T H E CATALYTIC HYDROGENATIOS OF CARBON SUBOXIDEL BY K E m - m n A. K O B E ? AXD L. K. R E Y E R ~ O N
Of the known oxides of carbon, carbon monoxide and carbon dioxide have both been hydrogenated under a variety of conditions using different catalysts. The character of the catalysts used and the conditions of hydrogenation have been the determining factors in the type of products formed. The investigation here reported concerns itself with the hydrogenation of a third oxide of carbon commonly called carbon ~ u b o x i d e . ~This oxide of carbon, c302, offered interesting possibilities in as much as we are dealing with a highly unsaturated molecule as well as a supposedly reactive one. If the commonly accepted structure of carbon suboxide, 0 = C = C = C = 0 , is correct we have four double bonds which can be reduced. A study of the catalytic hydrogenation of this molecule might give important information concerning the directive influence of a catalyst in the reduction of parts of the molecule. For example the carbon to carbon double bond may be reduced most easily or the carbonyl group may be attacked first. In any event the reduction of carbon suboxide should give rise to different products than are obtained by the reduction of carbon monoxide and carbon dioxide which have only a single carbon atom in the molecule. The following investigation reports the results obtained in the catalytic reduction of carbon suboxide.
Experimental The method chosen for the preparation of the carbon suboxide was that of Ott and Schmidt4 since this method has many advantages over the original method of Diels and Diacetyl tartaric anhydride, a substance easily prepared from tartaric acid and acetic anhydride, was used as the substance from which the suboxide was prepared. The apparatus was fairly simple and gave a good yield of carbon suboxide which was readily separated from the other products of the reaction. The yield of carbon suboxide ( 4 1 7 ~obtained ) by Ott and Schmidt was rather low. Diels, Beckmann and Tonnies6 reported that they had secured a yield of 55-6occ by modifying the apparatus of Ott and Schmidt, but gave ' T h e material here presented formed a part of a thesis submitted to the graduate faculty of the University of Minnesota by Kenneth A. Kobe in partial fulfillment of the requirements for the degree of Doctor of Philosophy, July 1930. * DuPont Fellow in Chemistry, 1928-1929. 'Reyerson and Kobe: Chem. Rev., 7, 479 (1930). Ott and Schmidt: Ber., 5 5 , 2126 (1922). 5 Diels and Wolf: Ber., 39, 689 (1906). Diels, Beckmann and Tonnies: Ann., 439, 76 (1924).
3026
KENNETH A. KOBE AND L. H. REYERBON
no data for their runs so that it is impossible to know rchether or not these runs were consistent Since the apparatus of Ott and Schmidt is rather delicate, it was decided to modify the construction. It p a s believed that better results would be obtained if the vires of the heating element were wound horizontally on a support member with practically no space between them and the glass walls of the containing vessel Furthermore the flask holding the diacetyl tartaric anhydride should be attached to the tube containing the heating element so that the former could be easily disconnected for cleaning and recharging. A two-liter balloon flask, A , (Fig I ) , was used to hold the diacetyl tartaric anhydride The support member of the heating element was made of five
asbestos rings, hI, which were separated from one another by glass rods, N. The rings had notches in them and 3 meters of platinum wire (.SI mm. diameter) were strung across the rings in such a manner that the direction changed on each ring, thus giving a criss-cross effect. Finally the rings were covered with an insulating cement. The tube B was made from Z - ~ / L + ' ' Pyrex tubing constricted at the bottom and sealed onto the neck of a two-liter balloon flask. After the neck and lead-in tubes, 0, were sealed on, the heating element was slipped into the tube, and the lead-in wires, P, were pulled through the tubes. The top was then drawn down and a small tube sealed on. The top of B was extended above the heating element for some distance so that if necessary the top could be cut off, the tubes, 0, cut off and the heating element removed for repairs. The flask h and tube B had the glass joints ground smooth and these were separated by a ring of rubber steam packing, F, which was coated with a thick rubber solution when put in place. The flasks h and B were then tightly clamped together (clamps not shown) by aluminum rings which could be drawn together by screw clamps. A series of three traps, C,D,E, and a manometer, J, were sealed onto the generator. The system was
CATALYTIC HYDROGENATION OF CARBON SUBOXIDE
3027
evacuated to a pressure of about a millimeter of mercury and this was maintained in the apparatus during a run by continuously operating a pump. The pump was exhausted outside of the room since carbon monoxide is a product of the reaction. The flask A was heated by a melted salt mixture, K, consisting of I O parts KNOI and 8.5 parts KaKOs. This mixture has a melting point of 135'. The heat was supplied by a flat burner, L. In all runs 200 grams of diacetyl tartaric anhydride' were placed in the flask A and the system evacuated. The temperature of the bath K was raised t o 180' a t the beginning of the run and increased to 220' toward the end. A current of 7 . 2 to 7 . 7 . amperes through the filament heated it to a dull reddish yellow. A new filament was never found as effective as one that had been used. The vapors of diacetyl tartaric anhydride were drawn through the heated filament where decomposition into carbon suboxide, acetic acid, carbon monoxide, and carbon dioxide took place. The products of the
TABLE I Yields of Carbon Suboxide Run
Time of Run 8 hrs., 4 j min.,
I1 I 2
8 hrs.
13
9 hrs.,
min. 8 hrs., 2 5 min. 11 hrs., 30 min. 8 hrs. 9 hrs. 9 hrs., 30 min.
13 15
16
I7 I8
IO
Current amps. 7.2
Residue grams
79
7.7
15
7.6
7.3
36 33 80 37 30
7 . 2
25
7.2 7.2 7.2
C301 grams
32 42 40 43 39.5 45 39 46
I$ld /C
50.8 66.6 63 5 68.2 62.7 '
71.4 61.9 73 . o
reaction with the exception of carbon monoxide were frozen out in trap C which was cooled in liquid air. The pressure drop caused by the carbon monoxide passing thru the line gives an estimate of the decomposition taking place. At the conclusion of a run the acetic acid was separated from the carbon suboxide and dioxide by placing a n alcohol bath at - 3 5' about tube C for 30 to 40 minutes and condensing the suboxide and dioxide in trap D cooled in liquid air. Trap D was then surrounded by an alcohol bath at - I I O to 115' and the carbon dioxide pumped off for about an hour. Some carbon suboxide was lost during the process but the amount was not great. The carbon suboxide was then distilled into a container immersed in liquid air. The data for the runs using this apparatus are given in Table I. After the run was completed and the apparatus cut apart the tarry deposit on the heating element was burned off by passing a current through the wires and blowing a slow stream of air or oxygen through the tube B. In this way the possibility of a short circuit in the heating element during subsequent experiments was avoided.
-
Wohl and Oesterlein: Ber., 34, 1144(1901).
KENNETH A . KOBE ASD L. H. RETERSOS
3028
Hydrogenation In the actual hydrogenation a flow method was employed. The carbon suboxide was first distilled into tube A (Fig. 2 ) and this was immersed in an alcohol bath maintained at - j0"C. Electrolytic hydrogen, which had been freed from oxygen and water vapor, was bubbled through the carbon suboxide and the mixed gases passed through I j cc. of catalyst in tube D. The vapor pressure of carbon suboxide at - j o o is 45 mm. The hydrogen-carbon suboxide ratio was therefore of the order of 15 to I , to 16 to I depending upon the barometric pressure since the pressure of the mixed gases was maintained a t very nearly that of the surrounding atmosphere. After passing the catalyst the gases were led through the trap F which was maintained at -60".
nc
FIG.z
Products of the reaction, not condensed in F, were frozen out in traps G and H which were cooled by liquid air. Excess hydrogen together with any carbon monoxide formed during the reaction passed the traps cooled in liquid air and was allowed to escape. The temperature of the catalyst was maintained by an electric heating coil which was wound about tube E. The thermometer, C, was used to follow the temperature of the catalyst during a run. With a catalyst present there was always a marked rise in the temperature of the catalyst (sometimes as much as 50') when the gas mixture first came in contact with the granules of active material. The heating current was then adjusted so that the temperature fell to the starting value, and this was maintained to the end of the run. In run IV at 300' the catalyst was badly fouled and carbonaceous material was deposited on the sides of tube D. When the catalyst was removed and boiled in dilute nitric acid a red colloidal suspension was formed. This indicated considerable polymerization of the suboxide on the catalyst surfaces. The catalyst used and the quantity of reaction products are summarized in Table 11.
CATALYTIC HTDROGESATION O F CARBON SUBOXIDE
3029
TABLE I1 Run
I1
Temp. 2 ooo
I11 11-
zooo
300’
V
zooo
T’I
2 SO0
VI1 X XI
zooo
zooo
zooo
Catalyst
Sickel-silica gel used in Run I Fresh nickel-silica gel Catalyst from run 111, heated and reduced Palladized-silica gel Catalyst from run T’ heated and reduced at 300’ Sickel-silica gel X o catalyst 20 cc. 8-14 mesh pyrex
Grams Grams of of C302 liquid used produced
Liters of gas
S.T.P.
39
8
-
34
5
4 0
30
4
3 15
35
5
2 0
32
5
2 8
42
4.5
13
I
12
I
drop drop
4
05
1
31
1.18
The Character of the Reaction Products In considering the reaction products we shall designate as liquid-products whatever was condensed in trap F and as gaseous products those substances which were frozen out in traps G and H. The analysis and identification of the gaseous products will be taken up first. A%tthe conclusion of a run bulbs G and H were shut off from bulb F and connected by a tube to a ten liter bottle filled with water in such a manner that gases could displace it. The liquid air was removed from around the bulbs and they were allowed to warm up to room temperature. The frozen products of reaction vaporized and displaced water from the bottle. h very small amount of liquid, about one half cc. usually remained unevaporated. This gave a color test with Schiff’s reagent, but no phenyl hydrazone could be formed. The quantities were so small that no further tests were run on this liquid. The gas confined over water was allowed to stand for a day so that any carbon suboxide would react and dissolve in the water. The gas from run I11 was analysed in a Hempel gas absorption pipette system but the accuracy was not sufficiently high. A11 succeeding analyses w r e made in the gas analysis apparatus developed by the U.S. Steel Corporation.8 These results showed the pas to be a mixture of an unsaturated hydrocarbon, a saturated hydrocarbon, carbon monoxide, carbon dioxide, hydrogen, oxygen, and nitrogen. Since no special precautions were taken to keep traces of air out of the large bottle or the connecting tubing and the ratio of nitrogen to oxygen was found to be almost that of air, it was concluded that the nitrogen and oxygen came from such sources. A typical gas analysis is given in Table 111. This was made on the gas mixture obtained in run VII, “Methods of Chemists of the C. S. Steel Corporation for sampling and analysis of Carnegie Steel Corporation (1927).
gases.”
3030
KENNETH A . KOBE AKD L. H. REPERGON
TABLE I11 Carbon dioxide Unsaturated hydrocarbon Oxygen Carbon monoxide Hydrogen Saturated hydrocarbons as C3Hs Sitrogen
I
I1
Average
44.5 29.7 .6
44.5 29.5 .6
44.5 29.6 .6
2.2
2.0
2.1
17 5
18.2
18.2
19.1
18.2
2.1
2.1
2.2
2.2
2.2
2.8
The principal hydrocarbon product was the unsaturated one so that its identification was next undertaken I t was first identified by gas analysis methods and later established by the formation of a derivative. A complete analysis of the gas was first made. A sample of the original mixture was then taken and the carbon dioxide removed. Small portions of this residue were then mixed with oxygen and exploded. The decrease in volume and the amount of carbon dioxide formed was measured. The decrease in volume and the carbon dioxide which should result from the combustion of all the gases except the unsaturated was calculated from the complete gas analysis. By subtraction, the changes produced by the unsaturated hydrocarbon were obtained. The data for the analysis of the products of run V are given in Table I V and the results of the analysis of the products of run VI are given in Table V. The columns headed by the letters A, B, C, or D record the analytical results obtained on using separate samples of gas taken from the same source. The values are given in cubic centimeters of gas.
TABLE IV Volume of gas taken Volume after COZ removed
100.0
87.6 B
A
Vol. used for combustion Oxygen added to 5'01. after explosion Volume after COZabsorption Contraction COS
12.0
15.2
93.6 79.0 ;2.6 14.6 6.4
93.3 74.7 66.3 18.6 8.4
C 15.6 93.4 74.0
65.3 19.4 8.7
Calculated amounts from complete analysis Unsaturates
co '23%
Hz Air
A
B
C
1.98
2. j I
2 4 7
.04
.05
.OS
I9 6.03 3.75 __
.24 7 63 4.75
.2j 7.82 4.88
'
11.99
'
15.18
15.57
3031
CATALYTIC HYDROGENATION OF CARBON SUBOXIDE
TABLE I V (Continued) Contractions calculated from above B
A
Due to C3Hs Due t o CO Due to HP
57
75
.72 02
02
02
04 __
11
46
11
9 63 14 6
I2
20
I 2 50
Q
Contraction found Difference due to unsaturated
C
73 __
-
18 6 6 4
5 0
I9 4 6 9
Carbon dioxide calculated from above Due to C3H8 Due to CO
57
.72
04
,oj
61 6 4 5 8 I 98 5 8
COS found Difference due to unsaturated Unsaturated C'OZ Contraction COz/unsaturated Contraction/unsaturated
5 0
'75 .Oj
__
_-
.ii 8.4
7.6
.80 8.7 8.1
2.jI
2.57
7.6 6.4
8.1 6.9 3.15 2.68
2
93
3.02
2
52
2
54
-4w. 3.03 2.58
TABLE T Unsaturated
A 1.76
CO?
5 3i
C
B 2
Contraction 3.38 C02/unsaturated 3.05 Contraction/unsat. 2.49 COz/contraction = 2.96/247 =
23
6 60 5 68
I.
D
2.48
1.8j
Avr.
7.27
5.37 4.34 2.90 2.35
2.57
6.22
2
96
2.93
2
54
2.51
2.96
197
If the unsaturated hydrocarbon were propylene the combustion reaction 2C& -t 9 0 2 . . . . . .6co~ 6H20 6 volumes of COS would give the following theoretical rations: = 3, 2 volumes of C3HB
+
5 volumes contraction z volumes C3H6
=
2.5,
Of
'OZ
-
1.20.
It is evident
5 volumes contraction
from the results that the unsaturated hydrocarbon gives values which check the theoretical values for propylene almost exactly. It is very doubtful that any of the hydrocarbon was cyclopropane which is the other hydrocarbon having the formula C3Hs. In the first place the unsaturated hydrocarbon
3032
KENNETH A. KOBE A S D L . H. RETERSOS
was readily absorbed in broniine water.Q In th:. second place cyclopropane readily isomerizes to propylene in the presence of catalysts at the operating temperatures used in these researches.'O The gaseous products from Run VI1 were transferred to a bottle over bromine water and bromine was slowly added from a separatory funnel until a bromine color remained. The excess of bromine was removed by sodium sulfite and the solution extracted twice with ether which was then dried over calcium chloride. The ether was distilled off and the main fraction collected at 137' to 144'. The refractive index (.ibbe), density and Carius halogen were determined on this fraction. In Table TI these results are compared with the known constants of propylene dibromide and I ,3 dibrompropane.
TABLE TI N,?"
hpt.
Values found CH3CHBrCHd3r CH2BrCHL'H pBr
I 3 7-1 44
I .;I I
140
I .520
167
1.523
dim,
(26')
.893(26O) 1.933 1.979 I
';Br i6.6 i9.2
79.2
These results establish the fact that propylene was the unsaturated product of the hydrogenation. Since propylene was proved to be the unsaturated product in the hydrogenation of carbon suboxide it was assumed that the small trace of saturated hydrocarbon found was propane. h summary of the analysis of the gaseous products for the various runs calculated on an air-free and hydrogen-free basis is given in Table VII. The air and hydrogen are not reaction products so are left out of the summary.
TABLE 1-11 Run
Con C3H6 CO C3HS Total volume of gas 72 yield of CZH,
I11 49.;
\
