for a study of the stability of a copper porphyrin. The sample of etioporphyrin I was furnished through the courtesy of J. Gordon Erdman of the Mellon Institute. The Ohio Oil Co. furnished the crude oil sample from Mill Iron Well No. 79-C, Curtis formation, Wyo., and the Skelly Oil Co., the B. C. Prescott No. 3 oil from the Ten Sleep sand, Wyo. The Canadian oil, Lloydminster, was furnished through the courtesy of G. W. Hodgson of the Research Council of Slberta, Canada, and the Venezuela No. 1 oil, Pederanallis field, was furnished by the Creole Corp.
LITERATURE CITED
(1)Blumer, Max, AXAL.CHEM.28, 1640 (1956). (2) Corwin, Alsoph H., Fifth World Petroleum Congress, Section V, Paper 10,p. 6,1959. (3) Costantinides, G.,Irich, G., Lomi, C.,
Fifth World Petroleum Congress, Section V. PaDer 11. 1959. (4)Erdman,* J. G., Ramsey, V. G., Kalenda, S. W., Hanson, UT.E., J. Am.
Chem. SOC.78,5844 (1956). (5) Dunning, H. N., Carleton, J. K., ANAL.CHEM. 28, 1362 (1956). (6) Dunning, H. N.,Moore, J. W., Myers, A. T., Ind. Eng. Chem. 46,2005 (1954). (7) Fisher, L. R., Dunning, H. K., ASAL. CHEM. 31, 1194 (1059).
(8)Groennings, Sigurd, Ibid., 25, 938 (1953). (9) Lucas, J., Orten, J. M., J. Biol Chem. 191,287 (1951). (IO) Resnick, F. E , Lee, L. A., Powell, A,, -4XAL. CHEM.27,9288 (1955). (11) Stern, A.,Wenderlein, H., 2. physik. Chem. 175A,405 (1936). (12) Treibs, Alfred, rlnn. Chem. Liebigs 410,42(1934). (13) Willstatter, R., Mieg, W., Ibid., 350, I (1906).
w.
RECEIVEDfor review June 14, 19GO. Accepted October 24,1960. This research is being administered by the Colorado School of Mines Research Foundation, Inc., Golden, Colo., under a grant from the Colorado School of hlines Foundation, Inc.
Titrimetric Determination of Hexahydro-lI3,5-trinitros-triazine (RDX) and Octahydro-I,3,5,7-tetranitros-tetrazine (HMX) with Ferrous Sulfate JAROMiR SIMEtEK Military Academy A. ZGpotocki, Brno, Czechoslovakia b The reactions which take place when RDX or HMX are dissolved in concentrated sulfuric acid are explained and also the factors which affect the amount of nitric acid liberated from these compounds. The determination of RDX and HMX in admixiure i s based on the determination of nitric acid liberated from them in sulfuric acid. A colorimetric estimalion can b e used and a titrimetric determination using ferrous sulfate is described.
S
(3) based the determination of R D X and H h I X in admixture on a determination of HK03which resulted from the hydrolysis of RDX and HXX in concentrated H2SOr. They determined the HNOI colorimetrically after reduction with FeS04, as the complex Fe(KO)+2. This reaction has also been used for the determination of HSO3 and HKOZ ( 2 ) and some organic nitrates (1, 6). Semel et al. showed that in Concentrated H2S04, R D X liberated a little more than two thirds and H h I X more than one third of the total HKOs. The reaction proceeds according to the equation EMEL, LACCETTI, AND ROTH
+ +
(-CHZXSO~)~ 22H20 H?S_OI zNH3 zCHzO zHN03 (1) 1: = 3 for R D X and 4 for HMX. This phenomenon was also observed by the author when attempting to determine RDX and H M X by titration with FeS04. Furthermore, i t was found that 3,7-dinitro-1,3,5,7-tetrazobicyclo260
+
ANALYTICAL CHEMISTRY
[3.3.l]nonane did not liberate HXO, under these conditions ( 5 ) . I n another study made for nonanalytical purposes, the author quantitatively evaluated the decomposition of RDX in concentrated HzSO4 (4). Results of this study, with other more recent unpublished information, explain the lower in the titrimetric and yield of "03 colorimetric determinations of R D X and H M X and also indicate some of the problems in these determinations. The dissolution of both R D X and HNX in concentrated H2S04involves two reactions, the first being the rapid reversible cleavage of HS03. leading to the equilibrium state
+ +
+
(CHZXNOZ), nH+ nHlSOa 3 (CHSH~),, nSOz+ ~ H S O - ~ (2)
n
+
3 for R D X and 4 for HlIX. The equilibrium state, which depends on the concentration of H2S04as solvent, is characterized by the amount of cleaved " 0 3 . The dependence of the amount of HKoa on the concentration of HzSO4 in a 0.005BI solution is showi in Figure 1. The next reaction is the irreversible destructive decomposition of partly denitrated R D X or HJIX due to Reaction 2 and is, for example,
Because of Reaction 3, Reaction 2 is reversible only temporarily, within the period of existence of hexahydro-striazine or octahydro-s-tetrazine heterocycle. Reaction 3 is also rapid; the rate of destructive decomposition of a n 0.3M solution of RDX in 97.5% is shown in Figure 2 which illustrates that approximately 12% of the RDX decomposed irreversibly during the dissolution. The beharior of H M X is similar and the decomposition of RDX and H h I X can be written as follows:
+
(CHzNKOz), 2rH+ = ( n - z)CH20 ( n - z)SZO
+
zNOz+
+
+ xCHFXH~
(4)
and a t the dilution of the reaction mixture Kith water
z ~ ~ 2 = h %~C zH ~ O+ r
=
n
~
~
= 3 for R D X and 4 for H X X ; z depends on the concentration of and equals approximately 0 to 2.7 for RDX and 0 to 2 for HMX; (see Figure 1). The mechanism of the reaction was demonstrated by the determination of all products of decomposition and by proving the presence of partly denitrated R D X in H&04solution. I n the equilibrium state of Reaction 2, a t a concentration of 85 to 100% H&04 the amount of "03 cleaved is approximately linearly proportional t o the concentration of H2S04. Because of this, the possibility of using this reaction for the indirect determination
a
+
0
30
60
90
4
7
Figure 2. Dependence of reversibility of Reaction 3 on time; per cent RDX reversibly decomposed 0.3M solution in 97.5% H2S04 at 20" C.
zoi
% (
40
Figure 1. Dependence of per cent of -NO; groups liberated as NO; from RDX and HMX on concentration of HzS04 used as solvent O.OO5M solutions ot 20' C.
of concentration of high percentage H2S04 was considered, but was abandoned because of the inflection in the region of 96% HzS04. It was expected that the equilibrium of Reaction 2 would be affected by temperature. However, the temperature a t which the dissolution of R D X in H2S04 was carried out had very little effect on the amount of liberated HNOs as shown by the folloa~ingtable: RDX. O.O05M, Dissolved a t C.
data: R D X grains, 0.003 to 0.020 mm. in 97.5% Hi304 yielded 75.7% --NO2 as "03; with grain sizes of 0.21to 0.5 mm., the yield was 74.5%.
-NO2
&sod, %
-NOz, % (as "03)
The only slightly higher results obtained n hen dissolution took place a t 60" C. m r e probably caused by an increase in the rate of Reaction 3 with temperature. This reaction proceeds simultaneously with the cleavage of "03 and competes with it more a t the higher temperatures. The dependence of the amount of H S 0 3 yielded from R D X on its initial concentration in 97.5% H2SO4 is shown in Figure 3. Another factor affecting liberated is the the amount of "03 size of the crystals of R D X being dissolved under otherwise equal conditions. This phenomenon is due also to the effect of Reaction 3 but the effect is relatively low as shown by the following
groups liberoted as NOS+(%) a t
20" C.
REAGENTS AND APPARATUS
R D X and H M X were of highest purity and were prepared in this laboratory. Sulfuric acid, 96.1% and 99.4%, C.P.
Solvent,
Figure 3. Dependence of fission of RDX in 97.5% HzS04 on initial concentration of RDX in H & 0 4 (moles per liter)
Acetone, C.P. Diatomaceous silica, Super-Cel Johns-Manville. Ferrous ammonium sulfate solution, 0.1N. Dissolve 39.3 grams of Fe(hTH4)2(S04)2.6H20 in 200 ml. of water and after cooling add 300 ml. of concentrated H2SOdin portions. Add water to 1000 ml. Determine the factor of solution using analytical reagent grade K N 0 3 under the conditions of sample analysis. Automatic 10-ml. buret with pyrogallol closing. Potentiometric indicator electrodes, Pt/stainless steel AKW extra S (Poldi, Czechoslovakia) ; Titroscop galvanometer (Czechoslovakia). ANALYSIS
OF
SAMPLE
Dissolve approximately 0.5 gram of accurately weighed sample in acetone and dilute to 250 ml. with acetone. Transfer 25 ml. of this solution to a 150ml. beaker containing 5 grams of diatomaceous silica and evaporate the
mixture completely. Add 80 ml. of HzS04 to the residue and stir the mixture with a glass rod. Let stand 2 hours a t 20" f 5" C. and titrate with a 0.1N solution of ferrous ammonium sulfate. When mixtures containing T N T are analyzed, the finely pulverized sample containing ca. 0.04 gram of RDX or 0.08 gram of H M X can be mixed with diatomaceous silica and several milliliters of acetone. The mixture is then dried and treated as described. Figure 4 illustrates the dependence of the amounts of R D X or HMX on the amount of determined nitrogen (from "03) for 99.4 and 96.1% H2S04. The analysis can be shortened by finishing the destructive decomposition of the sample a t a higher temperature. The sample is dissolved in H2S04 a t 20" =t5" C. for 15 minutes and the solution is then heated a t 50" C. for 20 minutes. After cooling, the solution is titrated with the ferrous salt. Although the accuracy of the analysis with this modification is almost the same, the ratio of the dependence of milligrams of "03 to milligrams of R D X or H M X is somewhat different. Results of determinations of R D X and HRIX are shown in Tables I and I1 (96.1% HzS04used). VOL. 33, NO. 2, FEBRUARY 1961
261
Table I. Determination of HMX in Synthetic HMXIRDX Mixtures
6
(Sample dissolved in HsSOl at 20' C.; titrated after 2 hours) HMX, % Found
Added
Recovery
100
100.06 100.20 99.83 100.03
100.06 100.20 99.83 100.03
80
80.10 79.52 80.00 79.87
100.12 99.40 100.00 99.84
60
59.41 60.2.5 59.56 59.74
99.02 100.41 99.26 99.56
50.10 50.23 49.75 50.03
100,20 100.46 99.50 100.05
50
i
I
I
Grand av. 99.87 Std. dev. 0.46
DISCUSSION
Because of the steep dependence of from the amount of liberated "01 R D X or HMX on the concentration of H2SOr, the concentration of the hydroscopic acid must be kept constant and the linear dependence of absorption to concentration maintained.
Table II.
Determination
Since Reaction 2 is reversible temporarily, the amount of ferrous sulfate solution by the colorimetric method must be known as well as the time interval between the dissolution of RDX or H M X in sulfuric acid and the addition of this solution. However, the effects of these factors can be eliminated, for example, by allowing the solution of
of RDX in RDX/TNT Mixtures
(A. Dissolved in H 8 0 , a t 20' C.; titrated after 2 hours. B. Dissolved in H,S04 for 15 minutes at 20' C., warmed 20 min. a t 50' C., cooled, and titrated). RDX, %
Added 100
80
50
A Found
Recovery
Added
100.31 99.82 99.86 99.99
100 31 99.82 99.86 99 I99
100
80.15 80.34 79.82 80.10
100.18 100.42 99.77 100.12
80
50.03 50.12 49.89 50.01
Grand av. Std. dev. ~~~
262
~~
0
ANALYTICAL CHEMISTRY
100.06 100.24 99.78 100.02 100.03 0.26
50
B Found
Recovery
100.25 99.93 99.72 99.97
100.25 99.93 99.72 99 97
79.71 79.83 80.18 79.90
99.64 99.80 100.23 99.89
50.30 50.08 49.82 50.06
100.60 100.16 99.64 100.13
RDX or H M X to remain in the HzS04 for about 2 hours before adding the solution of ferrous salt; during this time the irreversible decomposition of the nonionized portion of the =KNOg linkages takes place and, thereby, the destruction of the heterocyclic compounds. It was also found that 0.005M nitric acid in concentrated sulfuric acid does not react with formaldehyde and that the amount of "08 does not decrease even after 24 hours a t 30' C. The determination must be carried out a t concentrations of RDX or H M X in H2S04lower than O.OO5M so that the equilibrium of Reaction 2 is not affected. For a titrimetric determination, the titration with ferrous salt must be done only after the decomposition of RDX or HhIX. ACKNOWLEDGMENT
The author thanks Miloslav Cupik for his faithful services in the laboratory. LITERATURE CITED
(1) Bandelin, F. J., Pankrata, R. E., ANAL.CHEM.30,1435 (1958). (2) English, F. L., Zbid., 19, 850 (1947). (3) Semel, S., Laccetti, M. A., Roth, M., Zbtd., 31, 1050 (1959). (4) Simerek, J., Chcm. listy 51, 1699 (1_957). (5) Simerek, J., Chem. prcmysl 7, 285 (1957). (6) Swann, M. H., Adams, M.L., ANAL. CHEM.28,1630 (1956).
Grand av. 100.01 Std. dev.
0.37
RECEIVEDfor review March 14, 1960. Accepted October 10, 1960.
