Cobalt, Raney

Raney cobalt, which is prepared from a commercially available cobalt aluminum alloy in the same way as is Raney nickel, has been shown to have catalytic activity but it is generally less active than Raney nickel and more sensitive to variations in the reaction procedure and catalyst aging than the nickel catalyst. 

Raney cobalt is useful for the hydrogenation of oximes and nitriles to primary amines. 

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In a much different approach based on cyanamide, acrylonitrile, and acetonitrile, cyanoacetamidine [56563-07-6] (32) is cyanoethylated and the condensation product [56563-10-1] (33) is dehydrogenated and hydrogenated direcdy to Grewe diamine in the presence of Raney cobalt and ammonia (56). 

Raney cobalt is generally less effective than Raney nickel, but may be of use when the rupture of other bonds must be avoided. The important use of Raney nickel desulfurization for the structure determination of thiophenes and for the determination of the absolute configuration of optically active thiophene and benzene derivatives has been stressed earlier. 

In addition to the Raney nickel catalysts, Raney catalysts derived from iron, cobalt, and copper have been examined for their action on pyridine. At the boiling point of pyridine, degassed Raney iron gave only a very small yield of 2,2 -bipyridine but the activity of iron in this reaction is doubtful as the catalyst was subsequently found to contain 1.44% of nickel. Traces of 2,2 -bipyridine (detected spectroscopically) were formed from pyridine and a degassed, Raney cobalt catalyst but several Raney copper catalysts failed to produce detectable quantities of 2,2 -bipyridine following heating with pyridine. 

Nickel, rhodium, palladium, platinum, and Raney cobalt (43) have all been used successfully in reductive alkylations. Platinum is the most used by far (J6). With small carbonyl molecules, such as acetone, palladium is about as effective as platinum, but as the molecular weight increases, platinum is apt to be more effective (SO). 

Aziridines, like oxiranes, undergo hydrogenolysis easily with or without inversion of configuration, depending on the catalyst, reaction parameters, and various additives 65aJ08). For example, hydrogenolysis of 2-methyl-2-phenylaziridine in ethanol occurs mainly with inversion over palladium but with retention over platinum, Raney nickel, or Raney cobalt. Benzene solvent or alkali favor retention over palladium as well. 

Partially extracted Raney cobalt is very active, but it is easily poisoned by sulfur and tends to lay down carbon more readily than Raney nickel (21). Cobalt is less active than nickel and much less selective to methane... 

This type of catalyst is not limited to nickel other examples are Raney-cobalt, Raney-copper and Raney-ruthenium. When dry, these catalysts are pyrophoric upon contact with air. Usually they are stored under water, which enables their use without risk. The pyrophoric character is due to the fact that the metal is highly dispersed, so in contact with oxygen fast oxidation takes place. Moreover, the metal contains hydrogen atoms and this adds to the pyrophoric nature. Besides the combustion of the metal also ignition of organic vapours present in the atmosphere can occur. Before start of the reaction it is a standard procedure to replace the water by organic solvents but care should be taken to exclude oxygen. Often alcohol is used. The water is decanted and the wet catalyst is washed repeatedly with alcohol. After several washes with absolute alcohol the last traces of water are removed. 

Finely powdered cobalt can detonate spontaneously in air. Its behaviour depends on its surface texture. Raney cobalt is much more dangerous than Raney nickel, which is more commonly used (see nickel). 

Catalysts - A commercial Raney nickel (RNi-C) and a laboratory Raney nickel (RNi-L) were used in this study. RNi-C was supplied in an aqueous suspension (pH < 10.5, A1 < 7 wt %, particle size 0.012-0.128 mm). Prior to the activity test, RNi-C catalyst (2 g wet, 1.4 g dry, aqueous suspension) was washed three times with ethanol (20 ml) and twice with cyclohexane (CH) (20 mL) in order to remove water from the catalyst. RCN was then exchanged for the cyclohexane and the catalyst sample was introduced into the reactor as a suspension in the substrate. RNi-L catalyst was prepared from a 50 % Ni-50 % A1 alloy (0.045-0.1 mm in size) by treatment with NaOH which dissolved most of the Al. This catalyst was stored in passivated and dried form. Prior to the activity test, the catalyst (0.3 g) was treated in H2 at 250 °C for 2 h and then introduced to the reactor under CH. Raney cobalt (RCo), a commercial product, was treated likewise. Alumina supported Ru, Rh, Pd and Pt catalysts (powder) containing 5 wt. % of metal were purchased from Engelhard in reduced form. Prior to the activity test, catalyst (1.5 g) was treated in H2 at 250 °C for 2 h and then introduced to the reactor under solvent. 10 % Ni and 10 % Co/y-Al203 (200 m2/g) catalysts were prepared by incipient wetness impregnation using nitrate precursors. After drying the samples were calcined and reduced at 500 °C for 2 h and were then introduced to the reactor under CH. 

Under relatively mild conditions the Ru/C catalyst poisoned with Sn (lines 1 and 2), the Ir/C catalyst (lines 14 and 15), and the Raney-cobalt catalyst modified with CoCl2 (line 19) seem likely systems to try when initiating a search for an effective method for selectively hydrogenating the C=0 bond in an a, 3-unsaturated aldehyde. 

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... 

Aluminium-cobalt alloy (Raney cobalt alloy)... 

The finely powdered Raney cobalt alloy is a significant dust explosion hazard. 

Finely divided cobalt is pyrophoric in air [1], Raney cobalt catalyst appears to be less hazardous than Raney nickel [2],... 

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... 

Recently another family of dendrimers has become commercially available. These polyamines were developed by Meijer and de Brabander-van den Berg of DSM Research and are based on Vogtle s initial synthesis [7]. In this case the troublesome reduction step was performed using a Raney cobalt hydrogenation catalyst and other process improvements have permitted this synthesis to be continued up to the fifth generation with multikilogram quantities available. 

The Raney nickel process applied to alloys of aluminum with other metals produces Raney iron, Raney cobalt, Raney copper and Raney zinc, respectively. These catalysts are used very rarely and for special purposes only. 

Also, Klabunovskii reported pressure dependences of the OYs in enantio-differentiating hydrogenations of ethyl acetoacetate (EAA) with ruthenium (67), Raney cobalt (65), and RNi catalysts (69) modified with TA, c. Additives. Additives which are added to the reaction system often exert a remarkable effect on the OY of the enantio-differentiating hydrogenation of M A A (23-25). Water is one such additive. For example, in most hydrogenations with amino acid MRNis, the direction of differentiation was reversed by the addition of small amounts of water as shown in Fig. 14 (23, 25). 

Three syntheses of 1,2-dicyanocyclobutene (2) have been previously described. The first, involving dehydration of cyclobutene-1,2-dicarboxamide does not specify the yield.9 The second procedure involves a concomitant chlorination and catalytic dehydrochlorination of 1,2-dicyanocyclobutane in the gas phase, yielding 1,2-dicyanocyclobutene (2) in a mixture of several other products.10 The third method consists of dechlorination of 1,2-dichloro-1,2-dicyanocyclobutane using metals, such as zinc copper couple,11 Raney nickel,11 and, especially, Raney cobalt.2 In comparison with this last-mentioned synthesis, the overall yield of the present procedure is 5-10% higher. Furthermore, the reaction is performed in less time and utilizes considerably cheaper reagents. 

The use of hydrodesulfurization in the determination of the structures of unknown benzo[6]thiophenes is becoming increasingly recognized about 100 examples have now been recorded. Two sets of experimental conditions are commonly used the benzo[6]thiophene may be treated with Raney nickel alloy directly in alkaline medium (the method of Papa et al.7M), or it may be boiled in ethanol with Raney nickel of varying reactivity (commonly W-7). Even under mild conditions, nonaromatic double bonds are usually saturated, halogens are removed, and nitro groups are reduced. Raney cobalt has about one-tenth the activity of Raney nickel in the hydrodesulfurization of benzo [6]thiophenes.765... 

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