Biphasic system reaction

Chauvin s group described the selective hydrogenation of cyclohexadiene to cyclohexene through making use of the biphasic reaction system [46]. Since the solubility of cyclohexadiene in [BMIM][SbFg] is about five times higher than the solubility of cyclohexene in the same ionic liquid, the latter was obtained in 98 % selectivity at 96 % conversion. 

Finally, a special example of transition metal-catalyzed hydrogenation in which the ionic liquid used does not provide a permanent biphasic reaction system should be mentioned. The hydrogenation of 2-butyne-l,4-diol, reported by Dyson et al., made use of an ionic liquid/water system that underwent a reversible two-... 

Lin and coworkers disclosed that, at room temperature, nonenzymatic chemical addition was still observed in a water-organic solvent biphasic reaction system, though the volume of aqueous phases was relative small. Lin developed a method of preparing an active enzyme meal that contained essential water to retain its power for catalysis and found a new catalytic reaction system by application of the prepared meal in a nonaqueous monophasic organic medium (Figure 5.7). There was no problem over a wide range of temperature (from 0-30 °C) when the reactions were carried out under micro-aqueous conditions [50]. 

The closely related Todd reaction, useful for the preparation of dialkyl phosphorochloridates and phosphoramidates, also involves the use of amines with dialkyl phosphites.146152 180-182 Although the reaction proceeds using preformed salts of the dialkyl phosphites,183 the use of tertiary amines facilitates the reaction by allowing all reagent materials to be in solution. Biphasic reaction systems utilizing phase-transfer catalysts and crown ethers have also been successful for this reaction.158-161... 

Figure 5.14 Sol-gel immobilized TEMPO is an off-the-shelf alcohol oxidation catalyst. In a biphasic reaction system and in organic solvent it yields carbonyls in water it yields carboxylates.

SILC was also used without covalently anchoring the ionic liquid fragment to the silica support. In this case, [bmim][PF6] was simply added to silica in acetone together with the catalyst. [Rh(norbornadiene)(PPh3)2]PF6 and the solvent evaporated to yield the supported catalyst-philic phase. Catalyst evaluation on the hydrogenation of model olefins showed enhanced activity in comparison to homogeneous and biphasic reaction systems, in analogy to Davis s observations. Also... 

Hydroformylations were also carried out in IL/SCCO2 biphasic reaction systems [7]. In particular, it was demonstrated that continuous-flow systems could be operated successfully for the Rh-catalysed hydroformylation of hex-I-ene [24] and I-dodecene [25]. 

Similar to the above case, hydroformylation of 1-hexene using a water-soluble rhodium catalyst [RhH(CO)(TPPMS)3] gave lower yields when a-cyclodextrin was added to the biphasic reaction system [14]. Again, the reason was suspected in the interaction between the cyclodextrin and the rhodium catalyst. 

Catalysis in ionic liquids is not limited to biphasic reaction systems. When the reaction mixture is homogeneous, an extraction solvent that is immiscible with the ionic liquid can be used to remove the product. A number of organic solvents display little or only limited miscibility with these liquids. However, this advantage is of limited value in practice, because one major incentive for using ionic liquids is to avoid volatile organic compounds. 

Hailing, P.J. (1984) Effects of water on equilibria catalysed by hydrolytic enzymes in biphasic reaction systems. Enzyme Microb. Technol., 6, 513-516. 

As a unique medium for asymmetric hydroformylation, supercritical carbon dioxide has recently been examined, which can be carried out in an extremely low catalyst concentration. The reactions of styrene (16a) and pentafluorostyrene (16e) catalyzed by Rh-BINAPHOS appear to give mixed results that are highly dependent on the reaction conditions [77,78], Enantioselectivity up to 92-95% ee for 16a or 85 % ee for 16e has been observed [78]. A biphasic reaction system has also been examined for the reaction using Rh(acac)(CO)2 with a sulfonated diphosphine ligand BINAS [79], The reaction proceeds smoothly at 40°C and 100 atm in high conversion with excellent branched aldehyde selectivity (95%), but enantioselectivity is very low (18% ee). The use of these newer reaction conditions is still in the very early stage and further development is expected in the next decade. 

In the context of biphasic reaction systems, phase transfer catalysis should also be mentioned. It should be noted that it is not limited to aqueous-organic reactions or liquid-liquid systems, but is also sometimes employed in... 

In order to improve the efficiency of the process, the hydrophilic nature of the catalyst was increased by introduction of w-sulfo groups into both diphenylphos-phino groups of the ligand 6. Under the biphasic reaction system which uses a porous hydrophilic support and conventional organic solvents, the novel catalyst bearing the sulfonylated ligand remains in the hydrophilic phase and can be separated easily. Using the so-called supported phase asymmetric catalyst system, the... 

The concentration change of aqueous hydrogen peroxide in the biphasic reaction system as a fimction of reaction time was investigated. Figure 17.8 shows that the rate of change of the concentration of the aqueous hydrogen peroxide is constant. This means that the reaction rate in the epoxidation of allyl chloride is zero-order with respect to hydrogen peroxide... 

Although perfluorinated hydrocarbons are well known, they have only recently found application in organic chemistry as a useful class of solvents. Their physical properties mice them unique for their use as reaction media. Since perfluorocarbons are immiscible with many common organic solvents, they are suitable for the formation of biphasic systems. This overview describes the utilization of perfluorocarbons as reaction media for various kinds of reaction such as oxidation, bromination, etc. In addition, a novel biphase reaction system based on perfluorinated solvents as well as its application in organic synthesis is presented. 

While the addition of toluene to form a biphasic reaction system had dramatically improved racemization rates, we were surprised to find that its combination with Amano PS-30 lipase led to incomplete conversion, although the enantioselec-tivity was still very good. This observation indicated that in spite of the significantly faster rate of racemization induced by the presence of toluene, the lipase was unacceptably inhibited and/or inactivated under these reaction conditions. 

Thermolysin immobilized on agarose gels as described in the experimental section was used as catalyst in a biphasic reaction system (acetate buffer 0,1 M and 10 mM CaCL/ethyl acetate (1 1) (v/v)). This medium could prevent the secondary reactions [1] and [2], since the dipeptide is more soluble in the organic phase than in water, and it allows to achieve high synthetic yields by removing the product from the aqueous phase. 

There have been many approaches to overcome the problem of low space-time yields in biphasic reaction systems with rhodium and other metals, such as the Ruhrchemie/Rhone-Poulenc process. Concerning two-phase hydroformylation of higher alkenes in an aqueous-organic reaction system, the different approaches can be categorized as follows ... 

Debenzylation. Benzyl ether and benzylidene derivatives of carbohydrates are cleaved with NaBr0j-Na2S204 in a biphasic reaction system. Esters are stable under such conditions. 

The selective, chromium catalyzed trimerization of ethylene to 1-hexene was disclosed in a patent by SASOL [247]. In this work a biphasic reaction system was explored using alkylchloroaluminate ionic liquids as the catalyst phase. 

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