Hydroformylations of cyclohexene

In addition to rhodium(III) oxide, cobalt(II) acetylacetonate or dicobalt octacarbonyl has been used by the submitters as catalyst precursors for the hydroformylation of cyclohexene. The results are given in Table I. 

The hydroformylation of alkenes generally has been considered to be an industrial reaction unavailable to a laboratory scale process. Usually bench chemists are neither willing nor able to carry out such a reaction, particularly at the high pressures (200 bar) necessary for the hydrocarbonylation reactions utilizing a cobalt catalyst. (Most of the previous literature reports pressures in atmospheres or pounds per square inch. All pressures in this chapter are reported in bars (SI) the relationship is 14.696 p.s.i. = 1 atm = 101 325 Pa = 1.013 25 bar.) However, hydroformylation reactions with rhodium require much lower pressures and related carbonylation reactions can be carried out at 1-10 bar. Furthermore, pressure equipment is available from a variety of suppliers and costs less than a routine IR instrument. Provided a suitable pressure room is available, even the high pressure reactions can be carried out safely and easily. The hydroformylation of cyclohexene to cyclohexanecarbaldehyde using a rhodium catalyst is an Organic Syntheses preparation (see Section 4.5.2.5). 

Solvent effects on the rate of hydroformylation have been found to be small, however. A small increase in the rate of hydroformylation of cyclohexene has been found in the series methanol > benzene > heptane but the overall increase is only by a factor of 1 5 (158). Alcohols have been reported to increase the yield of hydrogenated products (66, 88). 

Example 11.1. Hydroformylation of cyclohexene with phosphine-substituted cobalt hydrocarbonyl catalyst. The most probable network of cyclohexene hydroformylation catalyzed by a phosphine-substituted cobalt hydrocarbonyl is shown on the facing page. HCo(CO)3Ph (cat) is in equilibrium with the CO-deficient HCo(CO)2Ph (cat ) and CO. For greater generality, quasi-equilibrium of these species with the 7r-complex, X, is not assumed. Actual hydroformylation olefin — aldehyde proceeds via a Heck-Breslow pathway (cycle 6.9 that includes the trihydride, X2) but without... 

The hydroformylation of alkenes using CO2 instead of CO is an attractive target reaction. Since ruthenium complexes are active catalysts for the reduction of CO2 to CO and also for hydroformylation, it is expected that the hydroformylation of an alkene with CO2 would be successful. Indeed, Sasaki and coworkers found that Ru4H4(CO)i2/LiCl catalyzed the hydroformylation of cyclohexene to give (hydroxymethyl) cyclohexane in 88% yield [141]. 

Scheme 12. Proposed mechanism for the Rh4(CO),2-catalyzed hydroformylation of cyclohexene, adapted from (240).

Natta and Ercoli (3) have studied the kinetics of the hydroformylation of cyclohexene using 1 1 synthesis gas (1 H2 l CO) at total pressures ranging from 120 to 380 atmospheres dicobalt octacarbonyl was used as the catalyst. The reaction may be written... 

Fla. 11-10. The rate of hydroformylation of cyclohexene at varying total pressures of equimolar amounts of CO and H,. 

High-temperature and pressure IR studies with the original phosphine-free cobalt system under conditions for catalytic hydroformylation of cyclohexene (150 , 250 atm) normally show Co2(CO)s and HCo(CO)4 as the only spectroscopically detectable species, with the hydride as the major species. With 1-octene or ethylene, the hydride is not observed and the only detectable species are Co2(CO)g and RCOCo(CO)4. With... 

Feng J, Garland M (1999) The unmodified homogeneous rhodium-catalyzed hydroformylation of cyclohexene and the search for monometallic catalytic binuclear elimination. Organometallics 18(8) 1542-1546... 

The classical kinetic investigation of Natta and co-workers (87-90) on the hydroformylation of cyclohexene in toluene solution in the presence of octacar-bonyl dicobalt showed that the reaction is first order with respect to olefin over a wide range of olefin concentrations and first order with respect to dihydrogen partial pressure. At high partial pressure of carbon monoxide (10 MPa), the rate is practically proportional to the catalyst concentration. The effect of the partial pressure of carbon monoxide is particularly remarkable. When the pressure of carbon monoxide is increased, the rate of hydroformylation increases and reaches a maximum at a pressure that depends on the temperature and the olefin substrate. Above this pressure, the rate is inversely proportional to its partial pressure. 

The group of Jenner showed that a catalytic system consisting of Ru3(CO)j 2, tri-cyclohexylphosphine, methyl formate, and water is active in the hydroformylation of cyclohexene (Scheme 3.18) [40]. The aldehyde formed is immediately reduced... 

Scheme 3.18 Ru catalyzed hydroformylation of cyclohexene with methyl formate.

In principle, the hydroformylation-acetalization sequence can be performed in two separate steps as sometimes described in the older literature. Thus, hydroformylation of cyclohexene was carried out with Co2(CO)g as catalyst at 180 bar syngas pressure [45]. The formed aldehyde was separated from the catalyst and subsequently reacted with ethylene glycol in the presence of sulfuric acid to give the corresponding cyclic acetal. ... 

Table 31 [322]. Formation of ketones by the hydroformylation of cyclohexene with isopropanol as hydrogen donor...

An additional gas such as dinitrogen, argon, or xenon present in the reaction medium in high concentration was found to decrease the rate of hydroformylation of cyclohexene, 1-hexene, or styrene inthe presence of RhH(CO)(PPh3). This effect was attributed to a competition between the additional gas and one of the reagents, alkene, dihydrogen, or carbon monoxide for a coordinative unsaturated site available on the catalytically active intermediates [56]. 

Fujita, S. I. Okamuta, S. Akiyama, Y Arai, M. Hydroformylation of Cyclohexene with Carbon Dioxide and Hydrogen Using Ruthenium Carbonyl Catalyst Influence of Pressures of Gaseous Components. Int. J. Mol. Sci. 2007,8,749-759. 

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