HYDROFORMYLATION OF 1-OLEFINS IN TERTIARY ORGANOPHOSPHINE-COBALT HYDROCARBONYL CATALYST SYSTEMS EDMOND R. TUCCI
Gulf Research and Development Co., Pittsburgh, Pa. 15230
The hydroformylation of propene and 1 -hexene has been investigated in a tertiary organophosphine-cobalt hydrocarbonyl catalyst system to determine the effects of this catalyst on branched-isomer formation. Trialkylphosphine complexes of the type HCo(CO)3(PR3) yielded 73% less branched-isomer formation than the conventional HCo( C0)4 system. This reduction in branched-isomer formation can be attributed to a decrease in 1-olefin isomerization prior to oxonation, or the preferential addition of HCo(CO)3(PR3) to the 1-olefin to form the more stable straight-chain alkyl- or acylcobalt hydrocarbonyl. The activity of the cobalt hydrocarbonyls to catalyze branched-isomer formation decreases in the order HCo(CO) 4 > HCo(C0)3(PAr3) > HCo(C0)3( PR3). In oxonating straight-chain 1 -olefins with HCo(C0)3( P B u ~ ) , branched-isomer formation was unaffected by an increase in the temperature ( 150-1 8OoC.), catalyst concentration ( 16-fold increase), and high CO partial pressures. The high selectivity (ca. 90%) of the HCo( CO)3( PR3) catalyst system to form straight-chain normal products over a wide range of reaction conditions is a distinguishing feature not observed in the conventional HCo(CO)4 catalyst system.
HYDROFORMYLATION of straight-chain 1-olefins in the con-
Experimental
ventional HCo(C0) catalyst system generally leads to the formation of linear aldehydes and large amounts of branched aldehydes (Hughes and Kirshenbaum, 1957; Roelen, 1948, 1952). Branched-isomer formation can result from 1-olefin isomerization by H C O ( C O )prior ~ to hydroformylation (Johnson, 1963) or by hydride addition from H C O ( C O )to ~ the terminal carbon of the 1-olefin. T o lessen branched-isomer formation, the use of dicobalt octacarbonyl-trialkylphosphine catalysts of the type Cog (CO)e(PR?)2 were investigated and have recently appeared in the patent literature (Greene and Meeker, 1966; Slaugh and Mullineaux, 1966). However, a comprehensive discussion concerning the nature of this unique catalyst and the scope of the oxonation reaction with this catalyst is quite sparse. Consequently, catalyst systems of the type HCo(C0) , ( P R J and H C o ( C 0 ) ,(PArr) were investigated to determine their effect on branched isomer formation. Since tertiary organophosphines possess strong complexing ability by virtue of their 0-donor and r-acceptor characteristics, a significant change in the olefin-isomerizing ability of HCo(C0) ,(PR3) or a change in the mode of addition of H C O ( C O ) ~ ( P R to ? ) the olefin might be expected. The over-all effect of using HCo(CO)3(PR3) instead of H C O ( C O )would ~ therefore be reflected in the extent of branched-isomer formation. An appreciable decrease in branched-isomer formation in the H C O ( C O ) ~ ( P Rsystem ~) was observed even a t oxonation temperatures that would normally lead to considerable isomer formation. This paper discusses these results and attempts to elucidate the role of tertiary organophosphines in the cobalt hydrocarbonyl-catalyzed oxonation of straight-chain 1-olefins.
Materials. The tertiary organophosphines were obtained from Carlisle Chemical Works and were found by chromatographic analysis to require no additional purification. Normal dodecanol of high purity was obtained from Humphrey Chemical Co., and high purity (99.7 mole %) propene was obtained from Matheson Co. The dicobalt octacarbonyl was prepared by reacting cobalt octanoate with about equimolar quantities of hydrogen and carbon monoxide a t 233 atmospheres for 1 hour a t 177°C. The synthesis gas (1.2 to 1 H, to CO) was generated a t Gulf Research and Development Co. A high-pressure 500-ml. stainless-steel reactor vessel, obtained from Autoclave Engineers Co., was used for preforming the dicobalt octacarbonyl and for the olefin oxonations. Transfers of tertiary organophosphines to the autoclave were performed with hypodermic syringes obtained from Feick Brothers Co. The oxonation product was analyzed chromatographically with an F & M Model 810 containing an 11-foot stainless-steel (%-inch) column packed with a Chromosorb W-Carbowax 20M (80 to 20 wt. SC mixture. Procedure. To the nitrogen-flushed 500-ml. stainless-steel autoclave was added 100-ml. of the solvent and the required amount of cobalt octanoate. The autoclave was flushed several times with synthesis gas and finally pressured to 2300 p.s.i.g. a t room temperature with synthesis gas. The autoclave was then heated to 177°C. and maintained a t 3500 p.s.i.g. for 1 hour. After cooling to about 25O C., the autoclave was depressurized, and the catalyst modifier was charged with a hypodermic syringe. The contents were mixed for 10 to 15 minutes a t about 40°C.
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I & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
to complete the complexation reaction, and the olefin oxonation was performed a t the desired temperature ( i 2 . C . ) and pressure by charging either propene or 1-hexene to the autoclave. At the end of the reaction period, the autoclave was cooled (20" C.) and the contents carefully drained into a nitrogen-flushed container for immediate chromatographic analysis to determine the isomer distribution and weight per cent of each component; runs were performed in duplicate. Tri-n-butylamine served as an internal standard in these chromatographic analyses.
0
z
P
90
90
80
80
70
70
f
60
60
P
50
50
4 J
L
Y
I z
0
->
w
L
>
J
L
"
Y -1 Y
0
1
2
3
4
5
6
PBu3/Co21COlg MOLAR RATIO
Results and Discussion
Effects of H C O ( C O ) ~ ( P B Uon ~ ) Branched-Isomer Formation. T h e oxonation of propene and to a lesser extent the oxonation of 1-hexene was investigated using a tertiary organophosphineemodified dicobalt octacarbonyl catalyst system. I n the hydroformylation of propene, the formation of branched isomers depends primarily on the direction of addition of the substituted cobalt hydrocarbonyl to the olefin. However, in the oxonation of 1-hexene, branched-isomer formation depends both on the addition reaction as well as the double-bond isomerization prior to the oxonation reaction. The tri-n-butylphosphine (PBu+coordinated cobalt carbonyl catalyst used in oxonating these two olefins appreciably inhibited the formation of branched isomers without showing any adverse side effect on the oxonation reaction. T h e effects of varying the [PBu]] [ C O ( C O ) ~ratio ] ~ in the oxonation of propene are shown in Figure 1. Both the selectivity to form straight-chain isomers and the propene conversion increase sharply as the PBu3 concentration approaches a P to Co ratio of one. Above this ratio, the excess PBui has essentially no effect on the selectivity and very little effect on the conversion. T o interpret these results, it is necessary to define the modified catalyst system by considering the complexation reactions between [ C O ( C O ) ~and ] ~ P B u r . The reactions between [ C O ( C O ) ~and ] ~ P B u j proceed through the following steps:
Figure 1. Effect of PBUS concentration on branched-isomer formation and propene conversion Oxonation of 0.19 mole propene a t 160°C. and 1000 p.s.i.g. H, to CO (1.2 to 1 ) for 1 hour in 110 ml. l-dodeconol containing 5.85 mmoles of Co2(CO)* and X mmoles of PBui
to the PBus-monosubstituted cobalt hydrotricarbonyl according t o the reaction
The reversibility in this catalyst system could lead to a steady-state catalyst system in which HCo(C0) ,(PBul) is in equilibrium with minute quantities of the unsubstituted cobalt hydrocarbonyl and dicobalt octacarbonyl. Also, if HCo(C0)i is assumed t o be in equilibrium with H C O ( C O ) ~(Breslow and Heck, 1961), HCo(C0)s could react directly with PBui to form HCo(CO)s(PBu3). Therefore, the complex equilibria in this catalyst system (under oxo conditions) may be represented by the reactions shown below. O X O CATALYST
E Q U-__ILIBRIA
-co [CO(CO)4],
2pB,,[CO (co),
(PB,,)
,]+[c0(c0),J-
