Hydrogenolysis catalyst effect

This catalyst effects reduction of aromatic and tertiary nitriles to methyl groups in yields >85%. Aliphatic nitriles, however, mainly undergo hydrogenolysis.3... 

The catalyst effects hydrogenolysis of large numbers of /-groups OH, Br, NH2, OH2OH, COOH, COOCHj, OSi(CH3)3. However, z-CH2Br is converted into CH3. 

Hydrogenolysis [1, 779, after citation of ref. 4], Homing and Reisner4 found palladium-on-charcoal very effective as a hydrogenation-hydrogenolysis catalyst without addition of perchloric or sulfuric acid. They found the catalyst effective also... 

On activity, comparison of runs 4 and 5 illustrates an increase by a factor of two on going from ethanol to methanol (polarity effect [3]). Addition of a catalytic quantity of sulfuric acid (run 4 compared to run 3) increases activity by a factor of ten [hydrogenolysis catalyst - [5]]. On selectivity, using alcohols in place of ether gives different intermediates (4h in EtOH, 4e in MeOH and 4g in dimethoxyethane) illustrating the concept of "reactive solvent" in the case of alcohols [6]. 

Reduction of 0.1 % Ru/TiOa at 758 K led to high values of 5,- in the n-hexane reaction at 633 K, reacting 94% when the precursor had been made by ion exchange lower values were found with 0.5% RU/HO2, and very low values after reduction at only 433 K. Thus as with the effect of sulfur, even the character of the most active hydrogenolysis catalyst is susceptible to modification. 

An interesting point is that the catalysts effective in glycerol hydrogenolysis were applied to the hydrogenolysis of THFA to 1,5-PeD. Silica- or carbon-supported rhodium catalysts modified with Re, Mo, or W show high activity and selectivity [38—44], while commercial hydrogenation catalysts such as Ru/C, copper chromite, and Raney Ni show much lower activity and selectivity (Table 1). In... 

G.C. Bond, J.C. Slaa, Catalytic and Structural Properties of Ruthenium Bimetallic Catalysts Effects of Pretreatment on the Behaviour or Various Ru/AljOj Catalysts in AUcane Hydrogenolysis, Journal of Molecular Catalysis A 96, 163, 1995. 

The sulfurization of the Pt, or allojdng it with inactive compounds (Au, Sn, Pb) decreases the effective size of the platinum ensembles, and therefore decreases the activity for hydrogenolysis (geometric effect). In the case of bimetallic catalysts such as Pt-Re, and Pt-lr, due to the very high hydrogenol3rtic activity of the second metal, these catalysts have to be presulfided before the operation, to avoid the initial high production of methane with a dangerous increase in temperature. 

Alkali moderation of supported precious metal catalysts reduces secondary amine formation and generation of ammonia (18). Ammonia in the reaction medium inhibits Rh, but not Ru precious metal catalyst. More secondary amine results from use of more polar protic solvents, CH OH > C2H5OH > Lithium hydroxide is the most effective alkah promoter (19), reducing secondary amine formation and hydrogenolysis. The general order of catalyst procUvity toward secondary amine formation is Pt > Pd Ru > Rh (20). Rhodium s catalyst support contribution to secondary amine formation decreases ia the order carbon > alumina > barium carbonate > barium sulfate > calcium carbonate. 

The well-known Adams platinum oxide can be prepared conveniently by the procedure of Adams et al. (2). Platinum oxides prepared in this way usually contain some traces of sodium, which in certain reactions can have an adverse effect. The sodium can be removed by washing with dilute acid (53). The Nishimuri catalyst (30% Pt, 70% Rh oxides) can be prepared by the same procedure as for platinum oxide or with variations from platinum and rhodium salts (64,65,66). This catalyst has much merit. It is usually most useful when hydrogenolysis is to be avoided (67,85,86). 

A frequent problem is selective reduction of an acetylene to the olefin in the presence of other easily reducible functions. Usually the reaction can be done without difficulty because of the relatively strong and preferential adsorption of the acetylenic function on the catalyst. Functions adjacent to the triple bond may cause special problems if the resulting allylic compound is itself susceptible to facile hydrogenolysis (18,23). The product composition is, as expected, sensitive to steric effects (82). 

The catalyst exerts some influence on the bonds broken in hydrogenolysis of saturated cyclopropanes (775), but in vinyl and alkylidene cyclopropanes the effect is pronounced. Platinum or palladium are used frequently. In one case, Nishimura s [124a) catalyst, rhodium-platinum oxide (7 3), worked well where platinum oxide failed (.75). An impressive example of the marked influence of catalyst is the hydrogenation of the spirooctane 42, which,... 

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