Volumetric and Spectrophotometric Determination of Oxamide in Nitrocellulose-Base Propellants JULIUS B.
APATOFF, JOSEPH COHEN, and GEORGE NORWITZ
Pitman-Dunn laboratories, Frankford Arsenal, Philadelphia 37, Pa.
b Accurate volumetric and spectrophotometric methods are proposed for the determination of oxamide in nitrocellulose-base propellants. These methods involve hydrolysis of the nitrocellulose and oxamide with 10% sodium hydroxide solution, steam distillation, and determination of the ammonia produced by the treatment. A correction must be made for nitrocellulose which reacts with alkali to produce some ammonia. The latter reaction was studied in detail.
L
in the literature on the analysis of oxamide, although this material is used in propellants and fertilizers. It is of considerable interest since i t has the highest melting point of any known organic compound (419" C.). A method has been described for the determination of oxamide in nitrocellulose-base propellants (7') by extraction with boiling water, hydrolysis to sodium oxalate with sodium hydroxide, and titration with permanganate. This method tends to give low and erratic results because of the difficulty of extracting the oxamide from the propellant. An improved method is proposed for the determination of oxamide in nitrocellulose-base propellants by treatment with sodium hydroxide solution, steam distillation, and determination of the liberated ammonia which is corrected for ammonia from the nitrocellulose. ITTLE IS REPORTED
EXPERIMENTAL
Apparatus and Reagents. A steam distillation apparatus with a 2-liter balloon flask for t h e water, a 1-liter balloon flask for t h e sample, and a 750-ml. Erlenmeyer flask for t h e distillat e. NESSLER REAGENT (1). Dissolve 70 grams of potassium iodide in 60 ml. of water, add 100 grams of mercuric iodide, swirl to dissolve, dilute t o approximately 150 ml., and add slowly with stirring to a cool solution of 160 grams of sodium hydroxide in 500 ml. of water. Dilute t o 1 liter and allow to stand overnight or longer. STANDARDKITROGENSOLUTION(1 ml. = 0.060 mg. of oxamide). Dry ammonium chloride in a n oven a t 110" C.; dissolve 0.7280 gram in water; dilute to 1 liter in a volumetric flask: 800
ANALYTICAL CHEMISTRY
pipet a 50 ml. aliquot into a 500 ml. volumetric flask; and dilute to the mark. Volumetric Method. Extract a 5-gram sample overnight with methylene chloride in a Soxhlet apparatus. Disassemble t h e extraction apparatus and allow t h e solvent t o evaporate from t h e propellant by exposing t h e thimble t o t h e air for a few minutcs. Assemble the distillation apparatus, Add about 11/2 liters of water to the 2liter balloon flask and 100.00 ml. of 0.1N hydrochloric acid t o the Erlenmeyer flask. Carry along a blank determination starting with the steam distillation. Place the dry propellant and 200 ml. of 10% sodium hydroxide solution into the 1-liter balloon flask. Heat the water in the 2-liter balloon flask t o boiling (do not heat the 1-liter flask). Control the heating so that the condensate comes over at a rate of 5 to 7 ml. per minute and collect 250 to 300 ml. Add 5 drops of methyl red indicator solution and titrate with standard 0.1N sodium hydroxide solution. To obtain the correction, carry through the procedure, including the methylene chloride extraction, an amount of nitrocellulose approximately equal to the amount of nitrocellulose in the sample. The nitrocellulose used need not be the same as that used in the manufacture of the propellant but i t should have a nitrogen content of 12.2 to 13.3%. The correction must be determined once for each type of propellant (for instance, HIVEL-4C). Calculate the per cent oxamide. The milliequivalent weight of oxamide is 0.0440. Spectrophotometric Method. PREPARATION OF CALIBRATKON CURVE. Transfer 2.0, 4.0, 6.0, 8.0, 10.0, and 12.0 ml. of standard nitrogen solution t o 50-ml. volumetric flasks. Carry along a reagent blank. Dilute t o about 45 ml. with water, add 1.00 ml. of Yessler reagent, and swirl. Dilute t o t h e mark, shake, a n d measure tht. per cent transmittance in 15 t o 30 minutes a t 415 mp in a spectrophotometer t h a t has been set to 100% transmittance with the reagent blank. Plot milligrams of oxamide against per cent transmittance. PROCEDURE. Proceed as in the first and third paragraphs of the volumetric method but weigh out 1 gram of sample, add 100 ml. of water t o the Erlenmeyer flask (instead of the acid), use 150 ml. of 10% sodium hydroxide solu-
tion, and collect 225 to 250 ml. of the distillate. Dilute the distillate to 500 ml. in a volumetric flask, pipet a 5-ml. aliquot into a 50-ml. volumetric flask, dilute to about 45 ml., and develop the color as described under the preparation of the calibration curve. Convert the reading t o milligrams of oxamide by referring to the calibration curve and calculate the per cent oxamide. RESULTS A N D DISCUSSION
Many experiments were conducted to separate the oxamide from the nitrocellulose in the propellant by various means but the results were unsatisfactory. It was best to treat the sample with 10% sodium hydroxide solution, steam distill, and determine the ammonia produced either volumetrically or spectrophotometrically. Olsen (6) showed that many amides including oxamide can be determined by treating with sodium hydroxide solution, distilling] and collecting the ammonia in standard hydrochloric acid. It is necessary to conduct a preliminary extraction of the propellant with methylene chloride to remove nitroglycerin and dinitrotoluene which cause erratic results with both the volumetric and spectrophotometric techniques. Diphenylamine and ethyl centralite are also removed in the methylene chloride extraction but these compounds (in amounts found in propellants) do not interfere with the volumetric or spectrophotometric methods. The extraction with methylene chloride has no effect on the oxamide. It was noted by Dehlent, Hunt, and Stanford ( 4 ) in their study of the use of oxamide as a fertilizer that the hydrolysis of oxamide is a two-step reaction that proceeds a t a moderate rate, as follows :
+ + NHiOH NH2COCOOH + 2H20 * (COOH)? + TU"40H
NHzCOCOIiH2
2H20 4 IiH2COCOOH
Accordingly, in the hydrolysis 1 gram of oxamide gives 0.387 gram of ammonia. This was confirmed experimentally. Since the hydrolysis of oxamide proceeds at a moderate rate i t becomes possible in the spectrophotometric
Table 1. Effect of Source and Nitrogen Content of Nitrocellulxe on Titration
0.1N Acid ronsumed, ml. Not Exextracted tracted with with meth- methylene ylene chlo- chloride ride
Sample (4.0 grams) Wood pulp, 12.28y0 N Wood pulp, 13.19% N Cotton linters, 13.27% IQ Cotton linters, 12.24% ?\i Cotton linters, 12.64% I\i
4.3 4.3 4.4 4.5 4.5
3.4 3.3 3.4 3.5 3.4
Table II. Effect c f Amount of Nitrocellulose on Titration
Nitrocellulose
0.1N Acid consumed. ml. Not Ext ra&:d extrarted
with (13.27% N), methylene grams chloride 1 .o 2 .o 3 .O 3.5 4.0 4.5
1.2 2.4 3.6 4.1 4.9 5.2
with methylene c~hloride 1 .o 2.2 2.6 3.3 3.8 4.5
Table 111. Effect of Pmount of Nitrocellulose on Color Obtained with Nessler Retrgent
Nitrocellulose (13.27% N), grams
Transmittance, % Not Extracted extracted with with methylene methylene chloride chloride
0.5 0.75 1 .o 2.0 3 .O 4.0 5.0
Table IV.
Nitrocellulose
92.0 90.0 88 .O 77.0 69 . O 59.0 52 .O
93.0 91 .o 89.5 80.0 73 .O 64.0 56.0
method to collect the ammonia under water. Ordinarily, in steam distilling significant amounts of ammonia, it is necessary t o have some acid in the receiving flask since most of the ammonia comes over very rapidly in the first few minutes. The fact t h a t no acid need be used in the recommended spectrophotometric method makes the results more reproducible, because the color obtained with Nessler reagent depends somewhat on the alkalinity and the salts present. These two factors are more difficult to control when acid is used to absorb the ammonia. In the steam distillation there is no danger of loss of oxamide as such because the vapor pressure of the compound is very low (3). A correction must be applied for ammonia produced during the hydrolysis of nitrocellulose. T h a t some ammonia is produced when nitrocellulose is treated with sodium hydroxide solution was first noted in 1855 by Bechamp (2) who identified ammonia by its odor. This finding was confirmed by Silberrad and Farmer in 1906 (8). No one, apparently, has studied the reaction quantitatively. A study of the reaction of sodium hydroxide with nitrocellulose to produce ammonia was made using the amounts of reagents described in the procedure. The findings can be summarized as follows: The amount of ammonia produced is independent of the source of the nitrocellulose (Table I). The amount of ammonia produced is independent of the per cant nitrogen in the nitrocellulose over the range of 12.2 to 13.3% nitrogen, the usual range of nitrogen found in nitrocellulose used in propellants (Table I). The amount of ammonia produced is proportional to the amount of nitrocellulose both in the volu-
Recoveries of Oxamide by Volumetric and Spectrophotometric Methods
(13.2% N), grams
Oxamide Oxamide added, grams found, grams Volumetric method
3.9 3.9 3.9 3.9 3.9 3.9
0.0536 0.0740 0.1223 0.1263 0.2012 0.2012
0.78 0.78 0.78 0.78 0.78 0.78
0.0450 0.0450 0.0450 0.0450 0.0450 0.0450
0.0529 0.0738 0.1201 0.1246 0.1993 0.1997
Recovery, yo 98.7 99.7 98.2 98.7 99.1 99.3 Av. 9 9 . 0
Spectrophotometric method 0.0440 0.0440 0.0438 0.0460 0.0457 0.0457
97.8 97.8 97.3 102.2 101.6 101.6 Av. 99.7
Table V. Analysis of HIVEL-4C Propellant Volumetrically and Spectrophotometrically (Nominal Composition 4.5% Oxamide)"
Oxamide volumetrically, % 4.57 4.56 4.53 4.54 4.58 4.53 Av . 4.55 Std. dev. 0 . 0 3 5
Oxamide spectrophotometrically, % 4.68 4.61 4.46 4.58 4.58 4.51 4.55 0.05
Contains in addition to oxamide:
74.20 nitrocellulose, 17.38 nitroglycerin, 0.86 diphenylamine, 2.23 ethyl centralite, 0.79 potassium sulfate, and 0.74 moisture
and volatiles.
Table VI. Assay of Oxamide Volumetrically (0.5-Gram Sample) Hydrorhlorir acid Boric arid absorption absorption
method,
100.1 99.9 100.3 99.6 99.9 100.1 99.98 Av. Std. dev. 0 . 2 4
method, % 98.i 100.1 99.9 100.3 99.9 99.98 0.23
metric and spectrophotometric methods (Tables I1 and 111). The amount of ammonia produced is consistently more when the nitrocellulose is extracted with methylene chloride (Tables I, 11, and 111). Apparently the extraction removes an impurity that has some effect on the mechanism of the hydrolysis. The weight of the nitrocellulose is not significantly changed by the methylene chloride treatment since nitrocellulose itself is insoluble in the solvent. One gram of extracted nitrocellulose was found to give 0.0020 and 0.0017 gram of ammonia by the volumetric and spectrophotometric methods, respectively. I n working with the spectrophotometric method, two calibration curves were prepared. One was made by distilling weighed portions of oxamide and taking aliquots, the other by using standard ammonium chloride solution without distillation. Both curves were identical and followed Beer's law. The use of the ammonium chloride solution is recommended. The recoveries obtained on adding oxamide to nitrocellulose and carrying the samples through the procedure were satisfactory for both the volumetric and spectrophotometric methods (Table IV). VOL. 35, NO. 7, JUNE 1963
801
The results obtained for oxamide in an actual commercial propellant containing oxamide (HIVEL4C) showed good precision by the volumetric and spectrophotometric methods and the two procedures agreed satisfactorily (Table V). As is customary in propellant analysis, the percentages of oxamide (and other ingredients listed in the footnote of Table V) are calculated on a volatile-free basis. The results obtained by the volumetric method for the assay of oxamide using a 0.5-gram sample and 200.00 ml. of 0.1N hydrochloric acid are shown in Table VI, left hand column. An alternative method to absorption of the ammonia into hydrochloric acid and back titration with sodium hydroxide is absorption into 100 ml. of 3% boric acid and titration of the ammonium borate with standard 0.1N hydrochloric acid, using bromophenol blue indicator (5). The authors considered using this method initially;
however, it was decided that the hydrochloric acid absorption method was more desirable since it furnished more conclusive evidence that ammonia was the volatile material that was titrated when the nitrocellulose was hydrolyzed with sodium hydroxide and the solution steam distilled as in the method. Subsequent work with oxamide and propellants containing oxamide showed that the boric acid absorption method could be used in place of the hydrochloric acid absorption method. The results obtained for the assay of oxamide using the boric acid absorption method are shown in Table VI, right hand column. These results are of the same order of accuracy and precision as the results fiom the hydrochloric acid absorption method.
LITERATURE CITED
(1) American Public Health Assn., New York, “Standard Methods for the Examination of Water, Sewage, arid 111dustrial Wastes,” 10th ed., p. 144,
1955. (2) Bechamp, A., Compt. Rend. 41, 817 (1855). (3) Bradley, R. S., Cleasby, 1’. C., J .
Chem. Sac. 1953, 1681. (4) DeMent, J. D., Hunt, C. M., Stanford, G., J. Agr. and Food Chemistry 9,453 (1961).
(5) Hillebrand, W. F., Lundell, G. E. F., Bright, H. A., Hoffman, J. I., “Applied Inorganic Analysis,” p. 784, Wiley, New York, 1953. (6) Olsen, S., Acta Chem. Scand. 3 , 1082 (1949). ( 7 ) “Propellants, Solid: Sampling, Examination and Testing,” Military Standard, MIL-STD-286A1 Method 219.1, August, 1961. (8) Silberrad, O., Farmer, R. C., J . Chem. SOC.1906, 1182.
ACKNOWLEDGMENT
The authors are indebted to Samuel Sitelman for his suggestions.
RECEIVED for review December 14, 3062. Accepted March 21, 1963.
Determination of Mixtures of Hydrazine and 1,l -Dimethylhydrazine (UDMH) Potentiometric and Spectrophotometric End Point Detection EUGENE A. BURNS’ and ELIZABETH A. LAWLER Propulsion Sciences Division, Stanford Research Institute, Menlo Park, Calif.
b The use of potentiometric and photometric end point detection in determination of mixtures of hydrazine and 1 , I -dimethylhydrazine mixtures by the salicylaldehyde method has been evaluated. The two-step equilibria of crystal violet indicator in glacial acetic acid, while complicating Type II photometric end point plots of the total alkalinity titration at 590 mp, yields a sharp end point directly from the titration curve at 630 mp. The end point of the salicylaldehyde adduct titration curve lacks sharpness, but with potentiometric and photometric detection, reproducible, accurate results are obtained. The overall dissociation constants, pKB, for hydrazine and 1,I -dimethylhydrazine in glacial acetic acid media were 5.82 and 6.1 0, respectively.
acid in glacial acetic acid media before and after treating the sample with salicylaldehyde. Because the hydrazinesalicylaldehyde adduct is neutral in glacial acetic acid and the Ill-dimethylhydrazine (UDMH) adduct is basic, it is possible to determine the concentrat,ion of the two components from these two titrations. The use of crystal violet as an internal indicator gives an ill-defined end point which varies significantly between operators and has been observed t o be dependent on the nature of the light used to illuminate the titration beaker. The method as presented by Malone (IO) includes an 8 p.p.t. inherent error and, when coupled with the end point detection difficulty, gives a marginal satisfactory method. I n an effort to minimize indeterminate end point error, we have eliminated the operator visual detection difficulties by use of photometric and potentiometric methods. ECENTLY, a method for the analysis of hydrazine-1,l-dimethylhydra- By advantageous selection of the size of zine mixtures wag proposed by Malone sample and volumetric glassware, we have reduced the inherent error from S ( I O , 11). The basis for this method is to 6 p.p.t. In addition, a determinate the determination of the alkalinity of the mixture by titration with percholoric error in the blank UDMH titration has
R
802
ANALYTICAL CHEMISTRY
been recognized and its remedy is incorporated. With the application of the above modifications the reproducibility obtainable in our laboratory for the UDMH titration of a 50-50 mixture has been reduced from a relative standard deviation of 4.4 to 0.93% and 0.69% for the potentiometric and photometric detection techniques, respectively. EXPERIMENTAL
Apparatus. A Beckman Model B spectrophotometer, modified in a manner similar t o t h a t described by Goddu and Hume (6),was used for the photometric titrations. For convenience, the spectrophotometer was modified further by a support for, and subsequent use of, a Beckman Zeromatic microelectrode pair, so that photometric and potentiometric data could be obtained simultaneously. A Beckman sleeve-type calomel electrode was used which contained glacial acetic acid saturated with lithium chloride. All apparent p H measurements have been made with re1 Present address, Propulsion Research Department, Space Technology Laborstories, Inc., Redondo Beach, Calif.
