Bifunctional catalysi

Another type of bifunctional catalysis has been noted with a,cn-diamines in which one of the amino groups is primary and the other tertiary. These substituted diamines are from several times to as much as 100 times more reactive toward imine formation than similar monofunctional amines. This is attributed to a catalytic intramolecular proton transfer. 

Zollinger s bifunctional catalysis (Sections II, D, 2, b and III, A) is probably further evidence in favor of the intermediate c-complex... 

Bifunctional catalysis in nucleophilic aromatic substitution was first observed by Bitter and Zollinger34, who studied the reaction of cyanuric chloride with aniline in benzene. This reaction was not accelerated by phenols or y-pyridone but was catalyzed by triethylamine and pyridine and by bifunctional catalysts such as a-pyridone and carboxylic acids. The carboxylic acids did not function as purely electrophilic reagents, since there was no relationship between catalytic efficiency and acid strength, acetic acid being more effective than chloracetic acid, which in turn was a more efficient catalyst than trichloroacetic acid. For catalysis by the carboxylic acids Bitter and Zollinger proposed the transition state depicted by H. 

Bifunctional catalysis has also been observed by Pietra and Vitali35 for a more typical nucleophilic aromatic substitution reaction, that of 2,4-dinitrofluorobenzene and piperidine in benzene. For this reaction triethylamine does not have an... 

Gomez GA, Morisseau C, Hammock BD, Christianson DW. Structure of human epoxide hydrolase reveals mechanistic inferences on bifunctional catalysis in epoxide and phosphate ester hydrolysis. Biochemistry 2004 43 4716-23. 

With some transition-metal complexes, the ligand is not only an ancillary ligand. Similar to the transition-metal, it takes directly part in the hydrogen transfer process. Such ligand-metal bifunctional hydrogenation catalysis is dramatically changing the face of reduction chemistry (Scheme 9) (for reviews of ligand-metal bifunctional catalysis, see [32, 37 0]). 

Figure 9.12. Bifunctional catalysis in the reforming of n-hexane. [After J.H. Sinfelt, Adu. Chem. Eng. 5 (1964) 37.]...

RARE EARTH MODIFIED SILICA-ALUMINAS AS SUPPORTS FOR BIFUNCTIONAL CATALYSIS... 

Feedstock Reactions Catalyst References Acetone Condensation-hydrogenation (bifunctional catalysis) Pd on sulfonated PS-DVB [6] Methanol, Raffinate II Condensation, hydrogenation Pd on sulfonated PS-DVB [61] Dioxygen dissolved in water Hydrogenation Pd on sulfonated PS-DVB [8]... 

For Se and Te, oxidation of the adatom takes place at potentials higher than that of CO oxidation. The adatom is always in its reduced state, and no bifunctional catalysis through the transfer of oxygen from the adatom to the CO molecule can take place. 

The three cycles have to turn over in the same range of temperature. This catalytic approach of the DeNOx reaction is not new. There is the same process for isomerization of alkanes, where there are also 3 catalytic cycles which have to turn over simultaneously (bifunctional catalysis). The kinetics of isomerization is given by only one cycle, the other two turning over very rapidly and are near equilibrium [13]. 

A major question has been that of bifunctional catalysis . For example, if a micelle contains both nucleophilic groups and groups which can transfer protons one might hope to achieve high rates of deacylation by having concerted nucleophilic attack and proton transfer (Scheme 6). Such concerted processes are well established in enzymic reactions, but evidence in... 

Catalytic Hydrogenations with Metal-Ligand Bifunctional Catalysis... 

The concerted delivery of protons from OH and hydride from RuH found in these Shvo systems is related to the proposed mechanism of hydrogenation of ketones (Scheme 7.15) by a series of ruthenium systems that operate by metal-ligand bifunctional catalysis [86]. A series of Ru complexes reported by Noyori, Ohkuma and coworkers exhibit extraordinary reactivity in the enantioselective hydrogenation of ketones. These systems are described in detail in Chapters 20 and 31, and mechanistic issues of these hydrogenations by ruthenium complexes have been reviewed [87]. 

Dehydrogenation of Imines and Alcohols by Shvo Complexes 191 Catalytic Hydrogenations with Metal-Ligand Bifunctional Catalysis 193... 

Wang, L-H. Zipse, H. Bifunctional Catalysis of Ester Aminolysis - A Computational and Experimental Study Liebigs Ann 1996,1501-1509. 

Bicycloguanidinium receptor, 16 787 Bidentate chelants, 5 709 Bidentate ligands, 9 396, 397 13 443 Bidentate phosphates ligands, 25 433 Bifunctional catalysis, 5 246-248 ... 

Catalysis by polymer-bound nucleophiles 455 Bifunctional catalysis 456 Stereoselective catalysis 459 Sulfate cleavage 463... 

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