Catalysts for reduction

Nitrates. Iron(II) nitrate hexahydrate [14013-86-6], Fe(N03)2 6H20, is a green crystalline material prepared by dissolving iron in cold nitric acid that has a specific gravity of less than 1.034 g/cm. Use of denser, more concentrated acid leads to oxidation to iron(III). An alternative method of preparation is the reaction of iron(II) sulfate and barium or lead nitrate. The compound is very soluble in water. Crystallisation at temperatures below — 12°C affords an nonahydrate. Iron(II) nitrate is a useful reagent for the synthesis of other iron-containing compounds and is used as a catalyst for reduction reactions. 

Rhenium oxides have been studied as catalyst materials in oxidation reactions of sulfur dioxide to sulfur trioxide, sulfite to sulfate, and nitrite to nitrate. There has been no commercial development in this area. These compounds have also been used as catalysts for reductions, but appear not to have exceptional properties. Rhenium sulfide catalysts have been used for hydrogenations of organic compounds, including benzene and styrene, and for dehydrogenation of alcohols to give aldehydes (qv) and ketones (qv). The significant property of these catalyst systems is that they are not poisoned by sulfur compounds. 

Platinum Catalyst for Reductions (Coll. Vol. i, 452) Preparation from platinum black by heating with oxygen underpressure. Laffiteand Grandadam, Compt. rend. 200, 456 (193s). 

Hydrogenation of 3-pyridinecarboxylic acids is apt to be accompanied by extensive decarboxylation (2S), but this unwanted reaction can be prevented by carrying out the reaction in the presence of one equivalent of base (33,79). Ruthenium (33), rhodium (29), platinum oxide (2S,59), and palladium (30) have all proved effective catalysts for reduction of pyridinecarboxylic acids to the saturated acid. 

Palladium catalyst foe partial ee DUCTION OF ACETYLENES, 46, 89 Palladium on charcoal, catalyst for reductive methylation of ethyl p-mtrophenylacetate, 47, 69 in reduction of l butyl azidoacetate to glycine J-butyl ester 4B, 47 Palladium oxide as catalyst for reduction of sodium 2 nitrobenzene sulfinate, 47, S... 

PdClJ , Rh(III) and Ru(III) act as homogeneous catalysts for reduction of FeClj by molecular hydrogen ° °. The kinetics of all three activation reactions fall into Class I. The Arrhenius parameters are... 

The current work indicates that sulfided platinum catalysts are, in general, more active and selective than Pt, Pd, or sulfided Pd catalysts for reductive alkylation of primary amines with ketones. The choice of the catalyst preparation parameters, especially the support, plays a major role in determining the performance of the catalyst. Diamines, especially of lower molecular weight, tend to react with ketones even at room temperature to form heterocycles such as imidazolidine, diazepanes, and pyrimidines. Hence, a continuous reactor configuration that minimizes the contact between the amine and the ketone, along with a highly active catalyst is desired to obtain the dialkylated product. In general, sulfided Pt appears to be more suited for the reductive alkylation of ethylenediamine while unsulfided Pd or Pt may also be used if 1,3-diaminopropane is the amine. 

Among early and group III transition metals, the yttrocene catalysts have been studied in greatest detail. However, related metallocenes show great promise as catalysts for reductive cyclization. Neodymocene-catalyzed cyclization of 1,5- and 1,6-dienes 14a and 15a proceeds readily in the presence of silane to afford cyclopentanes 14b and 15b.37 Lutetocenes and samarocenes also catalyze silane-mediated cyclization of 1,5-diene 14a to cyclopentane 14b.38 39 In the case of the samarium-based metallocenes, the feasibility of borane-mediated cyclization has been established, as demonstrated by the highly diastereoselective conversion of phenyl-substituted diene 16a to cyclopentane 16b (Scheme ll).40... 

Rh(COD)(PPh3)2]BF4 has been shown to be a good catalyst for reductive ami-nation of acetone with 4-anilino-aniline to give the commercial product 3-IPPD. In laboratory-scale comparative experiments, this catalyst - both in homogeneous phase or immobilized on Montmorillonite K10 clay - was found to be superior to the commercially applied Pt/C catalyst (Scheme 15.11) [80]. 

The Ni(II) complexes 6 and 7 have been found by Stiles [60] to be soluble catalysts for reductive dehalogenation when combined with NaBH4 or hydrazine at 25-45 °C in protic solvents. Reactivity toward the reducing system increased with the halogen content of the substrate. Aryl bromides were converted much faster than chlorides, polychlorobenzenes, however, reacted readily with stepwise loss of chlorine. 

Transfer Hydrogenation Catalysts for Reduction of C-C Double and Triple Bonds... 

The studies discussed above deal with highly dispersed and therefore well-defined rhodium particles with which fundamental questions on particle shape, chemisorption and metal-support interactions can be addressed. Practical rhodium catalysts, for example those used in the three-way catalyst for reduction of NO by CO, have significantly larger particle sizes, however. In fact, large rhodium particles with diameters above 10 nm are much more active for the NO+CO reaction than the particles we discussed here, because of the large ensembles of Rh surface atoms needed for this reaction [28]. Such particles have also been extensively characterized with spectroscopic techniques and electron microscopy we mention in particular the work of Wong and McCabe [29] and Burkhardt and Schmidt [30], These studies deal with the materials science of rhodium catalysts that are closer to the ones used in practice, which is of great interest from an industrial point of view. 

Reduction of enynes to (Z)-atkenes. Lindlar s catalyst is not useful as a hydrogenation catalyst for reduction of trienynes or of dienediynes. The best results can be obtained in CH3OH with zinc activated by successive treatment with Cu(OAc)2 (10%) and AgN03 (10%). This reduction results in conversion of the triple bond to a (Z)-double bond. The system does not reduce simple, nonactivated alkynes, and a-branched enynes are reduced slowly. The reduction is effected at 25° with (Z)-enynes, but temperatures of 45° are necessary for the (E)-isomers. Yields of pure tetraenes are 25-65%. 

Scheme 5.4 shows some examples of enantioselective reduction of ketones using I. Adducts of borane with several other chiral /i-aminoalcohols are being explored as chiral catalyst for reduction of ketones.102 Table 5.6 shows the enantioselectivity of several of these catalysts toward acetophenone. 

The multiple steps shown in Sch. 2 and discussed earlier for various catalysts for reduction of CO2 to CO, indicates that... 

Figure 7.8 Photosensitized cleavage of water based on bimolecular photoredox reaction between an electron donor D and an acceptor A. Cat. 1 and cat. 2 are charge storage catalysts for reduction and oxidation of water, respectively.

Fischli has used a related reagent, Cob(I)alamine,2 obtained by reduction of vitamin B,2 with zinc and acetic acid, as a catalyst for reduction with zinc and acetic acid of various unsaturated systems such as a,/ -unsaturated nitriles,3 esters,4 and carbonyl compounds,5 allylic alcohols and amines,6 and also isolated double bonds.6... 

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