I
W. A. SKINNER, ERNEST BISHOP, PARIS CAMBOUR, SAMUEL FUQUA, and PETER LIM Chemistry Department, Stanford Research Institute, Menlo Park, Calif.
Studies of the Reaction of Ethylene with Aluminum Trialkyls Data on product yield and distribution under various conditions point the way for economical production of primary alcohols T H E REACTION of an olefin with metal alkyls was first reported by Ziegler and Gellert ( 3 ) for lithium alkyls with ethylene. Later, Ziegler ( 4 ) found that ethylene could also be made to react with aluminum and beryllium alkyls. The discovery that aluminum alkyls could be synthesized directly from aluminum, hydrogen, and olefins ( 2 , 5, 70) aroused interest in the reactions of aluminum alkyls, because of their potential availability a t reduced costs of manufacture. Triethylaluminum is reported to react with ethylene at temperatures of 160' to 240' C. and at pressures of 60 to 230 atmospheres to yield mixtures of olefins and ethylene polymer (6). Olefins that are terminal vary from 85 to 87 weight % at lower temperatures to 1 weight % at the upper temperature range. The reaction of ethylene with triethylaluminum a t lower temperatures in the range of 60° to 120' C. has been reported (7) to yield only higher aluminum alkyls by addition reactions, whereas in the higher temperature range-i.e., 120" to 250' C., a thermal displacement reaction occurs. Above 150' C., dimerization of the olefins produced occurs (7).
Addition reaction: AI(CzHt.)a where x
+ y +P
Equipment
Manufact urer
Rocking bomb for gas-liquid mixing Distillation column aluminums
for
the
alkyl-
Chemicals Used
Suppliers
Ethylene, C.P. grade Ethylene, from alkane dehydrogenation Heptane, cyclohexane, and mixed xylenes-99 mole Decalin and Tetralin; fluorobenzene ( 1 O melting range)
yo
Triethylaluminum, 90% minimum material
25% volume solution in n-heptane Triisobutylaluminum, 50 solution in n-heptane
volume
%
The possibilities of producing straightchain terminal olefins or alcohols (9) via the reaction of ethylene with triethylaluminum has created consider/(CzH4)xCzHs CzH~),CeH, \(c~H~),c~H~
+ nC2Ha -+Al-(
= n
Displacement reaction: A~[(C~H&C~HE.]~ Al(CzH6)i f ~ H ( C Z H I ) ( ~ CH=CH2 -,, +
AlEt,
Dimerization reaction: 2R-CH=CHz
--+
R\ C=CHz /'
R(CHzh
If nickel, cobalt, or platinum salts are present, the displacement reaction occurs at temperatures as low as 50' C. At higher temperatures, these metals catalyze the isomerization of the terminal double bond producing internal olefins, unless acetylene or a substituted acetylene is present (8). I n practice, the number of ethylene units sandwiched between the aluminum and each of the three ethyl groups of the triethylaluminum molecule is not the same. Hence, terminal olefins or higher trialkylaluminums of varying chain length are produced.
American Instrument Co., Silver Spring Md. Podbielniak, Chicago, 111.
able interest in that reaction. The present study was undertaken to determine the variability of product kindhigher aluminum alkyls, terminal, internal, or branched olefins-yield, and chain length distribution with changing reaction conditions-temperature, pressure, solvents, time. The results of these studies indicate the type of product distribution of alkyl aluminums or olefins to be expected from the reaction of ethylene and triethylaluminum under various conditions of temperature, pressure, and concentrations of triethylaluminums.
{
Matheson Co., Inc., East Rutherford, N. J. Gulf Oil Corp., Pittsburgh, Pa. Phillips Petroleum Co., Bartlesville, Okla. Matheson Coleman & Bell Div., East Rutherford, N. J. Ethyl Corp., New York, N. Y. Industrial Chemicals Inc., South Bend, Ind. Hercules Powder Co., Wilmington, Del. Hercules Powder Co., Wilmington, Del. Experimental
A 1.4-liter stainless steel Aminco rocking bomb was used for the ethylenetriethylaluminum reactions. Good mixing of gas and liquid was necessary for optimum reaction rates. Ethylene, C.P. grade, was used for the majority of the experiments although for several runs ethylene obtained by the dehydrogenation of alkanes was used. No differences in reaction rates or products were noticed between the two grades of ethylene used. The benzene used was thiophene free; the heptane, cyclohexane, and mixed xylenes were all 99 mole yo. Decalin and Tetralin were practical grade materials. The fluorobenzene had a 1' melting range. Triethylaluminum from three sources was used. T h e triisobutylaluminum used was a 50 volume 7 0 solution in n-heptane. After each run between triethylaluminum and ethylene, the gases were vented slowly through a series of glass spiral traps immersed in Dewar flasks filled with dry ice-acetone slush. No material was ever found in the last trap. The trapped, liquid butene was redistilled from an ice bath and finally, a t room temperature, slowly into a graduVOL. 52, NO. 8
AUGUST 1960
695
40
c
30
I
I
I
2
4
6
28
I
'-
26 24
22
A L K Y L CHAIN LENGTHS (number of carbon o f o m s l
20
A
z
16
LL
Figure 1. Reaction of triethylaluminum with ethylene at 1000 p.s.i.g. Variation o f alkyl chain length of products as a function of reaction time
u J
16
,'" c
r
Initial ethylene pressure: 1000 p.s.i.g. Triethylaluminum: 0.3 mole Temperature: 90°& 3' C. Time: 15 hours 0 45 hours
:4
2
d
3
0
12 10
e
Figure 2. Poisson distribution in ethylene-triethylaluminum reaction based on random addition
E
4
ated trap immersed in a dry ice-acetone bath and the volume was measured. When the gas pressure reached 100 p.s.i.g., the bomb was inverted, and the liquid reaction products were removed into a glass container flushed out with dry nitrogen gas. Any butene evolved during this procedure was trapped as before. The triethylaluminum and higher alkylaluminums were decomposed by dropping them slowly into a vigorously stirred solution of 6 N hydrochloric acid in a three-necked flask. T h e butane evolved upon decomposition was trapped as before. The hydrocarbons produced by acid decomposition of the alkylaluminums
2
0 0
were distilled through an externally heated, Podbielniak column, 8 mm. in inside diameter. This column separated the Cg, CS,Clo, C12, CM: and c16 hydrocarbons very nicely from one another and from the waxy residue. Any butane or butene dissolved in the solution was trapped in a dry ice-acetone trap prior to the distillation of the hexene-hexane cut. The various cuts of mixtures of saturated and unsaturated straight chain and branched hydrocar-
Table I. Experimental Values for Product Distribution W e r e Obtained with Changing Initial Ethylene Pressure a t Three Concentrations of Triethylaluminum Heptane, Time, Temp., hll. Hr. C. 4 4 2 2 8 8
200 200 200 200 200 190
110 110 110 110 110 110
Initial C2H4 EtaAl, Pressure," Mole P.S.I.G. 925 0.60 850 0.30 0.90 900 0.60 900 850 0.30 850 0.36c
Olefins, Weight yo c 4
C6
1 1 16 7 14 16 29 38 21 16 19 21 1 5 6 6 3 6 5
a Saturated a t room temperature a t pressure indicated. num used.
Table II. Run No. 3266-29 3266-31 3266-32 3266-33 3266-34 3266-36 3266-39 3266-41
696
cl0
c 1 2
c14
23 27 12b 23 10 11
20 18
13 9
14 15 14
17 14
* Residue,
%.
CIS
CIS
7
5 '
gb
7b 13 13
33b 3Jb
Tributylalumi-
Product Distribution in the Ethylene-Triethylaluminum Reaction' in Various Solvents at Constant Pressure
Time, Et8A1, Pressure, Hr. Mole P.S.I.G. 930 4.0 0.6 950 4.0 0.6 950 4.0 0.6 950 4.0 0.6 950 4.0 0.6 950 4.0 0.6 1400 3.0 0.6 950 4.0 0.6
All runs at 110' C. ~
c g
Hydrocarbon, Weight yo Solvent, M1. C d Ce C S C ~ O CIZ c14 c16 Benzene, 300 6 13 24 27 17 8 5b Heptane,200 16 27 29 15 9 4b T e t r a l i n , 200 10 28 26 20 10 6$ Decalin, 200 20 30 21 16 9 4b Xylene, 200 15 30 27 15 8 3 Zb Cyclohexane,200 13 16 31 21 13 6* Benzene, 200 7 16 28 23 14 5 5b Fluorob enzene, 200 16 30 29 17 6 2b
Residue.
~
INDUSTRIAL AND ENGINEERING CHEMISTRY
Total product, G. 146 113 138 139 142 130 169 130
8 IO '2 I4 6 N U M B E R OF C A P B O W A T O W S
I6
20
22
24
bons were analyzed by comparison of their infrared spectra with standards made up of the pure hydrocarbons. Discussion
To avoid the displacement reaction, the first experiments were conducted a t 90"
+ 3' C. The variation of the alkyl chain length in the products as a function of reaction time is shown in Figure 1. These studies were conducted by displacing the alkyl groups on the aluminums, after the initial growth reaction with ethylene, using nickel acetylacetonate as the displacement catalyst and then distilling the olefins produced. The triethylaluminum regenerated by the displacement reaction was destroyed with dilute hydrochloric acid. The rare of the thermal displacenient reaction between ethylene and triethylaluminums a t 120" C. is approximately 20 times that a t 110' C. This value was obtained by determining the ratio of butene produced to the ethylene reacted at the two temperatures. At 110' C., the ratio of butene produced to ethylene reacted was 0.01. At 120' C., the ratio was 0.23. Katta ( 7 ) has indicated that the rate of the addition reaction is proportional to the product of the ethylene and triethylaluminum concentrations. Table I shows the effect of the triethylaluminum concentration on the product distribution in the ethylene-triethylaluminum reaction. Tributylaluminum was prepared by repeated contacting of 1-butene and triisobutylaluminum a t 110" C., removal of the gases, and analysis by mass spectrometer for isobutylene content.
-
ETHYLENE-ALUMINUM T R I A L K Y L S ~~
~
Table 111.
Product Distribution in the Reaction of Pure Triethylaluminum with Ethylene
Dimerization occurs at higher temperatures (150' C.) with the branched olefins decreasing from run 34 (160' to 170 Temp., Run No. 3516-25O 3516-34b 3516-47 3516-48 3516-49' 3516-50 3648-9
c.
140 160-170 134-146 170 150 140 140-160
Time, Hr. 1.75 2.0 1.5 2.0 1.5 2.0 1.0
EtzA1, Mole 0.72 0.72 0.36 0.72 0.54 0.54 0.72
Pressure, P.S.I.G. 900 500-1000 900 600 900 600 1300
CC 9.6 8.3 7.3 7.0 9.8 11.2 6.2
CE 16.9 12.7 17.7 13.2 13.9 20.3 14.6
Weight Per Clo 19.9 19.2 13.8 15.0 21.7 20.1 15.9 16.1 17.0 16.9 27.1 18.4 17.7 18.2
CS
Cent of All Products CIZ C14 CIS 14.6 9.6 5.2 16.3 10.9 6.8 14.9 9.1 9.Zd 15.2 10.0 8.0 15.9 10.5 6.9 12.1 6.7 4.2d 15.0 11.4 8.3
Weight Per Cent of Products Terminal Internal Branched No. Saturates Olefins Olefins Olefins 3516-34 c6 5.8 1.1 0.6 5.2 ca 5.5 5.1 1.2 2.0 ClO 5.7 5.1 1.1 3.1 c 1 2 5.8 3.6 1.6 5.3 c 1 4 3.8 2.4 1.2 3.5 CIS 2.5 4.3 4.3 4.3 35 16-48 CE 6. I 3.4 0.5 3.2 CS 6.5 3.8 1.6 4.0 c IO 5.3 4.5 1.6 4.7 ClZ 4.9 2.9 1.8 5.6 1.7 1.3 4.0 Cl4 3.0 Cl6 2.4 5.6 5.6 5.6 3516-49 0 0.7 CE 7.8 5.4 cs 10.6 5.6 0 0.8 ClO 11.0 4.6 0 1.3 0 1.6 ClZ 10.7 3.6 c 1 4 6.9 1.8 0 1.8 C16 4.5 1.2 0 1.2 a Temperature went to 166' C. momentarily. Pressure went t o 300 p.s.i.g. during first 30 minutes. Highly exothermic reaction. Pressure t o 500 p.s.i.g. before repressurizing. PresGreater than carbon chain in previous column. sure a t 720 p.s.i.g. for 15 minutes. Run No.
h
Carbon
This tributylaluminum was reacted with ethylene at 110' C. and 850 p.s.i.g. for 8 hours. The alkylaluminums produced were displaced with ethylene in the presence of nickel and the olefins isolated by distillation. No chain branching of the olefins was detected by infrared measurements. The product distribution as compared with a similar run made using triethylaluminum is shown in Table I. The similarity of the distributions in the two runs is surprising as it was thought that the use of tributylqluminum would shift the distribution two carbons higher. Because some isobutylene was recovered from the run, indications are that all of the isobutyl groups of the triisobutylaluminum were not displaced by 1-butene and became displaced by ethylene. Also some displacement of butyl groups of the tributylaluminum with ethylene probably occurred during the run. The reaction of triethylaluminum (0.6 mole) with ethylene in the absence of a solvent was conducted a t 110' C. and 1000 p.s.i.g. for 4 hours. During this time the pressure was kept constant by repressurizing as the pressure dropped. The aluminum alkyls were decomposed with dilute hydrochloric acid giving the following products: 9.4 grams of butane, the Co cut mixed with some heptane that was added to aid in the decomposition of the aluminum alkyls, 4.2 grams of octane, and 6.5 grams of higher al-
kanes. These data indicate that the reaction between triethylaluminum and ethylene is extremely slow at 110' C. when no solvent is present to dissociate the triethylaluminum dimer. A solubility effect is not operative here, because of the fast rate at higher temperatures when solubility is less and dissociation of the triethylaluminum dimer is favored. Benzene is a superior solvent for the growth reaction between ethylene and triethylaluminum giving a more desirable distribution of higher alkylaluminums produced per unit of time (Table 11). When diethyl ether, tetrahydrofuran, or diphenyl ether was used as a solvent for the ethylene triethylaluminum reaction, the reaction rate was appreciably slower than when the other solvents reported were used. All of these ethers complex with triethylaluminum and for the ethylene reaction, the electrophilic nature of aluminum in triethylaluminum must not be disrupted. If ethylene adds randomly to the chains on the trialkylaluminum, the chain lengths of the resulting hydrocarbons obtained upon acid treatment should follow the Poisson distribution:
w,
3
m -n 8-m n!
where W,, is the weight fraction of material to which n ethylene molecules have added and m is the over-all average
' C.) to run 49
ClS
Cia
5.0d
3.6 14.6d 9.1d 8.6d
12.6d
(150" C.) Total Product Weight, G. 249.9 443.9 102.0 377.2 202.2 123.1 301.2
number of ethylene molecules taken u p by the triethylaluminum. Figure 2 depicts some typical Poisson curves. The experimental results reported in Table 11, where the reaction was carried out a t 110' C., agree quite well with a Poisson type distributiod curve. The olefins produced under these conditions were less than 5Oj, of each cut distilled as determined by their infrared adsorption spectra. Due to the lengthy reaction times necessary to produce the product distribution sought in this investigationLe., peaks a t C ~toZ C14, higher temperatui-e runs were investigated. I n contrast to the reaction rate a t llOo C., triethylaluminum reacts rapidly with ethylene above 135' to 140' C.-temperatures where the dimer form is appreciably dissociated. Tables I11 and IV show the results of some of these higher temperature runs with triethylaluminum alone and in benzene solution. Figures 3 and 4 compare the product distribution curves with the Poisson curves. When growth and displacement reactions are occurring simultaneously, Poisson curves are not followed, as when only growth reaction occurs at lower temperatures. Trihexylaluminum (0.29 mole) prepared from 1-hexene and triisobutylaluminum was reacted with ethylene at 150' C. and 1000 p.s.i.g. for 1.5 hours. The distribution by weight % was as follow^: Cq, 8.2; CG, 14.8; Cs. 18.7; Cia, 14.9; Ciz, 11.9; (214, 10.4; C16, 6.9; CIS, 5 . 3 ; >CIS, 8.8. The total weight of products was 233.5 grams. For comparison, a run with triethylaluminum (0.29 mole) was made at 150" C. and 1000 p.s.i.g. for 1.5 hours. The distribution was: C d , 4.8; Cg, 9.6; (28, 11.1; Clo, 12.9; ClZ, 12.6; C14, 12.4; cis, 10.9; CIS, 9.0; >cis, 16.7. These results show that at 150' C. the hexyl groups of trihexylaluminum undergo rapid displacement to 1-hexene and triethylaluminum. Therefore, it is not advantageous to start with higher alkylaluminums when operating at 150' C. Because both olefins and higher aluminum alkyls are produced from the high temperature reaction of ethylene and triethylaluminum, it was desirable to determine whether higher terminal olefins would displace lower alkyl groups on aluminum alkyls. Triethylaluminum VOL. 52, NO. 8
AUGUST 1960
697
I
4
6
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8
IO 12 14 16 18 N U M B E R OF C A R B O N A T O M S
22
20
24
NUMBER O F C A R B O Y
26
Figure 4. Product distribution in the reaction of ethylene with the with triethylaluminum inbenzene and theoretical distribution
Figure 3. Product distribution in the reaction of pure triethylaluminum with ethylene and comparison with the Poisson distribution Table IV. Run No. 3266-27 3266-29 3266-37a 3266-39 3516-4 3516-20 3516-37 3516-43
Product Distribution in the Reaction of Ethylene with Triethylaluminum in Benzene
Temp.,
Time, Hr.
EtaA1, Mole
Pressure,
Benzene,
P.S.I.G.
M1.
C,
110 110 130-145 110 130 140-180 140 140
4 4 3 3 2 1 2
0.72 0.72 0.72 3.72 0.72 0.72 0.36 0.36
1000 930 950 1400 1000 700- 1000 1000
200 200
17 6 3 7 4 11 0.5 4
c.
1
ATOMS
200 200
200 200 200 200
1000
Weight Per Cent of All Products Ce C S CIO CIS C14 CIS CIS 11 56 18 27 22 17 8 9 13 24 27 18 12 6 24* 9 13 15 14 5 Sh 16 28 23 17 10 7 6O 17 19 20 13 8 10* 24 17 17 11 10 13 10 11 11 12 17 11 7 5b 19 17 20
CZO
22a
Total Product Weight, G. 103.4 145.8 302.5 168.8 235.7 260.0 227.6 126.0
Weight Per Cent of Products Run No. 3266-37 3516-4
Carbon No.
Saturate
c6
4.5 6.6 12.9 15.1 16.5 13.2 9.2 8.2
cs CE CS
ClO 3516-20 3516-37
C6
cs
ClO CB c8
ClO Ct2
Cl4 Cl6 z,
Terminal 4.5 6.4 4.1 3.5 3.6 >9.1 >5.7 >4.8 7.1 5.9 5.5 6.7
5.7 4.3 5.3 4.7 6.2 6.5
Olefins Internal 0 0 0 0 0
