore required. The blank-which is as high a8 0.5 ml. of 0.01 M mercuric nitrate in some instances ( 1 , 6)-is highly dependent on the conditions of the titration, such as: mercuric chloride concentration at the end point; indicator concentration ; acidity; and ionic strength. Close adherence to carefully @electedconditions is necessary for accuracy, and this makes for .some inflexibility and inconvenience in titration procedure. Particularly troublesome is the dependence of the blank on the amount of sought-for substance-i.e., chloride. Kolthoff and Sandell (3) recommend use of sodium nitroprus.
+
side as an indicator, but unpublished work (1) has shown this inferior to 1,5-diphenylcarbohydrazide. Among other things, nitroprusside is unstable, decomposing to cyanide, which reacts with mercuric ion. Potassium iodate and potassium periodate are superior to sodium nitroprusside, but inferior to 1,Sdiphenylcarbohydrazide (1). These difficulties are great enough to prevent widespread use of the mercurimetric procedure. Many of the difficulties are due primarily to inadequacy of the available chemical indicators. By u&2of an instrumental method to establish the end point, these difficulties may be circumvented. I n this paper, a comparison is made among the potentiometric, conductometric, and high frequency methods of establishing the end point for the mercurimetric determination of chloride. The limiting conditions, together with the relative advantages, of the high frequency procedure are given. COMPARISON O F POTENTIOMETRIC, CONDUCTOMETRIC, AND HIGH FREQUENCY TITRATION PROCEDURES
No extensive study has been madeof the possibility of establishing the end point potentiometrically for the mercurimetric titration of chloride. The prospect6 for doing so do not seem good. Silver-silver chloride or calomel electrodes are not stable in solutions containing mercuric ion ( 1 , 4 ) . Muller and Aarflot ( 5 )claim
