Catalytic Reaction with Subsequent Product Extraction

Catalytic Reaction with Subsequent Product Extraction 

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Catalytic Reaction with Subsequent Product Extraction... 

The first application involving a catalytic reaction in an ionic liquid and a subsequent extraction step with SCCO2 was reported by Jessop et al. in 2001 [9]. These authors described two different asymmetric hydrogenation reactions using [Ru(OAc)2(tolBINAP)] as catalyst dissolved in the ionic liquid [BMIM][PFg]. In the asymmetric hydrogenation of tiglic acid (Scheme 5.4-1), the reaction was carried out in a [BMIM][PF6]/water biphasic mixture with excellent yield and selectivity. When the reaction was complete, the product was isolated by SCCO2 extraction without contamination either by catalyst or by ionic liquid. 

In general, lanthanide catalysis does not change the endo/exo product ratio as compared to the uncatalyzed reaction. Neutralization of the reaction mixture followed by extractive workup allows for recycling of the lanthanide-containing aqueous phase in subsequent reactions with no diminished catalytic effect. 

It was interesting that the cell-free extract had the capacity to support the biosynthesis all the way to FAc 1, an end product of one of the fluorometabolite pathways. This observation indicates that all of the enzymes and cofactors required to support FAc biosynthesis were present and active in the cell-free extract, even though the integrity of the cells had been destroyed. This experiment showed that organic fluoride production was achievable in vitro from the S. cattleya protein extract. Subsequent purification of the fluorinase (5 -fluoro-5 -deoxyadenosine synthase), using standard purification protocols revealed that the true substrate for the enzyme was SAM 8 and not ATP 7 [8]. It transpired that ATP 7 and L-methionine (L-Met) were converted to SAM 8 in the crude cell-free extract and that the resultant SAM 8 was then processed by the fluorinase with the release of L-Met. Thus, a catalytic cycle where L-Met was regenerated to drive these two reactions had been inadvertently established (Scheme 1). The fluorinase catalyses the conversion of SAM 8 and fluoride ion to make 5 -FDA 5 as shown in Scheme 1 [8]. 

Enantioselective catalytic alkylation is a versatile method for construction of stereo-genic carbon centers. Typically, phase-transfer catalysts are used and form a chiral ion pair of type 4 as an key intermediate. In a first step, an anion, 2, is formed via deprotonation with an achiral base this is followed by extraction in the organic phase via formation of a salt complex of type 4 with the phase-transfer organocata-lyst, 3. Subsequently, a nucleophilic substitution reaction furnishes the optically active alkylated products of type 6, with recovery of the catalyst 3. An overview of this reaction concept is given in Scheme 3.1 [1],... 

Fig. 1.35. Experimental setup for the investigation of gas-phase catalytic activity of mass-selected metal clusters. The cluster ions are sputtered from solid targets with a CORDIS, mass-selected (Qi), and guided at low energies (Qo and Q2) into the temperature controllable octopole ion trap. By means of appropriate switching of the lenses Li and L2, the reaction products are extracted and subsequently mass-analyzed by another quadrupole mass filter (Q3) [32,186]...

The viologen reduction by EDTA in reverse micelles in the presence of Ru(bpy)3 is another example of vectorial photoinduced electron transfer [106], The accumulation of photoproducts is associated with the catalytic cycles depicted in Fig. 10(b). The oxidative quenching of the ruthenium complex occurs at the micelle outer boundary, while the regeneration of the dye takes place by the oxidation of EDTA in the inner core of the micelle. The reduction of the final product 4-dimethylaminoazobenzene is further mediated by the acceptor 1-benzylnicotinamide (BNA ). In Fig. 10(c), the photocatalytic reduction of methyl benzoylformate (MBF) by thiosulfate is described in the presence of the porphyrin ZnTPPS and the mediator quinolinium-3-carboxiamide (DCA ) [107]. This sequence of reactions occurs only in micelles such as those formed by hexadecyl-trimethylammonium bromide, which contain in the interior the ultimate donor acceptor. Finder illumination, ZnTPPS photoreduces DCA to DCQ, which is subsequently extracted into the micelle core. Within the microenvironment, DCA is regenerated via reduction of MBF, while the oxidized porphyrin is reduced by thiosulfate outside the micelle. 

The coupled catalytic system of Scheme 8.7 was more recently immobilized in an ionic liquid, [bmimJPFfi [136]. After completion of the reaction, the product diol is extracted from the ionic liquid, and the osmium, NMO, and flavin stay in the ionic liquid. The immobilized catalytic system was reused 6 times without any loss of activity. In a subsequent study, ionic liquid [bmimjPFg was employed to immobilize a robust system where the flavin of the previous system had been replaced by VO(acac)2 or MeRe03 (MTO) [137]. A range ofalkenes were dfliydroxylated with this system, and it was demonstrated that for some of the alkenes the catalytic system can be recycled up to five times. 

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