Hydrogenation catalysts Raney nickel

The alloy hydride exhibits different reactivities in comparison with classical hydrogenation catalysts (Raney nickel, Pd, Ph). The alloy is not poisoned by thiophene ring, there is no reduction of oximes nor hy-drogenolysis of benzylic C-0 bonds. The compound SmMg reacts with anthracene dissolved in THF (13). The complex absorbs hydrogen and then catalyzes the hydrogenation of ethylene. 

Nitro groups are efficiently reduced with hydrogen over Raney nickel catalyst (I. Fel-ner, 1967), with hydrides, or with metals. 

Dry reduced nickel catalyst protected by fat is the most common catalyst for the hydrogenation of fatty acids. The composition of this type of catalyst is about 25% nickel, 25% inert carrier, and 50% soHd fat. Manufacturers of this catalyst include Calsicat (Mallinckrodt), Harshaw (Engelhard), United Catalysts (Sud Chemie), and Unichema. Other catalysts that stiH have some place in fatty acid hydrogenation are so-called wet reduced nickel catalysts (formate catalysts), Raney nickel catalysts, and precious metal catalysts, primarily palladium on carbon. The spent nickel catalysts are usually sent to a broker who seUs them for recovery of nickel value. Spent palladium catalysts are usually returned to the catalyst suppHer for credit of palladium value. 

Nickel(II) chlorophyll derivatives undergo catalytic hydrogenation with Raney nickel as catalyst to yield stereoisomeric isobacteriochlorins in which ring A of the chlorophyll derivatives is reduced.16... 

The hydrogenation of HMF in the presence of metal catalysts (Raney nickel, supported platinum metals, copper chromite) leads to quantitative amounts of 2,5-bis(hydroxymethyl)furan used in the manufacture of polyurethanes, or 2,5-bis(hydroxymethyl)tetrahydrofuran that can be used in the preparation of polyesters [30]. The oxidation of HMF is used to prepare 5-formylfuran-2-carboxylic acid, and furan-2,5-dicarboxylic acid (a potential substitute of terephthalic acid). Oxidation by air on platinum catalysts leads quantitatively to the diacid. [32], The oxidation of HMF to dialdehyde was achieved at 90 °C with air as oxidizing in the presence of V205/Ti02 catalysts with a selectivity up to 95% at 90% conversion [33]. 

Hydrogenation over Raney nickel was found to be even less stereoselective. 2-, 3- and 4-methylmethylenecyclohexenes gave different mixtures of cis and irons dimethylcyclohexanes depending not only on the structure of the starting alkene but also on the method of preparation and on the freshness of the catalysts. The composition of the stereoisomers ranged from 27-72% cis to 28-73% irons [340],... 

Hydrogenation using Raney nickel is carried out under mild conditions and gives cis alkenes from internal alkynes in yields ranging from 50 to 100% [356, 357, 358, 359, 360]. Half hydrogenation of alkynes was also achieved over nickel prepared by reduction of nickel acetate with sodium borohydride (P-2 nickel, nickel boride) [349,361,362] or by reduction with sodium hydride [49], or by reduction of nickel bromide with potassium-graphite [363]. Other catalysts are palladium on charcoal [364], on barium sulfate [365, 366], on... 

Triple bonds in side chains of aromatics can be reduced to double bonds or completely saturated. The outcome of such reductions depends on the structure of the acetylene and on the method of reduction. If the triple bond is not conjugated with the benzene ring it can be handled in the same way as in aliphatic acetylenes. In addition, electrochemical reduction in a solution of lithium chloride in methylamine has been used for partial reduction to alkenes trans isomers, where applicable) in 40-51% yields (with 2,5-dihydroaromatic alkenes as by-products) [379]. Aromatic acetylenes with triple bonds conjugated with benzene rings can be hydrogenated over Raney nickel to cis olefins [356], or to alkyl aromatics over rhenium sulfide catalyst [54]. Electroreduction in methylamine containing lithium chloride gives 80% yields of alkyl aromatics [379]. 

A number of organic species, including amides, oximes, and nitriles, undergo reductive amination, a variety of reduction reactions that produce cimines. In general, these processes involve imines, R=N-R, or related species. Reduction processes include hydrogenation using Raney nickel as the catalyst (for nitriles), the reaction with sodium/EtOH (for oximes), and the use of lithium aluminum hydride, LiAlH (for amides or nitriles). Figure 13-16 illustrates the preparation of amphetamine by reductive amination. 

The biologically important sugars paratose (3,6-dideoxy-D-nho-hexose) and tyvelose (3,6-dideoxy-D-arafctno-hexose) have also been conveniently prepared203 by routes involving reductive dechlorination by hydrogenation over Raney nickel catalyst these 3,6-dideoxy-... 

Nakazaki s synthetic approach is conspicuous by its remarkable straightforwardness it has been proved to be so far the simplest synthetic route to the target compounds. In their first synthesis of 61a54a), Nakazaki and coworkers started from cyclododecyne (62a), whose oligomerization with two molecules of butadiene afforded the bicyclic 63a. The cis[10.8] precursor 64a, obtained by partial catalytic hydrogenation with Raney nickel catalyst, was dissolved in cyclohexane, which contained xylene as photosensitizer, and the solution was irradiated with a medium pressure Hg lamp for 12 h. Examination of the reaction mixture by means of GLC indicated that the product was a 2.4 1 mixture of (Z) 64a and (E) 61 a, and the further study54b) showed that this ratio could be raised to 1 2 by irradiation of a hexene solution with a low pressure Hg lamp. 

Aldehydes and ketones are reduced to 1° and 2° alcohols, respectively, by hydrogenation with metal catalysts (Raney nickel, Pd—C and Pt02). They are also reduced to alcohols relatively easily with mild reducing agent, e.g. NaBH4, or powerful reducing agent, e.g. LiAlILj. The key step in the reduction is the reaction of hydride with the carbonyl carbon. 

Catalytic hydrogenation using H2 and a catalyst reduces aldehydes and ketones to 1° and 2° alcohols, respectively. The most common catalyst for these hydrogenations is Raney nickel, although Pt02 and Pd—C can also be used. The C=C double bonds are reduced more quickly than C=0 double bonds. Therefore, it is not possible to reduce C=0 selectively in the presence of a C=C without reducing both by this method. 

The dithioketal can be reduced directly to the hydrocarbon by hydrogenation over the sulphur-removing catalyst Raney nickel ... 

The reduction of 1,10-phenanthroline (4) occurs preferentially in the pyridine rings. Chemical reduction affords a low yield of 1,2,3,4-tetrahydro- 1,10-phenanthroline,243 but hydrogenation with Raney nickel as catalyst gives good yields of the 1,2,3,4-tetrahydro (45) and/or the 1,2,3,4,7,8,9,10-octahydro (46) derivative depending on reaction conditions.244 Hydrogenation of certain substituted 1,10-... 

Fig. 23. Dependence of the anodic overpotential of hydrogen-consuming Raney-nickel anodes of equal catalyst loading on the particle size of the catalyst.

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