Solid-supported catalysts

The hydrazone was subsequently treated with KOH under the action of MW to undergo Wolff-Kishner reduction (leading to PhCH2Ph) within 25-30 min in excellent yields (95 %). As an extension, the reaction of neat 5- or 8-oxobenzopyran-2(lH)-ones with a variety of aromatic and heteroaromatic hydrazines is substantially accelerated by irradiation in the absence of any catalyst, solid support, or solvent [66] (Eq. 14). 

Keywords Immobilized metal catalysts Heterogenized homogeneous catalysts Solid supported catalysts Industrial catalysis ... 

Fig.5 illustrates the PO selectivity (S) as a function of mass Peclet number. The selectivity was increased with increasing the total reaction gas flow rate (F) passing through the membrane pores, such as S= 18-41% according to F= 70-130 cmVmin at 483K, indicating an effective role of the convection flow in the membrane pores for the enhancement of S compared to intraparticle diffusion in spherical catalyst solid supports used for conventional packed bed reactors. This result experimentally proves the validity of our previous work based on the mathematical analysis [7]. 

Many superacid-catalyzed reactions were found to be carried out advantageously not only using liquid superacids but also over solid superacids, including Nafion-H or certain zeolites. We extensively studied the catalytic activity of Nafion-H and related solid acid catalysts (including supported perfluorooctanesulfonic acid and its higher ho-... 

The ability of iron(III) chloride genuinely to catalyze Friedel-Crafts acylation reactions has also been recognized by Holderich and co-workers [97]. By immobilizing the ionic liquid [BMIM]Cl/FeCl3 on a solid support, Holderich was able to acetylate mesitylene, anisole, and m-xylene with acetyl chloride in excellent yield. The performance of the iron-based ionic liquid was then compared with that of the corresponding chlorostannate(II) and chloroaluminate(III) ionic liquids. The results are given in Scheme 5.1-67 and Table 5.1-5. As can be seen, the iron catalyst gave superior results to the aluminium- or tin-based catalysts. The reactions were also carried out in the gas phase at between 200 and 300 °C. The acetylation reac-... 

Minimum Fluidization Velocity (Umf). The lowest velocity at which the full weight of catalyst is supported by the fluidization gas. It is the minimum gas velocity at which a packed bed of solid particles will begin to expand and behave as a fluid. For an FCC catalyst, the minimum fluidization velocity is about 0.02 ft/sec. 

Since 1978, several papers have examined the potential of using immobilised cells in fuel production. Microbial cells are used advantageously for industrial purposes, such as Escherichia coli for the continuous production of L-aspartic acid from ammonium fur-marate.5,6 Enzymes from microorganisms are classified as extracellular and intracellular. If whole microbial cells can be immobilised directly, procedures for extraction and purification can be omitted and the loss of intracellular enzyme activity can be kept to a minimum. Whole cells are used as a solid catalyst when they are immobilised onto a solid support. 

Chemistry on solid support has gained tremendous importance during the last few years, mainly driven by the needs of the pharmaceutical sciences. Due to the robust and tolerable nature of the available catalysts, metathesis was soon recognized as a useful technique in this context. Three conceptually different, RCM-based strategies are outlined in Fig. 11. In the approach delineated in Fig. 1 la, a polymer-bound diene 353 is subjected to RCM. The desired product 354 is formed with concomitant traceless release from the resin. This strategy is very favorable, since only compounds with the correct functionality will be liberated, while unwanted by-products remain attached to the polymer. However, as the catalyst is captured in this process by the matrix (355), a higher catalyst loading will be required, or ancillary alkenes have to be added to liberate the catalyst. 

For the use of a novel phosphine-free ruthenium catalyst with m-bromopyridine ligands [196a] in the CM-based release of azide-protected carbohydrates from a solid support, see Kanemitsu T, Seeberger PH (2003) Org Lett 5 4541... 

Most industrial catalysts are supported, i.e. distributed in fine form (1-10 nm) on the surface of a porous, high surface area and usually inert support (e.g. Si02, y-Al203> Ti02).15 In this book, however, we will deal quite often with catalysts in the form of a porous film deposited on a solid electrolyte. 

Both questions have been recently addressed via a surface diffusion-reaction model developed and solved to describe the effect of electrochemical promotion on porous conductive catalyst films supported on solid electrolyte supports.23 The model accounts for the migration (backspillover) of promoting anionic, O5, species from the solid electrolyte onto the catalyst surface. The... 

In 2003, the microwave-assisted coupUng of aryl hahdes with acetylenes using a palladium catalyst were carried out employing a modified Smith Process vial [49]. These vessels, equipped with a polypropylene frit and screw cap at the bottom, and sealed with an aluminum crimp cap fitted with a silicon septum at the top (Fig. 8), faciUtated the processing of approximately 1 g of solid support. Notably, they are compatible with stirring of the reaction mixture and monitoring of the temperature and pressure. 

Benzofurans have been prepared by microwave-accelerated cyclocondensation of differently substituted salicylaldehydes 182 with esters of chloroacetic acid 183 in the presence of K2CO3 (used as the solid support) and tetrabutyl-ammonium bromide (TBAB) as phase transfer catalyst [120]. This method seemed general regarding the variations at the benzene ring and the nature of the ester moiety (Scheme 66). 

A modified Pechmann microwave-assisted reaction has been reported using an electron-rich phenol 229 and an a,/l-unsaturated acid in order to obtain coumarins without a substituent in position 4 [147]. Even in this case, the use of an acid solid catalyst (the support) was needed. Best results were obtained with Dowex or Amberhte-15 at 120 °C for 15 min (Scheme 84). 

The field of synthetic enzyme models encompasses attempts to prepare enzymelike functional macromolecules by chemical synthesis [30]. One particularly relevant approach to such enzyme mimics concerns dendrimers, which are treelike synthetic macromolecules with a globular shape similar to a folded protein, and useful in a range of applications including catalysis [31]. Peptide dendrimers, which, like proteins, are composed of amino acids, are particularly well suited as mimics for proteins and enzymes [32]. These dendrimers can be prepared using combinatorial chemistry methods on solid support [33], similar to those used in the context of catalyst and ligand discovery programs in chemistry [34]. Peptide dendrimers used multivalency effects at the dendrimer surface to trigger cooperativity between amino acids, as has been observed in various esterase enzyme models [35]. 

This symposium addressed several important issues in bromine chemistry. A major part has been devoted to stereochemistry and mechanism of electrophilic bromination of olefins. Other topics included new selective methods of bromination and oxybromination, brominations in presence of solid supports and catalysts, organobromine compounds as synthons, recent developments in brominated fire retardants and toxicological and environmental aspects of brominated compounds. 

K. Smith, ed., "Solid Supports and Catalysts in Organic Synthesis", Ellis Horwood, Chichester, (1992). 

J. H. Clark and C.N. Rhodes, Clean Synthesis Using Porous Inorganic Solid Catalysts and Supported Reagents , Royal Society of Chemistry, Cambridge, 2000. 

Base catalysis is another area which has received a recent stimulus from developments in materials science and microporous solids in particular. The Merk company, for example, has developed a basic catalyst by supporting clusters of cesium oxide in a zeolite matrix [13]. This catalyst system has been developed to manufacture 4-methylthiazole from acetone and methylamine. 

Another successful approach to catalyst immobilisation involves attachment of the carbene precursor to a peptide on solid support. Treatment with base generates the corresponding carbenes that undergo in situ complexation to Pd(ll) centres (Scheme 6.33). Again, the main drawback of this approach was the low reactivity of the catalytic system that only allowed the coupling of aryl iodides and bromides [116], The reasons for this outcome are in need of further studies. 

Scheme 6.33 Pre-catalyst immobilisation by attachment to a peptide on solid support...

As anticipated in the introduction, cross-linked polymers swell, to variable extent, when put in contact with liquids. Therefore, the working state of any cross-linked organic pol5uner under solid-liquid conditions, no matter if it is a catalyst, a support or a carrier for solid state S5mthesis, is the swollen state. In macroreticular CFPs swelling does not involve the whole polymeric mass it is... 

Zeolites have ordered micropores smaller than 2nm in diameter and are widely used as catalysts and supports in many practical reactions. Some zeolites have solid acidity and show shape-selectivity, which gives crucial effects in the processes of oil refining and petrochemistry. Metal nanoclusters and complexes can be synthesized in zeolites by the ship-in-a-bottle technique (Figure 1) [1,2], and the composite materials have also been applied to catalytic reactions. However, the decline of catalytic activity was often observed due to the diffusion-limitation of substrates or products in the micropores of zeolites. To overcome this drawback, newly developed mesoporous silicas such as FSM-16 [3,4], MCM-41 [5], and SBA-15 [6] have been used as catalyst supports, because they have large pores (2-10 nm) and high surface area (500-1000 m g ) [7,8]. The internal surface of the channels accounts for more than 90% of the surface area of mesoporous silicas. With the help of the new incredible materials, template synthesis of metal nanoclusters inside mesoporous channels is achieved and the nanoclusters give stupendous performances in various applications [9]. In this chapter, nanoclusters include nanoparticles and nanowires, and we focus on the synthesis and catalytic application of noble-metal nanoclusters in mesoporous silicas. 

The selective deposition technique seems a surface modification of oxides. In this regard, the modification of material surface is generally carried out in the field of the catalyst preparation. Catalysts are divided into heterogeneous and homogeneous catalysts. The former is well known to be used in the petroleum industry and almost all catalysts are solid, in particular, the supported catalysts. The supported catalysts are composed of the main... 

Phase-transfer catalysis is a special type of catalysis. It is based on the addition of an ionic (sometimes non-ionic like PEG400) catalyst to a two-phase system consisting of a combination of aqueous and organic phases. The ionic species bind with the reactant in one phase, forcing transfer of this reactant to the second (reactive) phase in which the reactant is only sparingly soluble without the phase-transfer catalyst (PTC). Its concentration increases because of the transfer, which results in an increased reaction rate. Quaternary amines are effective PTCs. Specialists involved in process development should pay special attention to the problem of removal of phase-transfer catalysts from effluents and the recovery of the catalysts. Solid PTCs could diminish environmental problems. The problem of using solid supported PTCs seems not to have been successfully solved so far, due to relatively small activity and/or due to poor stability. 

Depending on the process requirements catalysts are produced in a variety of ways. Fig. 3.12 shows some typical processes used in catalyst manufacture. In all cases the process starts from a solution. The various process steps used arc explained in subsequent sections. Solid catalysts can be subdivided in bulk catalysts and supports and catalysts prepared by impregnation of shaped supports. 

---