Aromatization hydrogen transfer

These measures blocked all side reactions, such as oxidative aromatization, hydrogen transfer, and thermal disrotatory back reaction, as well as increasing the proportion of the C form at the UV irradiation pss. 

Hydrogenation of aromatic nitro compounds is very fast, and the rate is limited often by the rate of hydrogen transfer to the catalyst. It is accordingly easy to use inadvertently more catalyst than is actually necessary. Aliphatic nitro compounds are reduced much more slowly than are aromatic, and higher catalyst loadings (6,11) or relatively lengthy reduction times may be... 

Boric acid esters provide for thermal stabilization of low-pressure polyethylene to a variable degree (Table 7). The difference in efficiency derives from the nature of polyester. Boric acid esters of aliphatic diols and triols are less efficient than the aromatic ones. Among polyesters of aromatic diols and triols, polyesters of boric acid and pyrocatechol exhibit the highest efficiency. Boric acid polyesters provide inhibition of polyethylene thermal destruction following the radical-chain mechanism, are unsuitable for inhibition of polystyrene depolymerization following the molecular pattern and have little effect as inhibitors of polypropylene thermal destruction following the hydrogen-transfer mechanism. 

During the cracking process, fragmentation of complex polynuclear cyclic compounds may occur, leading to formation of simple cycloparaffins. These compounds can he a source of Ce, C7, and Cg aromatics through isomerization and hydrogen transfer reactions. 

In the reaction of two olefins, both olefins must be adsorbed on active sites that are close together. One of these olefins becomes a paraffin and the other becomes a cyclo-olefin as hydrogen is moved from one to the other. Cyclo-olefin is now hydrogen transferred with another olefin to yield a paraffin and a cyclodi-olefin. Cyclodi-olefin will then rearrange to form an aromatic. The chain ends because aromatics are extremely stable. Hydrogen transfer of olefins converts them to paraffins and aromatics (Equation 4-11). 

Certain catalyst properties appear to increase coke formation. Catalysts with high rare earth content tend to promote hydrogen transfer reactions. Hydrogen transfer reactions are bimolecular reactions that can produce multi-ring aromatics. 

The use of H-labeled substrates has been used to determine details of the dehydrogenation of ciT-dihydrodiols produced by dioxygenases from aromatic substrates (Morawski et al. 1997), and it was possible to demonstrate the specificity of hydrogen transfer from the dihydrodiol substrates to NAD. 

Sobolewski AL, Domcke W, Dedonder-Lardeux C, Jouvet C (2002) Excited-state hydrogen detachment and hydrogen transfer driven by repulsive (l)pi sigma states a new paradigm for nonradiative decay in aromatic biomolecules. J Phys Chem Chem Phys 4 1093—1100... 

Phenolic compounds may enhance the rate of decomposition of aromatic ether, because the phenoxy radical may be stabilized by solvation (18) or hydrogen bonding (19) with phenolic compounds and may result in the subsequent hydrogen transfer reaction from hydrogen donating solvent or phenols (20). 

The above results show that the dihydro-aromatics do not directly contribute to rearrangements. Secondly the dihydroaromatics rapidly aromatize by hydrogen transfer or dispropositionation. This implies that the rearrangement... 

A different result was obtained in the cycloaddition to methylenecyclo-propanes 216-218 tearing alkoxycarbonyl substituents on the cyclopropyl ring. In this instance, 1,2,3-triazoles 220 isomeric with the triazolines 219 were formed in the reaction [57]. The formation of triazoles 220 is rationalised by the intermediate formation of triazolines 219, which are unstable under the reaction conditions and undergo a rearrangement to the aromatic triazoles via a hydrogen transfer that probably occurs with the assistance of the proximal ester carbonyl (Scheme 35). The formation of triazoles 220 also confirms the regio-chemistry of the cycloaddition for the methylene unsubstituted methylene-cyclopropanes, still leaving some doubt for the substituted ones 156 and 157. 

The pulse experiments demonstrated that active sites for propane dehydrogenation are formed upon exposure of the oxide form of gallium modified ZSM-5 to propane itself. A constant 1 1 ratio of hydrogen produced to propane consumed is attained after a number of pulses with little propene formation, which suggests that, after propane dehydrogenation to propane, aromatization proceeds through hydrogen transfer reactions. 

This involves rate-determining proton transfer, equation (37) in principle it should show general acid catalysis, but in practice this usually cannot be seen as the catalyzing acid is simply H30+ . A typical example would be aromatic hydrogen exchange, such as the detritiation of tritiated benzene shown in equation (38) 147... 

Ab initio electron correlated calculations of the equilibrium geometries, dipole moments, and static dipole polarizabilities were reported for oxadiazoles <1996JPC8752>. The various measures of delocalization in the five-membered heteroaromatic compounds were obtained from MO calculations at the HF/6-31G level and the application of natural bond orbital analysis and natural resonance theory. The hydrogen transfer and aromatic energies of these compounds were also calculated. These were compared to the relative ranking of aromaticity reported by J. P. Bean from a principal component analysis of other measures of aromaticity <1998JOC2497>. 

Considerable interest remains in catalyzed hydrogen-transfer reactions using as donor solvents alcohols, glycols, aldehydes, amides, acids, ethers, cyclic amines, and even aromatic hydrocarbons such as alkylben-... 

In the presence of strong alkali, the rhodium analog of 62, or RhCl(C8H,2)PPh3, hydrogenates aliphatic ketones at 1 atm and 20°C, and after treatment with borohydride the systems similarly reduce aromatic ketones to the alcohols (526). Deuterium exchange data for acetone reduction were interpreted in terms of hydrogen transfer within a mononuclear hydroxy complex containing substrate bound in the enol form (63). 

HTC (2) [Hydrogen transfer catalysis] A catalytic process for reducing aromatic nitrocompounds. Developed by Rohner in 1993. 

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