Biphasic and Flow Systems Involving Water or Supercritical Fluids

Abstract

Two processes are described for improving reaction rates for relatively hydrophobic substrates in aqueous biphasic systems. In the first, 1-octyl-3-methylimidazolium bromide ([Octmim]Br) increases the rate of hydroformylation of 1-octene from 8% conversion in 24 h to full conversion of 1.5 h. Phase separation is fast and catalyst retention is good. 1-Hexyl-3-methylimidazolium bromide gives little rate enhancement, whilst 1-decyl-3-methylimidazolium bromide gives stable emulsions., The mechanism of action of these additives is discussed. In the second approach, functionalising PPh 3 with amidine groups allows the rhodium catalysed hydroformylation of 1-octene in toluene with a very high reaction rate. The catalyst can be switched between toluene and water by bubbling CO 2 and back into toluene by bubbling N 2 at 60°C. This switching has been used to separate the catalyst from hydrophobic (from 1-octene) or hydrophilic (from allyl alcohol) aldehydes obtained from hydroformylation reactions. CO 2 expanded liquids have been shown to be effective media for transporting substrates and catalysts over supported ionic liquid phase (SILP) catalysts. The advantages offered over all gas phase and liquid phase catalysts are discussed.

First efficient catalyst recycling for the iridium-catalysed hydroformylation of 1-octene

“…13,[15][16][17][18][19][20][21] This paper describes for the first time the development of a new catalyst recycling concept for the iridium-catalysed hydroformylation of 1-octene. 13,[15][16][17][18][19][20][21] This paper describes for the first time the development of a new catalyst recycling concept for the iridium-catalysed hydroformylation of 1-octene.…”

“…After the reaction, the mixture can be separated into two liquid phases using a separator at lower temperatures. 13,[15][16][17][18][19][20][21] This paper describes for the first time the development of a new catalyst recycling concept for the iridium-catalysed hydroformylation of 1-octene. First, opportunities of controlling and optimizing the reaction to achieve high yields and selectivities toward the desired aldehydes and to supress hydrogenation were to be identified.…”

Comparison of phase transfer agents in the aqueous biphasic hydroformylation of higher alkenes

“…4 Besides the fluorous solvents, hydroformylation reactions have been carried out in all so-called green solvents, such as ionic liquids 5 and supercritical CO 2 , 6 or even in solvent combinations like IL or fluorous and scCO 2 7 and with a solid support. [8][9][10][11] In all these reaction media a single phase is formed at reaction temperature and phase separation is accomplished by a change of temperature in order to isolate the product and to recycle the catalyst. Microemulsions 12,13 and polymers as a phase mediator 14 and as a catalyst support 15 have already been applied for the hydroformylation of short alkenes and higher alkenes, but with monodentate ligand-based water soluble catalyst complexes only.…”