PICESSURII
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V. L. HUGHES and ISIDOR KIRSHENBAUM Chemicals Research Division, Esso Research and Engineering Co., Linden, N. J.
Isomer Distribution in the Oxo Reaction )Temperature and type of olefin have the greatest influence on isomer product distribution, low temperature and terminal olefins favoring formation of the straight-chain product
SINCE
the Oxo reaction was discovered in 1938 by Roelen (77), the kinetics and mechanism have been investigated from the standpoint of olefin structure and reaction conditions (5-70, 73, 74). Little has been reported on the distribution of isomers in the product (7-3), but it is known that reaction of a straight-chain terminal olefin, such as I-butene, leads to two isomeric aldehydes (or alcohols).
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for preparing an alcohol of mono-isomeric composition, effects of process variables on product composition were studied. The variables included temperature, pressure, hydrogen-carbon monoxide mole ratio, catalyst concentration, and olefin type. ReFults showed that the percentage of straightchain aldehyde or alcohol in the reaction product can be controlled, within limits, by proper choice of operating conditions. I n addition, new insight as to the mechanism of reaction was obtained. Experimental Conditions
Starting Materials. Cobalt carbonyl, dissolved in hexane, was used as catalyst in all experiments. The caf-bonyl solution was prepared by subjecting a hexane solution of cobalt oleate to a pressure CH~--CH~-CH~=CHZ CO Hz + CH 3-CH 2-CH z-CH 2-CH 0 . of 3500 pounds per square inch gage of CH 3-CH2-CH-CHO carbon monoxide and hydrogen at I I 160' C. for 3 hours. The solution was CH 3 stored in a container a t a pressure of 200 Similarly, higher olefins give three pounds per square inch gage of carbon monoxide and samples were withdrawn principal isomeric products. When 1as required. Cobalt was determined heptene is oxonated to form alcohols, for example, the principal products on a sample which was first treated are 1-octanol, 2-methyl-I -heptanol, and with bromine to destroy the carbonyl. 2-ethyl-1-hexanol. In general, pubThe cobalt was extracted with water lished data indicate a straight chainand a small portion of the water exbranched chain isomer distribution of tract was analyzed spectrophotometabout 1 to 1 in the product aldehyde or rically, using the nitroso-R complex alcohol (7, 3). One exception is the (4). recent article by Goldfarb and Orchin ( 2 ) , Propylene and 1-butene were obtained which reported yields of straight-chain from Matheson Co., Rutherford, N. J., product as high as 80% when l-penand were 99+y0 pure. The main imtene was oxonated a t 110' C. and an purities in each case were higher boiling initial pressure of 3250 pounds per materials. square inch gage of hydrogen and 1-Heptene was obtained from Humcarbon monoxide in a 1 to 1 ratio. phery-Wilkenson, New Haven, Conn., T o determine factors controlling isoand was about 92% I-heptene. The mer distribution and the best method main impurity was trans-2-heptene.
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Pure 1-heptene was obtained by distilling the 92% 1-heptene through a 6 foot X 2 inch column packed with metal helices. Low reflux rates were used to attain equilibrium conditions, and the last 2570 was discarded. 2-Heptene, obtained from the Phillips Chemical Co., Bartlesville, Okla., was 95y0 pure. No I-heptene was evident in the infrared spectra. Carbon monoxide and hydrogen were obtained in individual cylinders at 2000 pounds per square inch gage from Matheson-Coleman. The gases were compressed separately to desired pressures, the carbon monoxide being added first and the hydrogen later a t reaction temperature. Equipment a n d Procedure. All experiments were carried out in electrically heated rocked Aminco 3-liter bombs. Temperatures were controlled by relays to about &2' C. Pressures and temperatures were recorded automatically during an experiment. The Oxo product was hydrogenated over a Harshaw U O P nickel catalyst or a barium-promoted copper-chromia catalyst. Reproducible results were obtained with both procedures. The alcohol products were distilled using a 15-plate I-inch Oldershaw column. A Flexa-pulse timer (manufactured by the Eagle Signal Co., Moline, Ill.), was used to control the reflux ratio. A 5 to 1 reflux ratio was sufficient to separate the olefins, alcohols, and higher boiling materials. Analyses. Bromine number was used to determine total olefin in the hydrocarbon fraction. The per cent of each olefin was obtained by infrared type analysis. The sum of these two checked the bromine number value very well (usually within 2 to 3%). VOL. 49, NO. 12
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DECEMBER 1957
1999
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Figure 1 . Effect of temperature on product distribution in 1 -butene reaction
Figure 2.
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Effect of low temperature on oxonation Top. 1 -Heplene Bottom. 1 -Butene
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Octanol and pentanol isomers were analyzed by mass spectrometer, calibrated with synthetic I-octanol, 2methylheptanol, and 2-ethylhexanol. The butanol isomer distribution was determined in a Perkin-Elmer vaporliquid fractometer a t 80" C. An A column, diocty1 phthalate substrate, was used in the 6.5-foot column. Results checked those obtained by mass spectrometry to better than 0.5%. In preparing a sample of Oxo product for chromatographic analysis, the product was flash distilled to remove it from higher boiling materials. Precise fractional distillation was not necessary before analysis to separale the
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Figure 3.
I 100
Qf Temperature
Exploratory studies showed that the isomer distribution of an Oxo product depends upon operating conditions. Of these, temperature was the most important variable. Low temperatures favor higher percentages of the normal isomer, but a limit is reached, beyond which essentially constant yields are obtained. Data demonstrating this point were obtained with I -butene. Olefin type was very important in determining the nature of the product
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Effect of olefin structure on product distribution
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alcohols from hydrocarbons or traces of aldehydes.
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1-Heptene 2-Heptene
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Oxonation of 1-Butene. 1-Butene yields only two isomers on oxonationn-amyl alcohol and 2-methylbutanol. Studies have shown that low temperature favors the production of n-am)l alcohol. In the range of 70' to 90 " C., the normal isomer comprises about 757, of the product, the straight chainbranched ratio being 2.4 to 2.7/1. The effect of temperature on the percentage of straight-chain isomer is shown in Figure 1 and Table I. Although the percentage of straightchain alcohol increases sharply bethveen 150" and 90" C., a leveling off in the curve appears to relate temperature with yield of straight-chain isomer. Thus, there seems to be little advantage in oxonating below the 70" to 90" C. region when straight-chain compounds are desired. The rate of the Oxo reaction is also sensitive to temperature, as would be expected. Decreasing the temperature from 140" to 100" C. reduces the reaction rate by a factor of 25. From the data in Table I1 it has been possible to calculate an apparent energy of activation, assuming a first order reaction, of 24 kcal. per mole. This is somewhat lower than the value obtained by Natta for cyclohexene (9). The reaction rate can be increased by increasing catalyst concentration and varying the hydrogen-carbon monoxide ratio. In obtaining the data in Table I, it was not possible to keep the catalyst concentration the same at all temperatures, At 140' to 180' C, the catalyst concentration was 0.0870 (on olefin feed), calculated as cobalt. The reaction was extremely rapid and exothermic at much higher catalyst concentrations.
HIGH PRESSURE Table 1.
O n the other hand, a catalyst concentration of 0.5% cobalt was required a t 70' to 90' C. to obtain a reaction rate sufficiently higher to produce about 90+% conversion in a reasonable time (
