I
WILLIAM L. FIERCE and WALTER J. SANDNER The Research Center, The Pure Oil Co., Crystal Lake, 111.
A New Method for the Synthesis of Cyanogen The catalytic, vapor-phase reaction of hydrogen cyanide with nitrogen dioxide produces cyanogen in excellent yields. By-product nitric oxide can be oxidized to nitrogen dioxide by air or oxygen and recycled
first svnthesized bv Gay-Lussac by the thermal decomposition of silver cyanide (2). Since that time many additional synthetic methods have been reported. Materials used in preparing cyanogen were hydrogen cyanide, cyanogen halides, metal cyanides, oxamide, and ammonium oxalate (2). From a commercial viewpoint, hydrogen cyanide is the preferred starting material because it is a largescale product of the petrochemical industry ( 9 ) . Oxidation of hydrogen cyanide was first reported by Ricca and Pirrone who investigated the oxidation in dilute sulfuric acid solutions ( 8 ) . They found that small yields of cyanogen could be produced by the use of oxidizing agents such as sodium persulfate, manganese dioxide, lead dioxide, and stannic oxide. Three additional processes for the oxidation of hydrogen cyanide to cyanogen have been reported in recent years. Lacy and coworkers obtained cyanogen in excellent yields by oxidizing hydrogen
cvanide bv chlorine in the gas Dhase (6). Hydrogen chloride is a by-product of the reaction. I n the presence of catalysts such as activated carbon or silica gel the reaction proceeds at temperatures as low as 200' to 300' C. Moje has patented a process for the airoxidation of hydrogen cyanide using a silver catalyst (7). The maximum cyanogen yield reported was 22.870 in a run in which the reactor temperature was 500' C. and the reaction time was 3 minutes. A low temperature process for preparing cyanogen from hydrogen cyanide has been developed by Fierce and Millikan ( 4 ) . When hydrogen cyanide is passed into a slurry of cupric oxide in water at room temperature, cyanogen is evolved and a complex metal cyanide is precipitated. An additional quantity of cyanogen can be produced by heating the precipitated cyanide to above 100' C. This article describes an investigation of the use of nitrogen dioxide as the oxidizing agent for converting hydro"
I
?
P!
NC-C-NHz CYANOFORMAMIDE
HpN-C-C-NHz OXAMIDE
I
HO! IIJOH H2N-C-C- NHz OXA L D IHY D ROX AM I D E
H2N-CH2-COOH
HYDROLYSIS
\
I
-
(CN)2
2-CYANOPYRIDINE
REDUCTION
HzN-CHz-CHz-NH2 ETHYLENEDIAMINE
CYANOGEN
Background Literature Oxidation of Hydrogen Cyanide to Cyanogen
Subject
Ref.
In dilute sulfuric acid solution con-
ventional oxidizing agents such as manganese dioxide give small yields of cyanogen The chlorine-hydrogen cyanide reaction in the vapor phase gives excellent yields of cyanogen Air oxidizes hydrogen cyanide to cyanogen at about 500" C. in the presence of a silver catalyst Passing hydrogen cyanide into an aqueous slurry of cupric oxide produces cyanogen
(8)
(6)
(7) (4)
gen cyanide to cyanogen. The result is a new, catalytic, vapor-phase procedure for preparing cyanogen based on the following reaction: 2HCN
+ NO,
+
(CN),
+ NO + H,O (1)
The effective catalysts include lime glass beads and compounds of sodium, magnesium, and calcium on supports of low surface area ( 5 ) . I n runs a t atmospheric pressure of 200' to 350' C., cyanogen yields were high and troublesome by-products were absent. The reaction can be the basis of an economical, continuous process for producing cyanogen because the by-product nitric oxide can readily be separated from the product gas stream, oxidized to nitrogen dioxide by air or oxygen, and recycled. Thus nitric oxide is a carrier for oxygen in this process. Experimental
H! I H RHN-C-C-NHR DlALKY L OX AM I D I N E
ALCOHOLS
A
!H RO-C-CN CYANOFORM A L K Y LIMI DATE
HY YH HpN-NH-C-C-NH-NH2 O X A L D I IM IDIC ACID DI H Y D R A Z I D E
H! !H RO-C-C-OR OXALDl D I A LI M KIYDLA T E
Cyanogen's reactions point to a promising future as a chemical intermediate Reactions taken from review article on Cyanogen by 59 841 (1959).
T. K. Brotherton and J. W. Lynn, Chem. Revs.
The bench-scale apparatus used in this work was constructed entirely of glass and Tygon tubing. All runs were carried out at atmospheric pressure, and a standard procedure was used. Either nitrogen or helium, as a carrier gas, was bubbled through liquid hydrogen cyanide in a tube cooled by an ice-water bath. The gaseous mixture of hydrogen cyanide and carrier gas was blended with gaseous nitrogen dioxide and then directed to the reaction VOL. 53, NO. 12
DECEMBER 1961
985
Table 1.
Run
No.
The Reaction Was Catalyzed b y Lime Glass But Not b y Lead or Borosilicate Glass Space Velocity Charge of Total Gas. Temp., Charge Viii-% Mole Ratio, Yield/Pass, Type of O c. Gas' HCN HCN/NOz (CN)zb Glass Used Thermal, Noncatalytic Runs
1 2 3 4
195 305 410 345
260 266 257 855
5
10
100 225 344 415 509 415
238 242 211 222 217 295
11 12 13 14
304 373 317 417
208 213 222 216
23.1 25.0 22.1 28.3
1.21 1.34 1.14 3.03
...
0.3 0.7 1.7 7.5
...
0.0 5.9 32.3 59.7 38.2 72.5
Lime Lime Lime Lime Lime Lime
... ...
Runs with Lime Glass Beads 6 7 8 9
30.1 29.4 24.5 28.4 29.9 30.5
2.6 2.5 2.5 3.0 3.1 10.0
Runs with Lead and Borosilicate Glass 26.4 29.0 32.0 30.2
2.5 3.0 3.4 3.1
1.3 7.2 60.5 1.7
Lead Lead Borosilicate Borosilicate
.
' The space velocity is based measured at 25O C.
b
on the total volume in the reaction zone. Gas volumes were moles cyanogen formed Yield per pass = 100 X moles limiting reactant charged
zone. The reactor consisted of an electrically heated Vycor or borosilicate glass tube with a diameter of 21 mm. and a volume of 92 ml. in the heated zone. The average run required 20 minutes. Gas samples of the charge and product gases were analyzed by means of a mass spectrometer. All components of the gas streams except nitrogen dioxide were determined by this procedure. The amount of nitrogen dioxide charged was determined by using a calibrated flowmeter and by weighing the gas cylinder before and after use. All reactants and carrier gases were obtained from commercial sources and all except hydrogen cyanide were used without further purification. The hydrogen cyanide used was fumigant grade material and was distilled before use. Mass spectrometric analyses indicated that no more than trace amounts of impurities were present in the gas streams charged to the reactor. Two types of runs for the oxidation of hydrogen cyanide by nitrogen dioxide included-thermal runs in which the reactor tube was empty; and catalytic runs in which the reactor was charged with various solid catalysts. Results and Discussion
Noncatalytic Runs. I n the absence of catalysts, the reaction of hydrogen cyanide with nitrogen dioxide at elevated temperatures produces small yields of cyanogen. Table I shows these experimental conditions and results. Three variables were involved in these runs-temperature, space velocity, and
986
mole ratio. Although the effects of these variables cannot be evaluated precisely, some general observations are possible. I n Runs 1, 2 , and 3 the yield increased with temperature, while the space velocity and mole ratio were held almost constant. In R u n 4 the cyanogen yield improved when the space velocity was increased to 855 and the mole ratio was increased to 3.03. The factor responsible for the improved results in R u n 4 was the increase in mole ratio. Effects of Glass Surfaces. Study of the thermal, noncatalytic reaction was interrupted unexpectedly because glass surfaces were found to have a definite effect upon cyanogen yields in the reaction of hydrogen cyanide with nitrogen dioxide. Table I shows the experimental conditions and results of runs in which the reactor was charged with lime glass beads having a diameter of 4 mm. Although the experimental conditions were similar to those of the thermal runs, the cyanogen yields were much higher. The effect of temperature is shown by the results of Runs 5 through 9. Under the conditions shown there was a small yield of cyanogen at 225' C., and the highest yield was observed in the run a t 415' C. R u n 10 gives some indication of the effect of the reactant mole ratio upon cyanogen yields. Good cyanogen yields are favored by the presence of a large excess of hydrogen cyanide. In a run not shown in Table I the cyanogen yield was reduced drastically when the lime glass beads were coated with a thin film of boric oxide (7). To accomplish this, beads in the reactor were rinsed with a 5% aqueous
INDUSTRIAL AND ENGINEERING CHEMISTRY
solution of boric acid. Heating the wet beads a t 350' C. in the presence of nitrogen deposited a thin film of boric oxide. A run was then carried out using experimental conditions which were the same as those of R u n 8, Table I. The cyanogen yield per pass was only 1.0% in contrast to the yield of 59.7% given by the uncoated beads. Thus the factor responsible for the catalytic activity of lime glass beads is located a t the surface of the glass. The catalytic effect noted with lime glass beads was not observed when two other types of glass were evaluated. Table I shows the results of standard runs in which the reactor was charged with 2.5-mm. lead glass beads and with '/,-inch I.D. borosilicate glass helices. The experimental conditions were the same as those runs with lime glass beads. However, the cyanogen yields were much lower. In fact, the yields were about the same as those observed in runs with an empty reactor tube. Table I1 shows the approximate compositions of lead, lime, and borosilicate glasses. These data account for the unusual effect of lime glass surfaces on the oxidation of hydrogen cyanide. Lead and borosilicate glasses have much higher contents of compounds such as lead oxide, potash, and boron oxide. Although these compounds may have a poisoning effect on the reaction between hydrogen cyanide and nitrogen dioxide, there is a more significant factor. Lime glass differs most from the other glasses in its content of soda, lime, and magnesia. Compounds of calcium, sodium, and magnesium can catalyze the oxidation of hydrogen cyanide to cyanogen by nitrogen dioxide. Consequendy, the soda, lime, and magnesia present in lime glass probably caused its catalytic effect on the oxidation. Effects of Other Catalysts. Table 111 shows a series of runs designed to test the catalytic activity of silver metal and compounds of sodium, calcium, magnesium, beryllium, and zinc. The silver catalyst was prepared by the method of Wan (70). Other catalysts were pre-
Table II. Compositions of Commercial Glasses (3) Type of Glass Boro-
Lime
Silica, Si02 Soda, Nan0 Lime, CaO Magnesia, MgO Alumina, A1208 Lead oxide, PbO Potash, KzO Boron oxide, BzOa
72 15
Lead silicate 68 10
SO 4
1 ... ... ... ...2 ... 15 ... ... 6 ... ... ... 14 9
3 1
C Y A N O G E N SYNTHESIS Table 111.
Run No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Compounds of Sodium, Calcium, Magnesium, and Silver on
Comp. Applied to Support None None NaCl NaCl CaClz CaClz Mg Clz MgClz MgClz MgClz Be(N0a) z Be(NOa)z Ag Ag Zn(SO& Zn(S03~
Support Used Pumice Pumice Pumice Pumice Pumice Pumice Pumice Pumice Alumina Alumina Pumice Pumice Corundum Corundum Pumice Pumice
pared by applying 10% by weight of the metal salt to Italian pumice or Alcoa F-10 alumina of 8- to 14mesh size. A standard procedure was used in drying and calcining these catalysts. First, a slurry of pumice and an aqueous solution of the metal chloride was heated and stirred to remove excess water. Then the material was held a t 230' F. for 18 hours to dry it thoroughly. Next the product was calcined for 6 hours a t a temperature which was slowly raised from 400' F. to 900" F. Finally, it was calcined for 2 hours a t 1000" F. This treatment converts the less stable metal chlorides to the corresponding oxides. For example, the catalyst used in Runs 7 and 8 was composed of magnesium oxide on pumice, with only a trace of chlorine present. The results (Table 111) point out the variations in the catalytic effects of these materials. Runs 1 and 2 show that pumice alone has a low order of catalytic activity. The cyanogen yields were somewhat higher than in runs with an empty reactor tube under similar conditions. However, the results were much better when compounds of sodium, calcium, or magnesium were supported on the pumice. The catalyst prepared from magnesium chloride had the highest activity of any of the catalysts tested. I n Runs 7 and 8, the nitrogen dioxide was completely consumed. I n both runs the hydrogen cyanide conversions were over 60% with selectivities for cyanogen of about 100%. This catalyst was more active a t temperatures below 200" C. than any other material evaluated. The active catalysts of Table I11 promote the reaction shown in Equation 1. The view that the reaction takes this course is supported by mass spectrometric analyses of the product gases. No other products were detected. The molar amount of hydrogen cyanide
Temp.,
c.
180 317 210 356 191 382 195 351 276 374 184 290 157 304 179 332
Low Surface Area Supports Were Effective Catalysts
Space Vel. of Total Charge Gas
Charge Gas, Vol. yo
HCN
Mole Ratio, HCN/NOz
410 410 436 406 506 498 468 445 425 493 430 563 478 505 498 508
29.9 33.7 34.7 32.8 33.6 33.0 30.2 32.8 30.1 39.3 32.8 45.0 27.0 27.9 33.2 33.1
2.3 2.6 3.2 2.8 2.8 3.1 2.8 2.7 2.4 3.6 3.0 5.4 2.2 2.5 3.1 3.1
consumed was double that of the nitrogen dioxide. Table I11 provides some additional information of the type of catalyst needed in the hydrogen cyanide-nitrogen dioxide reaction. The catalyst used in Runs 9 and 10 differed from the highly active magnesium-containing catalyst of Runs 7 and 8 in that the support used in preparing this catalyst was activated alumina instead of pumice. This change created a catalyst with entirely different characteristics. Although the conversions of hydrogen cyanide and nitrogen dioxide were high, very little cyanogen was produced. The main effect of the catalyst was to promote complete oxidation of the hydrogen cyanide, I n Runs 11 and 12 (Table 111), the support was pumice and beryllium was the metal evaluated. Beryllium was selected for study because it is a member of the same group of the periodic table as calcium and magnesiumGroup IIA. In many instances the members of a given group of the periodic table are similar in their catalytic effects. However, in this case the results show that the catalyst containing beryllium was low in selectivity for the formation of cyanogen. Although conversions of both reactants were relatively high, the major reaction was complete oxidation of the hydrogen cyanide. Runs 13 and 14 (Table 111) show that silver on an inert support is also an effective catalyst for the formation of cyanogen. Although the conversions of hydrogen cyanide were lower than in comparable runs with sodium, calcium, or magnesium-containing catalysts, the selectivity for cyanogen reached 94%. The results were a little better than those given by lime glass beads under similar conditions. Runs 15 and 16 (Table 111) illustrate
HCN Consurne&
Yo
3.8 19.6 31.9 77.7 11.5
77.0 61.8 73.3 76.5 52.7 11.3 37.3 0.0
28.7 11.3 12.7
Selectivity, Based on Yield/Pass, Based on HCN Chg. NO2 Chg. 3.4 13.8 23.4 72.4 5.1 65.2 60.4 73.3 0.0 3.7 4.0 11.2 0.0 27.0 0.0 2.9
HCN
Consumed
4.0 18.1 38.0
100 7.3 99.6 84.0 100 0.0 6.8 6.0 30.3 0.0 33.8 0.0 4.5
90.0 70.4 73.6 93.2 44.6 84.8 97.8 100 0.0 7.1 35.0 30.0 0.0
94.0 0.0 22.8
that many catalysts are not effective in this process for preparing cyanogen. The results show that applying zinc sulfate to pumice produces a material which has much less catalytic effect than pumice alone. I n fact, the cyanogen yields were about equal to those given by an empty, unpacked reactor tube. In runs not shown in Table 111, silica gel and activated alumina were also found to lack catalytic activity when tested by the standard procedure. Acknowledgment
The authors wish to thank K. P. Yates and his associates for the mass spectrometric analyses. literature Cited
(1) Bell, E. R., Dickey, F. H., Raley, J. H., Rust, F. F., Vaughn, W. E., IND. ENG.CHEM.41, 2597 (1949). (2) Brotherton, T. K., Lynn, J. W., Chern. Revs. 59, 841 (1959). (3) Corning Glass Works, Corning, N. Y., "Properties of Selected Commercial Glasses," Booklet B-83, 1949. (4) Fierce, W. L., Millikan, A. F. (to The Pure Oil Co.), U. S. Patent 2,841,472 (July 1, 1958). (5) Fierce, W. L., Sandner, W. J. (to The Pure Oil Co.), Ibid., 2,884,308 (April 28, 1959). (6) Lacy, B. S., Bond, H. A., Hinegardner, W. S. (to E. I. du Pont de Nemours & Co.), Ibid., 2,399,361 (April 30, 1946). (7) Moje, W. (to E. I. du Pont de Nemours & Co.), Zbid., 2,712,493 (July 5, 1955). (8) Ricca, B., Pirrone, F., Ann. Chim. AflpZicata 18, 550 (1928). (9) Sherwood, P. W., Pet. Proc. 9, 384 (1 9 54). (10) Wan, Shen-Wu, IND. ENG.CHEM.45, 234 (1953). RECEIVED for review March 2, 1961 ACCEPTED August 11, 1961 Division of Industrial and Engineering Chemistry, 139th Meeting, ACS, St. Louis, Mo., March 1961. VOL. 53,
NO.
12
DECEMBER 1961
987
