1260
G. GELERNTER, L. C. BROWNING, S. R. HARRISAND C. M. MASON TABLE V C I H ~ O HM in
cci4
0.0270 .0255 .0240 ,0225 .0210 ,0195 .0180 ,0165 .0150 ,0135 .0120 .0105 .0090 .0075 .0060 .0045 .0030
0.0030 .0045 .0060 .0075 .0090 ,0105 .0120 .0135 .0150 ,0165 .0180 .0195 ,0210 .0225 .0240 .0255 .0270
Mean
8.t.
Obsd. s.t.
Ar
28.51 28.51 28.51 28.51 28.485 28.47 28.44 28.42 28.40 28.38 28.37 28.36 28.34 28.33 28.33 28.33 28.33
28.30 28.25 28.10 28.16 28.075 28.00 27.93 27.88 27.83 27.84 27.85 27.87 27.88 27.91 28.11 28.19 28.25
0.21 .26 .31 .35 .41 .47 .51 .54 * 57 .54 .52 .49 .46 .42 .22 .14 .08
TABLE VI Is, M in CCb
0.02250 .02125 .02000 .01875 .01750 ,01625 .01500 .01375 .01250 .01125 .01000 .00875 ,00750 .00625 .00500 .00375 .00250
CnHsOH, M in CClr
0.00250 .00375 ,00500 .00025 ,00750 ,00875 .01000
,01125 ,01250 ,01375 .0 1500 ,01625 , 0 1750 .01875 .02000 ,02125 ,02250
Mean s.t.
28.51 28.51 28.51 28.51 28.51 28.49 28.47 28.44 28.43 28.41 28.40 28.38 28.37 28.3G5 28.365 28.335 28.33
Au
0.18 .21 .24 .265 .29 ,308 .32 .33 .34 .30 .26 .215 .18 .145 .I1 .08 .02
Vol. 60
We now have the data necessary to calculate the equilibrium constant. Let (1) be the solutions for which the sum of the partial molarities is 0.030 M (Table V) and let (11) be the solutions for which the sum of the partial molarities is 0.025 M (Table VI). By interpolation of the values given in these tables it is possible t o see that different solutions show the same decrease Acr. From this it is possible, as has been shown, to calculate the equilibrium constant. In Table VI1 are given some of the pairs of solutions of (1) and (ll), both of which show the same decrease Au and the corresponding calculated value of the equilibrium constant. TABLE VI1 Ir, M
0.0240000 .0255000 .0233250 ,0270375 ,0232500 .0236250 ,0246375
CnHsOH, M
0.0060OOO .0045000 ,0066750 .0029625 .0067500 .0063750 .0053625
11,M
0.016125 .019OOO ,011250 .021250 .0125OO ,015000 .0175OO
CrHsOH, M
0.008875 .006000 .013750 .003750 ,012500
.01000 .OO7500
K ,inst. 1.445 1.27 1.336 1.29 0.916 0.836 1.58
The average value of the apparent equilibrium constant of the complex C2H60H Iz a t 25A0.1' is hence 1.239. This value is in good agreement with those obtained by other workers using different methods.* The method which we have used can therefore be regarded as applicable, at least in this case, to the determination of the equilibrium constant, although the intervention of other phenomena may limit the application of this method. The authors wish to express their gratitude to Prof. Piccardi, Director of the Institute, for his very valuable advice.
+
(8) J. H. Hildebrand and R. L. Glascock, J . Am. Chem. Soc., 31, 26 (1909); J. Groh, Z. onorg. Chem., 162, 299 (1927); J. Kleinberg and A. W. Davidson, Chem. Revs.,42, 60G (1948).
THE SLOW THERMAL DECOMPOSITION OF CELLULOSE NITRATE* BY GIDEONGELERNTER, LUTHERC. BROWNING, SAMUEL R. HARRISAND CHARLES M. MASON Contribution from the Physical Reseallch Section, United States Bureau of Mines, Bruceton, Pa. Received October 86. 1966
Studies on the slow thermal degradation of cellulose nitrate in a current of inert gas and the decomposition a t low pressures of cellulose nitrate tagged with isotopic N16on the sixth carbon atom are described. The lower thermal stability of the nitrate groups in the second and third positions of the glucoside unit was established by the thermal decomposition studies with isotopir nitrogen and a chemical reaction sequence postulating early cleavage between the second and third carbon atoms formulated on the basis of the total experimental data obtained.
The decomposition of cellulose nitrate must proceed through a sequence of reactive intermediates or possibly several competing sequences. This study was made in an attempt to trace the main sequence of the decompositiol; and consisted of two distinct sets of experimental data: one involves the slow decomposition under low pressure of cellulose nitrate tagged with N15 on the sixth carbon atom of the glucoside unit; the other one (1) This work was supported by the Office of the Chief of Ordnance under Army Project 503-02-001, Ordnnnce Project TB3-0110,
involves samples of high nitrogen cellulose nitrate which were heated in a current of inert gas and a study made of the gaseous products of decomposition. Experimental I. Slow Thermal Decomposition of NI6-Tagged Cellulose Nitrate.-6-NI6-Tagged cellulose nitrate was prepared according t.o Grassie and Purves,* by nitration in two separate atnges, using N'6-enriched nitric acid for the first step. Three samples of tagged cellulose nitrate (No. 1, 2 and 3) (2)
V. R. Grasaie and C. B. Purves, private communication.
SLOW THERMAL DECOMPOSITION OF CELLULOSE NITRATE
Sept., 1956
were prepared. The "6-enrichment of the preparations and residues of decomposition was determined by mms spectrometer analysis of the nitric oxide collected in the nitrometer (Table I).
TABLE I ANALYTICAL DATAON SAMPLESUSED A N D RESIDUES OBTAWED
Sample
Untagged cellulose nitrate High-nitrogen cellulose nitrate Cellulose 6-mono-nitrate I st preparation 2nd preparation 3rd preparation Cellulose nitrate No. 1 No. 2 No. 3 Residue from run 25 run 26 run 27
Nitrogen, %
%
(of total N)
ll.B
0.38
14.0
0.38
.. 6.12 6.88
21.1 21.6 21.69
10.8 10.95 11.79
13.0 10.5 9.39
8.55 9.17
14.0 13.0 14.0
8.44
I n these experiments, small charges of cellulose nitrate were heated in a vacuum system and the gaseous product8 collected with a Toepler pump. The system was arranged so that the decomposition product, could be collect,ed in successive fractions, some corresponding to very short periods of time. The gas samples were analyzed on the mms spectrograph for N'6-enrichment and composition. The procedure was as follows: A weighed sample was placed in a sniall tube and connected to the vacuum system. The tube was enclosed by the thermostat (157-157.7") and the pressure allowed to rise to 1 mm. where it was maintained automatically by a "thermocap" relay,3 dibutyl phthalate manometer and Toepler pump arrangement which pumped the excess gaseous products into the gas collecting systcm. When succewive fractions were required, the system was evacuated between each fraction. After each run, t,he solid residue was weighed and analyzed for 1,otal and isotopic nitrogen. No attempt was made to freeze out NO, prior to contact with the mercury in the Toepler pump. Although there was some reaction between the mercury and NO,, it was felt that the main interest lay in the relative amount of N16 in the gaiieous products and that this would be affected only slightly, if at all. To test and standardize the proccdure, trial runs were made on untagged cellulose nitrate synthesized by thc same method as the "$-tagged material, and on samples of high nitrogen cellulose nitrate similar to the material used in the other experiments. 11. Slow Thermal Decomposition of Cellulose Nitrate in a Current of Inert Gas.-The apparatus for this study consisted of a rigid glass and metal train, mounted on a movable frame which could be lowered to immerse the reaction chamber and a heat-exchange coil into an oil thermostat. The reaction chamber was a straight cylindrical glass tube connected by ground-glass joints to the heat-exchnnge coil on the one side and to the lead-off tube and analytical train on the other. Samples of highly nitrated cellulose nitrate (14.0% h') were dried for several hours a t 70" arid weighed into the reaction tube where they were supported by a glass-wool plug. The system wns swept out thoroughly with argon which was first passcd through the hent-exchange coil. I t was then lowered into the thermostat and heat,ed for the desircd length of time. Volatile products of dccomposition were swept into the analytical absorption train and determined suhsequeiitly. The degraded solid residue was weighed to determine t o t d loss of wcight. Fractions of the solid residue were used for various analytical determinations (nitrogerr, carbonyl,, carboxyl, infrared absorptioii spectra). (3) Made by Niagara Electron Laboratories, Andover, N c w York.
1261
Carbonyl was determined by a modification of the Bryant and Smith4 method which employed small samples and corrected for the acidity originating from possible hydrolysis of unchanged residual produch by means of blank titrations made with and without reagent on a n undegraded cellulose nitrate sample. Titrations were performed with a pH meter to a p H 5.00. Carboxyl determinations were performed by the method of Unruh, McGee, Fowler and ken yo^.^ Infrared absorption spectra were taken on dispersions of the residual material in Nujol. For this purpose, a small amount of the sample (about 0.01 9.) was dispersed on a rock salt wfndow with a few drop of Nujol. An analytical train adapted from Milligane was used to determine mixtures of NOz,.NO, COZ,CO and Ha. Amounts of HzO and volatile organic products such as CH@, HCOOH, etc., were not determined. In the presence of organic materials, the possibility of reaction within the train itself did arise. This train consisted of a series of absorption flasks and absorption tubes. The f h t flask contained concentrated HzS04, the second concentrated HzSOI-HNOI (50: 1). This was followed by a tube containing ascarite, a tube filled with CuO kept at 350°, a tube with dehydrite, and finally another ascarite tube. The first HeSOl solution absorbed NO, and any NO up to equimolar with NO*. The H2SOrHN03 solution absorbed any excess NO. Cot was retained in the ascarite tube, whereas I12 and CO were oxidized by CuO to HzO and COz and absorbed in the two final tubes. The tubes were weighed to determine the amount absorbed directly. Aliquots were pipetted out from the absorption flasks and titrated with excess KMn04 and thereafter FeSOl solution. A second aliquot of the HlSOl solution wm treated in a nitrometer. NO2 and NO were computed from the two analyses on this absorbent. The nitrometer consisted of a micro-size nitrometer tube sealed to a straight 10-cc. pipet and mounted vertically on a wooden board. The board was clamped to a horizontal steel rod in such a manner that it oscillated freely by action of a steel lever arm from a mechanical shaker (160 oscillations per minute). Leveling bulbs, connected to the riitrometer by thick-walled flexible rubber tubing, rested on separate adjustable Btands. With this device, samples of very small size and of a wide range of nitrogen content could be analyzed.
Results I. Slow Thermal Decomposition of N15-Tagged Cellulose Nitrate.-Seven decomposition runs were made on the first two preparations of cellulose nitrate tagged with NL5. The results of these runs are given in Table I1 where runs 25, 26 and 27 are duplicate experiments on the decomposition of preparation no. 1, all a t 157.0 to 157.7'. Run 28 is a duplicate of 25, 26 and 27, except that preparation no. 2 was used. Several successive fractions are listed for each run. Preparation no. 3 was used in one run to verify the results obtained with the earlier samples. Analysis was performed only to determine the per cent. NI5. The three gaseous fractions collected with the preparation no. 3 corresponded to 1.7, 1.7 and 4.2% loss of weight, respectively. Their NI5content was 6.60, 6.67 and 6.95y0 NI5 of the total nitrogen in each fraction, respectively. The conditions were identical to those described in connection with run 3 1. The test procedure was modified i n run 29 by mixing ("diluting") the charge with cellulose, in runs 30 and 31 by the use of a lower temperature of decomposition, namely, 153.1 to 152.7",and in run 31 also by continuous removal of gaseous de(4) w. h f . D. Bryant and D. hI. Smith, J . Am. Chem. Soc.. 67, 57 (1935). ( 5 ) C. C. Unruli. P. A . hlcGee, W. F. Fowlcr and W. L. Kenyon. ibid.. 69, 849 (1447). (6) L. IC. BIiLhgan, THISJ O U R N A L .28, , 544 (1924).
G. GELERNTER, L. C. BROWNING, S. R, HARRIS AND C. M. MASON
1262
Vol. 60
TABLE TI COMPOSITION OF GASEOUS PRODUCTS OF DECOMPOSITION OF TAGGED CELLULOSE NITRATE %
Run
Prep. 1 25
26
27
Prep. 2 28
29 30
31
Fraction Sample wt., g.
1 2 3 1 2 3 1 2 3 4 5 1 2 3 4 1 2 1 2 3 1 2 3
0.0806
0.1047
0.1007
0,1001
0.0685 0.0699
0.0748
Mole % in product NO co
decomposition
NI6, %
NO2
NzO
cog
4.6 5.3 6.6 2.7 4.7 5.7 0.8 .7 3.3 5.7 6.3
9.6 10.8 12.2 9.8 10.6 11.3 9.7 9.7 10.6 11.1 12.6
1.5 0.1 .2 0.9
0.6 0.4 2.8 4.0 2.5
1.5 0.3 .2 .2 .2
13.5 12.2 17.6 13.0 10.0 37.1 18.1 12.4 10.7 13.7 11.7
64.2 51.0 33.4 59.1 54.4 24.8 56.5 59.3 53.4 46.8 29.9
0.67 1.0 3.0 4.0 1.5 4.0 3.1 3.75 3.75 1.34 2.68 2.68
6.93 7.38 7.77 8.19 6.93 7.78 7.28 7.85 8.30 7.09 7.35 7.67
0.6 .3 .2 .2 0.2 0.2 1.3 1.5 0.9 0.3 .2 .4
14.9 12.5 10.0 10.8 10.1 11.1 14.0 10.7 10.4 10.9 10.4 10.7
58.1 55.8 51.3 50.3 50.0 51.5 57.6 54.1 51.3 31.3 35.9 40.9
.1
..
composition products, that is, continuous operation of the Toepler pump. In each run, the percentage of NI5 of the total nitrogen in the gaseous products was well below the average percentage for the preparation used and there was a perceptible increase in the percentage of " 5 in the products from successive fractions. Results of these tests indicated a remarkable constancy of the initial NI5-content of the gaseous products. Mixing with cellulose proved quite ineffective. The rather small, though apparently in run 30 real, decrease of the total per cent. (lower temperature of decomposition) follows from the difference in stability itself. For, if the energy of activation of the G-group is higher, the decrease of its independent rate of decomposition should be more marked a t decreased temperatures. I n run 31, the lower values of N15, fraction by fraction, indicate a strong effect of the decomposition products on the further course of reaction, but the rather constant initid NI5 value makes it appear unlikely that initial values are much affected by induced decomposition. Evidence from these runs does not however go far enough to clarify these detailed aspects. 11. Slow Thermal Decomposition of Cellulose Nitrate in a Current of Inert Gas.-The series of experiments on decomposition in a current of inert gas, run on samples of 14y03'-cellulose nitrate, produced both volatile products and solid residues. NOz, NO, COS and CO were determined for each run. The values obtained are given i n Table 111. A number of tests were performed on the solid residues of decomposition. Nitrogen determina-
..
.. 0.4 .7 .I 9. I
0.6 6.6
2.1
Ha0
HCHO
3.7 1.8 2.4 3.1 1.9
9.1 14.8 19.6 20.3 29.6
2.5 14.9 18.2 9.4 13.2 38.1 8.0 11.3 13.3 16.8 17.3
6.8 1.5 2.1 2.1 2.2
8.3 11.3 13.6 17.4 7.9 11.0 9.9 12.6 14.3 7.0 8.7 12.7
15.1 19.7 21.9 18.7 23.5 24.6 14.8 18.9 21.0 44.9 43.3 33.4
3.0 0.4 2.0 2.0 1.7 1.6 2.4 2.2 2.1 2.0 1.5 1.9
14.0 19.6 25.4 10.5 17.9
..
..
tions on the residues generally agreed with the amount of NO and NOz found in the volatile products. Some carbonyl values obtained are listed in Table IV. It also seemed interesting to compare moles of carbonyl found with moles of NO2 obtained previously for the same runs. The values for carboxyl were negligibly low. The absorption spectra obtained were in general much like cellulose nitrate spectra with the nitrate bands reduced in intensity and with two new bands, one a t 2.9 p due to OH, and one a t 5.75 p which, on the basis of the chemical tests described, must be due to carbonyl, although carboxyl might show up in this same region. In a special series, three charges of cellulose nitrate, each weighing about 0.8 g., were heated at 152' in a stream of argon for 4, 8 and 15 hours, respectively. The corresponding losses of weight were 4.59, 18.15 and 39.3%. Infrared spectra were taken on the residues. Portions of these were also subjected to the carbonyl and carboxyl tests discussed above. Carbonyl was found to be 0.45 mmole/gram of degraded material for the first charge, and in excess of 1.5 mmoles for the second and third. X o carboxyl was present. The OH band a t 2.9 1.1 appeared clearly even in the first sample, whereas the band at 5.75 1.1 developed from a very slight shoulder in the first to a pronounced peak in the third, indicating the gradual accumulation of carbonyl in the residue. Discussion Introduction of isotopic N15 into the nitrate group on the sixth carbon atom of cellulose nitrate seemed the most logical way to determine the relattive initial stability of the nitrate groups on carbons two, three and six.
SLOWTHERMAL DECOMPOSITION OF CELLULOSE NITRATE
Sept., 1956
1263
TABLE I11 ANALYTICAL DATAOBTAINED IN THE SLOW THERMAL DECOMPOSITION OF CELLULOSE NITRATE (14.0% N)" Run
Size, g.
Temp., ' C .
% loss of wt., P
% loss of total N, X
% of
X/P
NO/NO*
COz
volatlles
% of
co ..
unrecovered volatiles
146.4 3.45 6.68 1.94 0.83 .. .. 146.4 6.37 10.38 1.63 1.21 .. .. .. 149 5.54 8.78 1.58 1.06 .. .. .. 6 152.4 5.33 8.80 1.65 1.33 .. .. .. 7 152.4 6.78 9.54 1.41 1.28 14.3 15.6 23.3 8 152.4 8.14 12.40 1.52 1.43 12.4 16.4 21.5 9 152.4 7.9 12.10 1.54 1.32 11.4 12.7 23.3 10 152.4 7.02 8.79 I . 25 1.33 12.9 14.5 31.6 11 152.4 .. 9.56 1.21 .. .. .. 12 152.4 5.48 8.10 1.48 1.18 .. .. .. 13 152.4 10.37 14.62 1.41 1.57 12.1 16.9 25.8 14 152.4 5.48 9.27 1.69 1.16 12.8 13.3 14.6 15 152.4 7.35 11 .o 1.49 1.22 11.8 .. 24.0 16 152.4 4.36 9.32 2.14 0.45 .. .. .. 17 152.4 4.20 9.32 2.22 0. 62 8.5 2.8 1.9 18 152.4 5.84 11.46 1.96 1.18 12.7 .. 5.2 150.0 G.48 10.7 1.65 1.25 14.3 19.2 12.3 19 20-a .:io 153.ci 1.84 3.79 2.06 0.56 10.9 4.7 3.1 20-b . '70 153.G 2 . 71 3.89 1.43 1.25 10. I 13.2 28.0 20-c .70 153.G 2.18 4.3 2.02 1.89 29.6 44.5 .. 20-d . 'io 153.ci 3.96 4.73 1.20 2.63 14.1 19.5 32.6 a All runs approximated four hours except no. 4 which was 10 hours and 20-a, b, c and d which were samples withdrawn a t 1.5-hour intervals.
3 4 5
0.67 1.03 1.04 1.03 1.04 1.08 0.30 1,05 0.52 .48 . 81.6 . '71 .49 ,21 .%5 .36 . 52
with caution, Many of the primary decomposition products undoubtedly are highly reactive and capable of further reaction a t any subsequent stage. CELLULOSE This explains the virtual absence of NO2 in the Carbon1 I C arbonyl/KOz Run (mmole/l 6 ) (mole ratio) gaseous products as well as the low concentration 18 0 477 0 91 of formaldehyde. Similarly, values for COZ, CO, 15 5G2 1 14 HzOarid NzOin Table I1 do not necessarily indicate 14 50 I 10 the quantities of these compounds formed directly 12 407 1 10 by decomposition. The observed lower stability of the 2,3-nitrate Unfortunately, the number of nitrate groups introduced per glucoside unit in two-stage nitra- groups and decreasing stability of the 6-nitrate tion by the method of Grassie arid Purves2 is group in the course of decomposition should be limited to about 2. This fact has been established still more marked with fully nitrated cellulose by Lemieux who considered it as due to "steric nitrate. hindrance".' The unriitrated group (mainly 2 or 3) The wide differences in composition of the volaapparently remains as hydroxyl. The N15-tagged tile products obtained in the slow thermal detest compound thus differs importantly from fully composition of cellulose nitrate in a current of nitrated cellulose nitrate. However, as both inert gas indicates an initial reaction followed in hydroxyl and nitrate groups are electronegative, varying extent by successive secondary reactions. though admittedly of different magnitudes, it is One means to study the extent of secondary reacbelieved that valid conclusions regarding the tion, or more particularly its onset, is to examine mechanism of decomposition may be drawn from the ratio of the per cent. loss of total nitrogen, X , the study of this material. As N15 occupies the t o the per cent. loss of total weight, P, since, if the sixth position in the glucoside unit, the fact that in initial reaction consisted-as has frequently been each run the percentage of XI5of the total nitrogen proposed-of the loss of NO, only, this ratio mould in the gaseous products, as shown in Table 11, reach a maximum value of 2.15. It is recognized was well below the average percenhage for the that this applies only during the initial time lag preparation used, and that there was it perceptible between reaction a t the 2,3-positions and of the 6increase in the percentage of in the products group. The ratios obtained are shown as X / P from succea,ive fractions, constitute clear-cut in Table 111. In some of the runs where the duraevidence for 1he lower thermal stability of the 2,3- tion of reaction was short or with very small iiitrate groups and for the decrease of the stability samples, the ratio approaches the value of 2.15. of the 6-nitrate group in the course of decompqsi- One may conclude that the lower value of the ratio tion. in other runs is attributed to secondary reactions. Whereas a high degree of significanve cannot he The ratio of KO to NO2 should be zero if NOz denied the N15 ratios ohtained, data on chemical is the primary product and no secondary reaction composition of the gas fractions have i,o be viewed has occurred. It is seen that the lowest values in Table I11 are given Iiy those runs in which, accord(7) R. 1'. I,emieux, Can J . Research 26B,485 (1947) MOLE^
O F CAlZBOhYL
TABLE IV DETERMINED I N DEIIRADED
NITRO-
€264
G. GELERNTER, L. C. BROWNING, S. R. HARRISAND C. M. MASON
ing to the ratio X / P , little secondary reaction has occurred. The presence of COz and CO in the reaction products in themselves indicate secondary reaction beyond the initial splitting off of NOz. Again it is to be noted that the per cent. of unrecovered volatiles likewise seems to increase with the degree of secondary reaction. The data in Table I11 may also be examined for the effect of charge size, temperature and time of treatment. Inasmuch as volatile products must pass through layers of solid, an increase in the size of charge should result in increased secondary reaction if the latter is a heterogeneous reaction between initial volatile products and solid residue. Comparison of runs no. 16 and 17 in Table I11 with other runs indicates a marked difference due to size, in both total amount of reaction, and in degree of secondary reaction. This, however, appears limited primarily to very small sizes. The effect of temperature on the degree of secondary reaction is not sufficiently clear within the narrow range used. The effect of time is shown by run No. 20 which consisted of a single charge heated in four successive 1.5-hour periods. The changing composition of the products may be taken to indicate a whole sequence of decomposition steps. With very small charges or a t an early stage, reaction appears to consist essentially in splitting off of NO2. Increase in either size of charge or duration of reaction leads to increased secondary reaction which is evidence for the strong effect of primary products on the further course of reaction. The two series of experiments combine to show that decomposition of cellulose nitrate essentially begins by splitting off of nitrogen dioxide in the 2and 3-positions followed by reaction of the NO2 split off with the residue and reaction products with ultimate disruption of the molecule. A general mechanism for the decomposition of the vicinal dinitrates may be written R-CHONOs
R-CHO’
+ NO2
--f
R~---hHONOr R’-LHONO, R-CHO‘ + RCHO R’--C’HONO*
+
R‘-(!!HONOI R’-C’HON02
+R’CHO
+ NO2
Kuhn and DeAngelis,* for example, found that this type of mechanism predominated in the decomposition of the vicinal dinitrites in the gaseous state. If it is considered that the limited mobility and low collision frequency in cellulose nitrate is comparable to the gaseous state, one may conclude from the experimental evidence presented showing (8) L. P. Kuhn and L. DeAngelis, J . A m . Chem. SOC., 76,328 (1954).
VOl. 60
the initial splitting off of NO2 from the second and third position on the cellulose nitrate, that the decomposition of the latter follows a mechanism similar to that proposed for the vicinal dinitrates. I n general, this agrees with the mechanism discussed by W ~ l f r o m . ~With this as the first stage in the decomposition, the second stage would be a heterogenous solid-gas interaction of the newly formed nitrogen dioxide with equally new aldehyde groups. A third stage follows quickly with the decomposition of the 6-nitrate group which may have been initially proceeding a t a slow rate but becomes accelerated by the likely exothermicity of stage 2. On the basis of experience with simpler nitrate esters,I0 the decomposition of the 6-nitrate group should involve splitting off of NOz, followed by splitting off of formaldehyde, followed by further rearrangement of the residue with fission of the glucoside structure. The presence of hydroxyl which was indicated in the infrared spectroscopic analysis of solid residues may point to some reaction beyond the stages considered or otherwise be evidence for the partial validity of an alternate mechanism, namely, abstraction of hydrogen by the intermediate alkoxy radical. Carbonyl, likewise observed, is used up in secondary reaction and can thus accumulate only slowly in the residue. The following sequence of chemical reactions summarizes the main stages deduced which seem to represent a t least the initiating sequence in an over-all process of decomposition which rapidly assumes further complexity: (1) decomposition of the 2,3-nitrate groups by the general mechanism of vicinal dinitrates; (2) reaction of NO2 with the newly formed aldehyde groups at positions 2 and 3; (3) accelerated decomposition of the 6-nitrate groups to give NOz, formaldehyde and a further rearrangement of the residue involving rupture of the cellulose chain. Acknowledgments.-The authors are especially indebted to R. A. Friedel, A. G. Sharkey and the staff of the Mass Spectrometer Section for their assistance and cooperation. The suggestion to use N15 in the 6-nitrate group as a means of studying the decomposition mechanism originated with Lester P. Kuhn of the Ballistic Research Laboratories, Aberdeen Proving Ground, Maryland. Ralph Klein and Morris Mentser participated in early discussions and the preliminary experimental work. (9) M. L. Wolfrom, J. H. Frazer, L. P. Kuhn, E. E. Dickey, 8. M. O b . , D. 0. Hoffman, R . S. Bower, A. Chaney. Eloise Carpenter and P. McWain, ibid.. 71, 6573 (1955). (IO) G . K. Adams and C. E. H. Bawn, Tram. Faraday Soc.. 46, 494 (1949); L. Phillips, Nature, 160, 753 (1947): 165, 564 (1950); J. B. Levy,J . Am. Chem. SOC.,76, 3254, 3790 (1954); Peter Gray, Tram. Faraday Soc., 61, 1370 (1955).
