Reaction catalytic hydrogenation

In a sense the formation of t) -H2 complexes can be thought of as an intermediate stage in the oxidative addition of H2 to form two M-H bonds and, as such, the complexes might serve as a model for this process and for catalytic hydrogenation reactions by metal hydrides. Indeed, intermediate cases between and... 

Aniline 77 was converted into its diazonium salt with nitrous acid and this was followed by reduction with stannous chloride to afford the corresponding arylhydrazine 78. Condensation of 78 with 3-cyanopropanal dimethylacetal 79 gave the arylhydrazone 80. Treatment of 80 with PPE resulted in cyclization to indole 81. The nitrile group was then reduced to the primary amine by catalytic hydrogenation. Reaction of the amine with excess formalin and sodium borohydride resulted in Imitrex (82). 

Treatment of the piperidine 74, obtainable from an aminonitrile such as 73, under N-methylation conditions leads to the dimethylamino derivative 75. The carbobenzoxy protecting group is then removed by catalytic hydrogenation. Reaction of the resulting secondary amine 76 with cyclohexene oxide leads to the alkylated trans aminoalcohol. There is thus obtained the anti-arrhythmic agent transcainide (77) [18]. 

More recently. Baker, Tumas, and co-workers published catalytic hydrogenation reactions in a biphasic reaction mixture consisting of the ionic liquid [BMIM][PFg] and SCCO2 [10]. In the hydrogenation of 1-decene with Wilkinson s catalyst [RhCl(PPh3)3] at 50 °C and 48 bar H2 (total pressure 207 bar), conversion of 98 %... 

E. Lamy-Pitara and J. Barbier The group of Professor Barbier and Dr. Lamy-Pitara was first to demonstrate NEMCA in an aqueous phase catalytic hydrogenation reaction (Chapter 10). This work is of very significant theoretical and potentially practical importance. 

Scheme 10.30. Domino Knoevenagel condensation/catalytic hydrogenation reaction in ionic liquid.

Photoassisted catalytic hydrogenation reactions invariably involve promoted loss of a ligand and generation of coordinatively unsaturated species. Examples in the literature are becoming increasingly common. 

Tetrasubstituted alkenes are among the most challenging substrates for catalytic hydrogenation reactions. Towards this end, Buchwald and co-workers recently reported efficient and highly enantioselective Zr-catalyzed hydrogenations of a range of styrenyl tetrasubstituted alkenes (Scheme 6.41) [123]. Precedents based on efficient polymerization reactions promoted by cationic zirconocenes led these workers to consider similar catalyst species, derived from dimethylzirconocene 107, for this purpose. 

Sokol skii, D. V., B. Y. Nogcrbekov and N. N. Gudeleva. 1986. Investigation of the activity of a palladium/glass membrane in catalytic hydrogenation reactions. Sov. Electrochem. 22(9) 1227-1229. 

In aqueous hydrochloric acid solutions, mthenium(II) chloride catalyzed the hydrogenation of water-soluble olefins such as maleic and fumaric acids [6]. After learning so much of so many catalytic hydrogenation reactions, the kinetics of these simple Ru(II)-catalyzed systems still seem quite fascinating since they display many features which later became established as standard steps in the mechanisms of hydrogenation. The catalyst itself does not react with hydrogen, however, the mthenium(II)-olefin complex... 

The black solution containing IL and lr(0) nanoparticles (-2.0nm in diameter, as determined by TEM) can also be recycled in catalytic hydrogenation reactions. The catalytic activity of these soluble iridium nanoparticles was also compared to that of the Crabtree catalyst ([lr(COD)(PCy3)py]PF( ) in BMI-PFg. These nanoparticles maintain an efficient activity for at least seven recycles, whereas the Crabtree catalyst suffers a significant reduction in activity during recycling reactions. 

G.M. Hamminga, G. Mul and J.A. Moulijn, Applicability of fiber-optic-based Raman probes for on-line reaction monitoring of high-pressure catalytic hydrogenation reactions, Appl. Spectrosc., 61, 470 78 (2007). 

H.U. Blaser, M. Lotz, F. Spindler, "Asymmetric Catalytic Hydrogenation Reactions with Ferrocene Based Diphosphine Ligands" in Handbook of Chiral Chemicals, 2nd Edition, D. J. Ager (Ed.), CRC Press, Boca Raton 2005... 

Addition of hydrogen atoms in the presence of a metal catalyst to double or triple bonds is known as hydrogenation or catalytic hydrogenation. Alkenes and alkynes are reduced to alkanes by the treatment with H2 over a finely divided metal catalyst such as platinum (Pt—C), palladium (Pd—C) or Raney nickel (Ni). The platinum catalyst is also frequently used in the form of Pt02, which is known as Adams s catalyst. The catalytic hydrogenation reaction is a reduction reaction. 

Sumimoto introduced a new sebacic acid process including several catalytic hydrogenation reactions.342 The synthesis starts with naphthalene, which is first partially hydrogenated to tetralin over cobalt oxide or molybdenum oxide, then to decalin over ruthenium or iridium on carbon. The selectivity to cw-decalin is better than 90%. In a later phase of the synthesis 5-cyclododecen-l-one is hydrogenated over Raney nickel to obtain a mixture of cyclododecanone and cyclodode-canol in a combined yield of 90%. The selectivity of this step is not crucial since subsequent oxidation of either compound leads to the endproduct sebacic acid. 

A knowledge of the kinetic parameters and, in particular, the orders of reaction of a catalysed reaction is important to the accurate definition of the reaction mechanism. However, catalytic hydrogenation reactions proceed through a series of elementary steps, only one of which may be ratedetermining. In consequence, the observed rate expressions give little or no direct information about most of the steps involved and kinetics alone are not sufficient for a precise description of the mechanism. 

Whilst, in principle, kinetic measurements should allow a differentiation between the two possible mechanisms, it must be noted that in catalytic hydrogenation reactions relatively few examples are sufficiently clear cut to allow this differentiation to be made. Thus, for example, it is quite commonly found that the experimentally observed orders of reaction are zero in the unsaturated substrate A and unity in hydrogen. Such results are readily interpreted by the adjacent-site mechanism by assuming A to be much more strongly adsorbed than hydrogen or by the Rideal— Eley type of mechanism. Clearly, kinetic measurements alone are insufficient for the establishment of mechanism. 

One of the characteristics of many catalytic hydrogenation reactions is the ability of the catalyst to promote the formation of more than one reaction product. Thus, for example, in the hydrogenation of acetylene, ethylene may be formed as an intermediate in the production of ethane and may be the major product in the initial stages of the reaction... 

It is clear that all three types of selectivity are relevant to catalytic hydrogenation reactions and from a consideration of the reaction scheme for alkyne hydrogenation (Fig. 4), it can be deduced that all three factors may be operative simultaneously. Clearly, the selectivity for the formation of the alkene relative to alkane will depend upon a number of factors. If both the alkene and the alkane are formed during one residence of the parent molecule on the surface, the selectivity will depend upon the relative values of k, and k2 (Type II selectivity) and upon the ratio kjk4 (Type II selectivity). Since both of these depend upon the specific properties of the catalyst, they have been termed the mechanistic selectivity factor [38], Once the alkene is produced, the system contains another potential adsorbate and Type I selectivity must be taken into account. It... 

The application of Absolute Rate Theory to the interpretation of catalytic hydrogenation reactions has received relatively little attention and, even when applied, has only achieved moderate success. This is, in part, due to the necessity to formulate precise mechanisms in order to derive appropriate rate expressions [43] and, in part, due to the necessity to make various assumptions with regard to such factors as the number of surface sites per unit area of the catalyst, usually assumed to be 10 5 cm-2, the activity of the surface and the immobility or otherwise of the transition state. In spite of these difficulties, it has been shown that satisfactory agreement between observed and calculated rates can be obtained in the case of the nickel-catalysed hydrogenation of ethylene (Table 3), and between the observed and calculated apparent activation energies for the... 

Despite the potential advantages of increased rates for catalytic hydrogenation reactions, there have been few reports on achiral homogeneously catalyzed reductions of unsaturated substrates. The first example of a... 

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