Commercially Available Catalysts

Micellar Catalysis Approaches In 2002, Davis and Sinou [113] reported the use of catalyst 2 for RCM applications in water. Despite the heterogeneity of the system. 

Polydimethylsiloxane (PDMS) Approaches In 2006, Bowden and coworkers [120] described an alternative strategy for conducting olefin metathesis reactions in water. The authors approach involved the incorporation of either catalyst 2 or 4 inside a solid polydimethylsiloxane (PDMS) matrix. The idea is very straightforward in that the incorporated catalysts are insoluble in the aqueous environment instead, they preferentially reside in the PDMS material. This allows the metathesis substrates to freely diffuse into the PDMS matrix, where catalysis can occur. Like the PTS example from Lipshutz, this strategy required no time-consuming or costly catalyst modification. 

The incorporated catalysts were easily prepared by simply adding CH2CI2 solutions of either 2 or 4 to the cross-linked PDMS slabs under an atmosphere of nitrogen. The PDMS swelled in the CHjClj solvent, which allowed the catalyst to readily diffuse inside. The solvent was then removed, and the slabs were rinsed and cut into small pieces for use. The resulting catalysts were successfully employed in various RCM and CM reactions in both water and water/methanol mixtures. Also of note, the PDMS catalyst system could be recycled a number of times, and the activity was shown to arise from the incorporated catalyst and not from any active species leaching into the aqueous solvent. 

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Often the catalysts described in the Hterature are not quite the same as those used in industrial processes, and often the reported performance is for pure single-component feeds. Sometimes the best quantitative approximations that can be made from the available Hterature are those based on reported kinetics of reactions with pure feeds and catalysts that are similar to but not the same as those used in practice. As a first approximation, one may use the pubHshed results and scale the activity on the basis of a few laboratory results obtained with reaHstic feeds and commercially available catalysts. 

In the laboratory, more than 160 bench-scale tests involving more than 40 catalysts were made in order to determine the optimum catalysts and process conditions for this application. Initial tests used commercially available catalysts, but early findings indicated that a whole new series of catalysts was required. 

RRM of enantiopure cyclopentene 382, induced by commercially available catalyst C, was the key step in Blechert s total synthesis of the bis-piperidine alkaloid (+)-astrophylline (384) [159]. Exposure of metathesis precursor 382 to only 1 mol% C provided within 2 h bicycle 383 in 82% yield (Scheme 75). 

An obvious drawback in RCM-based synthesis of unsaturated macrocyclic natural compounds is the lack of control over the newly formed double bond. The products formed are usually obtained as mixture of ( /Z)-isomers with the (E)-isomer dominating in most cases. The best solution for this problem might be a sequence of RCAM followed by (E)- or (Z)-selective partial reduction. Until now, alkyne metathesis has remained in the shadow of alkene-based metathesis reactions. One of the reasons maybe the lack of commercially available catalysts for this type of reaction. When alkyne metathesis as a new synthetic tool was reviewed in early 1999 [184], there existed only a single report disclosed by Fiirstner s laboratory [185] on the RCAM-based conversion of functionalized diynes to triple-bonded 12- to 28-membered macrocycles with the concomitant expulsion of 2-butyne (cf Fig. 3a). These reactions were catalyzed by Schrock s tungsten-carbyne complex G. Since then, Furstner and coworkers have achieved a series of natural product syntheses, which seem to establish RCAM followed by partial reduction to (Z)- or (E)-cycloalkenes as a useful macrocyclization alternative to RCM. As work up to early 2000, including the development of alternative alkyne metathesis catalysts, is competently covered in Fiirstner s excellent review [2a], we will concentrate here only on the most recent natural product syntheses, which were all achieved by Fiirstner s team. 

Table 5. Pt particle sizes in commercially available catalysts. ...

Figure 7. Cyclic voltammetry polarization curves for MEA made with different Pt-Ru/C catalysts [25], 3M (Pt/Ru = 1 1), 3M (Pt/ Ru = 1 2) and 3 M (Pt/Ru = 2 1) represent the catalysts prepared using the unprotected metal nanoclusters as building blocks E-tek (Pt/ Ru = 1 1) represents the commercially available catalyst (C14-30). All the catalysts have the same total metal loading of 30wt.%.

Groger has also reported a preliminary study on enantioselective acetyl migration in the Steglich rearrangement using one of Fu s commercially available catalysts and Birman s tetramisole-based organocatalyst [108]. 

We last reviewed organic synthesis applications of the Grubbs reaction on April 19,2004. The (relatively) robust nature of the commercially-available catalyst and its commercial availability have spurred the expanding exploration of the scope of this reaction. Through this month, we will feature some recent highlights. 

The examples reported to date do not allow a clear ranking of palladium catalysts with regard to their ability to catalyze the Suzuki reaction. It should also be kept in mind that palladium(O) complexes are air-sensitive, and the quality of commercially available catalysts of this type can vary substantially. Some successful Suzuki couplings are listed in Table 5.12. Further examples have been reported [184,186-196],... 

Process B washcoating of commercially available catalyst powders (step 1 - 6)... 

Authentic and synthetic solvent-refined coal filtrates were processed upflow in hydrogen over three different commercially available catalysts. Residual (>850°F bp) solvent-refined coal versions up to 46 wt % were observed under typical hydrotreating conditions on authentic filtrate over a cobalt-molybdenum (Co-Mo) catalyst. A synthetic filtrate comprised of creosote oil containing 52 wt % Tacoma solvent-refined coals was used for evaluating nickel-molybdenum and nickel-tungsten catalysts. Nickel-molybdenum on alumina catalyst converted more 850°F- - solvent-refined coals, consumed less hydrogen, and produced a better product distribution than nickel-tungsten on silica alumina. Net solvent make was observed from both catalysts on synthetic filtrate whereas a solvent loss was observed when authentic filtrate was hydroprocessed. Products were characterized by a number of analytical methods. 

Commercially available catalysts were used. With but few exceptions these were Harshaw-0402, Co-Flo, l/8-1nch tablets and Harshaw-N1-4301, N1-W, 1/16 In. extrusions. At constant coal catalyst solvent ratio and with H2 In large excess the principal variables which effect hydrogenolysis yield are temperature and catalyst type. As shown by data In Figure 7, the conversion... 

The catalyst for this reaction is copper chromite, 2 CuO Cr203, a relatively inexpensive commercially available catalyst used for both hydrogenation and dehydrogenation as well as decarboxylation. 

Catalysts based on copper/zinc mixed oxides are of great importance for industrial scale catalytic processes like low pressure methanol formation from synthesis gas and steam reforming of methanol yielding H2 and CO2. The commercially available catalyst for both reactions is the ternary system Cu-Zn0/Al20s [5], In consequence of its success, the Cu-ZnO system has prompted a great deal of fundamental work devoted to clarify either the role played by each component and the nature of the active site. 

Prior to entering the MPC dehydration step, the EB, MPC, and MPK stream from the PO recovery unit is washed and EB is removed by distillation. The MPC and MPK are sent to the dehydration reactors, where MPC is dehydrated to styrene using one of the commercially available catalysts. 

Route B was chosen as the superior process since a stable, commercially available catalyst can be used at very low molar concentration (technically superior) [9]. The number of reaction steps in route B is lower than in route D and the E selectivity is significantly higher. Thus, route B is more economical. All metals can be recovered and recycled. 

The Nafion-silica composite is rather expensive, thus the commercially available catalyst, SAC13 (containing 13% Nafion) costs approximately 1000 kg ... 

Unmodified acid clays have been little utilized as catalysts for Friedel-Crafts acylation reaction. Among the scanty information from the literature, the production of AQ 22 through cyclodehydration of BBA 21 is of some interest (Scheme 4.22). The reaction is performed in the presence of different clays at 350°C for 30 min. AQ 22 is directly recovered by sublimation from the reaction mixture. Some interesting results are achieved with commercially available catalysts such as Tonsil BW3, a mixture of mica, quartz, feldspar, and amorphous silica with bentonite and mont-morillonite KIO, product 22 being obtained in 78%-89% yield. Reusability studies show that Tonsil BW3 still gives product 22 in 60% yield after five... 

BACs can be activated toward Friedel-Crafts acylation with commercially available catalyst Envirocat EPIC . The catalyst is constituted by a natural clay impregnated with polyphosphoric acid. The reaction occurs... 

Bismuth(III) triflate tetrahydrate can be utilized as a more commercially available catalyst for the Fries rearrangement of PAs to 2-hydrox-yaryl ketones. In the reaction with 1-naphthyl acetate, bismuth triflate (10% mol) gives the best yield in 2-acetyl-l-naphthol, the amount of... 

The emission streams from purified terephthalic acid (PTA) plants commonly contain carbon monoxide, methyl bromide, and various volatile organic compounds (VOC s). Before the vent gas (offgas) is exhausted to the atmosphere, these contaminants (often regulated) must be destroyed, normally by the catalytic oxidation process. Currently, most commercially available catalysts are used at an inlet terrperature higher dian 350 C. The improvement of the catalyst activity is desired to increase the catalyst life-time and to reduce the operational cost. Additionally, the catalyst selectivity needs to be improved to minimize or eliminate the formation of polybromobenzenes (PBB s) which can cause plugging or blockage in process lines. 

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