Liquid catalyst recycling

CjCqmHBFJ Pd(PPh3)4 Na2C03 110 °C. Solid-phase reaction coupling of 4-iodophenol immobilised on a polystyrene-Wang resin with arylboronic acids DMF as co-solvent acceleration in the presence of the ionic liquid catalyst recycling not practical. [102]... 

Keywords olefin metathesis, ruthenium catalysts, ionic liquids, catalyst recycling. 

Ionic Liquids, Catalyst Recycle, Selectivity, and Product Separation... 

Slightly later, and independently of Cole-Hamilton s pioneering work, the author s group demonstrated in collaboration with Leitner et al. that the combination of a suitable ionic liquid with compressed CO2 can offer much more potential for homogeneous transition metal catalysis than only being a new procedure for easy product isolation and catalyst recycling. In the Ni-catalyzed hydrovinylation of... 

Jacobsen subsequently reported a practical and efficient method for promoting the highly enantioselective addition of TMSN3 to meso-epoxides (Scheme 7.3) [4]. The chiral (salen)Cl-Cl catalyst 2 is available commercially and is bench-stable. Other practical advantages of the system include the mild reaction conditions, tolerance of some Lewis basic functional groups, catalyst recyclability (up to 10 times at 1 mol% with no loss in activity or enantioselectivity), and amenability to use under solvent-free conditions. Song later demonstrated that the reaction could be performed in room temperature ionic liquids, such as l-butyl-3-methylimidazo-lium salts. Extraction of the product mixture with hexane allowed catalyst recycling and product isolation without recourse to distillation (Scheme 7.4) [5]. 

Figure 1 illustrates the process in more detail. The inert liquid is pumped upflow through the reactor at a velocity sufficient to fluidize the catalyst and to remove the reaction heat. The low Btu feed gas is passed simultaneously up the reactor where it is catalytically converted to a high concentration methane stream. The exothermic reaction heat is taken up by the liquid mainly as sensible heat and partly by vaporization (depending on the volatility of the liquid). The overhead product gases are condensed to remove the product water and to recover any vaporized liquid for recycle. The main liquid flow is circulated through a heat... 

The most important biphasic liquid systems are probably those that combine a conventional organic phase with another type of solvent, such as water, a fluorous organic solvent, or an ionic liquid [3]. In those cases the solvent can be considered as the support for the catalyst phase and we have therefore limited the examples in this review to those where the recycled liquid catalyst phase is recovered as a whole. 

A copper-free Sonogashira coupling reaction in ionic liquids and its application to a microflow system for efficient catalyst recycling, Org. Lett. 4, 10 (2002) 1691-1694. 

Gruttadauria, M., Riela, S., Lo Meo, P., D Anna, F., Noto, R. (2004) Supported Ionic Liquid Asymmetric Catalysis A New Method for Chiral Catalysts Recycling, the Case of ProUne-Catalysed Aldol Reaction. Tetrahedon Letters, 45(32), 6113-6116. 

An interesting example of the use of a second liquid phase is to facilitate catalyst recycle when the reactor is operated as a slurry reactor. 

Gas-expanded liquids (GXLs) are emerging solvents for environmentally benign reactive separation (Eckert et al., op. cit.). GXLs, obtained by mixing supercritical CO2 with normal liquids, show intermediate properties between normal liquids and SCFs both in solvation power and in transport properties and these properties are highly tunable by simple pressure variations. Applications include chemical reactions with improved transport, catalyst recycling, and product separation. 

Scheme 6.93) [192]. Using either of the two solvent systems, all studied cycloaddition reactions were completed in less than 1 min upon microwave irradiation at 50 °C employing 3 mol% of the catalyst. An additional advantage of using the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) as solvent is that it facilitates catalyst recycling. 

Feed to tails ratio may be defined as the ratio between the liquid fed to column (4) and the liquid in the catalyst recycle. Higher feed/tails ratios contribute to higher conversion since with only catalyst and heavy solvent being recycled more of the reactor volume is available for product. 

CHAPTER 7 CATALYST RECYCLING USING IONIC LIQUIDS... 

Since the focus of this contribution is clearly on catalysis and catalyst recycle using the ionic liquid methodology it is not possible to go into more detail on the materials science aspects of ionic liquids. However, it should be clearly stated that at least some understanding of the ionic liquid material is a prerequisite for its successful use as a liquid catalyst support in catalysis. Therefore, the interested reader is strongly encouraged to explore the more specialized literature [28],... 

In contrast, we intend to demonstrate the principle aspects of catalyst recycling and regeneration using the ionic liquid methodology. These aspects will be explored in more detail for the example of Rh-catalysed hydroformylation (see Section 7.2). First, however, we will briefly introduce important general facts concerning transition metal catalysis in ionic liquids (see Section 7.1.2). This will be followed by a consideration of liquid-liquid biphasic reactions in these media from an engineering point of view (see Section 7.1.3). 

Finally, these particles generated in ionic liquids are efficient nanocatalysts for the hydrogenation of arenes, although the best performances were not obtained in biphasic liquid-liquid conditions. The main importance of this system should be seen in terms of product separation and catalyst recycling. An interesting alternative is proposed by Kou and coworkers [107], who described the synthesis of a rhodium colloidal suspension in BMI BF4 in the presence of the ionic copolymer poly[(N-vinyl-2-pyrrolidone)-co-(l-vinyl-3-butylimidazolium chloride)] as protective agent. The authors reported nanoparticles with a mean diameter of ca. 2.9 nm and a TOF of 250 h-1 in the hydrogenation of benzene at 75 °C and under 40 bar H2. An impressive TTO of 20 000 is claimed after five total recycles. 

An effective catalyst recycling with no loss of catalytic activity was accomplished by removing the liquid phase via the liquid sampling valve and re-charging the autoclave with a solution containing the substrate. In all cases, no rhodium leaching occurred. Remarkably, the hydrogenation activity of the 1,3-bis-... 

Evans et al. (220) have also shown that this reaction is amenable to a catalyst recycling protocol. This cycloaddition is tolerant of a variety of solvents including hexanes, conditions under which Complex 266c is apparently insoluble. Nevertheless, in the presence of adsorbent (florisil), this reaction proceeds at reasonable rates to provide the cycloadduct in undiminished yields and selectivities. Indeed, the catalyst could be efficiently recycled by removal of the supernatant liquid and recharging the flask with fresh solvent and reagents. Under this protocol, five cycles may be executed with only a slight diminution in rate and no effect on selectivities, Eq. 182. 

Various types of POMs are effective catalysts for the H202- and 02-based environment-friendly oxidations. Most of these oxidations are carried out in homogeneous systems and share common drawbacks, that is, catalyst/product separation and catalyst recycling are very difficult. The heterogenization of POMs can improve the catalyst recovery and recycling. This chapter focuses on the development of (1) homogeneous catalysts with POMs and (2) the heterogenization for liquid phase-oxidations. 

The first application of a rhodium-ligand system was realized in the LPO-process (low pressure oxo Fig. 18). Huge stirred tank reactors are used, equipped with internal heat exchangers to control the heat of reaction. The solution of the catalyst recycle is simple but efficient. The catalyst remains in the reactor, products and unconverted propene are stripped by a huge excess of synthesis gas. Because of strong foaming, only a part of the reaction volume is used. After the gas has left the reactor, the products are removed by condensing, the big part of synthesis gas is separated from the liquid products and recycled via compressors. The liquid effluent of the gas-liquid separator... 

The best results, in terms of catalyst recycling, were obtained when toluene was used as a co-solvent with the ionic liquid. Without toluene, the yield of polymer produced decreases dramatically to only 10% in the third cycle compared to 98 % in the first. 

Gladysz JA, Tesevic V (2008) Temperature-Controlled Catalyst Recycling New Protocols Based upon Temperature-Dependent Solubilities of Fluorous Compounds and Solid/Liquid Phase Separations. 23 67-89... 

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