Alcohols hydrogenation-dehydrogenation

These pentahydrides have attracted attention as catalysts for hydrogenation of the double bond in alkenes. IrH5(PPr3)2 catalyses vinylic H-D exchange between terminal alkenes and benzene, the isomerization of a,f3-ynones, isomerization of unsaturated alcohols and dehydrogenation of molecules such as secondary alcohols [176],... 

Ruthenium NHC dihydride complex 26 was found to exhibit interesting reversible hydrogenation/dehydrogenation activity (Scheme 10.11) [35,36]. When excess acetone was used as a hydrogen acceptor, dehydrogenation of several alcohols was achieved (Table 10.5). 

A third possibility is represented by a two-step mechanism where the donor alcohol is dehydrogenated and the ketone reduced by the H2 produced. In this case, the easier the donor alcohol is dehydrogenated, the higher is the hydrogen availability on the catalyst surface and the faster is the reaction. If the donor is slowly dehydrogenated, the hydrogen availability is lower. 

Hydrogenation-dehydrogenation of allylie and homoallyKc alcohols. Treatment of cholesterol and A4-cholestenol with Raney nickel (previously washed with alcohol) and cyclohexanone in refluxing toluene results mainly in formation of 5/1-3-choleslanone (1). This hydrogenation-dehydrogenation proceeds much more rapidly with the allylie alcohol 4. 

When coniferyl alcohol is dehydrogenated, it loses its phenolic hydrogen atom to form first an aroxyl radical Ra (XI), which is in eflFect also present as the mesomeric radicals Rb (XII), Rc (XIII), and Rd (XIV). Of these limiting structures, Rb is the most favored. The existence of the radicals in these forms is recognized by their reaction products. In very dilute dioxane-water solution (1 1 vol.), the half-life of the radicals is about 45 seconds 13). 

A more recent process allows the manufacture of ethyl acetate from ethyl alcohol without the use of acetic acid or any other cofeedstocks. In the process (Fig. 1), ethyl alcohol is heated and passed through a catalytic dehydrogenation reactor where part of the ethyl alcohol is dehydrogenated to form ethyl acetate and hydrogen. 

Alkylated triazines of the current have also been prepared by heating melamine or melamine derivative and an alcohol in the presence of a hydrogenation-dehydrogenation mixed catalyst such as 5% palladium on carbon (50% hydrated) with 25 mg of Cu0/Cr203/Ni0/Ba0 and is reviewed (4). 

Supported copper-based catalysts are active for a great variety of reactions and there have been many fundamental studies of their catalytic and solid state properties. Among them, the oxidation of hydrocarbons and CO (1), alkanes (2) and alcohols (3) dehydrogenation, hydrogenation of ketones (4), allyl alcohols and a- and 6-unsaturated aldehydes and ketones (5), alcohol amination (6), low temperature water gas shift (7). methanol synthesis (8), oxidative condensation of methanol (9), hydrolysis of acrylonitrile to acrylamide (10), and removal of NOx pollutants (11). 

Addition reactions. Spiroacetal formation from dihydroxyalkynes is the result of a triple bond activation by iridium complex (1). Prenylation of an aldehyde from its mixture with 1,1-dimethylaUene under hydrogen is significant as the nucleophilic species is highly substituted. Alcohols are dehydrogenated in the presence of proper iridium complexes (cf. 2 and S ) therefore the same type of products are accessible while obviating hydrogen gas. ... 

Dehydroamination is performed in the presence of a hydrogenation-dehydrogenation catalyst and an alcohol. It has been proven that an aldehyde is formed as an intermediate. Formally, this transformation is obtained by three successive reac-tions-dehydrogenation of the alcohol (Oppenauer type oxidation), formation of an imine by nucleophilic attack then dehydration, and, finally, reduction of the imine (MPV-type reduction). In the last reaction step, it can be assumed that the dehydroamination pathway is similar to that of reductive amination. 

This evidence of reversibility in the acrolein-ethyl alcohol reaction at a temperature (396°, 1 atm.) where both allyl alcohol and ethyl alcohol are thermodynamically unstable with respect to the aldehydes and hydrogen indicated that the hydrogen transfer reaction was catalyzed by surfaces which were inactive for hydrogenation-dehydrogenation reactions. In order to explore the activity of magnesia and zinc oxide for hydrogenation, a number of these catalysts were tested for the direct hydrogenation of acrolein. 

An alternative method for the oxidation of alcohols is dehydrogenative oxidation via a hydrogen transfer reaction [2a]. The process of dehydrogenation of alcohols by... 

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