Amine-catalyzed systems mechanism

Studies undertaken in connection with the amine-catalyzed asymmetric alkene osmylation have recently clarified the peculiar mechanism of the hexacyanoferrate/CO2 mediated osmium re-oxidation in biphasic conditions36. Reversal of the osmate oxidation/hydrolysis sequence with respect to the previously described R3NO-mediated conditions was noted with this system. Thus, the monodiolate(amine) osmium(VI) ester 9 appears to be first hydrolyzed, releasing the diol and the amine ligand to the organic phase, and the resulting [0s02(0H)4]2 into the aqueous phase. 

Poly (oxy-2,6-dimethyl-1,4-phenylene) (poly (phen-ylene oxide), PPO) is widely used as a high-performance engineering plastic, since the polymer has excellent chemical and physical properties, e.g., a high Tg (ca. 210 °C) and mechanical toughness. PPO was first prepared from 2,6-dimethylphenol monomer using a copper/amine catalyst system.25 The HRP-catalyzed polymerization of 2,6-dimethylphenol gave the polymer consisting of exclusively oxy-l,4-phe-nylene units.26... 

Theoretical treatment of this polymerization is difficult because of the presence of both primary and secondary amine reactions as well as tertiary amine catalyzed epoxy homopolymerization. To obtain kinetic and viscosity correlations, empirical methods were utilized. Various techniques that fully or partially characterize such a system by experimental means are described in the literature ( - ). These methods Include measuring cure by differential scanning calorimetry, infra-red spectrometry, vlsco-metry, and by monitoring electrical properties. The presence of multiple reaction mechanisms with different activation energies and reaction orders (10) makes accurate characterizations difficult, but such complexities should be quantified. A dual Arrhenius expression was adopted here for that purpose. 

For these catalyzed systems, two main viscoelastic transitions were observed in the dynamic mechanical data as described in our previous publication (5) and shown in Figure 1(a) for tan 6. The low temperature, 3s transition provides information concerning the amine-epoxide reactions. Since the... 

In 2008, Diaz-Requejo, Perez, and coworkers developed a new silver-based catalytic system which proceeded the direct intermolecular amination of alkanes [33]. This new catalyzed system employed complexes [Tp Ag]2 8 as catalyst and Phl=NTs ([Ag]/[PhI=NTs]=l/20) as the nitrene source. The reaction was carried out in neat alkane at 80°C for 4 h. Linear and branched alkanes were converted to corresponding isomeric mixtures of amides in moderate to excellent yields (Scheme 12). The amination/amidation was favored at tertiary sites over secondary and primary sp C-H bonds of alkanes, and only a few examples were observed at primary sp C-H bonds. The reaction was inhibited when 2,6-di-tert-butyl-4-methylphenol (BHT) was present. Chloroalkanes were observed when CCI4 was used as solvent. These evidences indicated that the mechanism involved radical species. 

Several mechanisms have been proposed, but very few authors have shown that the orders in reactants depend on the nature of the reaction medium, although Madec and Mar6chal, studying the benzoic/1,2-epoxy-3-phenoxypropane system found that the overall order is 2 in xylene, chlorobenzene, and orthodichlorobenzene as solvent the authors suggested a bimolecular process. However, compared to the amine-catalyzed reaction, the reaction is very slow. 

On the basis of this discussion, we propose that the Ru3( CO) i2/NMe3-catalyzed WGSR follows the mechanism shown in Figure 3. A similar mechanism, involving nucleophilic attack by hydroxide instead of amine, has been proposed by Pettit and coworkers (4) for the Fe(C0)5/base system. 

Abstract The basic principles of the oxidative carbonylation reaction together with its synthetic applications are reviewed. In the first section, an overview of oxidative carbonylation is presented, and the general mechanisms followed by different substrates (alkenes, dienes, allenes, alkynes, ketones, ketenes, aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, phenols, amines) leading to a variety of carbonyl compounds are discussed. The second section is focused on processes catalyzed by Pdl2-based systems, and on their ability to promote different kind of oxidative carbonylations under mild conditions to afford important carbonyl derivatives with high selectivity and efficiency. In particular, the recent developments towards the one-step synthesis of new heterocyclic derivatives are described. 

The results given in this paper show that aliphatic amines do not catalyze the decomposition of peroxides, and compared with their effect at the start of reaction, they have much less effect on the later stages of oxidation, although they appear to retard the decomposition of peracetic acid. The reactions of radicals with aliphatic amines indicate that an important mode of inhibition is most probably by stabilization of free radicals by amine molecules early in the chain mechanism, possibly radicals formed from the initiation reaction between the fuel and oxygen. For inhibition to be effective, the amine radical must not take any further part in the chain reaction set up in the fuel-oxygen system. The fate of the inhibitor molecules is being elucidated at present. 

In retrospect, the postulated mechanism for amic acid back reaction to anhydride and amine as the main pathway to explain hydrolytic instability of the poly(amic acid) system may have prompted the search for more stable systems in the form of derivatized polyfamic acids). Realizing that if proton transfer in the internal acid catalyzed formation of the intermediate illustrated in Scheme 9 (reaction 1) can be prevented, then the potential for the amic acid back reaction might be eliminated [51]. This, of course, can be accomplished in... 

Allylic amide isomerization, 117 Allylic amine isomerization ab initio calculations, 110 catalytic cycle, 104 cobalt-catalyzed, 98 double-bond migration, 104 isotope-labeling experiments, 103 kinetics, 103 mechanism, 103 model system, 110 NMR study, 104 rhodium-catalyzed, 9, 98 Allylnickel halides, 170 Allylpalladium intermediates, 193 Allylsilane protodesilylation, 305 Aluminum, chiral catalysts, 216, 234, 310 Amide dimers, NMR spectra, 282, 284 Amines ... 

Nitro Reduction. Aromatic amines are susceptible to reduction by both bacterial and mammalian nitroreductase systems. Convincing evidence has been presented that this reaction sequence is catalyzed by CYP. It is inhibited by oxygen, although NADPH is still consumed. Earlier workers had suggested a flavoprotein reductase was involved, and it is not clear if this is incorrect or if both mechanisms occur. It is true, however, that high concentration of FAD or FMN will catalyze the nonenzymatic reduction of nitro groups. 

In this part, we wish to focus on the study of two types of silanes. Aminoorganosilanes are special members of the alkoxysilanes group. They carry the catalyzing amine function, required for chemical bonding with the silica surface, inside the molecule. This makes them more reactive than other organosilanes and reduces the complexity of the liquid phase reaction system to be studied. Only three components, silica, silane and solvent, are present. Furthermore there is a large interest in the reaction mechanism of silica gel with APTS, since this aminosilane is the most widely used compound of the organosilane family. 

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