I
RICHARD P. WELCHER, DONALD J. BERETS, and LEMUEL E. SENTZ’ Stamford Laboratories, Research Division, American Cyanamid Co., Stamford, Conn.
Stability of Cyanogen Cyanogen is stable enough to be handled in the laboratory and to be stored and shipped in Monel or stainless steel cylinders
THE
word “stability.” as applied to a chemical compound, is a broad term. I t denotes a resistance to one or more of several different kinds of possible behavior, such as polymerization, decomposition, and chemical reaction under a variety of conditions, such as heat, pressure, addition of reagent, or mechanical shock. T o be meaningful, the word must be limited in extension by a statement of the conditions under which it is true. When study of cyanogen was begun a t these laboratories, there was concern about its stability. T h e compound is known to be chemically reactive, one of the most reactive nitriles (3, 6, 9, 77, 20, 22). Cyanogen has a large positive (endothermic) heat of formation, a property generally viewed as an indication of instability. T h e value for cyanogen is 7 3 , 800 cal. per mole (73), as compared with 53,500 cal. per mole for acetylene (8). A third reason was the report by Berthelot that local decomposition to the elements occurred when cyanogen or acetylene vapor was heated, or was brought in contact with flame or electric spark. When mercury fulminate was used, cyanogen (and also acetylene) detonated (2). Barillet reported that little is known of conditions for the detonation of cyanogen to the elements ( 7 ) . Further evidence of .the instability of cyanogen was found by Pannetier and Laffitte, in a study of the flammability limits of cyanogen air mixtures (77). When nonflammable mixtures were sparked, very brilliant luminous particles were observed in the combustion tube. T h e authors suggested that the particles were carbon from decomposition of cyanogen to the elements. When
1 Present address, American Cyanamid Co., New Castle, Pa.
flammable mixtures were sparked, there was a slight delay, followed by an extremely violent explosion having the characteristics of a detonation rather than combustion. Finally, instances are known of the explosive polymerization of other nitriles, such as cyanogen chloride and hydrogen cyanide, in the presence of certain impurities or additives (75, 76). T h e present study consisted of two parts. The stability of pure cyanogen to heat, pressure, and chemical additives was first investigated. Subsequently, cyanogen was subjected to severe mechanical shock.
Stability to Heat, Pressure, and Chemical Reagents Perret and Krawczynski, confirming an earlier report by Schutzenberger, observed that gaseous cyanogen could be kept indefinitely at room temperature and atmospheric pressure in absence of moisture and light (78, 20). Materials such as potassium cyanide, potassium carbonate, and sodamide catalyzed the formation of paracyanogen a t elevated temperatures and atmospheric pressure. If such a polymerization were initiated by traces of reagents or impurities during laboratory handling or storage in cylinders, it could be hazardous. For this reason prolonged tests in evacuated sealed tubes were carried out with liquid cyanogen under its own vapor pressure a t 65’ C. T h e tubes contained small quantities of acids, salts, bases, and metals. Apparatus and Procedure. Cyanogen was prepared from copper sulfate and sodium cyanide by a modification of the classical procedure first described by Jaquemin (72) and later improved by H a h n and Leopold (7). T h e apparatus was swept with dry nitrogen
throughout the reaction. A warm solution of sodium cyanide (294 grams = 6.00 moles) in 450 grams of water was added dropwise over a period of 0.7 hour to cupric sulfate pentahydrate (750 grams = 3.00 moles) at 90’ to 100’ C. Heating was continued for 0.5 hour. The yield was greatly improved by the use of as little water as possible, an elevated reaction temperature, efficient stirring, and short addition time. T h e outgas from the condenser was passed through the usual safety trap, silver nitrate scrubber, and drying towers into two cold traps a t -80’ C. The 59.2 grams of crude cyanogen corresponded to a yieId of 76%. T h e only impurity detected by infrared analysis was carbon dioxide (less than 5%). T h e cyanogen was dried by two distillations through Drierite, and freed of carbon dioxide by distilling and discarding the first 10% of the distillate. A gas sample of the remaining cyanogen contained less than O.Ol% carbon dioxide, no hydrogen cyanide, and no water (infrared analysis). T h e tests were carried out in 18 X 150 mm. borosilicate glass ignition tubes, which were rinsed with acid, washed with water, dried, and provided with a constriction to facilitate sealing. They were charged with the quantity of additive listed in Table I, and connected to a borosilicate glass manifold for chargin,< with cyanogen. The tubes were repeatedly flushed with nitrogen, evacuated, and finally chilled in dry ice. Pure cyanogen was distilled into each tube until it contained 0.5 to 2 grams of cyanogen, and the tube was then sealed off. T h e tubes which were to have air or carbon dioxide atmospheres were charged with cyanogen as above, but were brought to atmospheric pressure with air or carbon dioxide before sealing. T h e other tubes were sealed at VOL. 49, NO. 10
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Table 1.
Tubea 1 2 3 4
5 6
7 8
9 10 11
12 13 14
Stability of Cyanogen under Self-Pressure at 65" C. Length of Time t o First Visible Sign Appearance after of Change, Days 100 Days b 18 h 23 E,c 23 c.a 23 d 23 d 18 d 23 0 23
Quantity of Additive, SVt. % None None 5 % Monel turnings 4 % No. 304 stainless steel turnings 367, copper wire Air atmosphere Carbon dioxide atmosphere 20Y0 hydrogen cyanide 0 . 2 7 , water 77, concentrated sulfuric acid 0.57, glacial acetic acid 0.9% sodium cyanide 0.097, sodium carbonate 0 . 2 5 % powdered sodium hydroxide
6
d
9
e d
6 6 6
9
d d d
Each tube contained 0.5-2.0 a . of cvanonen. Clear colorless liquid with brown spots on tube walls or brown ring at liquid surface. Metal slightly discolored. Clear colorless liquid, brown film on tube walls. (Brown film on tube walls prevented certainty that liquid was completely colorless.) e Clear colorless liquid, white solid on walls of tube. a
~
-
reduced pressure, so as to have only a cyanogen atmosphere during the test. After sealing, the tubes were put in a brass rack suspended in a thermostated diethylene glycol heating bath. The bath and rack were covered with a steel plate. The apparatus was so arranged that the bath could be lowered to permir visual inspection of the tubes without handling them. The entire apparatus was located in a continuously ventilated hood behind a safety screen. The bath temperature was maintained a t 62' to 67" C. during the 100-day test. At this temperature the vapor pressure of cyanogen is about 17 atm. (70). Results and Conclusions. The results of the tests are summarized in Table I. In every test most of the cyanogen remained unchanged, but a small deposit of solid material appeared after 6 to 23 days. I n the tube containing sulfuric acid the deposit was white. I n all the other tubes the deposit was a brown solid which was not investigated further. It might have been paracyanogen, as suggested by Perret and Krawczynski (78), a reaction product of cyanogen and the additive, or a polymer of hydrogen cyanide resulting from reaction of cyanogen with the additive t 76). Because polymerization or decomposition of cyanogen would have transformed colorless liquid cyanogen into colored solid products, it was concluded that pure cyanogen does not polymerize or decompose a t moderate temperatures; acids, bases? and salts cause a somewhat accelerated change of a small part of the cyanogen, but do not induce chain polymerization or decomposition; and pure cyanogen may be safely stored in hlonel or stainless steel cylinders without the addition of a stabilizer.
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"
I
Stability of Cyanogen to Mechanical Shock Still undetermined was the stability of cyanogen to mechanical shock. Apart from the observations of Berthelot and Pannetier, the literature was silent, and there were no data at the Bureau of Explosives. Upon discussion with explosives experts it became apparent that for a substance suspected of instability to shock no single test will give a definite assurance of safety under diverse circumstances. I n a standard impact test on a solid. for example, the momentum of a falling weight is imparted directly to the material. T h e result gives a comparative rating of the stability of a compound to this kind of impact only, which may bear little relationship to the type of impact sustained in laboratory handling or in shipping. For low-boiling cyanogen, moreover, the difficulty of carrying out such a test in the absence of moisture precluded the test. Therefore three tests were devised, in which the mechanical shock was generated by impact, blasting caps, and armor-piercing bullets. Because in the handling of cyanogen anv shock would be transmitted through the walls of a container, it appeared appropriate to apply the test impact to the container. T o avoid the difficulty of measuring the impact energy expended on the container itself, the net impact upon the cyanogen was maximized by the use of severe impacts and relatively fragile containers. Apparatus a n d Procedure. Cyanogen was prepared and purified as described above. IhiPAcT TESTS.Borosilicate glass banjo-shaped ampoules of about 0.7-cc. volume were sealed to a manifold, re-
INDUSTRIAL AND ENGINEERING CHEMISTRY
peatedly flushed Lvith nitrogen and evacuated, then charged ij-ith liquid cyanogen by distillation in a closed system a t reduced pressure [boiling point, -21.2' C . ; melting point, -27.9' C. ( 4 ) ] . When the bulb was full, the ampoule was sealed off. Each conrained approximately 0.5 gram of cyanogen. One larger ampoule containing approximately 20 grams of cyanogen was similarly prepared. The tests were carried out at a n isolated site by use of a 17-pound steel weight supported by a rope passing over a pulley. The distance from the bottom of the suspended weight to the base plate was 5.5 feet. These conditions provided an impact of approximately 94 footpounds. The base plate had a small circular depression 3/a inch in diameter and l/d inch deep, in which the ampoule was placed to give greater compression. The bottom of the weight and base plate were polished with steel wool before each test. The apparatus was placed within a semicylindrical steel safety shield to protect the person who manipulated the weight. Six ampoules were tested satisfactorily. Four contained solid cyanogen a t the moment of impact, the fifth had solid and some Iiquid phase, and the sixth contained only liquid cyanogen when the weight was released. In the large ampoule the cyanogen was solid when the weight dropped. The impact was sufficient to reduce the ampoules to powdered glass, which was not scattered but remained in a compact pile on the base plate. The large ampoule was partly shattered, partly powdered. A cake of solid cyanogen could be seen beneath the weight for a moment after the drop. After each drop the base plate and weight were examined for carbon and marks. I n no case was rhere any visible or audible indication of detonation, soot, indentation, or other marking on the base plate or weight. TESTSWITH BLASTINGCAPS. Preliminary tests showed that ten No. 6 instantaneous blasting caps were not able to rupture a 1.5-inch steel pipe bomb (wall thickness 0.145 inch) but did rupture a 1-inch aluminum pipe bomb (wall thickness 0.133 inch). Accordingly, bombs were prepared from clean 18-inch lengths of 1-inch aluminum pipe fitted with clean iron pipe caps. The pipe threads were lubricated with Masters metallic compound. One bomb was capped empty; the second was charged with 97 grams of water and capped; the third contained 97 grams of cyanogen in an atmosphere free of air. The desired number of h-0. 6 instantaneous blasting caps were connected and fastened side by side to the outside of the bomb. The manner of attachment
S T A B I L I T Y OF C Y A N O G E N Table II. Testing Cyanogen with Blasting Caps Bomba Test Contents 1
2
. .. ,
4 5
A W A
6
C
7
C
3
Conditions Five caps alone Five caps alone Five caps on bomb Five caps on bomb Eight caps on undamaged end of bomb used in test 3 Five caps on bomb Eight caps on undamaged part of bomb used in test 6
Loudnessb Meter 1 Meter 2 Effect on Bomb -4.5 -3 -4.5 -2.9 -4.5 -3 Bomb dented and ruptured -4.2 -2.5 Bomb dented and ruptured 2.8 1 Bomb dented and ruptured
... ...
-
+
-4.5
-4
-3.8
-0.5
Eight caps just above -3.8 - 1.5 pipe cap at nonleaking end of bomb used in test 7 ' A, W, and C signifying air, water, and cyanogen (Figure 1 ) . Deviation from 100 db. 8
C
and position of the caps were the same for each test but the last. I n every case the caps were attached to the upright bomb below the surface of the liquid cyanogen. The bomb was placed in the same spot within a sand-bag barricade. T h e caps were fired with a magneto. The loudness of each blast was measured by using a General Radio sound level meter, and checked with a General Radio sound survey meter, suitably placed about 65 feet from the barricade, and protected in the event that the cyanogen should detonate. The meters were not calibrated; the 100-decibel scales were used. Care was taken in the positioning of the bomb and stationing of observers, to ensure reproducible sound measurements. The results of the eight tests are summarized in Table 11. The bombs are shown in Figure 1. A., W., and C signify the contents of the bomb: air, water, or cyanogen. The numerals correspond to the test numbers of Table 11. The difference between the loudness readings (on a given meter) for the controls and the cyanogen bomb was not significant. Damage to the bombs for a given number of caps was very similar. No carbon was found inside the cyanogen bomb. TESTS WITH ARMOR-PIERCING BULLETS. The bombs consisted of clean pieces of steel pipe 8 inches long and 1 inch in diameter (wall thickness 0.133 inch). fitted with iron pipe caps. Five bombs were prepared. T h e first contained air only; the second contained 57 grams of water; the third was charged with 53 grams of cyanogen containing approximately 1% carbon dioxide. A fourth bomb was loaded with 58 grams of crude cyanogen prepared from hydrogen cya-
Bomb dented but not ruptured Bomb deeply dented but not ruptured. One pipe cap loosened slightly, permitting slow audible leak Pipe cap and threaded end of bomb blown off; pipe cap split
Figure 1. Tests with blasting caps show stability of cyanogen to shock
nide and chlorine (74). It contained ' cyanogen chloride approximately 1% and a trace of hydrogen cyanide. The fifth bomb was charged with 20 grams of pure dry cyanogen prepared and purified as described above. The bombs containing cyanogen were charged while evacuated, so that the atmosphere in the bomb was free of air. Each bomb was painted with a target stripe 3/4 inch wide and 2 to 4 inches long, to indicate that part of the upright bomb which contained liquid cyanogen, and to make the bomb more readily visible. The bomb was placed in a sandbag barricade backed up by a bank of earth. The 30.06 armorpiercing bullets were fired from a site approximately 90 feet from the barricade. The bombs arc shown in Figures 2 and 3. The order of the bombs, left to
right, is the same as that in which they are described above. Each shot completely pierced the bomb, the bullet holes, front and back, being very similar for all the bombs. In the case of the bombs containing 53 and 58 grams of cyanogen, the end of the bottom pipe cap was blown out. O n the bomb containing 20 grams of cyanogen the point of impact was a t one side just above the lower pipe cap. Here there was one enlarged hole comprised of both entry and exit; the end of the pipe was cracked, but not blown
Figure 2. Tests with armor-piercing bullets show stability of cyanogen to shock (front view)
Figure 3. Tests with armor-piercing bullets show stability of cyanogen to shock (rear view)
Off.
Results and Conclusions. There was no doubt that detonation did not occur in the impact tests. Detonation of 0.5 gram of cyanogen would have formed nearly 0.25 gram of soot; 20 grams of cyanogen would have given 9 grams of carbon. No soot was observed on the weight or
Y
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base plate. Detonation would have scattered the powdered ampoule, but the glass was found in a compact pile. Both liquid and solid cyanogen were tested to learn if a difference in sensitivity existed. Two sizes of sample were used, because there is no best sample size for a n impact test. I n standard impact tests small samples (0.1 to 0.5 gram) are generally used for convenience. The results reported here did not rule out the possibility that a 1-, IO-, or 100-pound batch of cyanogen could be detonated, but they made such an event improbable. I n these tests, cyanogen was not detonated by a 94-foot-pound blow. By comparison, standard impact tests by the Bureau of Mines showed that mercury fulminate and diazodinitrophenol were detonated by an impact of 1 footpound, black powder required 14 footpounds, while guanidine nitrate was not detonated by a 10,500-foot-pound blow. The tests with blasting caps were selected in preference to dropping a cylinder of cyanogen from a height because it appeared that the former test would result in a far greater shock, but similar in kind to that which cyanogen might encounter in shipment or laboratory handling. Calculation showed that the complete detonation of 97 grams of cyanogen would release energy equivalent to that from the detonation of 300 grams of T N T . I t was obvious from the sound level, bomb damage, aiid absence of carbon that detonation did not occur. The greater resistance to rupture of the bomb containing cyanogen was attributed to the vapor pressure of cyanogen [about 90 pounds per square inch a t 27’ C. (lo)], acting to support the walls of the bomb. The test with an armor-piercing bullet was considered very severe. The greatest shock was thought to occur when the bullet, after passing through the material to be tested, struck the rear wall of the container. As in the preceding tests, comparable damage to the bombs and the absence of carbon were clear evidence that no detonation had occurred, The rupturing of the pipe caps on two of the cyanogen bombs was attributed to the additive effects of the pressure from the bullet and the vapor pressure of cyanogen. A similar hydraulic effect is observed when a tin can fuli of water is pierced with a bullet; the can appears to explode. O n the basis of these negative results. it was concluded that cyanogen is insensitive to mechanical shock more severe than Jvould be encountered in shipment or laboratory handling. Because cyanogen and acetylene have comparable endothermic heats of formation. comparison of their behavior is interesting. I n impact tests, pure liquid
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acetylene in steel cylinders was detonated by the explosion of a picric acid cartridge, if the cartridge was adjacent to the liquid acetylene (79, 27). When the cartridge was fastened to the part of the cylinder containing acetylene vapor, detonation did not occur. When a single bullet was shot through the acetylene vapor in the cylinder, detonation did not occur. Shooting a bullet through liquid acetylene was not attempted, but Rasch was confident that detonation would occur in such a test (79, 27). Discussion I n evaluating the results of the present study, the question arises as to the stability of cyanogen under conditions different from those used here. When the possibility of the rapid polymerization or decomposition of a highly endothermic substance such as cyanogen, is tested, one cannot prove that such a hazardous transformation will never occur. A specific catalyst or set of conditions might initiate the transformation. While in this sense the present results are negative, they delineate areas within which one may feel reasonably safe. One factor which was not completely examined was size. Although the tests with blasting caps and bullets were very severe, relatively small quantities of cyanogen and containers of comparatively small diameter were used. The literature of acetylene is a useful guide. Reppe and his associates determined the factors which can change a decomposition to a detonation: gas temperature and pressure! vessel dimensions, temperature of the igniter, moisture content, and dilution (5). Today, before carrying out a reaction involving acetylene under pressure many chemists consider it advisable to determine whether a given reaction mixture is safe, or can decompose under the reaction conditions. Hanford and Fuller have described a practical test to answer the5.e questions (8). In view of the great importance of vessel diameter, temperatures, and pressures for acetylene, it is desirable to extend the study of the stability of cyanogen to higher pressures and temperatures in a vessel large enough so that the wall effect will become less important. This study should precede large scale pressure reactions of cyanogen, or transfer of cyanogen under pressure in large-bore tubing. The test method of Hanford and Fuller might be useful here. A number of substances were not tested in the present study. Among these, two classes have been suggested as possible sources of hazard, pariicularly in large scale reactions: peroxides, introduced deliberately as initiators or accidentally as impurities in other rea-
INDUSTRIAL AND ENGINEERING CHEMISTRY
gents, and bases soluble in cyanogen. such as ammonia or amines. These substances should be tested before use on a large scale. Acknowledgment For their helpful suggestions and criticisms the authors wish to thank H. A. Campbell, T. C. George, and W. G. McKenna of the AAR Bureau for the Safe Transportation of Explosives and Other Dangerous Articles, Lerov V. Clark and Ralph G. Gutelius of the Explosives Department of this company, and Donovan J. Salley of these laboratories The authors are grateful also to three other associates: Kenneth Matsuda for a special sample of cyanogen used in the tests, Edward J. Condon for expert shooting, and Merrill C. Behre of the Explosives Department for assistance in the tests with blasting caps. Literature Cited Barillet, F., Znd. chim. 26, 615 (1939). Berthelot, M., CornFd. rend. 93. 613-19 (1881). Bucher, 3 . E. (to Nitrogen Products Co.), U. S. Patent 1,194,354 (1916). Cook, R . P., Robinson, P. L., J . Chem. SOC.1935, pp. 1001-5. Copenhaver, J. W., Bigelow, M. H., “Acetylene and Carbon Monoxide Chemistry,” Chap. VIII, Reinhold, New York, 1949. DeLaMater, G. B. (to Mallinckrodt Chemical Works), U. S. Patent 2,732,401 (1956). Hahn, G., Leopold, W., Ber. deut. chem. Ges. 68, 1974-86 (1935). Hanford, W. E., Fuller, D. L., IND. ENG.CHEM.40,1171-7 (1948). Hawkins, P. J., Janz, G. J., J . Chem Sac. 1949, pp. 1479-88. Hodgman, C. D., “Handbook of Chemistry and Physics,” 37th ed., p. 2229, Chemical Rubber Publishing Co.. Cleveland, 1955. Jacobsen, O., Emmerling, A., Ber. deut. chem. Ges. 4, 947-56 (1871). Jaauemin, G., Combt. rend. 100, 10056 (1885). Knowlton. J. W.. Prosen. E. J., J . Research Nail. Bur. Standards 46, 489-95 (1951). Lacv, B. S., Bond, H. A , , Hinegardner 6 r . S. (to E. I. du Pont de Nemours & Co.), U. S. Patent 2,399,361 (1946). Migrdichian, V . , “Chemistry of Organic Cyanogen Compounds,” p. 98, Reinhold, New York, 1947. Ibid., p. 349. Pannetier, G., Laffitte, P., Compt. rend. 226, 341-2 (1948). Perret. -. ..., A,., Krawczvnski. A.. Bull. SOC. chim. France 51, 622-36 (1932). Rasch, H., Acetylen Wzss. u . Ind. 4, 170 (1 9fll1. \ - ’ - - / -
Schutzenberger, P., Bull sac. chin. France ( 2 ) 43, 306-7 (1885). Voeel, J. H., “Handbuch fur AceGlen,” p. 751, F. Vieweg & Son, Brunswick, Germany, 1904. Woodburn, H. M., Morehead, B. A., Bonner, W. H., J . Org. Chem. 14, 555-8 (1949); Papers 11--IX, J . Org. Chem., 1950 to date. EmivED for review February 11, 1957 ACCEPTED June 22, 1957
