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Catalysts catalyst-substrate

C. Methyl dl-anti-3-hydroxy 2-methylpentanoate. Freshly distilled methyl 3-hydroxy-2-methylenepentanoate (14.4 g, 0.1 mol) is added to the biphosphinorhodium catalyst (catalyst/substrate ratio 1/250) (Note 8) in the flask from step A. Methanol (40 mL, distilled from Mg(0Me)2) is added. The... [Pg.161]

Diastereoselective Hydrogenation since -OH directs the H2, there is a possibility for control of stereochemistry - sensitive to H2 pressure catalyst cone, substrate cone, solvent. [Pg.33]

In Chapter 6 we survey what has been accomplished and indicate directions for future research. Furthermore, we critically review the influence of water on Lewis acid - Lewis base interactions. This influence has severe implications for catalysis, in particular when hard Lewis acids and bases are involved. We conclude that claims of Lewis-acid catalysis should be accompanied by evidence for a direct interaction between catalyst and substrate. [Pg.178]

A number of smaller but nevertheless important apphcations in which activated alumina is used as the catalyst substrate include alcohol dehydration, olefin isomerization, hydrogenation, oxidation, and polymerization (43). [Pg.156]

Cordierite [12182-53-5] Mg Al Si O g, is a ceramic made from talc (25%), kaolin (65%), and Al O (10%). It has the lowest thermal expansion coefficient of any commercial ceramic and thus tremendous thermal shock resistance. It has traditionally been used for kiln furniture and mote recently for automotive exhaust catalyst substrates. In the latter, the cordierite taw materials ate mixed as a wet paste, extmded into the honeycomb shape, then dried and fired. The finished part is coated with transition-metal catalysts in a separate process. [Pg.302]

Class (2) reactions are performed in the presence of dilute to concentrated aqueous sodium hydroxide, powdered potassium hydroxide, or, at elevated temperatures, soHd potassium carbonate, depending on the acidity of the substrate. Alkylations are possible in the presence of concentrated NaOH and a PT catalyst for substrates with conventional pX values up to - 23. This includes many C—H acidic compounds such as fiuorene, phenylacetylene, simple ketones, phenylacetonittile. Furthermore, alkylations of N—H, O—H, S—H, and P—H bonds, and ambident anions are weU known. Other basic phase-transfer reactions are hydrolyses, saponifications, isomerizations, H/D exchange, Michael-type additions, aldol, Darzens, and similar... [Pg.186]

This model prediets that tri-substituted and tetra-substituted olefins would also be poor substrates. Thus it was not until 1994 that a study in the epoxidation of higher substituted olefins appeared. Indeed Jaeobsen revealed that tri-substituted olefins, and even tetra-substituted olefins ean be excellent substratesA new model was put forth that encompasses a skewed side-on approach of tri-substituted olefins to the Mn-oxo eomplex. The observation that certain tetrasubstituted olefins undergo epoxidation with good enantioseleetivity suggests that further studies are needed in order to fully understand the transition state geometry of the catalyst and substrate. [Pg.37]

Double-bond migrations during hydrogenation of olefins are common and have a number of consequences (93). The extent of migration may be the key to success or failure. It is influenced importantly by the catalyst, substrate, and reaction environment. A consideration of mechanisms of olefin hydrogenation will provide a rationale for the influence of these variables. [Pg.29]

Acetylenes have hijh synthetic utility, and hydrogenation of the triple bond occurs in many reaction sequences (7). Often the goal of this reduction is formation of the cis olefin, which usually can be achieved in very high yields (for an exception, see Ref. 10). Continued reduction gives the paraffin. Experimentally, both the relative and absolute rates of acetylene and olefin hydrogenation have been found to depend on the catalyst, substrate, solvent, reaction conditions, and hydrogen availability at the catalyst surface. Despite these complexities, high yields of desired product usually can be obtained without difficulty. [Pg.53]

Hydrogenation of styrene oxide over palladium in methanol 66 gives exclusively 2-phenylethanol, but in buffered alkaline methanol the product is l-phenylelhanol. If alcoholysis of the epoxide by the product is troublesome, the problem can be eliminated by portion-wise addition of the epoxide to the reaction, so as always to maintain a high catalyst-to-substrate ratio. The technique is general for reactions in which the product can attack the starting material in competition with the hydrogenation. [Pg.139]

Nickel catalysts have been used for many dehydrohalogenations (30), but these catalysts are much more suspectible to poisoning by halide ion than are noble metals. As a result, the catalyst-to-substrate ratio must be much higher when using nickel, and reduction times are apt to be lengthy (36). Reductive deiodination of 6 to 7 was achieved over Raney nickel in methanol containing triethylamine. Despite massive loadings, the reduction was slow (20). [Pg.149]

The rate ratio of hydrogenation to hydrogenolysis varies with the catalyst, substrate structure, and environment in a partially predictable way. [Pg.167]

Biphasic catalysis in a liquid-liquid system is an ideal approach through which to combine the advantages of both homogeneous and heterogeneous catalysis. The reaction mixture consists of two immiscible solvents. Only one phase contains the catalyst, allowing easy product separation by simple decantation. The catalyst phase can be recycled without any further treatment. However, the right combination of catalyst, catalyst solvent, and product is crucial for the success of biphasic catalysis [22]. The catalyst solvent has to provide excellent solubility for the catalyst complex without competing with the reaction substrate for the free coordination sites at the catalytic center. [Pg.219]

The Brpnsted coefficient a represents the sensitivity of the rate to the acid strength of the catalyst. It is a measure of the degree of proton transfer from catalyst to substrate in the transition state. For nearly all reactions where BH+ contains acidic N-H or O-H groups, a is in the range 0-1. [Pg.234]

Fig. 3. Steady state concentration profiles of catalyst and substrate species in the film and diffusion layer for for various cases of redox catalysis at polymer-modified electrodes. Explanation of layers see bottom case (S + E) f film d diffusion layer b bulk solution i, limiting current at the rotating disk electrode other symbols have the same meaning as in Fig. 2 (from ref. Fig. 3. Steady state concentration profiles of catalyst and substrate species in the film and diffusion layer for for various cases of redox catalysis at polymer-modified electrodes. Explanation of layers see bottom case (S + E) f film d diffusion layer b bulk solution i, limiting current at the rotating disk electrode other symbols have the same meaning as in Fig. 2 (from ref.
Fewer examples are reported for organic electrode reactions some alkyl halides were catalytically reduced at electrodes coated with tetrakis-p-aminophenylporphy-rin carboxylate ions are oxidized at a triarylamine polymer and Os(bipy)3 in a Nafion film catalytically oxidizes ascorbic acid Frequently, modified electrodes fail to give catalytic currents for catalyst substrate combinations that do work in the homogeneous case even when good permeability of the film is proven... [Pg.67]

Catalyst to Substrate ratio Reducing Agent Reducing Agent to substrate ratio Time HPLC Area % ... [Pg.222]

At a certain point (0.08 % w/w catalyst to substrate ratio) there ensued a drop in reaction rate, together with a gradual loss of selectivity. Thus, a treadeoff point was chosen so that a minimal load of catalyst could be used in the process, without an undue sacrifice in rate or selectivity. [Pg.224]

Catalyst to substrate ratio (% w/w) Catalyst recycle Time (h) 6(a) HOjC COjH 2(a)... [Pg.225]

The exact mechanism has still not been completely worked out. Opinions have been expressed that it is completely intermolecular, completely intramolecular, and partially inter- and intramolecular. " One way to decide between inter- and intramolecular processes is to run the reaction of the phenolic ester in the presence of another aromatic compound, say, toluene. If some of the toluene is acylated, the reaction must be, at least in part, interraolecular. If the toluene is not acylated, the presumption is that the reaction is intramolecular, though this is not certain, for it may be that the toluene is not attacked because it is less active than the other. A number of such experiments (called crossover experiments) have been carried out sometimes crossover products have been found and sometimes not. As in 11-14, an initial complex (40) is formed between the substrate and the catalyst, so that a catalyst/substrate molar ratio of at least 1 1 is required. [Pg.726]


See other pages where Catalysts catalyst-substrate is mentioned: [Pg.156]    [Pg.133]    [Pg.84]    [Pg.156]    [Pg.156]    [Pg.133]    [Pg.84]    [Pg.156]    [Pg.164]    [Pg.169]    [Pg.5]    [Pg.173]    [Pg.181]    [Pg.149]    [Pg.156]    [Pg.156]    [Pg.6]    [Pg.200]    [Pg.405]    [Pg.124]    [Pg.132]    [Pg.5]    [Pg.345]    [Pg.171]    [Pg.195]    [Pg.255]    [Pg.251]    [Pg.17]    [Pg.264]    [Pg.92]    [Pg.320]    [Pg.224]    [Pg.705]   


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Advantages of Polymer Reagents, Catalysts, and Substrates

Alkene substrates catalysts

Alkyne substrate catalysts

Allene substrates catalysts

Catalyst coating metallic substrate pretreatment

Catalyst substrate complex

Catalyst substrate complex, schematic

Catalyst-substrate binding

Catalyst-substrate contact time

Catalyst-substrate interaction

Catalysts catalyst-substrate interactions

Catalysts substrate transport influencing

Catalysts, Substrates, Conditions

Catalytic activity catalyst substrate

Diastereomeric catalyst-substrate adducts

High substrate/catalyst ratios

Hydrogenation high substrate/catalyst ratios

Hydrogenation substrates and transition metal catalysts

Late alkene substrates catalysts

Late alkyne substrates catalysts

Metal Catalysts with Nonreducible Substrates in Aqueous Solution

Metal Catalysts with Nonreducible Substrates in Organic Solvents

Metal Catalysts with Reducible Substrates

Metal oxides, catalysts Metals, transition, substrates

Metathesis in Natural Product Synthesis: Strategies, Substrates and Catalysts. Edited by Janine Cossy

Molecular complexes substrate-catalyst

Polymeric catalyst-substrate complex

Step of Substrate to Polymer-Cu Catalysts

Substrate Scope and Catalysts

Substrate Synthesis, Purity and Catalyst Loading

Substrate-to-catalyst-ratio

Substrate/catalyst ratio

Transition metal catalyzed alkene substrates catalysts

Transition metal catalyzed alkyne substrates catalysts

Transition metal catalyzed allene substrates catalysts

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