Cobalt, hydrogenation nitriles

NBR can be partially or even completely hydrogenated (to eliminate carbon-carbon double bonds) in nonaqueous solution by using suitable catalysts (e.g., cobalt, rhodium, mthenium, iridium, or palladium complexes) to give hydrogenated nitrile rubbers (H-NBRs). Completely saturated H-NBR grades are cross-linked with peroxides. 

Adiponitrile undergoes the typical nitrile reactions, eg, hydrolysis to adipamide and adipic acid and alcoholysis to substituted amides and esters. The most important industrial reaction is the catalytic hydrogenation to hexamethylenediarnine. A variety of catalysts are used for this reduction including cobalt—nickel (46), cobalt manganese (47), cobalt boride (48), copper cobalt (49), and iron oxide (50), and Raney nickel (51). An extensive review on the hydrogenation of nitriles has been recendy pubUshed (10). 

Hydrogenation Catalysts. The key to catalytic hydrogenation is the catalyst, which promotes a reaction which otherwise would occur too slowly to be useful. Catalysts for the hydrogenation of nitro compounds and nitriles are generally based on one or more of the group VIII metals. The metals most commonly used are cobalt, nickel, palladium, platinum, rhodium, and mthenium, but others, including copper (16), iron (17), and tellurium... 

Eatty amines are made by dehydration of amides to nitriles at 280—330°C, followed by hydrogenation of the nitrile over nickel or cobalt catalysts ... 

Supported palladium, zirconium-promoted cobalt on kieselguhr, or nickel on kieselguhr can be used under relatively mild conditions to effect reduction of the nitrile function without hydrogenating the ring. 

Catalysts show remarkable product variation in hydrogenation of simple nitriles. Propionitrile, in neutral, nonreactive media, gives on hydrogenation over rhodium-on-carbon high yields of dipropylamine, whereas high yields of tripropylamine arise from palladium or platinum-catalyzed reductions (71). Parallel results were later found for butyronitrile (2S) and valeronitrile (74) but not for long-chain nitriles. Good yields of primary aliphatic amines can be obtained by use of cobalt, nickel, nickel boride, rhodium, or ruthenium in the presence of ammonia (4J 1,67,68,69). 

Teter et al. filed a series of patents aimed at the production of organic compounds containing nitrogerf or the production of nitriles and amines from ammonia and olefins by passing mixtures of olefin and NH3 over transition metals, mainly cobalt deposited on various supports at 250-370°C and 100-200 bar [27- 3]. With cobalt on asbestos, a mixture of amine, nitrile, olefin hydrogenation product, polymers, and cracking products is obtained (Eq. 4.1) [31]. 

In 1989, Isayama and Mukaiyama reported a related Co-catalyzed coupling reaction that employs a,b-unsaturated nitriles, amides, and esters with PhSiLb as a hydrogen source [9]. Cobalt-bis(diketonato) complex, Co(II)(dpm)2 [dpm = bis(dipivaloylmethanato)] (5mol%), exhibited high catalytic activity at 20 °C in the coupling of excess acrylonitrile and ben-zaldehyde to provide b-hydroxy nitrile 4 in 93% yield (syn anti = 50 50) (Scheme 5). N,N-Dimethylacrylamide and methyl cinnamate both reacted... 

Isophorone diamine is synthesized traditionally by aminoreduction of iso-phoronenitrile. Raney cobalt was used for this process. More recently, a new two-step process was patented. The first step consists of synthesizing the imine and the second one of hydrogenating the latter. Ra-Ni was used as catalyst at 150°C and 60 bar hydrogen pressure. Under these conditions, the catalyst reduces the nitrile groups and is able to cleave the N-N bonds, too. Ammonia is required to promote primary amine formation during nitrile hydrogenation (Scheme 4.151).554... 

Various other reducing methods are employed for the conversion of (3-nitro alcohols to amino alcohols, namely, electrochemical reduction.107 The selective electrohydrogenation of ni-troaliphatic and nitroaromatic groups in molecules containing other groups that are easy to hydrogenate (triple bond, nitrile, C-I) are carried out in methanol-water solutions at Devarda copper and Raney cobalt electrodes (Eq. 6.55).107... 

The aqueous Co(CN)52- solutions under H2 have been found to catalyze hydrogenolysis of C4-unsaturated alcohols to butenes but, more remarkably, with acetylenic alcohols besides hydrogenated products secondary nitriles are also formed by addition of HCN (stoichiometric with respect to cobalt) (195) ... 

The addition of hydrogen cyanide (HCN) to carbon-carbon double bonds activated by electron-withdrawing groups in the presence of a base as a catalyst (a variation of the Michael Reaction) has been known for a long time. Nitriles were also obtained by hydrocyanation of branched olefins, such as isobutylene and trimethylethylene, in vapor phase reactions in particular the reactions over alumina (3) and cobalt-on-alumina (4) were reported in the late 1940s and early 1950s. Addition of HCN to conjugated dienes in the presence of cuprous salts (vapor and liquid phase) was reported as early as 1947 (5). 

In the simplest case, reaction of a primary monoamine via a two-fold Michael reaction with acrylonitrile (bis-cyanoethylation) led to the dinitrile (Fig. 1.1). Subsequent reduction of the two nitrile functions - by hydrogenation with sodium borohydride in the presence of cobalt(II) ions - afforded the corresponding terminal diamine. Repetition (iteration) of this synthetic sequence, consisting in Michael addition followed by reduction, provided the first - structurally variable - access to regularly branched, many-armed molecules. 

Cobalt is a good catalyst for hydrogenation reactions it is used in the synthesis of low molecular weight hydrocarbons and for the conversion of nitriles in primary amines [37]. It can as well be applied in Fisher-Tropsch synthesis [30], The structure of cobalt is HCP (see Figure 2.6) and the electronic arrangement of Co is [Ar]3d74s2]. 

Following the development of sponge-metal nickel catalysts by alkali leaching of Ni-Al alloys by Raney, other alloy systems were considered. These include iron [4], cobalt [5], copper [6], platinum [7], ruthenium [8], and palladium [9]. Small amounts of a third metal such as chromium [10], molybdenum [11], or zinc [12] have been added to the binary alloy to promote catalyst activity. The two most common skeletal metal catalysts currently in use are nickel and copper in unpromoted or promoted forms. Skeletal copper is less active and more selective than skeletal nickel in hydrogenation reactions. It also finds use in the selective hydrolysis of nitriles [13]. This chapter is therefore mainly concerned with the preparation, properties and applications of promoted and unpromoted skeletal nickel and skeletal copper catalysts which are produced by the selective leaching of aluminum from binary or ternary alloys. 

Other Raney catalysts have been prepared. Raney cobalt has been described by several authors (28,29). The active cobalt has been claimed to be especially suitable for the reduction of nitriles. The preparation of an active copper has been described by Faucounau (30). Paul and Hilly (31) have described the preparation of Raney iron. It is claimed that Raney iron reduces acetylenic bonds to ethylenic bonds with no further hydrogenation occurring. 

Cobalt boride catalysts have been shown to be highly active and selective in the hydrogenation of nitriles to primary amines.103,104 Barnett used Co boride (5%) supported on carbon for the hydrogenation of aliphatic nitriles and obtained highest yields of primary amines among the transition metals and metal borides investigated including Raney Co.104 An example with propionitrile, where a 99% yield of propylamine was obtained in the presence of ammonia, is seen in eq. 7.29. 

Urushibara Co catalysts can be prepared exactly in the same way as the corresponding Ni catalysts, using cobalt chloride hexahydrate instead of nickel chloride hexahydrate as starting material. Similarly as with Raney catalysts, Urushibara Co has been found to be more effective and selective than Urushibara Ni in the hydrogenation of nitriles, affording high yields of primary amines.105,106... 

There have been many known cases where high yields of primary amines were obtained over cobalt catalysts in the hydrogenation of nitriles. Hydrogenation of 3,4-... 

High yields of primary amines have also been obtained over cobalt boride as catalyst,26,53,54 which has been found to be not only highly selective but also less inhibited by solvent and ammonia than other cobalt and nickel catalysts in hydrogenation of nitriles.26 The hydrogenation of propionitrile in isopropyl alcohol over cobalt boride (5% on C) in the presence of 15 1 molar ratio of ammonia to the nitrile gave propylamine in a high yield of 99% (eq. 7.29). 

Co arene chemistry has been expanded by the preparation of a number of (arene)Co(j7" -diene)+ and (arene)Co( , -enyl) complexes starting from (10). Hydrogenation of (10) in the presence of an arene and a base (piperidine or quinuclidine for obvious stabilization of coordinatively unsaturated cobalt intermediates) gives cyclooctenyl complexes (37) (equation 53). This reaction occurs with a large niunber of arenes even CeFg gives an j -arene complex. The resulting complexes (37) are moderately active catalysts in the pyridine synthesis from alkynes and nitriles (Section 5.1.4). 

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