Biphasic liquid/supercritical

A summary of the research activities of the last four years reveals three different important trends (a) The design of new ionic ligands for excellent catalyst immobilisation in ionic liquids and high regioselectivity (b) the successful application of cheap, halogen-free ionic liquids in the biphasic Rh-catalysed hydroformylation (c) the successful development of unusual multiphasic reaction concepts for Rh-catalysed hydroformylation, namely catalysis in ionic liquid/supercritical C02 and SILP-catalysts. 

In biphasic reactors or two-phase partitioning bioreactors (TPPB), the substrate is located mostly in the immiscible phase and diffuses to the aqueous phase. The enzyme catalyzes conversion of the substrate at the interface and/or in the aqueous phase. The product/s of the reaction then may partition to the organic phase. The system is self-regulated, as the substrate delivery to the aqueous phase is only directed by the partitioning ratio between the two phases and the enzymatic reaction rate [53]. The use of ionic liquid/supercritical carbon dioxide for enzyme-catalyzed transformation is gaining attention [69]. 

Hernandez FJ, de los Rios AP, Gomez D, Rubio M, ViUora G. A new recirculating enzymatic membrane reactor for ester synthesis in ionic liquid/supercritical carbon dioxide biphasic systems. Appl Catal B 2006 67 121-126. 

Ionic Liquids/Supercritical Carbon Dioxide as Advantageous Biphasic Systems in Enzymatic Synthesis... 

Ionic liquids/supercritical carbon dioxide (ILs/scCOj) biphasic systems have recently been considered as interesting clean alternatives to classical organic... 

In order to optimize and/or improve the behaviour of bioprocesses in ionic liquids/supercritical carbon dioxide biphasic systems, a better understanding of the chemical reaction and mass-transfer phenomena in these biphasic systans is required. In this context, de los Rfos et al. [38] analysed the chemical reaction and the mass-transfer phenomena in the synthesis of bntyl propionate from vinyl propionate and 1-butanol catalysed by CaLB immobilized on dynamic monbranes at... 

Chapter 8 focuses on the properties of ionic liquids/supercritical carbon dioxide biphasic systems for enzymatic applications. 

Other biphasic C—C bonding reactions were carried out with fluorous solvents, for instance Suzuki- and Sonogashira-couplings [124] or ethene or propene oligomerizations [125, 126], Further new solvent systems use ionic liquids for the linear dimerisation of 1-butene to octenes [127] or the hydrovinylation of styrene with a combination ionic liquid/supercritical carbon dioxide [128] (cf. Section 7.4). 

Last but not least, the success of aqueous-phase catalysis has drawn the interest of the homogeneous-catalysis community to other biphasic possibilities such as or-ganic/organic separations, fluorous phases, nonaqueous ionic liquids, supercritical solvents, amphiphilic compounds, or water-soluble, polymer-bound catalysts. As in the field of aqueous-phase catalysis, the first textbooks on these developments have been published, not to mention Job s book on Aqueous Organometallic Catalysis which followed three years after our own publication and which put the spotlight on Job s special merits as one of the pioneers in aqueous biphasic catalysis. Up to now, most of the alternatives mentioned are only in a state of intensive development (except for one industrial realization that of Swan/Chematur for hydrogenations in scC02 [2]) but other pilot plant adaptations and even technical operations may be expected in the near future. 

Hernandez, F. J., A. P. de los Rfos, D. Gomez, M. Rubio, and G. Vfllora. 2006. A New Recirculating Enzymatic Membrane Reactor for Ester Synthesis in Ionic Liquid/ Supercritical Carbon Dioxide Biphasic Systems. Applied Catalysis B Environmental Cl (1-2) 121-126. 

Acid zeolites have also been tested for the racemisation of alcohols under biphasic conditions.Their scope was found, however, to be limited to benzylic alcohols, since electron-rich benzylic alcohols were not suitable substrates because of the formation of dimers. Under optimised conditions, based on the use of H-Beta zeolite, CALB lipase, and an excess of vinyl octanoate at 60 °C, enantiopure (R)-l-phenylethyl octanoate (>99% ee) was obtained in 90% yield from 1-phenylethanol. In addition, Lozano et al. have recently performed the DKR of this alcohol in the presence of acidic zeolite catalysts (CBV400) in an ionic liquid-supercritical carbon dioxide system with a continuous reaction system. Therefore, when Novozym 435 was employed at 50 °C and 100 bars in the presence of vinylpropanoate as the acyl donor, the expected (R)-phenylethylpropionate was produced in excellent yield of 98% with enantioselectivity of 97% ee and without any activity loss during 14 days of operation. 

In this chapter, latest advancements in solvent engineering in bioreductions and greener needs for bioreaction media have been discussed in depth with recent examples. Solvents for bioreductions may be categorized as (i) aqueous (ii) water/water-miscible (monophasic aqueous-organic system) (iii) water/ water-immiscible (biphasic aqueous-organic system) (iv) nonaqueous (mono-phasic organic system, including solvent-free system) and (v) nonconventional media (e.g., ionic liquids, supercritical fluids, gas-phase media, and reverse micelles). 

EXAMPLES OF REACTIONS IN IONIC LIQUIDS - SUPERCRITICAL FLUIDS BIPHASIC SYSTEMS... 

When biocatalysis is conducted in ionic liquid/supercritical fluids biphasic systems, the major function of ILs is to protect the enzyme, whereas the supercritical fluid dissolves the substrate and extracts the product Both enzyme stability and... 

P. Lozano,. M. Bernal, M. Vaultier, Towards continuous sustainable processes for enzymatic synthesis of biodiesel in hydrophobic ionic liquids/supercritical carbon dioxide biphasic systems, Fuel 90 (2011) 3461-3467. 

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