Hydrogenation and Dehydrogenation

7- Tetrahydroindole and N-vinyl-4,5,6,7-tetrahydroindole, which are now readily prepared from cyclohexanone oxime and acetylene, may become a source of difficult-to-obtain octahydroindole and N-ethyloctahydroindole. 

7- tetrahydroindoles. Raising the temperature to 200°C at a hydrogen pressure of 50-60 atm does not give rise to any significant hydrogenolysis only traces of the cleavage product are present in the reaction mixture. N-Ethyloctahydroindole (89% yield) has been obtained instead of the expeeted unsubstituted NH-octahydroindole 

SCHEME 2.18 Ethylation of 4,5,6,7-tetrahydroindole during its catalytic hydrogenation in ethanol. 

It has been reported [434,435] on the alkylation of ammonia, aliphatic, and some aromatic amines by primary and secondary alcohols upon heating under hydrogenation on Raney Ni. However, the data on alkylation of indole or pyrrole in similar conditions were absent until the work [433]. In this work, it has been shown that reductive alkylation may also be affected by other primary alcohols (e.g., butanol), although in the latter case, reduction proceeds with greater difficulty than in ethanol N-butyloctahydroindole is detected in the reaction mixture only by chromatography. 

No presence of acid or base was needed, and no activity was observed under the same conditions when using an analogous nonfunctionaUzed pincer complex [41]. 

The catalyst 18 has also been immobilized on a silica sol gel and applied in the same acceptorless dehydrogenation reaction, resulting in a slower reaction although with a clear advantage in recyclabihty and stabilization compared to the 

Dibenzobarrelene-based PC(sp )P complexes of Pd and Pt have also been reported recently by the same group, although they were found to be only moderately active catalysts for H/D exchange of benzene, indicating a lower potential as catalysts than their Ir analogs [43]. 

The analogous iridium formate complex was synthesized by Kaska and coworkers by reacting CO2 with a Ir(lll) dihydride complex. However, in this case, the formate complex proved to be unstable, undergoing disproportionation to form the hydrogen carbonate complex and the carbonyl dihydride, overall corresponding to the reverse water gas shift reaction CO2 -H H2 - CO-P H20[45j. Reduction of CO2 to the methanol level has since been effected using an aromatic nickel pincer complex and a cascade reaction involving a ruthenium pincer complex in one step [46]. 

(b) Eberhard, M.R. (2004) Org. Lett., 6, 2125. (c) Similar results were obtained for other C-C coupling reactions Olsson, D., Nilsson, P., El Masnaouy, M., 

Since hydrogenation and dehydrogenation have been extensively covered in a number of previous review articles (1-7), the discussion here is largely confined to recent developments. 

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Finely divided palladium is a good catalyst and is used for hydrogenation and dehydrogenation reactions. It is alloyed and used in jewelry trades. 

P/Pd denotes the ratio pNC/Pc3n6 or PncSPco The p0, range isO-6 kPa. Hydrogenation and dehydrogenation reactions. ... 

Besser, R. S., Ouyang, X., Suranga-LiKAR, H., Hydrocarbon hydrogenation and dehydrogenation reactions in micro-fabricated catalytic reactors, Chem. Eng. Sci. 58 (2003) 19-26. 

Figure 15. Turnover rate for cyclohexene hydrogenation and dehydrogenation as a function of particle size. Reaction conditions are lOTorr CeHio, 200 Torr H2, and 310K for hydrogenation and 448 K for dehydrogenation, respectively [18].

Dittmeyer, R., V. Hollein, and K. Daub, Membrane reactors for hydrogenation and dehydrogenation processes based on supported palladium, ]. Mol. Catal. A Chem., 173,135-184, 2001. 

Gryaznov, V.M., M.M. Ermilova, L.S. Morozova, and N.V. Orekhova, Palladium alloys as hydrogen permeable catalysts in hydrogenation and dehydrogenation reactions, ]. Less-Common Metals, 89,529-535,1983. 

By using combinations of hydrogenation and dehydrogenation reactions it has been possible to obtain nickel derivatives of the Curtis macrocycle containing from zero to four imine groups (Curtis, 1968 1974). Related reactions in the presence of a variety of other central metal ions have been described. The electrochemical oxidation of the Cu(ii) complex of the reduced Curtis ligand proceeds initially via a two-electron step to yield the monoimine complex (296) (Olson Vasilevskis, 1971). 

A noteworthy feature of the Seager-Anderson experiment was that after hydrogenation of a diode it could be restored practically to its prehydrogenation state by heating for 10 minutes at 200°C. This process of hydrogenation and dehydrogenation could be repeated many times, producing the same sequence of C-V profiles each time. 

Since a catalyst hastens the attainment of equilibrium, it must act to accelerate both forward and reverse reactions. For example, metals are good hydrogenation and dehydrogenation catalysts. 

Skeletal (Raney ) catalysts are made by a very simple technique. An alloy of two metals in roughly equal proportions, where one metal is the desired catalytic material, and the other is dissolvable in hydroxide, is first made. This alloy is crashed and leached in concentrated hydroxide solution. The soluble metal selectively dissolves, leaving behind a highly porous spongelike structure of the desired catalytic metal. Catalysts formed by this technique show high activity and selectivity, and have found wide use in industry, particularly for hydrogenation and dehydrogenation reactions. 

Skeletal catalysts are primarily used for hydrogenation and dehydrogenation reactions. The first application of skeletal nickel was hydrogenation of cottonseed oil [1], Skeletal catalysts have since... 

As an example the reaction with aniline may be selected. In accordance with the scheme formulated, the first reaction product obtained is anilinoquinol (R=NH.C8H5). The reaction does not stop at this stage, however. Between this first reaction product and unchanged quinone still present there promptly occurs a reciprocal hydrogenation and dehydrogenation characteristic of very many of the reactions of quinone. 

Shortly summarised, the process may he regarded as resulting from a series of successive hydrogenation and dehydrogenation reactions similar to that of Cannizzaro (p. 220), and taking place as follows d-glucose in the form of a phosphoric ester first decomposes into two molecules of glyceraldehyde-phosphoric add ... 

Coupling of Hydrogenation and Dehydrogenation Reactions Nonporous Pd-based membranes... 

Gryaznov, V. M. and A. N. Karavanov. 1979. Hydrogenation and dehydrogenation of organic compounds on membrane catalysts (review). Khim.-Farm. Zh. 13(7) 74-78. 

Although the mechanism of the platinum catalysis is by no means completely understood, chemists do know a lot about how it works. It is an example of a dual catalyst platinum metal on an alumina support. Platinum, a transition metal, is one of many metals known for its hydrogenation and dehydrogenation catalytic effects. Recently bimetallic platinum/rhenium catalysts are now the industry standard because they are more stable and have higher activity than platinum alone. Alumina is a good Lewis acid and as such easily isomerizes one carbocation to another through methyl shifts. 

In a polymerization system, not only tertiary alkyl ions but also ions of the allyl type, because of their stabilizing resonance, would be formed readily. Hence, some hydrogenation and dehydrogenation of the primary polymer (e.g., RCH2CH2CH=CHR ) would occur in the following manner ... 

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