Stepwise hydrogenation

Figure 2. Stepwise hydrogen atom transfer from Tetralin...

Figure 4. Stepwise hydrogen atom exchange between coal and naphthalene. The starting naphthalene was deuterated completely. To simplify the scheme only a- and f -position are shown.

The presence of a significant kinetic isotope effect for the losses of OH from the nitroazoles (ThAd = 4.6) supports the suggestion that the fragmentations are adequately described by a stepwise hydrogen transfer, followed by cleavage of the OH moiety or, alternatively, rearrangement to structures which can eliminate OH and H2O98. 

Azobenzene was also present during the hydrogenation of nitrosobenzene and a stepwise hydrogenation process of nitrosobenzene to azoxybenzene to azobenzene to aniline is a credible route. No azoxybenzene was observed during the hydrogenation of nitrobenzene. 

A purely bifunctional mechanism was assumed to be operative in the CO oxidation on Pt3Sn surfaces as well as on other Pt alloys with oxophilic transition metals [157-159]. Here, the oxophilic Sn surface atoms are believed to provide nucleation sites for water and, following stepwise hydrogen abstraction, for its subsequent oxygenated surface products OH and O. CO oxidation on Sn atoms is unlikely [131,160] such that no competition for Sn sites occurs between water and CO molecules. All Pt atoms are covered with CO. 

A mechanism for C02 hydrogenation over Cu on Zr02 was presented by Bell and coworkers.39 C02 is suggested to adsorb on zirconia as bicarbonate, which undergoes stepwise hydrogenation to produce formate (1), dioxomethylene, and, finally, methoxy species ... 

Anthracene and phenanthrene are converted to their 9,10-dihydro derivatives in high yield. Other partially hydrogenated intermediates formed by further stepwise hydrogen addition can also be isolated under suitable experimental conditions.10 18 Platinum and palladium exhibit different selectivities in the partial hydrogenation of polycyclic aromatics under mild conditions 108... 

Scheme 39. Stepwise hydrogenation of Ru5(CO),3(/r5-CCPPh2XA -PPh2) (/9). Asterisk indicates structures proposed on the basis of NMR spectroscopy.

Figure 8 Schematic of the stepwise hydrogenation of a nitrile to a primary amine via an imine and secondary reaction of the product primary amine with the imine intermediate.

FT synthesis kinetics are similar on Co and Ru catalysts and reflect similar CO activation and chain growth pathways on these two metals. These kinetic expressions are consistent with the stepwise hydrogenation of surface carbon formed in fast CO dissociation steps (26). Chemisorbed CO and CH t species are the most abundant reactive intermediates, as expected from the high binding energy of CO and carbonaceous deposits on Co and Ru surfaces (7, 76-80). As a result, reaction orders in CO remain negative at the usual inlet pressures but can become positive as CO reactants are depleted by transport limitations within pellets or by high levels of conversion within the catalyst bed. 

Schweizer and l,ight° found 5% rhodium on ciirbon satisfactory for the stepwise hydrogenation of 3 H-pyrrolizine (1). 

S. Girellini, R. S. Holmes, T. J. Allinger, N. L., J. Phys. Chem. 1980, 84, 1810 - 1814. The stepwise hydrogenation of this diene is more nearly normal in its Ahyd//, as seen by comparison with norbomene. See however dihydronorbomenes (2) and (3) immediately below. 

Cyclohexadiene was converted totally on a Ni catalyst when the benzene conversion was - 5-6%. From this point onwards, the concentration of cH dropped dramatically with a simultaneous increase in its specific radioactivity exceeding that of cH, when the Bz conversion reached 10% as shown in Fig. 3. The formation of radioactive cyclohexene from [ C]-benzene supplied further evidence of the existence of stepwise hydrogenation, even if it is not the exclusive route. 

There is stepwise hydrogenation via diimine N2H2, an unstable intermediate, and diazene N2H4 (hydrazine) to ammonia ... 

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