Dec. 20, 1955
CONTROLLED THERMAL DECOMPOSITION O F CELLULOSE NITRATE
clinical-size fractions still give a higher ratio of 1,6’- to non-l,B’-linkages, with the possible exception of dextran B-512. Several possible explanations could be advanced to account for the usual increase in ratio. For example, molecular heterogeneity may have existed in the original dextran,l b b the degradation changing the properties sufficiently to permit a fractionation on the basis of structure which was not accomplished before hydrolysis. In the absence of fractionation on a structural basis, hydrolysis of non-l,6‘-linkages will in most cases cause an increase in apparent ratio, regardless of whether the hydrolysis rate constant of non-1,6’linkages or the relative number broken were higher or lower than for 1,6’-linkages. Thus, there is a multiplicity of factors which may influence the apparent ratio for the isolated fraction. The absence of a significant change in the ratio for dextran B-512lsa undoubtedly reflects the relatively small proportion of non-l,6’-linkages present and the resulting fact that most of the degradation of the polymer would be as a result of hydrolysis of 1,6’-linkages, for which no change in formic acid production would be obtained on the corrected basis.
[JOINT
6573
The calculation of maximum and minimum DPN from the periodate oxidation data on the original dextran and the isolated fraction, using equations 1 and 3, is of interest as further evidence of whether the fraction is a result of a relatively homogeneoustype cleavage. The clinical-size fraction from dextran B-512 has a DPN between the calculated extremes and, therefore, could be a product of an essentially homogeneous cleavage. The observed values for the other three products, Table I, are significantly higher than the calculated maximum DPN. This suggests a departure from homogeneous-type cleavage or a fractionation of the products on the basis of structure. Evidence from other studies12 indicates that a t least one contribution to the results is the fact that apparently removal of external branches by cleavage of non1,6’-linkages leads to the formation of D-glucose and some oligosaccharides, which then are discarded in the isolation of the clinical-size fraction. While the same process apparently occurs with dextran B-512, i t represents a minor part of the total bond cleavage6 and has little influence on the periodate oxidation properties of the product. PEORIA,ILLINOIS
CONTRIBUTION FROM THE DEPARTMENT O F CHEMISTRY O F THEOHIO STATE USIVERSITY AND THE BALLISTIC RESEARCH OF ABERDEEN P R O V I N G GROUND] LABORATORIES
The Controlled Thermal Decomposition of Cellulose Nitrate.
P
BY 11.L WOLFROM, J. H. FRAZER,L. P. KUHN,E. E. DICKEY,S. M. OLIN,D. 0. HOFFMAN, R. S. BOWER, A. CHANEY, ELOISECARPENTER AND P. MC\VAIN RECEIVED JULY 15, 1958 The thermal decomposition of propellant cellulose nitrate (12.6% N), under ignition conditions, has been investigated a t 2-3 mm. A solid residue is formed which has been characterized analytically and which on denitration and hydrolysis yielded cellobiose, D-glucose, D-glUCOniC acid, D-erythrose and glyoxal. These results establish the material as a fragmented type of oxycellulose nitrate of an extremely low degree of polymerization. The results are interpreted on the basis of homolytic bond scission.
Since the initial preparation of cellulose nitrate by Pelouze3 in 1838 and the recognition of its military importance by Schonbein4in the following decade, there has been an increasing amount of research on the decomposition of this substance. The action of chemical agents such as acids, bases and reducing substances has been investigated under a variety of conditions; a number of simple and a few complex reaction products have been identified.5 A (1) This work was carried o u t under contract (OEMsc-1152 with t h e Office of Emergency Management, Office of Scientific Research and Development; W-33-019-ord-3978 and -6279, and DA-33-019ord-11, -163, -727 and -1466 with t h e Ordnance Department, United States Army) b y T h e Ohio S t a t e University Research Foundation (Projects 170, 212, 313, 402, 458, 496 and 589). Preliminary investigations were performed by D . 0. Hoffman and Prof. R. C . Elderfield in t h e Department of Chemistry of Columbia University, New York, N. Y. (2) hI. L. Wolfrom, Abslracfs P a p e v s A m . Chem. Soc., 127, 9 E (1955); preliminary paper. (3) T. J. Peiouze, Compl. r e n d . , 7 , 713 (1838). (4) C. F. Schonbein, Phil. Mag., 31, 7 (18471. ( 5 ) J. Barsha, in “Cellulose and Cellulose Derivatives,” “High Polymers,” Vol. V. 2nd edition, E . O t t , H. h l . Spurlin and Mildred W. Grafflin, E d . , Interscience Publishers, Inc., New York, N. Y., 1954, p. 751, gives an excellent review on t h e action of chemical agents on cellulose nitrate and cites many references t o the original literature.
list6 of the substances produced by the chemical agents follows (to provide comparison with those afforded by thermal decomposition) : inorganic nitrites and nitrates; nitrogen7; cyanides; oxides of nitrogen (NzO,’ NO7 and NOZ)and carbon (C07s8and COz); ammonias; oxalic, malic, formic,s glycolic, butyric, malonic, tartaric,s trihydroxyglutaric, dihydroxybutyric, hydroxypyruvic,s isosaccharinic and tartronic acids ; glucose; modified and degraded cellulosesg and their nitrates. The thermal decomposition of cellulose nitrate a t 108’ has been found to produce carbon dioxide and monoxide, nitric and nitrous oxides, methane and nitrogen.’O Hydrogen cyanide was found by ( 6 ) References are cited only for t h e products not noted by Barsha in reference 6. (7) A. Angeli, A t f i reale accad. Lincei, 28, I, 20 (1919), and Z . gcs. Schicss-u. Sprengslofw., 11, 113 (1922); S. N. Danilov and L. I. Mirlas, J . Gen. Chem. ( U . S. S. R.), 4, 817 (1934); G . G . Giannini, Gozz. chim. ital., 54, 79 (1924). ( 8 ) E . Knecht and B. R . Bostock, J . S o c . Chem. I n d . , 39, 163T (1920). (9) B. Rassow and E. Ddrr, J . p r a k l . Che7n., 108, 113 (1YZ-i): T. Tomonari, 2 . Eleklrochem., 40, 207 (1934); A. Nadai, Z . p h y s i k . Chem.. 136, 289 (1928). (10) R . Vandoni, C o m p l . r e n d . , 201, 674 (1933).
6574
JVOLFROM, FRAZER, KUHN,DICKEY,OLIN, HOFFMAN, BOWER,CHANEY AND MCWAIN
Vol. 77
Xuraourll when cellulose nitrate was ignited in pressure sufficiently low to remove the gaseous dea confined space. When cellulose nitrate was composition products rapidly from the high temheated until deflagration occurred, Trapani12 ob- perature zone. There was then left a solid residue. tained products which gave a color test (Rimini) The preparation and characterization of this mafor formaldehyde. The isolation of waterls and terial is the subject of the investigation herein rehydrocarbon^^^ from heated cellulose nitrate has ported. been reported. Desmaroux and associates15describe The apparatus employed in preparing the mathe isolation of a fibrous residue containing nitro- terial is shown in Fig. l. It consisted essentially of gen (ca. 50% yield) from the prolonged heating of a combustion chamber (C) attached to a large surge cellulose nitrate (11.9, 12.8 and 14.0% nitrogen; tank (I) and a high capacity vacuum pump. The nitrated ramie fiber) a t 108' under reduced pres- propellant type cellulose nitrate, in the form of thin sure which removed the gases produced from the strips, was ignited in the combustion chamber with sample. No further investigation of this residue a hot wire after the pressure in the apparatus had was reported. Rideal and Robertson16 investi- been brought to 2-3 mm. The cellulose nitrate Fated the thermal decomDosition of cellulose nitrate then underwent a self-sustained combustion, which, i t very low pressures a i d quantitatively Ignition 1, solid CH,OH-measured the composition of the gases Cellulose nitrate (12.6% N) residue 145a t 2-3 mm. evolved; they found hydrogen and formaldehyde to be present. HC1, Zn AcsO JPd-HZ Information concerning the decomposi$(NH,)HS tion of cellulose nitrate under conditions MeOH I11 IV VI f-- v similar to those prevailing when i t is used HCl as a propellant would be most valuable. Fig. 2.-Product relationships. However, under normal and higher pressures, all of the products are gaseous and Drovide however, was incomplete and a solid residue relittle information as to the -chemical na'ture of mained in high yield {ca. 50%). This solid formed the intermediate materials. I n the present work, as a cloud of fine particles that had been ejected propellant cellulose nitrate has been ignited a t a from the hot reaction sphere and had settled on the walls of the combustion chamber, from which they were removed. The material (product I, Fig. 2) was then subjected to a crude fractionation from methanol-water and the least soluble fraction (product 11. Fig. 2) representing the least altered product, was employed for characterization. Product I1 was an amorphous solid of a light yellow color that burned rapidly in air and left a carbonaceous residue. It was unstable toward moist air but could be stored in a dry atmosphere. Fig. 1.-Apparatus for the thermal decomposition of cellu- I t s heat of combustion and heat of explosion were lose nitrate: A, feeder tube, glass, 15 mm. 0.d. with a 19/38 measured (Table I) and were found to have changed ground glass stopper; B, igniter, a double loop of No. 24 from those of the initial material to the degree preChrome1 wire soldered t o leads which were led through the dictable from their difference in nitrogen content. rubber stopper and connected to a variable potential con- A number average molecular weight, obtained by trol; C, cold mater-jacketed glass decomposition chamber, an ebullioscopic method, showed an average degree 25 cm. long inside, 3 cm. diam. inside a t one end and tapered of polymerization of ca. G . Since the material was to a 28/15 glass ball joint a t the exit end; D and E, spiral undoubtedly highly heterogeneous, this number average will be grossly low. glass traps of 12 mm. 0.d. tubing connected by 28/15
-
.i
spherical joints and inserted into Dewar-held baths of solid carbon dioxide and acetone; F, vacuum release valve; G, stopcock to differential manometer; H, 15 mm. bore glass stopcock; I, surge tank, a steel pipe (0.3 X 1.3 in.) with gasketetl fittings and flanges; J, take-off t o a fine adjusting Meeker burner valve serving as a bleeder in adjusting pressure; K, connection t o a high capacity Cenco llegavac pump protected by a glass trap cooled by a Dewarheld bath of solid carbon dioxide and acetone. The system \%-ascapable of maintaining a vacuum set a t 2 mm. (11) H. Aluraour, Bull. sac. chim., [ 5 ] 3, 265 (1936). (12) E. Trapani, A l l i reale accod. Lincei, 26, I, 332 (1917). (13) A. V. Saposhnikov, J . Russ.P h y s . Chem. Sac., 38,1186 (1906); C. A , , 1 , 1323 (1907). (14) A. Koehler and h i . hiarqueyrol, M e i i i . poudvcs, 18, 101 (1921); C. A . , 18, 1866 (1922). (13) J. Desmaroux, R. Vandoni, L. Bri.;qaird and 'I'bereic Petipns, 4 1 r m . fioudrrs, 29, 134 (1939).
(IG) E . K. Rideal and A . J. B. Robertson, "Third Symposium on Combuition a n d Flame and Explosion Phenomena," Williams and lyilkins C o . , Baltimore, 52d., 1949, p. 536.
TABLE I HEATS OF COMSUSTIOSAND EXPLOSION OF THE SOLID CELLULOSE SITRATE (12.67, 3)DECOMPOSITION PRODUCT Heat of combus b I
SubstanceQ
cal / 6
H e a t of e x p l , e cal /g
Cellulose 2393 Y TOd X t r a t e (12 6% 3-) Product I 2553-2583 542 638 2700-2732 683-685 Product I1 a See Experimental part for preparation. Determined under 10 atm. of oxygen. c Determined under 50 atrn. of nitrogen. Calculated.
Product I1 was cliaracterized analytically (Table 11)by elemental analysis and by assays for various functional groups. For the latter, the methods developed for oxycclluloses were adapted to the material a t hand, which adaptation consisted p r i m pally in a correction for the inherent reagent instability of the products by extrapolation of rate curves
Dec. 20, 1955
CONTROLLED THERMAL DECOMPOSITION OF CELLULOSE NITRATE
to zero time. Thus there were found present significant amounts of carbonyl, carboxyl (mainly the uronic or keto acid type) and hydroxyl (in small part as a 1,2-glycol). An interesting point was that a definitive, low, non-ester methoxyl content was found, probably indicative of a partial glycosidation in the methanol made acid by the inherent acidity of the crude product I. TABLE I1 ANALYTICAL DATAFOR THE PRODUCTS OBTAINEDBY THE THERMAL DECOMPOSITION OF CELLULOSE NITRATEUNDER Low PRESSURE’ Constituent, % in
Constituent b
Prod. IIC (purif. decompn. solid)
Prod. IIIC (prod. 11 denitrated by H r P d )
C 28.5-29.3 43.2 H 3.4-3.7 6.4 Ashd Trace 5.2 N (Dumas) 9.3-9.9 1.9 N (duPont nitrometer) 9.35 0.0 N (Kjeldahl) .. 1.5 8.0 22.5 OHe (total) 1.1 .. 1,2-Glyc01,~as OH OR (glycosidic) 1 . 2 (OMe) 0 . 7 (OEt) .. Carboxyl as COS 3.70 3.2h 1.8h Free carbonyl (aldehyde 2.4i .. and ketone), as CO 3.7j 4.5’
Prod. IVC (prod. I1 denitrated by NH4HS)
.. .. .. .. 0.0
..
23.6
..
..
6575
strong band for C-nitro a t 7.25 p l 9 does not appear. Although neither the Dumas nor the nitrometerz0 assays distinguish between nitrate and nitrite nitrogen, the absence of significant amounts of nitrite ester groups is established since nitrite esters have strong bands a t 6.1 and 12.7 p,20anot present in Fig. 3. Product I1 exhibited a strong nitrate test (diphenylamine in sulfuric acid) and a faint nitrite test (with N,N-dimethylaniline, enhanced by the previous addition of alkali6). The latter is probably ascribable to a nitrate ester group in the a-position to a carbonyl or carboxyl g r o ~ p . ~ ~ b The nitrogen content of product I1 had decreased to ca. 9.5% from the original content of 12.6%. I
2
1
4
6
I
1
8
10
I
12
14
A, P.
Fig. 3.--Infrared spectrum of cellulose nitrate (12.6% nitrogen), -----,and product I1 (Fig. 2), -. The spectra were determined using the method and instrument described in ref. 17.
The purified ignition residue (product 11) was denitrated with palladium and hydrogen21to yield product 111; by ammonium hydrogen sulfide to give IV; and, with considerable degradation, by 2.7i reductive acetylation. 2 2 Analytical data obtained 2.9j on products I11 and IV are shown in Table 11. S 5.0k Denitration produces the expected large increase 5.8‘ in hydroxyl value. Product I1 is a sensitive mate1.7” 12.6% N cellulose nitrate; pressure 2-3 mm. See rial and the denitration procedures effected unSee Experi- avoidable alterations in some of the functions Experimental portion for analytical details. Combustion residue; mental portion for preparation. present. Thus, in product IV, a considerable conelementary data calculated to the ash-free basis. e B y tent of sulfur was found, perhaps, in part, as thioacetylation. f By lead tetraacetate oxidation; W. S. Mc- carbonyl; likewise some ammonia nitrogen was Clenahan with R. C. Hockett, THIS JOURNAL, 60, 2061 present. The carboxyl content decreased markedly (1938); R. C. Hockett and W. S. McClenahan, ibid., 61, 1667 (1939). 0 By decarboxylation. By calcium either by reduction of lactones or by decarboxylaBy the Munson-Walker method, acetate exchange. tion. The isolation procedures may also have calibrated against D-glucose. f By oximation. k By iodine concentrated the less altered material so that the P. Schubert, J . BioZ. Chem., 114, 346 (1936). titration; M . denitrated product fraction may not correspond 2 By oxidation to sulfate; W. F. Hoffman and R. A. Gortexactly to the initial reactant fraction. 45, 1033 (1923). %I. M . Kolthoff ner, THIS JOURNAL, and E . B. Sandell, “Textbook of Quantitative Inorganic It was considered desirable to confirm and exAnalysis,” The Macmillan Co., New York, N. Y., 1936, tend the analytical data on these products by actual p. 534. degradative isolation work. This is a difficult The analytical data for product I1 were con- problem for all oxycelluloses and especially so for firmed qualitatively by its infrared absorption one that contains nitrate groups. Product VI, spectrum (Fig. 3 ) . A comparison of this spectrum obtained from the reductive acetylation of I1 with with that of cellulose nitrate” (Fig. 3) shows subsequent methanolysis, afforded methyl a-Dthe following changes: (a) the hydroxyl band a t 3 glucopyranoside after silicate column chromatography. After acetylation and subsequent silicate ,LL has become stronger while the nitrate bands a t 6.0, 7.8 and 11.8 1.1 have become weaker; (b) new column chromatography, product VI also yielded bands have appeared a t 5.75 and 6.35 p. The 5.75 a-cellobiose octaacetate. The denitrated product I11 was subjected to hydrolysis with sulfurous acid p band undoubtedly can be ascribed to a carbonyl (19) R. N. Haszeldine, J . Chem. SOC., 2525 (1953). function (aldehyde, ketone, carboxyl or ester). 0 ) W. W. Scott, “Standard Methods of Chemical Analysis,” On the basis of Kumler’s datal8 on nitrated glyco- 5th( 2edition, N. H. Furman, Ed., D. Van Nostrand Co., Inc., N e w York, late esters, the band a t 6.35 ,LL may be indicative of N. Y . , 1939, p . 662. a nitrate group on a carbon adjacent to a carboxyl (20a) P. Tarte, Bull. SOC. chim. Beiges, 6 0 , 240 (1931); J . Chem. function. The possibility that the band a i 6.35 p Phys., 20, 1570 (1952). (20h) L. P . Kuhn, unpublished work. is due to a C-nitro group seems unlikely since the (17) L. P. K u h n , Anal. Chem., 22, 276 (1950). (18) W. D. Kumler, THIS TOURNAL, 71, 4346 (1953).
1.so
..
(21) L. P. Kuhn, THIS JOURNAL, 68, 1761 (1946). (22) D. 0. Hobman, R. S.Bower and & L.‘I Wolfrom, . i b i d . , 69, 249 (1947).
and from the hydrolyzate there was isolated dialso ~ rectly D ( ?)-arabino-hexose p h e n y l o s a ~ o n e , ~ identified as the phenylosotriazole. Further reduction of product I11 (with hydrogen and Raney nickel) with subsequent acid hydrolysis, acetylation and silicate column chromatography, afforded D-glucitol (sorbitol; as the hexaacetate) . Cautious hydrolysis of 111, with dilute sulfuric acid, led to the isolation by column chromatographic methods, of D-gluconic acid (as the amide) and (after acetylaVI11 H 0x02 tion) of P-D(?)-glucopyranose p e n t a a ~ e t a t e . ~The ~ action of phenylhydrazine on this hydrolyzate would be expected to participate in any subsequent with subsequent silicic acid column chromatog- steps in a manner very similar to intermediate VII, raphy afforded D( ?)-glycero-tetrose phenylosa- it need not be of further concern. Intermediate VI1 should cleave and eliminate originating no doubt in a D-erythrose entity of the original 11. From product 11, and in much nitrogen dioxide in the same manner described for higher yield from product 111, there was obtained the vicinal dinitrites to give a stable unit IX. The on methanolysis with subsequent processing ac- existence of the unit I X in product I1 has been concording to Grangaard, Gladding and P ~ r v e s , * ~ CHlOSOr the bis-(2,4-dinitrophenylhydrazone)of glyoxal. ~ _ _ Consideration of the analyses and hydrolysis products obtained suggests that product I1 is a fragmented oxycellulose nitrate. Since both D glucose derivatives and a-cellobiose octaacetate c c have been obtained in fair yield after denitration H ONOn I I1 and hydrolysis, the polymer residue still contains XI H 0 x intact anhydro-D-glucose entities. The origin of the other units can be related to the initial cellu- firmed by the isolation of two carbon atom (glyoxal) lose nitrate through a consideration of the mech- and four carbon atom (D-erythrose) molecules after anisms of the thermal decomposition of less com- denitration and hydrolysis. X similar cleavage and elimination in VI11 with plex nitrates. the formation of formaldehyde and a new unstable Several recent investigations on the thermal decomposition of simple alkyl mononitrates have re- intermediate X may be expected. Since a good yield sulted in the belief that the initial step of the reac- of formaldehyde has been obtained from the thertion is the homolytic cleavage of the 0-N bond of mal decomposition of cellulose nitrate a t slightly the nitrate group with the formation of nitrogen higher pressure,2 this reaction is considered probdioxide and an alkoxyl radical, which react fur- able. As no five-carbon fragment derivable from ther.25 The same initial cleavage has been sug- the intermediate X has been isolated, this intermegested for the thermal decomposition of simple diate may subsequently decompose, possibly with mononitrites. 26 The nitric oxide formed from the ni- cleavage of the cellulose chain. Another probable reaction that the intermediates trites does not enter into subsequent reactions with the organic residues to the same extent that the VI1 and VI11 may initiate is the transfer of a hynitrogen dioxide does. Kuhn and DeXngelis2' have drogen atom from a carbon to the alkoxyl radical, found that vicinal dinitrites undergo thermal de- the net result being the conversion of the original composition with the formation of dialdehydes in nitrate group to a hydroxyl group. If the hydrowhich the bond between the carbons attached t o gen atom were removed from a carbon that was the nitrite groups is ruptured; in particular, the involved in the glycosidic bonds of the cellulose formation of adipic dialdehyde from trans-l12-cy- nitrate, an intermediate X I would be possible. CHIOX02 CIJ?OSOr clohexanediol dinitrite is of interest since a similar dinitrate group exists in the anhydro-D-glucose , 0, - (). units of cellulose nitrate. By analogy with simple nitrates, the homolytic cleavage of cellulose nitrate is believed to afford the \ , , \ , , intermediates VI1 and VIII. Another intermediate (from the cleavage of the I1 OXO? :I OK:01 nitrate group on carbon 3) is possible but, since it sI SI1 (23) Although insufficient material was obtained t o define t h e 'This intermediate could rearrange with cleavage of optical rotation, there is no reason t o believe t h a t t h e anhydro-Dthe cellulose chain and formation of the unit XI1 glucose unit, initially present, had undergone a n y optical inversion. (24) D. H. Grangaard, E. K . Gladding and C. B. Purves, P n P e r a t one of the new chain ends. This unit is a lacT r a d e J . , 1 1 6 , No. 7, 71 (1942). tone and may explain the acidity and carboxyl (25) G. K . Adams and C. E. H. Bawn, T r a n s . F a r a d n r SOC.,4 6 , content of product 11. In addition, the D-gluconic 494 (1949); I
