Supported organic phase catalyst

Renewed interest in this method came recently from its adaptation to the immobilization of water/ organic solvent biphasic catalysts, resulting in the so-called supported aqueous phase catalysts (SAPCs).117 The molecular catalyst is immobilized via water, which is hydrogen bonded to the surface silanol groups reactants and products are in the organic phase (Figure 11)... 

Co2(CO)6(tppts)2 is a brown-colored solid which is moderately stable in air, but is best handled and stored under an inert gas atmosphere. The compound is very soluble in water and insoluble in organic solvents like toluene or hexane. It exhibits in the 31P NMR (109.3 MHz, D20, 5°Q a singlet at 5 68.8 ppm. The IR displays a strong carbonyl stretching vibration at 1954 cm-1. The significant SO-absorptions are detectable at 1224 (sh, vst), 1200 (vst), 1039 (vst), and 623 (vst) cm-1. The compound has been used for carbonylation of phenyl ethyl bromide21 and on supported aqueous phase catalysts for the hydroformylation of olefins.22... 

Supported aqueous phase catalyst (SAPC) involves generating a thin water film on a high surface area support surrounded by a bulk organic solvent.20 SAPC suffers from mass transfer problems despite the sharp increase in interfacial surface area and leaching problems of the water-soluble catalyst. The SAPC method has been effectively applied to cyclohexene oxidations using a simple water-soluble ammonium molybdate catalyst with the aid of supported surfactant molecules.21... 

Supported liquid-phase catalysts (SLPC) Supported organic-phase (SOP) catalysts Supported aqueous-phase (SAP) catalysts... 

Initially, water was used as the hydrophilic liquid and these catalysts are therefore denoted as supported aqueous-phase catalysts (SAPCs) [7-10], Subsequently, we expanded this concept to other hydrophilic liquids such as ethylene glycol and glycerol [11], Reactions of liquid-phase, hydrophobic organic reactants take place at the film-organic interface. SAP catalysis differs significantly from SLP catalysis in that the latter is used for gas-phase reactants whereas the former is specifically designed for liquid-phase substrates. Additionally, with SLP catalysis, the reaction proceeds homogeneously in the supported film while in SAP catalysis it occurs at... 

Supported aqueous-phase catalyst (SAPC cf. Section 4.7) were combined with supercritical COz as a replacement for the organic liquid phase [21]. Ruthenium was supported on silica and combined with the ligand TPPTS in water with a scC02/H2 phase. The scC02 method yielded better conversions for the hydrogena-... 

Supported aqueous-phase catalysts (SAPC) can be seen as a special case of adsorption, whereby a water-soluble catalyst dissolved in a very polar solvent is adsorbed on a hydrophilic support forming a water film on the inner surface of the support [30,31]. In the case of supported liquid-phase catalysis (SLPC),the water film on the inner surface is replaced by a solvent of low vapor pressure (e.g.jphthalic acid esters) [2]. The reaction itself takes place in the supportedUq-uid or at the interface of the supported liquid film, or in the gas phase or organic phase when dealing with SLPC or SAPC, respectively. The use of SLPC catalysts is generally restricted to the synthesis of low-boiling compounds. 

Davis et al. described a new type of effective chiral catalysts, the so called "supported aqueous-phase catalysts". This hydrophilic complex is supported on a hydrophilic solid to create a large interface between the catalytic species and the organic reactants. The hydrophilicity of the ligands and the support creates an interaction sufficient to maintain immobilization of the sulfonized BINAP ligand (Scheme 7.12.) in a layer on the carrier. 

An SLPC consists of a homogeneous solution of a catalyst dispersed in the pore volume of the solid support and is a free-flowing solid that can be used as any conventional solid catalyst (Acres et al., 1966). Extensive studies have been reported by Rony (1969), Rony and Roth (1975), and Chen and Rinker (1978) on the preparation and properties of these catalysts. Catalysts in these systems are usually dissolved in apolar organic liquids. Therefore, we call them supported organic-phase (SOP) catalysts. 

The use of supported liquid-phase catalysts (SLPCs) in organic reactions was mentioned in Chapter 6. The diffusion-reaction problem in such catalysts is considerably more complicated than that for solid catalysts (Rony, 1969 Abed and Rinker, 1973 Livbjerget al., 1974, 1976). In a more recent analysis of SLPC systems, it has been shown (Datta and Rinker, 1985 Datta et al., 1985) that a critical parameter is the ratio of the effective diffusivity of a liquid-loaded pellet to that of a dry pellet ( JcA.l/ ca)- This ratio is a strong function of the liquid loading q and the gas-liquid partition coefficient of reactant A, as shown in Figure 7.8. Thus the effectiveness factor is a function of liquid loading. 

For instance substitution chlorination of organic compounds produces hydrogen chloride which must simultaneously desorb back in the gas phase to prevent supersaturation of the liquid phase. Another industrially important process involves "supported liquid phase catalyst", where the reactants have to be transferred from a bulk gas to a liquid reaction phase while the products are released back into the gas phase. Here the catalyst is in the form of a melt on a solid support and it finds applications in alkylation, carbonylation, hydroformylation and oxidation of inorganic and organic compounds. The subject matter was recently reviewed delicately by Villadsen and Liv-berg (11,12). Other examples of these interesting systems are shown in Table 6. 

Supported aqueous phase catalysts are well known [29, 30]. In these systems, a thin film of water present on the surface of a polar solid support is used to immobilize metal complexes, which are nonvolatile or insoluble in a mobile gaseous or liquid organic phase, respectively [30]. The concept was used successfully, for example, for the hydroformylation of oleyl alcohol over a supported rhodium complex [29]. Here, it was suggested that the reaction occurred at the interface between the aqueous and organic phase. However, the volatility of water necessitated... 

The important pharmaceutical, (S)-Naproxen was obtained (240) with high yield and 96% enantioselectivity by hydrogenation of 2(6 -methoxy-2-naphtyl)acrylic acid (Scheme 44) with a supported liquid phase catalyst containing [Ru(BINAPTS)(C6H6)C1]C1 dissolved in ethene glycol film on a controlled-pore glass (CPG-240). The other organic phase was a 1 1 mixture of chloroform and... 

Davis and Hanson developed a new concept of immobilizing homogeneous catalysts denoted as supported aqueous phase catalysts (SAPC) [15]. They reasoned that in aqueous biphasic catalysis the reaction mainly takes place at the interface. In order to increase this interface they used a high-surface-area hydrophilic support (figure 5). These materials have a thin film of water adhered to the surface, in which the water-soluble catalyst is dissolved. The reaction, performed in an organic solvent such as toluene, occurs at the water-organic interface. The supported catalyst has a... 

The best example of supported aqueous phase catalysis, in which a homogeneous catalyst is embedded in an aqueous layer over silica, is the use of tetrasulfonated BINAP ligand to reduce 2-(6 -methoxy-2 -naphthyl)acrylic acid (31 Fig. 6.4). The ee is dependent on the supported organic phase, and in this case, ethylene glycol on a porous glass gave up to 95% ee for the hydrogenation product (naproxen). 

Highly polar organocatalysts such as amino acids and peptides are almost insoluble in conventional organic solvents, but they are soluble in ionic liquids. Because of these physical properties, asymmetric syntheses in ionic liquids under biphasic condition have been reported [124], Recently, combinations of solid catalysts and ionic liquids have been studied intensively. The supported ionic liquid phase catalyst is a new generation of the supported liquid-phase catalyst [125]. The supported ionic liquid phase catalyst 232 is readily prepared by adsorption of (S)-proline 13... 

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