A UK research team claims to have developed a way of synthesising medium chain aldehydes in a continuous flow process using a homogeneous rhodium catalyst.

Previously the use of homogenous catalysts in continuous flow synthesis has proved problematic, because they are required to be both soluble in and separable from the reaction mixture.

However, according to a report from the Royal Society of Chemistry, the team from the University of St Andrews have got around this barrier by using the product of the reaction to dissolve the catalyst, which is then extracted while it is being formed with supercritical CO₂ (scCO₂).

The system achieves this result by mixing the alkene (octane) and aldehyde (nonanal) together, then forming a rhodium imidazolium catalyst while pressurising the system with CO₂, H₂ and scCO₂.

Then as the reaction commences, "scCO₂ can be used to transport everything continuously into and out of the reactor", according to Professor David Cole-Hamilton who led the research.

Source:

Catalyst problems dissolve away, 15/10/07
http://www.rsc.org/Publishing/ChemTech/Volume/2007/11/Catalyst_problems_dissolve.asp

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