Polymer immobilized catalysts

As with organic solvents, proteins are not soluble in most of the ionic liquids when they are used as pure solvent. As a result, the enzyme is either applied in immobilized form, coupled to a support, or as a suspension in its native form. For production processes, the majority of enzymes are used as immobilized catalysts in order to facilitate handling and to improve their operational stability [24—26]. As support, either inorganic materials such as porous glass or different organic polymers are used [27]. These heterogeneous catalyst particles are subject to internal and external... 

Amorphous Systems (Polymer and Surface Immobilized Catalysts and Inorganic Glasses)... 

A number of insoluble or immobilized catalysts have been developed and applied to the carbonyl-ene reaction. As is evidenced by the entries below, the enantioselectivities are variable. Sasai23 has utilized a titanium-bridged polymer to effect an enantioselective carbonyl-ene (Equation (14)). A single substrate was examined, and the polymer could be reused up to five times without loss of enantioselectivity in the ene reaction. 

S. Kobayashi and R. Akiyama, Renaissance of immobilized catalysts. New types of polymer-supported catalysts, micro-encapsulated catalysts, which enable environmentally benign and powerful high-throughput organic synthesis, Chem. Commun., 2003, 449. 

With a view to producing catalysts that can easily be removed from reaction products, typical phase-transfer catalysts such as onium salts, crown ethers, and cryptands have been immobilized on polymer supports. The use of such catalysts in liquid-liquid and liquid-solid two-phase systems has been described as triphase catalysis (Regen, 1975, 1977). Cinquini et al. (1976) have compared the activities of catalysts consisting of ligands bound to chloromethylated polystyrene cross-linked with 2 or 4% divinylbenzene and having different densities of catalytic sites ([126], [127], [ 132]—[ 135]) in the... 

Furthermore, polymer-assisted solution-phase syntheses also show several advantages over Merrifield-type syntheses. Fxcept for some industrially employed heterogeneous catalysts the requirement of high loading capacities for the sohd supports is not necessarily of prime importance for immobilized catalysts. Because not every site needs to react, lower loadings are acceptable. The recovered catalyst is often available for immediate reuse. A discussion on immobilized catalysts should also include a brief listing of obstacles associated with their use, particular in comparison to their soluble analogs ... 

Some successful attempts to immobilize catalysts for the oxidation of alcohols to carbonyl compounds involve the attachment of TEMPO-derivatives to a solid phase. Bolm et al. were the first to immobilize l-hydroxy-2,2,6,6-tetramethylpiperi-dine to modified silica gel (SG-TMP-OH) (11) and applied in the oxidation of multifunctional alcohols [68]. Other groups further investigated the use of polymer-supported TEMPO [69]. This system allowed the oxidation of alcohols to aldehydes and ketones, respectively, using bleach to regenerate the immobilized ni-troxyl radical (Scheme 4.6). 

Other examples involve the immobilization of ruthenium porphyrin catalysts [74]. While Severin et al. generated insoluble polymer-embedded catalysts 16 by co-polymerizing porphyrin derivatives with ethylene glycol dimethacrylate (EGD-MA) [74 a], Che et al. linked the ruthenium-porphyrin unit to soluble polyethylene glycol (PEG) 17 [74b]. Both immobilized catalysts were employed in a variety of olefin epoxidations with 2,6-dichloropyridine N-oxide (Gl2pyNO), providing similar conversions of up to 99% and high selectivities (Scheme 4.9). 

The preparation of polymer-supported iridium catalysts (61) and (62) for the stereoselective isomerization of double bonds using polystyrene based immobilized triphenyl phosphine were recently reported by Ley and coworkers (Fig. 4.5). The immobilized catalyst is potentially useful for deprotection strategies of aUyl ethers [130]. 

A variety of SCS and PCP Pd (II) pincer complexes were prepared and immobilized on polymer or silica supports. (Figure 2 shows supported PCP complexes on poly(norbornene) and silica). Insoluble supports such as mesoporous silica and Merrifield resins along with soluble supports such as poly(norbornene) allowed for generalization of our observations, as all immobilized catalysts behaved similarly. The application of poisoning tests, kinetics studies, filtration tests, and... 

Conductive polymers are useful semiconductors or coating materials to construct solar cells. A new photodiode is proposed to be made from a film of a polymer metal complex. Immobilized catalysts on polymers are used for solar energy storage systems. 

Polymer immobilization The polymers used in the immobilization of spent materials can be classified into two main categories thermoplastic and thermosetting polymers. The first type is fed in the form of a solid, and then melts upon heating and combines with the waste. On the other hand, thermosetting polymers are supplied in a liquid form and are then polymerized to a solid form, combining with the waste upon heating or in the presence of catalysts. 

Fyfe et al. (354) have combined 31P and 13C CP/MAS NMR studies first to identify the polymer-immobilized catalyst (Scheme 4, compound ii) formed from the precursor i by treatment with Pd(PPh3)4 and, second, to monitor the carbonyl insertion reaction using 13C-enriched CO to yield iii. The use of isotopically enriched CO was required so as to record meaningful signals above those emerging from the carbon-rich polymer background. 

Screen-printed electrodes manufactured with the use of carbon-containing ink were used, (i) Catalytic system was inserted into carbon ink prior to ink immobilization on polymer substrate (ii) catalyst or polymer matrix (nation), containing catalyst, was immobilized on the working surface of the transducer. Table 27.1 displays the results of urea determination with the application of catalytic systems inserted into ink or immobilized on the transducer by different techniques. Optimum results (minimum mean square deviation and maximum correlation between the introduced and determined concentrations) are... 

In this paper we consider two specific challenges. First, how might transition metals be linked to phosphazene high polymers Such systems are of interest as immobilized catalysts or materials with unusual electrical properties. Second, how can bioactive agents be attached to polyphosphazenes to prepare, for example, targeted, slow release chemotherapeutic agents ... 

A very interesting technique that has been used widely in the MTO-catalyzed olefin oxidation reaction is the microencapsulation technique. This technique uses poly(4-vinylpyridine) (PVP), either 2% or 25% cross-linked with divinylbenzene (PVP-2% or PVP-25%, Fig. 4), as well as poly(4-vinylpyridine-/V-oxide) (PVPN-2%, Fig. 4). In addition, 2% cross-linked PS (PS-2%, Fig. 4, X = CH2) and a mixture of PS-2% and PVP-2% (5 1, Fig. 4, X = N) have been used as support polymers. This approach is based on the physical envelopment of the Lewis-acidic MTO by the PS polymer, enhanced by interactions of the 7t-electrons of the phenyl rings with MTO. In the case of the pyridine-containing polymers, Lewis acid-Lewis base interactions between the pyridine moiety and MTO obviously play an important role. In the case of the PVP and PVPN polymers, MTO can be incorporated in the support matrix by mixing the polymer and MTO in ethanol to obtain the desired immobilized catalyst. 

Me-DuPhos-Rh catalysts also have been shown to be very effective in the enantioselective and diastereoselective hydrogenation of dehydroaminoacids immobilized on polymer supports.40... 

Gelbard, G. and Vielfaure-Joly, F. Polynitrogen strong bases as immobilized catalysts, React. Fund. Polym., 2001, 48, 65-74. 

Polymer-Supported Reagents. This field has grown enormously in the last few decades as chemists and engineers have harnessed the obvious merits associated with carrying out a reaction using a readily removable reagent. The concept is essentially an elaboration of the immobilized catalyst field that has been widely applied in industry, especially the petrochemicals industry, for over 50 years. 

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