Hydrogenation of double bonds

The presence of ammonia during hydrogenation suppresses formation of secondary amines and inhibits hydrogenation of double bonds in unsaturated nitriles. Eatty amines are used as corrosion inhibitors, flotation agents, quaternary salts for sanitizing agents and textile fabric softeners, and surface-active agents. 

NO2 NR, PIP, 1,4-BR Raney Ni, Zn-AcOH Partial reduction of NO, groups complete hydrogenation of double bonds... 

Nickel metal successfully catalyzes the hydrogenation of double bonds in unsaturated hydrocarbons such as propylene and butene. Can this metal also catalyze the dehydrogenation of alkanes such as propane and butane ... 

Ir(cod)(PPh3(PhCN)]BF4 Hydrogenation of double bond of vinyl epoxides 736... 

Table 21.6 Diastereoselective hydrogenation of double bond in cyclic esters and carboxylic acids. 

A major advantage that nonenzymic chiral catalysts might have over enzymes, then, is their potential ability to accept substrates of different structures by contrast, an enzyme will select only its substrate from a mixture. Striking examples are the chiral phosphine-rhodium catalysts, which catalyze die hydrogenation of double bonds to produce chiral amino acids (10-12), and the titanium isopropoxide-tartrate complex of Sharpless (11,13,14), which catalyzes the epoxidation of numerous allylic alcohols. Since the enantiomeric purities of the products from these reactions are exceedingly high (>90%), we might conclude... 

Hydrodesulfurisation of thiophene must be accompanied by hydrogenation of double bonds otherwise there may exist thermodynamic constraints [46],... 

Cyclic olefin copolymers are copolymerized from linear and cyclic (norbornene) olefins (as shown in Figure 4.21) followed by hydrogenation of double bonds. 

Although many catalytic reactions are not well understood, a large amount of work has been done on hydrogenations of double bonds. The metal surface acts as a source of electrons. The tt bonds as well as hydrogen atoms are bound to this surface. Then the hydrogen atoms react with the complexed carbons one at a time to form new C—H bonds. No reaction occurs without the metal surface. The metal in effect avoids what would otherwise have to be a free radical mechanism that would require considerably more energy. The mechanism is outlined as follows. 

In this special field, earlier work had been done in other laboratories, such as by the Schering Company, Berlin (36), and by Ipatieff (37) in connection with his work on the hydrogenation of camphor and of other organic compounds. At both places, the favorable effect of alkali oxides and earth alkali oxides on nickel, cobalt and copper has been investigated. Similarly, Paal and his coworkers (38) have used a palladium-aluminum hydroxide catalyst in 1913 for the hydrogenation of double bonds. Bedford and Erdman (39) had reported that the catalytic action of nickel oxide is enhanced by the oxides of aluminum, zirconium, titanium, calcium, lanthanum, and magnesium. 

Hydrogenation of double bonds is practiced with some elastomers such as SBR and NBR to increase high temperature and oxidative resistance [Hsieh, 1998 Hsieh and Quirk, 1996, Wrana et al., 2001], Only partial hydrogenation is performed since some double bonds are required to achieve the subsequent crosslinking required to achieve elastic behavior. 

Mechanism. The generally accepted mechanism for the hydrogenation of double bonds over heterogeneous catalysts was first proposed by Horiuti and Polanyi,50,51 and was later supported by results of deuteration experiments. It assumes that both hydrogen and alkene are bound to the catalyst surface. The hydrogen molecule undergoes dissociative adsorption [Eq. (11.1)], while the alkene adsorbs associa-tively [Eq. (11.2)]. Addition of hydrogen to the double bond occurs in a stepwise manner [Eqs (11.3) and (11.4)] ... 

The electrochemical hydrogenation of double bonds can be performed either electrocatalytically at Raney nickel, palladium, or platinum modified electrodes [32] or via electron transfer under Birch conditions to the intermediate anion radical [33]. Examples are given in the dihydrogenation of phthalic acid (Eq. 22.15) and the hydrogenation of heteroaromatic compounds (Eq. 22.14). 

Examples on the use of these and other heterogeneous catalysts in the hydrogenation of double-bonded functional groups are found throughout this review. 

Fig. 18. Model for the dehydrogenation of ra-butyl alcohol. The model is of general significance for the hydrogenation of double bonds and the dehydrogenation of...

Hydrogenation of double bonds can also be performed at the mercury cathode using methanol/tetramethylammonium salts as SSE 301 The solvated electron, stabilized by (CH3)4N+ and transferred in the electrical double layer to the double bond, is assumed to be the reductant. As in CH3NH2/LiCl conjugated double bonds may be reduced, while isolated ones remain untouched. Terminal triple bonds are hydrogenated to double bonds. 

There are many examples of the straightforward hydrogenation of double bonds. Thus, hydrogen and palladium-charcoal in aqueous acetic acid reduce strychnine to 21,22-dihydrostrychnine, and reduce tetra-hydrostrychnine (I,XXXIV) to hexahydrostrychnine (44). Strychnidine, strangely enough, was not easily reduced with this catalyst, and good results were obtained only when Adams PtC>2 catalyst was used in glacial acetic acid (87). 

The attempted hydrogenation of double bonds at either the 7,8- or 8,9-positions in a 5a-steroid system results merely in migration of the double bond to the 8,14-position [59],... 

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