Hydroformylation cyclohexene oxide

In view of the many differences noted above between the hydroformylation of olefins and epoxides, it is not surprising to find that changes in structure result in a different order of reactivity in each case. Thus for epoxides the reactivity to cobalt hydrocarbonyl is cyclohexene oxide > propylene oxide, whereas with olefins the order is terminal olefins > internal olefins > cyclic olefins (145). 

Dimerization of the formed cx,P-hydroxy aldehyde may become a serious issue in the hydroformylation of epoxides with acidic metal catalysts. Orchin s group observed chiefly self-acetallzatlon products in the stoichiometric ring-opening reaction of cyclohexene oxide with CO and HCo(CO) (Scheme 6.108) [23]. 

Scheme 6.109 Tandem hydroformylation-acetalization of cyclohexene oxide.

The hydroformylation of ethylene oxide gives acrolein in very low yields, which is not surprising in view of its extraordinary reactivity in the main, resinous products are obtained. The reactions of ethylene oxide, propylene oxide, cyclohexene oxide, styrene oxide and epichlorhydrin were studied by Takegami et al. [297] at normal conditions. They found that generally internal and conjugated olefin oxides were more reactive than terminal ones and established the following order of reactivity cyclohexene oxide (appr. 5) > styrene oxide > propylene oxide (1) > ethylene oxide epichlorhydrin (1/20-1/10) (the numbers give the relative reactivity). 

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. 

Hydr/formyUttion. Swiss chemists recommend rhodium(lII) oxide as catalyst for hydroformylation of olefins. Thus they have prepared cyclohexanecarboxaldchyde (2) in 95% yield from cyclohexene (1). Lower yields were obtained using cobalt catalysts. 

An example is the hydroformylation reaction of cyclohexene catalyzed by the unsaturated compound HCo(CO)3 which is formed under reaction conditions from the precursor HCo(CO)4. Following the usual mechanism (see, e. g., [18]), the catalytic cycle is depicted in Scheme 1. Since the oxidative addition of H2 to the acylcobalt complex is the rate-determining step in this case the rate equation follows eq. (2) (cf. Section 2.1.1) ... 

---