Hydrogenolysis Of Benzyl Alcohol Research Articles

Selective Alcohol Dehydrogenation and Hydrogenolysis with Semiconductor-Metal Photocatalysts: Toward Solar-to-Chemical Energy Conversion of Biomass-Relevant Substrates

Photocatalytic conversion of biomass is a potentially transformative concept in renewable energy. Dehydrogenation and hydrogenolysis of biomass-derived alcohols can produce renewable fuels such as H2 and hydrocarbons, respectively. We have successfully used semiconductor-metal heterostructures for sunlight-driven dehydrogenation and hydrogenolysis of benzyl alcohol. The heterostructure composition dictates activity, product distribution, and turnovers. A few metal (M = Pt, Pd) islands on the semiconductor (SC) surface significantly enhance activity and selectivity and also greatly stabilize the SC against photoinduced etching and degradation. Under selected conditions, CdS-Pt favors dehydrogenation (H2) over hydrogenolysis (toluene) 8:1, whereas CdS0.4Se0.6-Pd favors hydrogenolysis over dehydrogenation 3:1. Photochemically generated, surface-adsorbed hydrogen is useful in tandem catalysis, for example, via transfer hydrogenation. We expect this work will lead to new paradigms for sunlight-driven conversions of biomass-relevant substrates.

A simple and efficient hydrogenation of benzyl alcohols to methylene compounds using triethylsilane and a palladium catalyst

Hydrogenolysis of benzyl alcohols using triethylsilane (Et 3SiH) and a catalytic amount of palladium(II) chloride (PdCl 2) is described. The reaction takes place under mild conditions affording high yields of the corresponding methylene compounds in short reaction times.

A comparative study on the adsorption of benzyl alcohol, toluene and benzene on platinum

The adsorption of benzyl alcohol, toluene and benzene on platinum was studied using cyclic voltammetry combined with on-line mass spectrometry (DEMS). Flow cell procedures allow the detection of volatile products formed during adsorption of these molecules and their displacement with CO, as well as during the oxidative and reductive stripping of the adsorbed layer. Three adsorption potentials were chosen: 0.20, 0.35 and 0.50 V versus reversible hydrogen electrode (rhe). Toluene and benzene adsorb without dissociation. Total hydrogenation of the ring with formation of methyl-cyclohexane and cyclohexane, respectively, was observed suggesting that the aromatic ring of the adsorbed species lies on the surface. For benzyl alcohol, the presence of the OH group favours the dissociative adsorption: the rupture of the CC bond between the ring and the CH 2OH group produces CO and benzene. Hydrogenolysis of benzyl alcohol also occurs in the Pt(H) region with formation of toluene. Both adsorbed toluene and benzene from benzyl alcohol react with H 2 producing methyl-cyclohexane and cyclohexane, respectively. Thus, benzene and toluene formed from benzyl alcohol also seem to adsorb with the aromatic ring parallel-oriented on the surface.

Liquid phase hydrogenolysis of dibenzyl ether over metals of the VIIIth group

It has been shown that depending on the catalyst and the solvent used, during the conversion of dibenzyl ether to toluene hydrogenolysis of C-O ether bonds, dehydrogenation and hydrogenolysis of benzyl alcohol formed, hydrogenation and decarbonylation of benzaldehyde, and the recombination of benzyl radicals and the benzylation of toluene can take place. The activity of catalysts in hydrogenolysis reactions of dibenzyl ether and benzyl alcohol to produce toluene decreases as follows: Pd/C>Pd>Raney Ni>Rh, whereas the selectivity drops down in the order: Raney Ni>Pd>Pd/C>Rh. The reaction rates depend on the solvent and diminish in the order: ethanol>2-propanol>benzene.

Stereochemistry and Mechanism of Catalytic Hydrogenation and Hydrogenolysis. III. Catalytic Hydrogenolysis of Benzyl-type Alcohols and Their Derivatives

Abstract In order to obtain evidence for the mechanism we proposed of the catalytic hydrogenolysis of benzyl-type alcohols and their methyl ethers, optically active 2-phenyl-2-butanol (Ia), 2-phenyl-2-methoxybutane (IIa), ethyl atrolactate (Ib), and ethyl 2-phenyl-2-methoxypropionate (IIb) were hydrogenolyzed over Raney nickel and Pd(H) catalysts under hydrogen or helium atmosphere in an ethanol solution. In all cases, the hydrogenolysis proceeded stereoselectively with retention of configuration over Raney nickel catalyst but with inversion of configuration over palladium catalyst. A reverse stereoselectivity was observed when the benzyl alcohols (Ia and 2-phenyl-1,2-dihydroxypropane (Ic)) and methyl ethers (IIa) and (IIb) were hydrogenolyzed in the presence or absence of various additives over nickel catalysts. It was also found that the hydrogenolysis of benzyl alcohols always proceeds with retention of configuration over nickel catalyst containing sodium hydroxide. Various binary mixtures of Ia, IIa, Ib and IIb were hydrogenolyzed competitively over Raney nickel and Pd(H) catalysts. The order of relative rates was found to be Ia\gtrsimIb\gtrsimIIa\gtrsimIIb over Raney nickel, and IIa\gtrsimIa>>IIb\gtrsimIb over Pd(H) catalyst. The results support our mechanism. The catalytic hydrogenolysis is a competitive reaction of two courses (SNi type and SN2 type reactions), and the stereoselectivity reflects the difference of the free energy levels of the transition states to form π-benzylic complexes. The free energy levels of the corresponding transition states depend on stereoelectronic factor, affinity of substituents for catalyst metal, catalyst hindrance and electronic effects of substituents. The acetates (IVa) and (IVb) of Ia and IIa were hydrogenolyzed with inversion of configuration over nickel and palladium catalysts, whereas the stereoselectivity of the hydrogenolysis of the benzoate (V) of IIa depended on the kind of catalyst. The results are also explained on the basis of our mechanism.