Hydrogenolysis of C-O bonds

The metals are also different in the transformation of the cis- and trans-2,3-dimethyloxiranes. The cis-2,3-dimethyloxirane is transformed at a much higher rate than the trans isomer on Pt and Pd catalysts, whereas on Ni the two isomers are converted at almost the same rate.7 

Pd and Ni are the most widely used catalysts for the hydrogenolysis of C-O bonds. The rates of hydrogenolysis increase in the order OH OR OAr OCOR. This order corresponds to the leaving-group properties of these moieties, which is characteristic of S -type reactions. The stereochemistry of the reaction depends mainly on the metal. Inversion of the configuration of carbon is characteristic of Pd whereas retention is usually observed with Ni [2,11]. 

Zeolites have also been used for the hydrogenolysis of alcohols. For example, hydrogenolysis of 2-phenylethanol was achieved over Cs-exchanged zeolite X catalyst [15], 

Glycerol and other polyols can be converted into propane-1,2-diol with high selectivity on sulfur-modified Ru on carbon the reaction is not simple hydrogenolysis but rather dehydrogenation, then dehydroxylation and hydrogenation of the enol produced [16-18], 

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ABSTRACT New catalysts for hydrogenolysis of C-O bond are proposed. The catalysts were prepared by anchoring of Mo, (Ni,Mo) and (Co,Mo) complexes to the surface of a new carbon support Sibunit. Two types of the active component were prepared - oxide and sulfide forms. The catalysts were tested in a model reaction of tetrahydroftiran hydrogenolysis. As shown, the catalysts are active in the purposeful reaction of C-O- bond hydrogenolysis and do not catalyze the side reactions -polymerization and dehydration of tetrahydrofuran. 

Heterogeneous catalytic transfer hydrogenolysis of C-O bonds in aliphatic and aromatic ethers has been reviewed [90]. As an example, catalytic transfer... 

Elevated temperature is usually needed for the hydrogenolysis of C-O bonds in alcohols [12]. Hydrogenolysis of primary alcohols can be deseribed as an 8 2-like reaction involving hydride attack on the carbon, whereas transformation of a tertiary alcohol is closer to an S jl-type reaetion [2,13]. Tertiary alcohols can be hydrogenolyzed much faster than secondary. Alcohols are readily converted to the corresponding 0-alkylisoureas. Hydrogenolysis of these compounds leads to hydrocarbons (Scheme 1) [14]. 

It is widely accepted that a benzyl-nitrogen bond is not as readily cleaved as a benzyl-oxygen bond. The presence of nitrogen can, however, influence the hydrogenolysis of C-O bonds. It has been reported that butylamine completely prevented the hydrogenolysis of the benzylic C-O bond [62]. The same effect was observed for molecules containing both benzylic C-O and C-N bonds [62,63]. In a mixture of A-benzylcyclohexylamine and benzyl cyclohexyl ether only the C-N bond was hydrogenolyzed on Pd/C, whereas in the presence of HCl the... 

Catalytic hydrogenolysis of C—O bonds of benzyl esters and similar compounds by deuterium has rarely been used for preparation of labeled compounds, whereas predeuterated Pd in D20 is recommended for formation of deuterated alcohols from epoxides.63... 

The best way to reduce a furan to a tetrahydrofuran is using Raney nickel catalysis, though ring opening, via hydrogenolysis of C-O bonds can be a complication. Most furans are not reduced simply by metal/ammonia combinations, however furoic acids and furoic acid tertiary amides give dihydro-derivatives. 

Selective Hydrogenolysis of C-O Bonds Using the Interaction of the Catalyst Surface and OH Groups... 

Hydrogenolysis of glycerol to 1,2- and 1,3-propanediols (PrD) seems to be simple judging from the reaction formula as below (1, 2) because the hydrogenolysis of C-O bonds apparently means the dissociation of C-O bonds and insertion of hydrogen atoms. 

The conversions of acetic anhydride to acetaldehyde and of ethylidene diacetate to ethyl acetate both involve hydrogenolysis of C—O bonds, whereas the hydrogenation of acetaldehyde to ethanol involves 0=0 reduction. An appropriate choice of hydrogenolysis versus hydrogenation catalyst functions should enable discrimination between the reaction pathways and the development of highly selective processes to both ethyl acetate and propionic acid, respectively. However, a clear disadvantage common to both is the requirement for recycling of stoichiometric quantities of acetic acid (see the next section). 

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