Issue 5, 2005

Continuous flow homogeneous hydroformylation of alkenes using supercritical fluids

Abstract

The hydroformylation of long chain alkenes, carried out as a continuous flow process by using a catalyst made in situ from [Rh(CO)2(2,4-pentanedioate)] and [1-propyl-3-methylimidazolium][Ph2P(3-C6H4SO3)] dissolved in 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonamide), is reviewed. The substrates are introduced into and the products are removed from the reactor dissolved in continuously flowing supercritical carbon dioxide. Optimisation studies allow long term operation with rates up to 500 catalyst turnovers h−1 and rhodium leaching into the product as low as 0.012 ppm. Using a different ligand based on the xantphos skeleton, linear ∶ branched ratios in the product aldehydes can be as high as 40 ∶ 1, but the rate is somewhat lower (272 h−1) and the rhodium retention is slightly less efficient. By removing the ionic liquid and dissolving the catalyst in the mixture of products and substrates that develops during the reaction, it is possible to carry out the reaction at much lower pressures (125 bar). 1-alkyl-3-methylimidazolium salts of [Ph2P(3-C6H4SO3)] are used as ligands and the success of the reaction depends crucially on the alkyl chain employed in the imidazolium cation. Too long a chain causes large amounts of rhodium leaching, whilst too small a chain causes the solubility of the ligand to be too low so that the reaction is very poor and unliganded rhodium is rapidly extracted from the system. The best results are obtained using a pentyl chain, which gives a rate of 162 h−1 and rhodium leaching of 0.1–0.5 ppm. Comparisons of these systems with current commercial systems are made and consideration is given to the design of a plant suitable for operating these reactions in a totally emissionless fashion.

Graphical abstract: Continuous flow homogeneous hydroformylation of alkenes using supercritical fluids

Article information

Article type
Paper
Submitted
01 Nov 2004
Accepted
31 Mar 2005
First published
20 Apr 2005

Green Chem., 2005,7, 373-379

Continuous flow homogeneous hydroformylation of alkenes using supercritical fluids

P. B. Webb, T. E. Kunene and D. J. Cole-Hamilton, Green Chem., 2005, 7, 373 DOI: 10.1039/B416713A

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements