Cyclooctene hydroformylation

The rate of hydroformylation depends on the structure of the olefin, the order being as follows straight-chain terminal olefins > straight-chain internal olefins > branched-chain olefins. Cyclohexene reacts more slowly than cyclopentene, cycloheptene, or cyclooctene. 

With olefins, CO, and H2 catalytic hydroformylation takes place even at 25 and subatmospheric pressure. Rates and product distributions depend on substrate type, [S], [H2], [CO], ligand type, [L], [Rh], and temperature. Rates with selected olefins are given in Table 10. Note that 2-pentenes react about 25 times slower than 1-pentene, and that 2-methyl-1-pentene (a hindered terminal olefin) is slower still. Cyclooctene is much faster than cyclohexene, presumably because of ring strain effects on olefin coordination, t Butadiene reacts rapidly with the catalyst to form an inert (tt-crotyl)Rh(CO)L2 complex and no gas uptake occurs at 25 . 1,5-Hexadiene can be successfully hydroformylated, because the hydroformylation rate (to primarily linear dialdehyde) is fast compared to the rate of isomerization... 

A similar in situ spectroscopic strategy was undertaken to determine if a Heck and Breslow binuclear elimination mechanism might be present in the unmodified rhodium-catalysed hydroformylation of alkenes. In one study alone, over 15 substrates were investigated where the acyl species RCORh(CO)4 was always observed, but under the conditions used, only the linear term was statistically supported [49], However, hydroformylation of two substrates, namely, cyclohexene and cyclooctene, exhibited outlier behaviour. With these two substrates, full conversion of the catalyst precursor Rh4(CO)i2 was never observed. Further detailed study of cyclohexene could not verify a statistically supported quadratic contribution [50, 51], The in situ study of cyclooctene at much lower CO partial pressure was more fruitful, as RCORh(CO>4, HRh(CO>4 and Rh2(CO)g were all observed simultaneously [52]. At the mean reaction conditions used in this study, 40% of product formation arose from the quadratic term k2[Rh]. Therefore, it appears that... 

Liu G, Li CZ, Guo LE, Garland M (2006) Experimental evidence for a significant homometallic catalytic binuclear elimination reaction Linear-quadratic kinetics in the rho-ditmi catalyzed hydroformylation of cyclooctene. J Catal 237(l) 67-78... 

Undec-lO-enal is a widely employed synthetic aroma compound with a citrus, waxy, fatty odor accompanied by a green, soapy nuance. It can be produced by hydroformylation of 1,9-decadiene (Scheme 6.25). The required substrate is accessible, for example, by olefin disproportionation of cyclooctene with ethylene [100]. The diene was reacted with syngas in the presence of a heterogenized Rh catalyst in a flow reactor to give undec-lO-enal and 2-methyldec-9-enal in 80% overall yield and a slight dominance of the linear aldehyde. The isomers could be separated by distillation. The smell of the branched aldehyde is very similar to that of... 

The two double bonds in (I) are not both hydroformylated at the same rate. At 80-100 and 100 atm CO/Hg (1 1), only one of the double bonds reacts and cyclooctene aldehyde (IV) is formed. This can react further in two ways. At synthesis gas pressures above 200 atm, the second double bond is hydroformylated, at its original position, to a mixture of dialdehydes (V). Under 200 atm, the double bond is isomerized into conjugation with the aldehyde group. The a,p-unsaturated aldehyde (VI) is hydrogenated, slowly at 100 °C and rapidly at 150 °C, to the saturated aldehyde (VII), which may be hydrogenated to the monool (II) by raising the temperature to 210 °C. 

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