A Spectrophotometric Method for the Determination of Hydrazine GEORGE W. WATT AND JOSEPH D. CHRISP The Cniversity of Texas, Austin, Tex. a t acid concentrations greater than 1 X , Thus, for a hydrazine concentration of 0.13 p.p.ni., the relative transmittancy is increased 1.6% if the acid concentration is 2 .If, and 4.5% if the acid concentration is 3 31. For hydrazine concentrations of the order of 0.26 p.p.m. in the presence of 1 31 hydrochloric acid, use of 15.0 ml. rather than 10.0 ml. of the color reagent results in a decrease in transmittancy amounting to only 2.59/. Spectral Characteristics. The transmittancy of hydrazine solutions of different concentrations A as measured at frequent intervals over the range 400 to 700 mp; per cent transmittancy ie plotted against wave length in Figure 1, which shons one transmittancy minimum a t 458 mp. A plot of log transmittancy (458 mp) against concentration showed good agreement with Beer's law over the concentration range investigated-Le., up to a hydrazine concentration of 0.77 p.p.m. Stability of Color. Colored solutions containing different quantities of hydrazine showed no measurable change in transmittancy in 12 hours, an increase of 0.6% (absolute) in 34 hours, and an increase of 1.6% in 5 days.
HE yellow color developed upon addition of p-dimethylaminobenzaldehyde t o solutions of hydrazine in dilute hydrochloric acid solutions has been used as the basis for the development of a spectrophotometric method for the determination of hydrazine. These systems are characterized by a transmittancy minimum a t 458 mp. Good agreement a i t h Beer's law is displayed a t hydrazine concentrations up t o 0.77 p.p.m.; the optimum concentration range is 0.06 t o 0.47 p,p.m., over which the relative error does not exceed 1%. Data are given for the per cent relative error introduced by the presence of urea and seniicarbazide; ammonium ion does not interfere with the determination. Methods for the determination of hydrazine depend upon its basic character or reducing properties (6-9, 1 1 ) and are, of course, subject to interferences owing t o the presence of other substances having similar properties. I n connection with a research program in progress there arose the need for an analytical method relatively free of interferences resulting from the presence of appreciable concentrations of urea and semicarbazide. The procedure described in this paper is based upon the observation by Pesez and Petit (IO) to the effect t h a t a characteristic color results upon addition of a solution of p-dimethylaminobenzaldehyde in ethyl alcohol and hydrochloric acid to hydrazine in dilute hydrochloric acid solution. EXPERIMENTAL
Apparatus. Transmittancy measurements were made with a Beckman RTodel D U spectrophotometer using Corex cells of 1.003-em. light path. The instrument was operated a t constant sensitivity using slit widths of the order of 0.02 to 0.10 mm., corresponding to nominal band widths of about 0.3 to 1.6 mp. Materials. T h e purity of hydrazine dihydrochloride (Eastman S o . 1117) and semicarbazide hydrochloride (Eastnian No. 226) was established as 99.8 and 99.47,, respectively, by means of the Jamieson method (6). p-Dimethylaminobenzaldehyde (Eastman KO. 95) Lias used as received; urea was purified by recrystallization from methanol. All other materials employed in this work were reagent grade chemicals that were used without further purification. Preparation of Standard Hydrazine Solutions. Solutions of 0.5 to 1.0 gram of hydrazine dihydrochloride in 1 liter of distilled water were standardized by titration with standard potassium iodate solution (6) as follows: A mixture consisting of 10.0 ml. of the hydrazine solution, 20 ml. of distilled water, 25 ml. of concentrated hydrochloric acid, and 15 ml. of chloroform was prepared in an iodine bottle and cooled to about 10' C. in an ice bath. After addition of approximately one half of the quantity of potassium iodate solution required in the complete titration, additional concentrated hydrochloric acid solution was added to give a total acid concentration within the range 3 to 6 X , and the titration was then carried to completion. If all of the required acid is added initially, the pink color of the iodine-chloroform layer does not appear a t the beginning of the titration. Appropriate aliquots of these stock solutions rvere diluted to the desired concentration, made 1 Jf with respect to hydrochloric acid, and used in the color development. Color Development. The color reagent employed had the following composition: p-dimethylaminobenzaldehyde,0.4 gram; ethanol, 20.0 ml.; concentrated hydrochloric acid, 2.0 ml. Ten milliliters of this reagent was added to aliquots of the standardized hydrazine solution selected so that the final hydrazine concentration would be within the range 0.02 to 0.8 p.p.in., and the resulting mixtures were diluted to a total volume of 25.0 ml. x i t h 1 -11 hydrochloric acid solution. Blanks consisted of 10.0 ml. of the color reagent in 25.0 ml. of solution 1 M with respect to hydrochloric acid. At room temperature the yellow color develops immediately and is stable after a period of 10 minutes. For a given concentration of hydrazine the per cent transmittancy is unchanged if the hydrochloric acid concentration is less than 1 M but increases
NzH,,
P.P.M.
0,0.18 0,
0.25
Q , 0.31
410
430
450
WAVE LENGTH, Mr Figure 1. Spectral Curves for Hydrazine with p-Dimethylaminobenzaldehyde
Effect of Temperature. For a color-developed sample containing hydrazine a t a concentration of 0.2 p.p.m., the effect of temperature over the range 20' to 40" C. was found to amount to +0.14% absolute transmittancy per l oC.; this effect was completely reversible. Reproducibility. Over the hydrazine concentration range 0.1 to 0.3 p.p.m., samples having the same hydrazine concentration gave an average deviation of 0.1 % absolute transmittancy. Solutions color-developed with color reagent that had stood for 1 week gave the same per cent transmittancy as those color-
2006
V O L U M E 24, NO. 12, D E C E M B E R 1 9 5 2
P * I 60
I
2007 Transmittancy measurements were made over a considerable interval on either side of 458 mp. The mole ratio of semicarbazide and/or urea to hydrazine and the corresponding per cent relative errors are listed in Table I. Both of these substances lead t o a decrease in per cent transmittancy; a shift in the minimum was observed using solutions containing 110 moles of urea per mole of hydrazine. Colored solutions containing up to 5000 moles of ammonium chloride or nitrate per mole of hydrazine showed no change in per cent transmittancy and no shift in the minimum.
i
40
I-
i’ /”
70
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T
UREA, 5 2 9 P P M
0,SEYICPRBbZIDE. 150 P P M 0,HYDRPZINE, 031 P P H K
/
40 400
420
430
460
440
WAVE LENGTH, M p
30k-
Figure 2. Spectral Curves for Hydrazine, Semicarbazide, and Urea with p-Dimethylaminobenzaldehyde developed Jyith freshly prepared reagent. A s a check on the stability of hydrazine in hydrochloric acid solution, standard solutions of hydrazine dihydrochloride (0.65 p.p.m. hydrazine in 1 171 hydrochloric acid) were stored for 6 days in a glass-stoppered flask, color-developed in the usual manner, and used in transmittaney measurements. The resulting values corresponded t o from 4 t o 5% relative decrease in hydrazine concentration. However, no change in hydrazine could be detected during the first 12 hours of this storage period. Six standard samples containing hydrazine a t concentrations unknown t o the analyst m r e analyzed over the working range of concentration. The rrlative error was found to vary from 0.6 to 1.1$%. Interferences. The extent of interference o\ving to the presence of semicarbazide, urea, and ammonium salts Tvas evaluated by measuring the transmittancies of color-developed solutions containing fixed quantities of hydrazine (0.26 or 0.13 p.p.m.) and varying quantities of the potentially interfering additive.
Table I.
Per Cent Relative Error Resulting from Presence of Semicarbazide and/or Crea
hiole Ratios Semicarbazide t o hydrazine
Urea t o hydrazine
Hydrazine, P.P.M. 0 13 0 26 70Error relative t o hydrazine
14
-.
L
0 0
1.3
I
3 2 4 6 12 5
5 15 25
55
1.6 4.3 7.6
15 25
2.7 2.7
110 220 5
2@v /
1.6
4 3 6 0 0 8
0.6 1.0 1.6
/
10
HYDRAZINE, P.P.M.
Figure 3. Calibration Curve for Hydrazine with p-Dimethylaminobenzaldehyde a t 458 RZp The spectral curves for semicarbazide and urea (Figure 2) indicate that high concentrations of these substances may be tolerated n ithout serious interference. The colored solutions of urea were stable, but those containing semicarbazide were unstable. X spectral curve was plotted for a colored solution of semicarbazide every 24 hours for 3 d a j s. The curve characteristic of semicarbazide was progressively replaced hy that characteristic of hydrazine with a minimum at 458 mp. DISCUSSION
The calibration curve for this method for the determination of hydrazine is shoTvn in Figure 3, in n hich per cent absorptancy (100 - % transmittancy) at 458 mp is plotted against log concentration of hydrazine in parts per million; each experimental point was established by many replicate measurements. The utility of this method of plotting for evaluation of the most appropriate working range and maximum accuracy has been discussed by Ayres ( 2 ) . The curve exhibits maximum slope a t about 63% absorptancy, in agreement with Beer’s lan hence a mavimum accuracy corresponding t o 2.7% relative analysis error per 1yo absolute photometric error, or about 0.6y0 relative error for a precision of 0.2% in making the measurements. To attain this precision it was found necessary to exercise every precaution t o avoid cross contamination of solutions via transfer pipets. Maximum accuracy is obtained a t hydrazine concentrations of the order of 0.2 p.p.ni., but in view of the observed temperature coefficient of transmittancy, it is necessary t o hold the temperature constant in order t o achieve this accuracy. ~
ANALYTICAL CHEMISTRY
2008 I n order t o keep the relative analysis error within 1.0%, the hydrazine concentration must be \Tithin the limits 0.06 t o 0.47 p.p.m. ; these limits were determined exactly as described by ilyres and Young (S), assuming 0.2% absolute photometric error. The susceptibility of hydrazine t o catalytic oxidation and/or decomposition (1, 4 ) was confirmed; results shovi that hydrazine solutions should be analyzed as soon as possible after preparation. I n the present method, errors become appreciable after 12 hours. For this reason, freshly prepared standard hydrazine solutions iyere used in all measurements involved in the calibration data. With reference t o interferences, it is clearly evident that the progressive change in the spectral curve for semicarbazide results from the slow hydrolysis of this component to produce hydrazine. Although the rate of hydrolysis is slow, the color reagent is more sensitive t o hydrazine than to semicarbazide, and this causes a shift in the minimum transmittancy to that characteristic of hydrazine. I n the study of interferences, therefore, freshly prepared solutions of semicarbazide were employed. -4s shown by the data of Table I, a t a hydrazine concentration of 0.26 p.p.m. (29.7% tmnsmittancy a t 25" C.), a molar concentration of semicarbazide 25 times as great as that of hydrazine introduces a relative error of only 1,3%, but the magnitude of the error increases with decrease in hydrazine concentration. A relative error of 1.6% results when the molar concentration of urea is 55 times as great as that of hydrazine. If both urea and semicarbazide are present, the relative error is increased over
t h a t attributable to either component in the absence of the other, but the increase is not great. Thus, if the hydrazine concentration is 0.26 p.p.m,, the per cent relative error is 1.6 if the solution contains 25 moles of urea and 25 moles of semicarbazide per mole of hydrazine. ACKNOWLEDGMENT
The work described in this paper !vas supported by the U. S. S a v y Bureau of Ordnance under Contract K123s-67363, Task Order 2. LITERATURE CITED
Audrieth, L. F., and Mohr, P. H., I n d . Eng. Chem., 43, 1774 11951 ).
h y r e s , G. H., A s i L . CHEY, 21, 652 (1949). Ayres, G. H., and Young, Fiedeiick, Ibid., 22, 1280 ( 1 9 5 0 ) . Bray, W, C.. and Cuy, E. J , J . Am. Chem. Soc., 4 6 , 8 5 8 (1924). Gilbert, E. C., J . Am. Chem. Soc., 4 6 , 2 6 4 8 (1924). Jamieson, G. S.,Am. J . Sci., 3 3 , 3 5 2 (1912). Kolthoff, I. AI,,J . Am. Ckem. S o c . , - 4 6 ,2009 (1924). Kurtenacker, A , , and Knbina, H., 2. anal. Cliem., 64, 388 (1924).
Penneman, R. A , , and .ludrieth, L. F., ANAL.CHEM.,20, 1058 (1948).
Pesez, M , , and Petit, .i..BUZZ.S O C . chim. France, 1947, 122-3. Smith, G. F., and Wilcox, C. S., IXD. EXG.CHEM.,ASAL. ED., 1 4 , 4 9 (1942).
RECEIVED for review J u n e 10, 1952.
-4ccepted September 25, 1952.
63. 4,6-Dinitroresorcinol Contributed by WALTER C. MCCRONE AND IRENE CORVIN, .4rmour Research Foundation of Illinois Institute of Technology, Chicago 16, Ill.
OH I
o~H-A U-OH
X-RAYDIFFRACTIOS DATACell Dimensions. a = 11.07 A . ; b = 5.03 A , ; c = 11.79 A . Formula Keights per Cell. 4 (4.01 calculated from x-ray data). Formula Keight. 200.11. Density. 1.786 (flotation in aqueous zinc chloride); 1.781 (x-ray).
I
ii-O* Principal Lines Structural Formula for 4,6-Dinitroresorcino1 E X C E L L E N T crystals of 4,6-dinitroresorcino1 can be obtained either by sublimation or by recrystallization from ethyl alcohol. Both techniques give massive crystals and tablets shoxing the forms: prism, f IlO], orthopinacoid ( loo), and basal pinacoid (001J. Good crystals can also be obtained from thymol on a microscope slide. CRYSTAL MORPHOLOGY Crystal System. Monoclinic. Axial Ratio. a : b : c = 3.394:1:2.344. Interfacial Angles (Polar). 110 h IT0 = 136" 40'. Beta Angle. 48". OPTICALPROPERTIES Refractive Indices (5893 A , ; 25" C.). a = 1.598 f 0.002. 0 = 1.6T3 i 0.002. -/ = 2.01 (calculated from a,P , and 2V). Optic Axial Angles (5893 A.; 25' C.). 2V = 50" ( + ) (measured). 2 E = 91" Dispersion. r > v . Optic Axial Plane. 010. Acute Bisectrix. y. Extinction. y A a = 3" in acute p. = 1.752. Molecular Refraction ( R )(5893 A.; 25' C.). R (calcd.) = 40.2; R (obsd.) = 45.7.
d
12.07 6.28 5.91 4.68 4.35 4.23 3.92 3.68 3.29 3.06 2.93 2.85 2 74 2.67 2.60 2.52
1/11
04 04 04 37 0 42 0 31 0 13 0 11 1 00 0 04 0 03 0 26
0 0 0 0
0 05
0 17 0 04 0 12
d 2.46 2.40 2.34 2.27 2.18 2.14 2.09 2.01 1.951 1,850 1 a21 1.778 1.729 1.640 1 571 1.533
1/11 0.07 0.06 0.04 0.04 0.04 0.04 0.07 0.05 0.04 0.04 0.02 0.02 0 02 0.04 0.02 0.02
FTJSIOX DATA. 4,6-DinitroresorcinoI sublimes readily t o give large well-formed crystals (Figure 1). Some of the crystals show an off-center optic axis interference figure mith 2V = 50°( +) and strong inclined dispersion, r > v . On further heating melting occurs with slight decomposition a t 215' C. The melt solidifies spontaneously in large areas of uniform orientation separated by large gas bubbles (Figure 3). The shrinkage cracks are very characteristic. Crystals showing the "hour-glass" type of crack give a B z , figure; crystals showing the straight cracks show an off-center optic axis figure.
