Decomposition of Nitronium Perchlorate

9 Decomposition of Nitronium Perchlorate M. D. M A R S H A L L and L. L. L E W I S

Downloaded by CORNELL UNIV on September 28, 2016 | http://pubs.acs.org Publication Date: January 1, 1966 | doi: 10.1021/ba-1966-0054.ch009

Callery Chemical Co., Callery, Pa.

The decomposition reaction for nitronium perchlorate is believed to involve the formation of nitrosonium perchlorate and oxygen. The other products (NO , Cl , ClO ) observed during the decomposition appear to be the result of the subsequent decomposition of nitrosonium perchlorate. This mechanism is clearly demonstrated in vacuo by a preponder ance of oxygen in the volatiles during the early stages of the decomposition of nitronium perchlorate in vacuo and by the products of the latter stages which describe the decomposi tion of nitrosonium perchlorate. In sealed tubes, the reac tion of dinitrogen tetroxide with nitronium perchlorate ulti mately predominates, giving nitrosonium perchlorate and oxygen as products. This reaction is catalyzed by dinitrogen tetroxide. 2

2

2

I V T i t r o n i u m perchlorate begins to decompose slowly at approximately ^ 50° C , producing gaseous products. There is some evidence that the stability of the sample is related to the purity. Despite efforts b y several investigators to obtain high purity samples, however, decomposition is significant when a temperature of 60° C . is reached. B y establishing the mechanism of decomposition, we hoped to obtain information that would allow us to prevent or suppress the decomposition. The decomposition of nitronium perchlorate between 70° and 112° C . has been reported by Cordes (2) to proceed to the gaseous products ΝΟ2, C l , C I O 2 , N O 3 C I , and 0 . As a result of some screening experiments we were aware that at 65° C . i n sealed tubes, nitrosonium perchlorate was a major decomposition product. W e were also aware that dinitrogen te troxide, at least i n the liquid phase, would quantitatively convert nitronium perchlorate to nitrosonium perchlorate. Thus, a mechanism involving only gaseous products appeared unlikely. T o avoid any such back reaction of dinitrogen tetroxide w i t h nitro nium perchlorate, we decided to carry out our study under vacuum, with 2

2

82

Holzmann; Advanced Propellant Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1966.

9.

M A R S H A L L AND LEWIS

Nitronium Perchlorate

83

continuous removal of products. W e chose a temperature of 65° C . w h i c h would give a significant decomposition rate but at which the gaseous products could be handled by the pumping system.


Experimental The decompositions were carried out i n glass reactors of 50-100 cc. volume equipped with a 12-mm. charging tube and a stockcock. Since nitronium perchlorate is extremely moisture reactive, aU transfers were conducted i n a dry atmosphere, and die charging tube was sealed off under dry nitrogen. E v e n with utmost care, however, a small amount of hy drolysis occurs. Consequently, after completing the sample transfer to the reactor, the hydrolysis products ( H N 0 and H C 1 0 ) were removed at room temperature by subjecting the sample to a high vacuum until a constant weight was obtained. (The effectiveness of this procedure was demonstrated by adding a measured amount of water to a sample of nitronium perchlorate, and after pumping according to the procedure described, the weight loss was measured for the sample and the nitric and perchloric acids titrated in the recovered volatiles. A U values were theo retical within limits of the analyses. ) 3

Figure 1.

4

Apparatus

The reactor was connected to a small glass vacuum system through a short glass coupling, and immersed i n the constant temperature bath con trolled to 65.0° ± 0.1° C . The vacuum system (Figure 1) was equipped with a M c L e o d gage for measuring pressure, a Toepler pump for handling


84

ADVANCED PROPELLANT

CHEMBTRY

noncondensables, and a removable trap for entraining condensable prod ucts for later analyses. The Toepler pump was placed after the diffusion pump so that the latter could aid i n collecting the small quantity of non condensables. Fluorolube grease was used throughout the system. The nitronium perchlorate initially charged was standard production grade material of better than 9 7 % purity. The N O C 1 0 content was measured by the procedure outlined by Vogel (13) and was below 0.05%, the limits of the analysis. The sample was further purified by subjecting it to a high vacuum, as described previously. The sample used for experi mentation had a purity i n excess of 9 9 % . The decomposition was monitored at 65° C . while continuously sub jecting the sample to pumping. The volatile decomposition products were passed through a —196° C . trap, where condensables were removed and periodically analyzed. Noncondensables, consisting entirely of oxygen, were measured either continuously or periodically to check their rate of removal. The weight loss of the sample was checked against volatiles re covered or measured, and appropriate analyses were carried out on the residue. Sublimed nitronium perchlorate was weighed with the residue. In most runs, the sublimed solias were measured and analyzed.


4

Results and

Discussion

The decomposition experiments a l l followed the same pattern. This consisted of: (1) an immediate deposition of sublimed materials on the cooled reactor walls within 1 minute after placing the sample i n the 65° C . bath; (2) an induction period of 24—40 hours during which no visible evi dence of volatiles was observed; (3) an initially slow, but rapidly acceler ating production of oxygen which maximized at approximately 100 hours with concurrent appearance of yellow condensable i n the —196° C . trap; finally, (4) a noticeable decrease i n the rate of oxygen evolution, which diminished slowly throughout the remainder of the run. Oxygen Evolution. A plot of the total oxygen evolved vs. time gave the typical sigmoid curve characteristic of solid decomposition (Figure 2 ) . The induction and acceleration periods are clearly evident along w i t h the subsequent lower rate of total oxygen evolution during the decay stage. A plot of the rate of oxygen evolution for one experiment is also shown i n Figure 2. The peak rate of oxygen release occurred at approxi mately 100 hours at about a 10% weight loss and with more than 8 0 % of the nitronium perchlorate still intact i n the sample (80% value obtained from a similar run stopped at this point and the solids analyzed). The amount of oxygen released per gram of weight loss incurred also varied throughout the run. Table I summarizes these data for two ex periments. The change from 15.5 to 6.5 for the mmoles of 0 per gram weight loss is significant i n that it denotes a mechanism change or the increasing importance of a secondary reaction. The 15.5 and 6.5 values are also 2


9.


M A R S H A L L A N D LEWIS

•

z. —

l b

*

9 HRS ÎT°RMM TFMR S

Κ

2. 2 _ 1-3 •1. 5

•

3

)°

Ό .

ι

Ο


ΌΤΑ - °2 •VOL VED-

•AVERAGE RAT Ε FOFi 16 Η I •AV6. RATE FOR8HR 5. OR-ESS STORED I I 39 HRS. AT ROOM TEMP 2

ι

τ

ι STORED

· 69HR

1/

ο

β

S AT ROOMTEMI .β · 73 HRS AT ROOM TE MR

«Xi

•0 0 20

60

100

140 180 220 260 300 340 380 420 460 500 TIME (HOURS)

Figure 2.

Oxygen evolution of NO ClO t

g

at 65°C.

Table 1. Summary of Condensables Produced Total Time hrs.

o

Wt. Loss gram

Run No. 7 73 92 112 132 154 174

2

Produced mmoles

mmoles 0% per gram wt. loss

mmoles NO% per gram wt. loss

N0 Produced mmoles 2

0.160 0.140 0.161 0.154 0.163 0.150

2.46 2.01 2.13 1.93 1.80 1.47

15.5 14.3 13.3 12.6 11.1 9.8

0.90 0,77 0.93 0.99 1.07 1.02

5.6 5.5 5.8 6.4 6.6 6.8

0.341 0.177 0.129 0.103

3.98 1.32 0.88 0.66

11.7 7.3 6.8 6.5

4.32« 0.78

6.7« 7.6

Run No. 2 198 298 397 492

* Value for period 0-397 hours.

significant since they cannot be obtained from nitronium perchlorate de composition reactions giving only gaseous products, but they must arise from a combination of reactions i n which the production and decomposi tion of NOCIO4 is involved. The highest and lowest possible values ob tainable from NO2CIO4 for this ratio are shown b y the equations: (mmoles 0 /gram wt. loss) 2

NO2CIO4 NO2CIO4

—

N O t + |C1 - f 2 0 N 0 + C10 + |0 2

2

2

2

2

13.8 6.9

O n the other hand, values of 31.3 and 3.9 are possible from the production and decomposition, respectively, of nitrosonium perchlorate.


86

ADVANCED PROPELLANT CHEMISTRY

(mmoles 02/gram wt. loss)

Νοαο + io N o + cio + è 0

NO2CIO4 Νοαοι

4

31.3 3.9

2

2

2

2

Volatiles Condensable at —196° C . The condensed materials were identified as N 0 , C l , and C10 by means of infrared and mass spec trometry. The sample was hydrolyzed and analyzed for chlorine and nitrogen content. The combined gram atoms of chlorine ( C I 2 + C10 ) invariably equaled the gram atoms of nitrogen found within the limits of the analyses. The nitrogen dioxide produced (measured as nitrogen in the hydrolysate) per gram of weight loss of sample slowly increased as the decomposi tion progressed. The values for two runs are shown i n Table I. It is again significant that the value of 7.6 mmoles of N 0 per gram of weight loss of sample obtained over the last period from 397 to 492 hours of decomposition for run No. 2 cannot be obtained from any decomposi tion reaction one may write for N0 C10 . It is, however, nearly theo retical for the decomposition of NOCIO4 to volatiles: 2

2

2


2

2

2

4

mmoles N C ^ / g r a m wt. loss NOCIO4

N0

2

+ CIO2 (CI, + o ) 2

+

|0

7.7

2

and in a separate experiment, a value of 7.6 mmoles of N 0 per gram of weight loss was observed for the decomposition of NOCIO4 under similar conditions. Analysis of Solids. I n our original hypothesis, we believed the for mation of NOCIO4 i n the residue would be avoided by carrying out the decomposition under vacuum. B y doing so, we hoped to prevent the back reaction of the N 0 produced i n the decomposition with N0 C10 . Nevertheless, NOCIO4 was observed i n the residue i n substantial quanti ties, possibly suggesting its formation by a different mechanism. Its pres ence was confirmed by x-ray (6), Raman ( J ) , and wet analysis (13) techniques. Figure 3 shows the NOCIO4 found i n the residue and the N 0 C 1 0 decomposed as a function of time. W i t h the limited data available, the peak production of NOCIO4 is observed to coincide with the peak rate of NO2CIO4 decomposition. The NOCIO4 also appears to decompose at a faster rate than the nitronium perchlorate as indicated by the slopes of the curves. This would most certainly be true if, as we suspect, nitrosonium perchlorate is also being continuously produced from the decomposition of nitronium perchlorate during this period. A study of the decomposition of NOCIO4 under conditions identical to this study gave the following results: ( 1 ) nitrosonium perchlorate de composes with no noticeable induction period, giving only the gaseous products, N 0 , C10 , C l and 0 ; nitronium perchlorate is reported as a 2

2

2

4

2

2

2

2

2


4

9.


M A R S H A L L AND LEWIS

major product of this decomposition at 99° C . ( I I ), but only trace quanti ties were observed i n our study; (2) the decomposition of N O C I O * pro ceeds at a faster rate than that of N 0 C 1 0 , even after the acceleratory period of the latter compound. This observation is consistent with conclu sions of Rosolovskii (11).


2

4

Several interesting facts concerning the sublimed solids should be noted: (1) sublimation occurred immediately upon heating the sample to 65° C ; (2) the sublimed solids were shown to be N 0 C 1 0 , both by x-ray and elemental analyses; (3) analyses d i d not detect the presence of N O C 1 0 ; (4) the rate of sublimation appeared to be comparatively con stant over the decomposition period; sublimation usually occurred at about one-half to one-third the rate of decomposition. These facts are signifi cant i n that they indicate that the sublimation is entirely independent of the decomposition. The Decomposition Mechanism. The vacuum decomposition of NO2CIO4 at 65° C . proceeds by a mechanism which must take into account a decreasing amount of oxygen evolved per unit weight loss of samples, an increasing amount of N 0 produced per unit weight loss of sample, the production of NOCIO4 as a product and its subsequent decomposition, and the decomposition of NOCIO4 as the predominant reaction i n the latter stages. The observations are best explained by the following two-step mechanism: 2

4

4

2

NOCIO4 + | 0

NO2CIO4 NOCIO4

N0

2

+ C10 (C1 + 0 ) 2

2

2

(1)

2

+

|0

2


(2)

88


Assuming the mechanism described, the mmoles of 0 and N O 2 pro duced per gram of weight loss of sample that would be expected at various ratios of Reactions 1 and 2 can be calculated. These are shown i n Table II. 2

Table II· Calculated Quantities e l 0 and N 0 Produced per Weight Loss of N 0 C I 0 2

2

2

4

Mmoles produced/gram wt. loss O2,


Ratio of Reactions 7:2

Assuming All CI as ClOt

NO*

10:0 10:1 10:2 10:3 10:4 10:6 10:8 10:10 8:10 6:10 4:10 2:10 0:10

31.2 22.5 19.1 17.3 16.2 14.9 14.2 13.8 13.4 12.9 12.5 12.1 11.6

31.2 19.0 14.4 11.8 10.3 8.5 7.5 6.9 6.3 5.8 5.2 4.5 3.9

none 3.5 4.8 5.5 5.8 6.4 6.7 6.9 7.0 7.2 7.4 7.5 7.7

O2,

Assuming ; CI as Cli

In the early stages of the decomposition when Reaction 1 is predomi nant, the oxygen-to-weight loss ratio would be at its highest and diminish as the concentration of NOCIO4 increases and Reaction 2 becomes signifi cant. A reverse trend would be expected for the N0 -to-weight loss ratio. The experimental values for these same ratios for the two experiments previously cited i n Table I follow these general trends. That Reaction 1 predominates in the early stages is supported b y the initially high experi mental values obtained for the ratio of 0 evolution per unit weight loss of sample. A theoretical value of 31.3 would be expected i f only Reaction 1 occurred since oxygen is the only volatile. This would be true only momentarily, since NOCIO4 decomposes rapidly at 65° C . without any induction period by Reaction 2 which would immediately become opera tive. A n y contribution by Reaction 2 would lower the oxygen-to-weight loss ratio since at its highest possible rate of oxygen production (giving N 0 , C l , and 0 as decomposition products), a theoretical value of 11.6 for the ratio of mmoles of oxygen to weight loss would be observed. T h e initial value of 15.5 observed after 73 hours is therefore a "net" figure for Reactions 1 and 2 during this initial interval and represents a substantial contribution from Reaction 1. A quantitative correlation of Reactions 1 and 2 with the oxygen ratio is not possible because of the uncertainty i n the quantity of C 1 0 decom posed to C l and 0 . O n the other hand, the amount of N 0 produced per weight loss can be directly correlated. The initial ratio of 5.6 for N 0 , for example, indicates that during the first 73 hours the ratio of moles of 2

2

2

2

2

2

2

2

2

2


9.

Nitronium Perchhrate

M A R S H A L L A N D LEWIS

89

NO2CIO4 decomposed to NOCIO4 decomposed averaged 10:3, or stated otherwise, approximately 3 0 % of the N O C 1 0 that was produced during this period by Reaction 1 subsequently decomposed. A t the conclusion of run N o . 1, during the interval of 154-174 hours, Reactions 1 and 2 were operating at an approximate 10:9 ratio. Thus, NOCIO4 decomposed at nearly the same rate as it was produced from N0 C10 . The 7.6 value for the N 0 ratio, obtained over the period of 397-492 hours of run No. 2 indicates that the decomposition of NOCIO4 ( Reaction 2) was occurring 10 times faster than the rate of NOCIO4 production b y Reaction 1, and rapidly diminishing the excess produced during the accelerated period of the N 0 C 1 0 decomposition. The 7.6 value for N 0 production and the 6.5 value for the oxygen evolution obtained i n the latter stages of the decomposition of N 0 C 1 0 are almost identical to corresponding values obtained from the decompo sition of NOCIO4 under similar conditions. The respective values for NOCIO4 were 7.6 and 6.9 mmoles per gram of weight loss, indicating the predominance of this reaction i n the latter stages of N 0 C 1 0 decomposi tion. As a further check on this mechanism the decomposition of N 0 C 1 0 was monitored b y Raman spectroscopy, employing the Raman cell as the reactor. The sample was analyzed by Raman periodically throughout the course of the decomposition at 65° C . A plot of the absorptions for N 0 + (1400 c m r ) and N O + (2300 c m r ) is shown i n Figure 4. As would be expected from the proposed mechanism, the rapid drop i n the N 0 + absorption coincides with the appearance and increase i n the N O + absorption. Figure 5 shows the oxygen production for the sample over the 4

2

4


2

2

4

2

2

2

4

2

4

4

2

1

1

2

100r

TIME (HOURS)

Figure 4. Raman analysis of decomposition of at 65°C.

NO ClO t

k


90


corresponding interval. A s noted i n previous experiments the peak rate of oxygen production occurred at approximately 100 hours. It is significant that the Raman data also indicate a break at about 100 hours i n the absorption curves for N 0 + which was decreasing, and N O + , which was increasing. Since a Raman spectrum of solids is predominantly a surface phenomenon, this agreement suggests an initially rapid surface reaction converting the surface N 0 C 1 0 to N O C 1 0 which then controls continued decomposition. 2


2

4

4

TIME (HOURS)

Figure 5. Oxygen evolution of Raman sample A mechanism for the decomposition of N 0 C 1 0 i n the presence of its decomposition products, as i n a sealed tube, would include the dinitrogen tetroxide-catalyzed conversion of N 0 C 1 0 to N O C 1 0 i n addition to Reactions 1 and 2. 2

2

NO2CIO4 + N2O4 N 0 2

—

4

4

NOCIO4 + Ν Ο 2

N 0

6

4

2

4

+

δ

iOt

W h e n a critical concentration of N 0 has been reached from the decom position of nitrosonium perchlorate, this catalytic conversion rapidly becomes the predominating reaction i n the mechanism. Previous work had shown this reaction to be quantitative i n the presence of liquid N 0 ( 9 ) . I n the course of this investigation, gaseous N 0 at ambient temperature i n less than equimolar quantities was also shown to effect the quantitative conversion, presumably by the above mechanism ( 9 ) . Discussion of Thermal Stability. The foregoing discussion does not explain the instability of N 0 C 1 0 , but with this information a reasonable picture of the decomposition process can be presented. The classical concept is that decompositions of solids probably initiate at defect sites on the crystal surface where circumstances offer a lowered 2

2

4

2

2

4

4


9.

MARSHALL AND LEWIS


energy of activation (4). I n the case of N 0 C 1 0 it appears most prob able that the decomposition initiates with NOCIO4 formation. Therefore, ion interactions are involved. It can be stated with confidence that the instability of N 0 C 1 0 is not inherent i n the nitronium ion. More stable nitronium species are known; N 0 B F is reportedly stable at 170° C . ( 7 ) , and ( N 0 ) A l ( C 1 0 ) and N 0 Z n ( C 1 0 ) a are quantitatively prepared at 125° C . ( S ) , a temperature at which N 0 C 1 0 rapidly decomposes. W e are also w e l l aware of stable perchlorate salts. Obviously, then the instability of N 0 C 1 0 is peculiar to the N 0 + and C10 ~ combination. The following mechanism is suggested as occurring at the crystal surface. 2

4

2

2

4

2

2

3

4

e

4

2

4

2

2


4

4

4

/ N 0

2

+

+ CIO4- ,

N O 2 C I O 4 (sublimed)

[NO2CIO4]

NOCIO4 + | 0

2

Nitronium perchlorate, as an ion complex may exist as a transitory inter mediate, which may either revert to ions, sublime, or decompose. A similar mechanism has been proposed for the decomposition of ammonium perchlorate ( 3 ) . Evidence for interaction between the N 0 + and C10 ~ has been observed i n the N 0 C 1 0 crystal lattice. Distortions from linearity i n the N 0 + , and from the tetrahedral angle for the CI—Ο bonds of the 0 0 ~ , as observed i n single crystal x-ray data, have been interpreted b y Truter et al. as being caused by interaction between cation and anion (12). In addition, both Raman and infrared spectra of nitronium perchlorate have shown the splitting of the perchlorate CI—Ο bands which, according to Hathaway ( 5 ) , is characteristic of bidentate coordination for the per chlorate group. T h e appearance of the Raman frequency at 571 c m . for N 0 C 1 0 has also been reported as direct evidence for distortion of the N 0 + i n the crystal lattice. Nebgen concludes (10) that a band for the N 0 + would not appear i n the Raman spectrum at this frequency i f the N 0 were linear. Thus, something less than a truly ionic crystal lattice is present i n N 0 C 1 0 , and decomposition may therefore be facili tated by this interaction. 2

2

4

4

2

4

2

4

2

2

2

+

2

4

Acknowledgments This research was supported b y the Advanced Research Projects Agency under the U.S. A r m y Research Office, Contract No. DA-31-124A R O ( D ) - 1 2 , Durham, N . C .


- 1

92


Literature Cited


(1) Angus, W. R., Leckie, A. H., Proc. Roy. Soc. (London) A150, 615 (1935). (2) Cordes, H . F., J. Phys. Chem. 67, 1693 (1963). (3) Galwey, A. K., Jacobs, P. W. M., Proc. Roy. Soc. (London) A254, 455 (1960). (4) Garner, W. E . , ed., "Chemistry of the Solid State," Chap. 7, Academic Press, New York, 1955. (5) Hathaway, B. M., Underhill, A . E . , J. Chem. Soc. 1961, 3091. (6) Klinkenberg, L. J . , Rec. Trav. Chim. 56, 749 (1937). (7) Kuhn, S. J., and Oláh, G. A., J. Am. Chem. Soc. 83, 4564 (1961). (8) McElroy, A . D., Guibert, C. R., Bellissimo, J. S., Hashman, J . S., Inorg. Chem. to be published. (9) McElroy, A . D., Marshall, M. D., to be published. (10) Nebgen, J . W., McElroy, A . D., Klodowski, H. F . , Inorg. Chem. 4, 1796 (1965). (11) Rosolovskii, V . Ya., Rumyantsev, E . S., Russ. J. Inorg. Chem. 8, 689 (1963). (12) Truter, M . R., Cruikshank, D. W. J., Jeffrey, G. Α . , Acta Cryst. 13, 855 (1960). (13) Vogel, A . I., "Quantitative Inorganic Analysis," 2nd ed., p. 285, Long mans, Green, and Co., London, 1951. RECEIVED June 23, 1965.


Decomposition of Nitronium Perchlorate

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