Titrimetric Analysis of Mixtures of Hydrazine and Methyl Hydrazine JOHN D. CLARK and JOSEPH R. SMITH liquid Rocket Propulsion laboratory,' Picafinny Arsenal, Dover, N. J. bMixtures of hydrazine and methyl hydrazine can b e analyzed titrimetrically b y a differential method. One aliquot of the sample is reacted with excess standard Chloramine-T solution, and a second is reacted with excess standard sodium hypochlorite solution in the presence of potassium bromide and a phosphate buffer. The unreacted oxidant is determined in each case b y back-titration with standard thiosulfate solution after the addition of potassium iodide and acetic acid. The reaction between Chloramine-T and either hydrazine involves a fourelectron change, as does the reaction between hydrazine and hypochlorite, but that between methyl hydrazine and hypochlorite involves an eightelectron change. Synthetic samples of known concentration were prepared and analyzed to determine the actual precision and accuracy of the method.
M
are available for the determination of hydrazine and of methyl hydrazine, but none has been reported for the analysis of their mixtures. This paper describes such a method, based upon a differential titration, using sodium hypochlorite and Chloramine-T (CT) as oxidants. Chloramine-T (1, 3) is the sodium salt of N-chloro-p-toluenesulfonamide. A satisfactory procedure for the determination of hydrazine, using CT as an oxidant, which was worked out by Clark (2) and which has been used for several years with excellent results, is equally successful with methyl hydrazine. An acidified sample of the hydrazine is added to excess standard CT solution, and the unreacted oxidant is determined by adding potassium iodide and acetic acid to the solution and titrating the liberated iodine with standard thiosulfate. The reaction between CT and hydrazine can be represented by: ANY METHODS
That between CT and methyl hydrazine is believed to be similar, and both involve a four-electron change. Kolthoff and Stenger (4) have recommended hypochlorite as a standard oxidant. Potassium bromide is added to the solution before the addition of the sample, and the more rapidly reacting hypobromite ion is the actual oxidizer. OCi
+ B;
e Ci + OB;
This mixed reagent, under alkaline conditions, is a satisfactory oxidant for the titration of hydrazine and methyl hydrazine, if the sample is protected from atmospheric oxygen and an excess of hypochlorite is used. The hydrazine is added to the excess oxidant in a NazHPOd-NasPOh buffer solution containing potassium bromide. Since the reaction is slow a t room temperature, the application of heat is necessary. The unreacted hypochlorite is dete:mined by adding acetic acid and potassium iodide and titrating the liberated iodine with standard thiosulfate solution. The relevant reactions are as follows: 2(OB;)
+ N2H4
4(0BF)
+ CHaNzHa 4 B; + Nz + 3 HzO + CO (eight electrons)
+
2 B;
+ Nt
+ 2 HzO(four electrons) -+
The infrared spectrum of the gas evolved from the methyl hydrazine reaction showed the CO band, and nothing else, thus lending credence to the somewhat improbable-looking reaction postulated. Neither the CT nor the hypochlorite method can be applied to the other hydrazine of current interest, unsymdimethyl hydrazine, since no conditions were found under which either reagent could be induced to react stoichiometrically with UDMH. EXPERIMENTAL
Special Reagents. Phosphate buffer solution. Dissolve 8/1 mole of N a r HPO4.12Hz0 (135 grams) and ~ [ C H S C ~ H ~ S O Z NICY~Z]H + ~2 Cf mole of NasP04. 12Hz0 (142 grams) in NP 2 [CH~C~H~SO~NHZI 1 liter of distilled water (previously boiled). Filter and then bubble nitrogen through the solution. Before August 1, 1960, the Liquid 0.1N Chloramine-T solution. DisRocket Propulsion Laboratory was the solve '/a mole (14.1 grams) of CHs Rocket Propulsion Laboratory of the U. S. CaH4S02NClNa (mol. wt. = 281.17) Naval Air Rocket Test Station, Lake in distilled water and dilute to 1 liter. Denmark, Dover, N. J.
+
+
1 186
ANALYTICAL CHEMISTRY
+
Use scrupulously clean glassware and protect the solution from dust,, grease, and organic matter in general. Standardization of Chloramine-T solution. (Should be done daily.) To a 500-ml. iodine flask containing 50 ml. of 0.5N K I solution and 50 ml. of HzO add 20 ml. of glacial acetic acid, and then, while stirring, 25 mi. of the CT solution. Titrate the liberated iodine with 0.1N sodium thiosulfate which has been standardized against potassium dichromate, using a starch indicator if desired. 0.15N Sodium hypochlorite solution. Dilute 200 ml. of commercial 5.25% sodium hypochlorite solution (Chlorox) to 1 liter with distilled water. Keep the solution in a dark glass bottle. Standardization of sodium hypochlorite solution. (This should be done before each series of assays.) Dissolve 3 grams of potassium bromide in 100 ml. of phosphate buffer solution in a 500ml. iodine flask. Add 25 ml. of hypochlorite solution. Place the flask on a heated magnetic stirrer (Thermostir) thermostated a t 60" C. Fit the flask with a water-cooled reflux condenser, to whose top is connected a trap containing 50 ml. of 0.5N KI, (to prevent the loss of any oxidizing potential), heat and stir slowly for 15 minutes. Disconnect the trap and cool the flask in an ice bath. Add the K I solution from the trap to the contents of the flask, and let stand for 2 minutes. Add 50 ml. of glacial acetic acid, and titrate the liberated iodine with standard thiosulfate, using a starch indicator if desired. Sampling. As both hydrazines are easily oxidized by atmospheric oxygen, absorb carbon dioxide, and fume badly, i t is necessary to protect the sample. The following technique works well: Pierce a small cork stopper with the needle of a 2-cc. hypodermic syringe, forcing the cork well down the shank of the needle. Choose a small test tube which will cover the point of the needle and fit the stopper. Draw 0.8 to 1.0 ml. of the mixed hydrazine into the syringe, cap the latter with the test tube, apd weigh the assembly to 0.1 mg. Empty the syringe into a 200-ml. volumetric flask containing 40 ml. of 1N H804, and diluted to an inch below the etch mark. Recap and reweigh the syringe, to get the sample weight by difference. Dilute to the mark and mix. Chloramine-T Titration. Pipet a 5-ml. aliquot of the sample solution into a 500-ml. iodine flask containing
50 ml. of distilled water and 50 ml. of standard 0.1N CT solution. Mix and allow to stand for 10 minutes. Add 30 ml. of 0.5N K I solution and 10 ml. of glacial acetic acid, mix, and titrate the liberated iodine with 0.1N standard sodium thiosulfate, using a starch indicator if desired. Sodium Hypochlorite Titration. Pipet a 5-ml. aliquot of the sample solution into a 500-ml. iodine flask containing 100 ml. of phosphate buffer solution, 3 grams of KBr, and 40 ml. of 0.15N standard sodium hypochlorite solution. Mix, place the flask on a heated magnetic stirrer set a t 60" C., connect the reflux condenser and the trap containing 50 ml. of K I solution, and heat, stirring slowly, for 15 minutes, as in the standardization. Disconnect the trap, cool the flask in an ice bath, and add the KI solution from the trap to its contents, and let stand for 2 minutes. Add 50 ml. of glacial acetic acid, and titrate the liberated iodine with standard thiosulfate, using a starch indicator if desired. Stopper the flask and allow it to stand for 5 minutes. If the iodine color reappears, one or two additional drops of thiosulfate will bring the permanent end point which is used in the calculations.
Table 1.
39.52
(Mean) Mean sq. dev. 60.65
(Mean) Mean sq. dev.
39.59 39.59 39.71 39.71 39.71 39.66
-
Dif.
Added
+0.07
60.48
+0.07
$0.19 1-0.19 +0.19 $0.14 0.024
60.71 60.83 60.71 60.90 60.92 60.81
[mmole iVzH4] - 2 imeq. CT]
f0.06 f O . 18
+
[meq. CT] = 4 [mmole NzH4] 4 [mmole CHSNZH~]
=
-
[meq. o c i ]
4
[mmole NnH4] X 0.032048 X 200 100 5 wt. sample
+
[mmole NzH,] 8 [mmole C H ~ N Z H ~ ]
100
200
0.046075 X
5
wt. sample
where [meq. CT]
=
milliequivalents Chloramine-T consumed
[rneq. OCl] = milliequivalents
hypochlorite consumed [mmole NzH,]
=
millimoles NZH4 in aliquot
[mmole C H ~ N Z H=~ ]millimoles CHaNzHa in aliquot Solving these equations [mmole CHsNlHa] [meq. OCi] E
- [meq. CTI 4
CHINZHI.H?SOI, % Found Dif.
(Mean) Mean sq. dev. 39.35
+0.06
+0.25 $0.27 +0.16 0.035
and, using a 200-ml. stock solution and a 5ml. aliquot as described above, %NzH,
= 4
NzH4.HzSO4, % Found
Added
CALCULATIONS
[meq. Oel]
Analysis of Synthetic Mixtures of NZH~'H~SO~-CHSNZH~' HzS04
RESULTS AND DISCUSSION
A synthetic solution, containing weighed amounts of N2H4.H2S04 and CHsNzHs.HzS04, was made up for analysis. The salts had been synthesized in this laboratory from the commercial hydrazines and analytical grade H2SO4, and purified by repeated recrystallization. They were analyzed by the CT method and by the classical iodate method, and both indicated a purity of 99.9+% for each salt. The synthetic solution was then analyzed by the foregoing procedure. The results are,given in Table I, from which the precision and accuracy of the method may be judged.
(M-1 Mean sq. dev.
60.43 60.43 60.70 60.70 60.43 60.54 39 34 39.21 39.34 39.12 39.26 39.25
-0.05
-0.05 +0.22
$0.22 -0.05 + O . 06 0.021 -0.01 -0,14 -0.01 -0.23 -0.09 -0.10 0.025
Equal precision was attained in the analysis of a (Classified) synthetic mixture containing the free bases. In these analyses the sampling and dilution procedures described above were used. The absolute accuracy in this case could not, of course, be dGermined, since commercial hydrazines do not make satisfactory primary standards. These results are satisfactory and are comparable to those of other titrimetric procedures. The only apparent disadvantage of the procedure is the comparative instability of the CT and the hypochlorite solutions, but since frequent standardization is not difficult, it is not felt that this slight inconvenience is of great importance. The method has been used, routinely, a t the Liquid Rocket Propulsion Laboratory, Picatinny Arsenal, for several months with completely satisfactory results. LITERATURE CITED
(1) Bray, W. C., Cuy, E. J., J. Am. Chem. SOC.46,858 (1924). (2) Clark, J. D., Analytical Procedures for Rocket Propellants, IV Hydrazine. Proj, No. TED-ARTSPP-502, Rept. No. 9, May 1951. (3) Kellogg, M. W. & Co., SPD-148, p. 46, March 1948. (4) Kolthoff, I. M., Stenger, V. A., IND. ENG.CHEM., ANAL.ED.7, 79 (1935). RECEIVEDfor review March 6, 1961. Accepted May 17, 1961.
VOL. 33, NO. 9, AUGUST 1961
1187
