Raney-type nickel catalysts

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. 

Two different sets of experimental conditions have been used. Buu-Hoi et al. and Hansen have employed the method introduced by Papa et using Raney nickel alloy directly for the desulfurization in an alkaline medium. Under these conditions most functional groups are removed and this method is most convenient for the preparation of aliphatic acids. The other method uses Raney nickel catalysts of different reactivity in various solvents such as aqueous ammonia, alcohol, ether, or acetone. The solvent and activity of the catalyst can have an appreciable influence on yields and types of compounds formed, but have not yet been investigated in detail. In acetic anhydride, for instance, desulfurization of thiophenes does not occur and these reaction conditions have been employed for reductive acetylation of nitrothiophenes. Even under the mildest conditions, all double bonds are hydrogenated and all halogens removed. Nitro and oxime groups are reduced to amines. 

Ziegler-Natta catalysts for, 26 536-540 Random scission initiation, 23 372 Random thermal motion, in silicon-based semiconductors, 22 237-238 Random walk process, 26 1022 Raney nickel catalyst, 74 48 77 121 Raney-type catalysts, 25 195 Range of ambivalence, 76 700 Range quantities, methods for obtaining, 74 432... 

Raney nickel catalysts, unpromoted or doped with molybdenum or chromium, were prepared from the precursor alloys of the type Ni A13. The structure and phase composition of the catalysts have been deternfmetl. Hydrogenation of valeronitri le at 90°C and 1.6 MPa in cyclohexane was performed to evaluate catalyst activities and the relative amounts of amines formed. Doping catalysts by chromium improved reaction rates and yields of primary amine, whereas molybdenum addition was ineffective. 

Hydrogenation of L-sorbose, with Raney nickel catalyst to poly-hydric alcohols is the subject of a recent patent this type of reduction had previously been shown to give the expected L-iditolI 1 and D-glucitol. The open-chain acetate, keto-L-sorbose pentaacetate, on reduction192 at low pressure with platinum catalyst, gave on subsequent acetylation hexaacetyl-D-glucitol (XLIV) and hexaacetyl-L-iditol (XLV), while... 

The Raney nickel residue is quite active and will ignite if allowed to become dry. It may readily be disposed of by pouring into dilute mineral acid. This nickel residue is sufficiently active for various types of catalytic hydrogenations requiring the use of Raney nickel catalyst. 

Adkins and Krsek (15), in comparing the various types of Raney nickel catalyst, found their activities to vary considerably in the hydrogenation of 0-naphthol. 

Dinitronaphthalene was readily hydrogenated over 30% Pd-C in ethanol at low hydrogen pressure to 1,8-diaminonaphthalene, isolated as the crystalline dichloride in excellent yield (eq. 9.41).85 Use of Adams platinum in the hydrogenation gave a red solution and a blue-gray product. Attempts to use Raney nickel catalysts of various types and under a variety of conditions were always unsuccessful. 

A number of different types of classic Raney nickel catalysts with varying activities have been prepared by the addition of the commercially available alloy to sodium hydroxide solutions. These catalysts have been designated as Wl, W2, W3, W4, W5, W6, W7 and W8. The procedures utilized to prepare these catalysts differ in the amount of sodium hydroxide used, the temperature at which the alloy is added to the basic solution, the temperature and duration of alloy digestion after addition to the base and the method used to wash the catalyst free from the sodium aliuninate and the excess base. These differences are listed in Table 12.1. 

Preparation procedures for the different types of classic Raney nickel catalysts. 

Millions of tons of benzene are hydrogenated each year to give cyclohexane, which is converted to nylon via adipic acid. Whereas this process has been carried out with heterogeneous Raney nickel catalysts until now, a homogeneous process using Ziegler-type catalysts is about to take over. Catalysts based on nickel and cobalt salts in combination with triethylaluminum hydrogenate benzene under relatively mild conditions (155 °C, 1 MPa). This process is called the IFP process (Institut Fran ais du Petrole) [97] (cf Section 2.3.1.4). 

In contrast to Raney nickel catalysts ( 3.4.1), heterogeneous hydrogenation catalysts based on Pt, Rh or Pd do not induce asymmetry in the presence of tartaric acid [113, 578], Platinum catalysts modified by cinchona alkaloids 3.1 and 3.2 cause asymmetric hydrogenation of the carbonyl group of a-ketoesters with a high enantiomeric excess (> 90%). From other types of ketones, the enantioselectivities are lower. 

The use of a Raney nickel catalyst which may be of similar type, from the interaction of 50% nickel-aluminium altoy with water at 100°C has been described (ref.61) which was employed under atmospheric pressure and did not effect ring reduction. 

An early study showing the presence of two intermediates was that of Soong et al. who studied the methanation of CO/H2 over Raney Nickel catalyst at 210 °C and at a H2/CO ratio of two. Two types of isotopic transient experiments were carried out. In the first type, the catalyst was exposed to CO/H2 (or CO/H2) until the reaction reached steady state after which the isotopic switch was made to CO/H2 (or CO/H2). In the second type of experiment, the catalyst was first exposed to CO/H2 until steady state was attained it was then exposed for a short time (2 min) to CO/H2 and then exposed again to C0/H2. 

Selective hydrogenation of aj unsaturated carbonyl contpoandsJ Several substrates of this type have been selectively hydrogenated to a, -unsaturated alcohols with catalysis by a chromium-promoted Raney nickel catalyst. ... 

The Raney nickel catalyst can usually be stabilized by 2 to 4 wt% titanium and additionally activated by a small percentage of molybdenum [95] or platinum [97]. Although Raney nickel has excellent hydrogen adsorption ability and relatively large surface area, some disadvantages have also been reported, such as high electrolyte diffusion resistance due to low pore volume and small pore size [98, 99], and insufficient conductivity [97]. One type of mitigation is to support Raney nickel on carbon blacks, which will decrease its electrolyte diffusion resistance and increase its electrical conductivity [97]. 

A process based on a nickel catalyst, either supported or Raney type, is described ia Olin Mathieson patents (26,27). The reduction is carried out ia a continuous stirred tank reactor with a concentric filter element built iato the reactor so that the catalyst remains ia the reaction 2one. Methanol is used as a solvent. Reaction conditions are 2.4—3.5 MPa (350—500 psi), 120—140°C. Keeping the catalyst iaside the reactor iacreases catalyst lifetime by maintaining a hydrogen atmosphere on its surface at all times and minimises handling losses. Periodic cleaning of the filter element is required. 

Several products other than 2,2 -biaryls have been isolated following reaction of pyridines with metal catalysts. From the reaction of a-picoline with nickel-alumina, Willink and Wibaut isolated three dimethylbipyridines in addition to the 6,6 -dimethyl-2,2 -bipyridine but their structures have not been elucidated. From the reaction of quinaldine with palladium-on-carbon, Rapoport and his co-workers " obtained a by-product which they regarded as l,2-di(2-quinolyl)-ethane. From the reactions of pyridines and quinolines with degassed Raney nickel several different types of by-product have been identified. The structures and modes of formation of these compounds are of interest as they lead to a better insight into the processes occurring when pyridines interact with metal catalysts. 

T-4)-J or Raney nickel and hydrogen.8 Alcohols of the benzylic type have also been reduced directly with hydrogen under pressure in the presence of various catalysts,9 and benzoic acids have been reduced to toluenes with rhenium-type catalysts and hydrogen at high temperatures and pressures.10... 

---