Catalyzing benzene hydrogenation

HYDROGENATION REACTIONS Formation, deactivation and degradatio of the active species for arenehydrogenation catalyzed by (ri -C3H5)Co[P(OMe)3]3. The mechanism of benzene hydrogenation catalyzed by (Ti -C3H5)Co[P(OMe)3]3. 

SUPRAMOLECULAR CLUSTER CATALYSIS BENZENE HYDROGENATION CATALYZED BY A CATIONIC TRIRUTHENIUM CLUSTER... 

This review covers the personal view of the authors deduced from the literature starting in the middle of the Nineties with special emphasis on the very last years former examples of structure-sensitive reactions up to this date comprise, for example, the Pd-catalyzed hydrogenation of butyne, butadiene, isoprene [11], aromatic nitro compounds [12], and of acetylene to ethylene [13], In contrast, benzene hydrogenation over Pt catalysts is considered to be structure insensitive [14] the same holds true for acetonitrile hydrogenation over Fe/MgO [15], CO hydrogenation over Pd [16], and benzene hydrogenation over Ni [17]. For earlier reviews on this field we refer to Coq [18], Che and Bennett [9], Bond [7], as well as Ponec and Bond [20]. 

This mechanism is identical to that of olefin hydrogenation catalyzed by [RuClH(PPh3)3] in benzene and in polar organic solvents such as dimethylacetamide [3]. It can be concluded therefore, that replacement of PPha with its mono-sulfonated derivative, TPPMS, brings about no substantial changes in the reaction mechanism, neither does the change from... 

Previous work has shown that the electronic characteristics of the benzene substituent in triarylphosphine chlororhodium complexes have a marked influence on the rate of olefin hydrogenation catalyzed by these compounds. Thus, in the hydrogenation of cyclohexene using L3RhCl the rate decreased as L = tri-p-methoxyphenylphosphine > triphenylphosphine > tri-p-fluorophenylphosphine (14). In the hydrogenation of 1-hexene with catalysts prepared by treating dicyclooctene rhodium chloride with 2.2-2.5 equivalents of substituted triarylphosphines, the substituent effect on the rate was p-methoxy > p-methyl >> p-chloro (15). No mention could be found of any product stereochemistry studies using this type of catalyst. 

In the case of monocyclic benzene oxides, independent of whichever isomer is predominant, most of the chemical reactions are of the oxide form. The exceptions are only hydrogenation and photochemical reactions. Hydrogenation of benzene oxide catalyzed by Pd-C furnishes nearly 70% of oxepane 172 along with cyclohexanol and some unidentified products.8 Similarly, photochemical reaction of 86 96 yields 2-oxabicyclo[3.2.0]hepta-3,6-diene (173). The structure of 173 was confirmed by hydrogenation to 2-oxabicyclo [3.2.0] heptane (174).8... 

The high activity of sodium mordenite for catalyzing benzene hydrogenation as reported by Minachev et al. This result is so unique that additional investigation is warranted. 

IrH5(PPr3)2 can activate the C—H bonds of benzene and catalyze the H—D exchange reaction of benzene and hydrogen (eq (71)) [81]. 

In benzene the complex slowly decomposes with elimination of hydrogen to give a new species whose structure is uncertain. The pentahydride (or its decomposition products) catalyzes the exchange of benzene hydrogen with gaseous deuterium.8 Reaction with trimethylphosphine is rapid with loss of hydrogen to yield a... 

More recently, catalytic hydrogenations of alkenes by other catalysts in water have been explored. For example, water-soluble ruthenium complex RuCl2(TPPTS)3 has been used for the catalytic hydrogenation of unsaturated alkenes (and benzene). Hydrogenation of nonactivated alkenes catalyzed by water-soluble ruthenium carbonyl clusters was reported in a biphasic system. The tri-nuclear clusters undergo transformation during reaction but can be reused repeatedly without loss of activity. The organometallic aqua complex [Cp Ir (H20)3] " ... 

In the commercially relevant reports of benzene oxidation catalyzed by framework metal-containing zeotype materials hydrogen peroxide or nitrous oxide (N2O) are used as oxidants. Thus phenol is produced without major by-product formation. 

In the case of benzene hydrogenation to cyclohexane or cyclohexene on platinum single crystals, a change in selectivity is observed from Pt(lll), which catalyzes the formation of both products, to Pt(lOO), where only cyclohexane is produced. This effect is due to the structure sensitivity of the cyclohexene-forming reaction, while the cyclohexane-forming reaction is structure insensitive. Interestingly, the same effect can be observed on nanoparticles of different shapes cuboctahedral particles, which contain (111) faces, catalyze the production of both products, whereas cubic nanoparticles (with (100) faces) produce only cyclohexane (Figure 8) . ... 

The free radical condition with w-BusSnH/AIBN in benzene has been employed to replace the nitro group with the hydrogen atom in 2-nitroalcohol 42 with excellent diastereoselectivity. On the other hand, secondary benzylic nitro group of 2-nitroalcohol 44 can be reduced to afford homobenzylic alcohol 45 by hydrogenation catalyzed by Pearlman s catalyst... 

For the iron-catalyzed reaction, one of the ortho or para hydrogens in benzene is replaced by chlorine. When an iron catalyst is not present, then the benzene hydrogens are unreactive, which is seen for the light-catalyzed reaction where one of the methyl hydrogens is replaced by chlorine. 

Production of a-methylstyrene (AMS) from cumene by dehydrogenation was practiced commercially by Dow until 1977. It is now produced as a by-product in the production of phenol and acetone from cumene. Cumene is manufactured by alkylation of benzene with propylene. In the phenol—acetone process, cumene is oxidized in the Hquid phase thermally to cumene hydroperoxide. The hydroperoxide is spHt into phenol and acetone by a cleavage reaction catalyzed by sulfur dioxide. Up to 2% of the cumene is converted to a-methylstyrene. Phenol and acetone are large-volume chemicals and the supply of the by-product a-methylstyrene is weU in excess of its demand. Producers are forced to hydrogenate it back to cumene for recycle to the phenol—acetone plant. Estimated plant capacities of the U.S. producers of a-methylstyrene are Hsted in Table 13 (80). 

Acid-catalyzed hydrogen exchange is used as a measure of the comparative reactivity of different aromatic rings (see Table 5). These reactions take place on the neutral molecules or, at high acidities, on the cations. At the preferred positions the neutral isoxazole, isothiazole and pyrazole rings are all considerably more reactive than benzene. Although the 4-position of isothiazole is somewhat less reactive than the 4-position in thiophene, a similar situation does not exist with isoxazole-furan ring systems. 

Tetrahydro derivatives are formed when either quinoxaline or 6-chloroquinoxaline is reduced with lithium aluminum hydride in ethereal solution. Similar reduction of 2,3-dimethylquinoxaline gives the meso-(cts)-1,2,3,4-tetrahydro derivative. This is shown to be a stereospecific reduction since lithium aluminum hydride does not isomerize the dl-(trans)-compound. Low temperature, platinum catalyzed, hydrogenation of 2,3-dimethylquinoxaline in benzene also gives meso (cis) -l,2,3,4-tetrahydro-2,3-dimethylquinoxaline. ... 

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