949
V O L U M E 20, NO. 10, O C T O B E R 1 9 4 8 Table I. Reduction of Nitroguanidine with Titanous Chloride
Nitroguanidine Uram 0.0841 0,0905 0.1407 0.1476 0,1289 0.1320 0.0900 0.0409
Excess Titanous Chloride
% 230 206
100 88
115 110 208 205
Time of Reflux Min. 10 10 5 5 15 15 15 15
Equivalents of Titanous Chloride Consumed per Mole of Sitroguanidine
Purity of Nitro-
guanidine
% 3.98 3.99 3.86 3.90 4.00 3.97 4.01 4.01
99.6 99.7 96.4 97.6 99.9 99.3 100.2 100.2
milliliter of 1N titanous chloride is equivalent to 0.02602 gram of oitroguanidine.
A specimen of pure nitroguanidine (recrystallized from water and dried) was analyzed by the foregoing procedure with the results shown in Table I.
Table 11. Reduction of RDX by Titanous Chloride Alone and by a Mixture of Titanous and Ferrous Chlorides
Weight of R D X
Excess TiCla Present
Gam
%
0.1537 0.1443 0.1400 0.1300 0.1500 0.1480 0.1566 0.1500 0,1500 0.1500 0,1086 0.1055 0,1019 0.1000 0.1023 0.1000 0.1028 0.1130 0.1017 0.1017
136 150 161 172 60 52 46 53 53 51 176 209 257 325 315 306 314 331 320 322
0.7 N FeCh .4dded 311. 0 0 0
0 20 20 20 20 20 20 20 20 20 20 20 20 20 20 22 30
Time of
Reflux
Eequivalents of TiCla Consumed per Mole of RDX
of R D X
7.00 7.00 7.19 7.39 10.50 11.22 11.09 11.04 11.04 11.14 11.66 11.68 11.86 11.78 11.93 11.88 11.90 11.96 11.84 1;. 81
58.3 58.3 59.9 61.6 87.5 93.5 92.4 92.0 92.0 92.8 97.2 97.3 98.8 98.2 99.4 99.0 99.2 99.7 98.7 98.4
Purity
%
Min. 20 20 20 20 5 lo lo 15
20 2o 20 30 30 30 30 30 30 30 30
PURITY OF RDX BASED ON NITRO NITROGEN CONTENT
In addition to standard titanous chloride and fpriic a l u m solutions, 0.7 N ferrous chloride is required. Weigh accurately 0.09 to 0.11 gram of dry sample into a 300Dissolve the sample in 25 ml. of glacial acetic acid and sweep out the air. Add 20 ml. of 0.7 ATferrous chloride and 115 ml. of 0.2 -V titanous chloride. The latter amounts to about 300% excess. Add 25 ml. of 37y0 hydrochloric acid and reflux the solution for 30 minutes. Titrate the excess titanous chloride with 0.15 ferric alum solution, adding 5 ml. of 20% ammonium thiocyanate near the end point. Make blank determinations to determine reducible impurities in the reagents and apply a correction value in calculating the results. One milliliter of 1IV titanous chloride is equivalent to 0.01851 gram of RDX. ml. flask provided with inlet tube for carbon dioxide.
The foregoing procedure was used to determine the purity of a plant sample of RDX, with the results shown in Table 11. SUMMARY
Correct conditions for the quantitative reduction of the nitro groups in nitroguanidine and cyclotrimethylenetrinitramine (RDX) were developed; four equivalents of titanous chloride are required for the reduction of each nitro group present. In the case of RDX, ferrous chloride as well as titanous chloride
must be used to effect complete reduction. iilthough the reactions appear to be stoichiometric, the reduction products were not isolated and equations were not written. LITERATURE CITED (1) Bebie. J., “ M a n u a l of Explosives, Military Pyrotechnics, a n d Chemical W a r f a r e Aaent,s.” 1st ed., New Y o r k , Macmillan Co., 1943. (2) Becker. TV. T V . , IKD. ENO.C H E Y . ,Ax.4~. 5 , 162 (1933). (3) Bernthsen, A , , a n d S u d b o r o u g h , J. J., Organic C h e m i s t r y . ” rev. e d . , New Y o r k , D. Van N o s t r a n d Co., 1933. (4) B u t t s , P. G.. Meikle, W. J., Shovers, J o h n , K o u b a , D. L.. a n d Becker. TV. W., .$SAL. CHEX.,20, 917 ( 1 9 4 s ) . (5) Callan, T., a n d Henderson, J. A. R., J . SOC.Chem. Ind., 41, 15761 T (1922). (6) Cottrell, T. L., MacInnes, C. A , a n d Patterson, E. M., Analyst. 71, 207 (1946). (7) Desvergnes, L., Chimie & Industrie, 28, 1035-44 (1932). (8) English. F. L., J . Ind. Eng. Chem., 12. 994-7 (1920). (9) K n e c h t , E., a n d Hihbert, E., “New Reduction M e t h o d s i n Volumetric A n a l p i s , ” 2nd ed., New York, Longmans, Green and Go., 1926. (10) Kolthoff, I. 34.. a n d Furman, N. H . , ”Potentiomet,ric T i t r a tions,” New Y o r k , J o h n Wiley & Sons, 1926. (11) R a t h s b u r g , H., Ber.. 54B.3183-4 (1921). RECEIVEDFebruary 9, 1947.
Fp.,
Determination of Potassium Perchlorate in Smokeless Powder PC. B. MELDRUM,
J R . , R. 4. CLARKE’, D. L. K O U B i , AND W . W. BECKES
Hercules Experiment Station, Tferczcles Powder C o m p a n y , IVilmington 99, Del.
D
LJRING World War 11, potassium perchlorate was added to certain types of smokeless powder for specific purposes, and a rapid method for its determination in powder wm needed. Two methods giving satisfactory results have been developed. The first, or explosion-Volhard method, consists in decomposing a ground powder sample by explosion in a Parr stainless-steel calorimeter bomb. The explosion quantitatively reduces the perchlorate to chloride, which may best be determined by Caldwell and lloyer’s (!?) nitrobenzene modification of the Volhard method (’7). The second, or nitric acid-titanous chloride method, is longer and less accurate than the explosion-Volhard method, 1
Present address, Oregon State Collaca, Corvallis, Ore.
but it avoids need for a Parr bomb. It involves decomposition of the powder sample with nitric acid, subsequent removal of nitrir acid and carbon black (if present), and determination of the potassium perchlorate by reduction with titanous chloride. The analysis of perchlorates by reduction with titanous chloride was first suggested by Knecht (3)and used by Knecht and Hibbert (4), who titrated potassium perchlorate in strong sulfuric acid solution, after adding oxalic acid to facilitate the reduction Rothmund and Burgstaller (5),however, did not consider the presence of oxalic acid necessary. Vil’yamovich (6) succeeded in completely reducing potassium perchlorate in strongly acid (sulfuric and hydrochloric) solution by using approximately 4004,
ANALYTICAL CHEMISTRY
950
When present in smokeless powder, potassium perchlorate may be determined by explosion of the sample in a calorimeter bomb and use of the Volhard method for chloride, or by decomposition of the sample with nitric acid, followed by reduction of the perchlorate with standard titanous chloride solution. The first method is preferable, if the equipment is available, because it is more accurate and requires less time
excess of titanous sulfate and refluxing for 2 houis. The authors have found that while a t least a 3 3 5 bykeight acid solution must be maintained, potassium perchlorate may be completely reduced by refluxing for 5 niinutes after the addition of only 1007, excebs of titanous chloride. PROCEDU-RE
Explosion-Volhard Method. T o decompose the sample, a stainless-steel bomb JTas used, manufactured by the Parr Instrument Company, designated LIode1 B, oxygen, single valve. During the explosion of a sample, the bomb should be placed behind a substantial shield or barricade, for safety. Add 25 ml. of water to the bomb, weigh a ground and blended 5-gram sample into the cup, and place the cup in the bomb. Attach the fuse wire, screw on the cover, and make the electrical connections. Explode the sample a t atmospheric pressure and allow the bomb to cool for 5 minutes in the air before releasing the gas. Wash the bomb thoroughly with several portions of water, using a total of 200 ml.; take particular care to wash through the valve and the inside of the bomb top and the posts. Evaporate the washings to about 80 ml. and dilute them to 100 ml. in a volumetric flask. Determine the chloride by the modified Volhard method, using a 10-ml. aliquot, 10 ml. of 35% nitric acid, 2 ml. of nitrobenzene, and 0.05 N silver nitrate and 0.05 S potassium thiocyanate solutions. Nitric Acid-Titanous Chloride Method. The preparation and standardization of the titanous chloride and ferric alum solutions have been described (1).
Table I.
Analysis of Saltless Powder Samples Containing Added Potassium Perchlorate
Potassium Perchlorate Added Gram
Potassium Perchlorate Recovered Gram
Recovery
%
Explosion-Volhard hlethod 0.4000 0.4065 0.4075 0.4028 0.4042 0.4000 0.4043 0.7900 0,4650 0.4000
0,3988 0.4028 0,4042 0.3984 0.4038 0.4000 0,4039 0,7837 0,4608 0,3988
99.7 99.1 99.2 98.9 99.9 100.0 100.4 99.2 99.1 99.7
Nitric Scid-Titanous Chloride hfethod
Weigh a &gram sample of powder into a 150-ml. beaker and add 70 ml. of 7oyOnitric acid. Cover with a watch glass and digest for 2 hours or until red fumes are no longer copiously evolved. Remove the cover glass, evaporate to about 10 ml., add 20 ml. of glacial acetic acid, and evaporate to approximately 10 ml. Filter the solution x-hile hot through a Gooch crucible or sintered-glass funnel. Wash the beaker with a small amount of hot water and filter this also. Transfer the filtrate and washings quantitatively back to the original beaker and evaporate to dryness on a steam bath. Add 25 ml. of water and evaporate the solution to dryness. Repeat the addition of water and its evaporation to effect the complete removal of nitric acid. Again add 25 ml. of water and heat the solution to approximately 70” C. Filter the warm solution through a Whatman No. 41 filter paper into a 100-ml volumetric flask Wash both beaker and filter paper with small portions of warm xater. Cool the flask to room temperature before diluting the solution to exactly 100 ml. Add a 10-ml. aliquot to a 300-nil. flask provided with an inlet tube for carbon dioxide. Sweep out the air, add 10 ml. of 9?% sulfuric acid and 1007, excess of 0.2 S titanous chloride solution (1 ml. for every 1.7 mg. of potassium perchlorate estimated to be present in the aliquot), connect the flask to a condenser, and reflux the solution for 5 minutes. Titrate the excess titanous chloride with the 0.15 *Vferric alum solution, adding 5 ml. of 20% ammonium thiocyanate near the end point. Make a blank determination to measure reducible impurities in the reagents. One milliliter of 1-V titanous chloride is equivalent to 0.01732 gram of potassium perchlorate. RESULTS
In order to test the explosion-Volhard method, kilo%n mixtures lyhose composition simulated that of regular-production potassium perchlorate powders were prepared and analyzed. Their preparation was accomplished by mixing known amounts of potassium perchlorate with ground samples of a saltless smokeless powder containing nitrocellulose, nitroglycerin, centralite, and carbon black. The analytical results obtained are given in Table I, together with results found by the nitric acid-titanous chloride method on similar samples. Finally, seven regular-production lots of smokeless powder to which 7.8% potassium perchlorate had been added during manufacture were analyzed by both procedures, ryith the results shown in Table 11. It may be seen from Tables I and I1 that, although the aveiage results found by the two methods agree reasonably Lvell, those obtained by the explosion-Volhard method are much more concordant. The latter method has the added advantage that results can be obtained in about 2.5 hours, while the nitric acid-titanous chloride method requires about 12 hours. ACKNOWLEDGMEIVT
The experimental work described in this article Lyas carried out a t the Radford Ordnance Works, operated by the Hercules Powder Company. Table 11. Analytical Results on Plant Samples of Smokeless Powder Formulated to Contain 7.8% Potassium Perchlorate Potassium Perchlorate Found Xitric acidtitanous chloride method,
Explosion-Volhard method, Sample
%
%
7.63 7.45 7.68
7.39 7.04 7.81 7.50 7.70 8.06 7.58
7.57
7.61 7.58 7.73
LITERATURE CITED
(1) Butts, P. G., Meikle, W. J., Shovers, John, Kouba, D. L., and Becker, W. W., ANAL.CHEM.,20, 947 (1948). (2) Caldwell, J. R., and Moyer, H. Y.,IND. ENG.CHEM.,ANAL.ED., 7, 38 (1935). (3) Knecht, E., Proc. Chem. Soc., 1909, 227. (4) Knecht, E., and Hibbert, E., “Kew Reduction Methods in Volumetric Analvsis.” DD. 25.84. New York, Longmans, Green ” and Co., 1925. (5) Rothmund, V., and Burgstaller, A., Chem.-Ztg., 1909, 245. (6) Vil’yamovich, E. T., Chem. Zentr., 1942, 1, 902. (7) Volhard, J., J. prakt. Chem. ( 2 ) , 9, 217 (1874); Ann., 190, 1 (1878). I
RECEIVED February 9, 1947.
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