Reduction, catalytic

Catalytic hydrogenation is unquestionably the workhorse of catalytic organic synthesis, with a long tradition dating back to the days of Sabatier [53] who received the 1912 Nobel Prize in Chemistry for his pioneering work in this area. It is widely used in the manufacture of fine and specialty chemicals and a special issue of the journal Advanced Synthesis and Catalysis was recently devoted to this important topic [54]. According to Roessler [55], 10-20% of all the reaction steps in the synthesis of vitamins (even 30% for vitamin E) at Hoffmann-La Roche (in 1996) are catalytic hydrogenations. 

A major trend in fine chemicals and pharmaceuticals is towards increasingly complex molecules, which translates to a need for high degrees of chemo-, regio- and stereoselectivity. An illustrative example is the synthesis of an intermediate for the Roche HIV protease inhibitor, Saquinavir (Fig. 1.14) [55]. It involves a chemo- and diastereoselective hydrogenation of an aromatic while avoiding racemisation at the stereogenic centre present in the substrate. 

Although catalytic hydrogenation is a mature technology that is widely applied in industrial organic synthesis, new applications continue to appear, sometimes in unexpected places. For example, a time-honored reaction in organic 

The Meerwein-Pondorff-Verley (MPV) reduction of aldehydes and ketones to the corresponding alcohols [61] is another example of a long-standing technology. The reaction mechanism involves coordination of the alcohol reagent, usually isopropanol, and the ketone substrate to the aluminum center, followed by hydride transfer from the alcohol to the carbonyl group. In principle, the re- 

More recently, Corma and coworkers [64] have shown that Sn-substituted zeolite beta is a more active heterogeneous catalyst for MPV reductions, also showing high ds-selectivity (99-100%) in the reduction of 4-alkylcyclohexanones. The higher activity was attributed to the higher electronegativity of Sn compared to Ti. 

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H2N (CH2)a NH2- Colourless solid when pure m.p. 4LC, b.p. 204 C. Manufactured by the electrochemical combination of two molecules of acrylonitrile to adiponitrile followed by catalytic reduction, or by a series of steps from cyclohexanone via adipic acid. Used in the production of Nylon [6, 6]. 

Dihydrostreptomycin, in which the CHO group in the middle ring is replaced by CH2OH, is made by the catalytic reduction of streptomycin, and has similar antibacterial properties. 

H02C(CH2)2C02H. Colourless prisms m.p. 182 C, b.p. 235°C. Occurs in amber, algae, lichens, sugar cane, beets and other plants, and is formed during the fermentation of sugar, tartrates, malates and other substances by a variety of yeasts, moulds and bacteria. Manufactured by the catalytic reduction of maleic acid or by heating 1,2-dicyanoethane with acids or alkalis. Forms an anhydride when heated at 235°C. Forms both acid and neutral salts and esters. Used in the manufacture of succinic anhydride and of polyesters with polyols. 

This may be prepared by the catalytic reduction of pure diphenyl (see Section 111,150). 

Both acids 3deld succinic acid, m.p. 185°, upon catalytic reduction (see Section 111,150), thus establishing their structures. Maleic and fumaric acids are examples of compounds exhibiting cis-trans isomerism (or geometric isomerism). Maleic acid has the cm structure since inter alia it readily 3delds the anhydride (compare Section 111,93). Fumaric acid possesses the trans structure it does not form an anhydride, but when heated to a high temperature gives maleic anhydride. 

CATALYTIC REDUCTION WITH ADAMS PLATINUM OXIDE CATALYST... 

By catalytic reduction of a p-unsaturated ketones, prepared from aldehydes by the Claisen - Schmidt reaction (see under Aromatic Aldehydes), for example ... 

Besides chemical catalytic reduction of carbon dioxide with hydrogen, which is already possible in the laboratory, we are exploring a new approach to recycling carbon dioxide into methyl alcohol or related oxygenates via aqueous eleetrocatalytic reduction using what can be called a regenerative fuel cell system. The direct methanol fuel cell... 

What goes on in this conversion is that the p-Nitropropene undergoes a catalytic reduction whereby it loses its propene double bond, and the nitro s oxygens get replaced with hydrogens. All this happens in one pot with, usually, just one reaction. 

While catalytic reduction of the indole ring is feasible, it is slow because of the aromatic character of the C2-C3 double bond. The relative basicity of the indole ring, however, opens an acid-catalysed pathway through 3if-indoleninm intermediates. 

As mentioned previously, aldehydes can be prepared by Stephen s method of reduction of nitriles by stannous chloride (37, 91). Polaro-graphic reduction of thiazolecarboxylic acids and their derivatives gives lower yields of aldehydes (58). Ozonolysis of styrylthiazoles, for example, 2-styryl-4-methylthiazole, followed by catalytic reduction gives aldehyde with 47% yield of crude product (30). 

Catalytic reduction over a platinum catalyst fails because of poisoning of the catalyst (101). 

Catalytic dewaxing Catalytic hydrogenation Catalytic properties Catalytic pyrolysis Catalytic reduction Catalytic reforming... 

The hydrogen can be used for organic hydrogenation, catalytic reductions, and ammonia synthesis. It can also be burned with chlorine to produce high quaHty HCl and used to provide a reducing atmosphere in some appHcations. In many cases, however, it is used as a fuel. 

Trifluoroethanol was first prepared by the catalytic reduction of trifluoroacetic anhydride [407-25-0] (58). Other methods iaclude the catalytic hydrogeaatioa of trifluoroacetamide [354-38-1] (59), the lithium aluminum hydride reductioa of trifluoroacetyl chloride [354-32-5] (60) or of trifluoroacetic acid or its esters (61,62), and the acetolysis of 2-chloro-l,l,l-trifluoroethane [75-88-7] followed by hydrolysis (60). More recently, the hydrogenation of... 

Goal Upgrading via Fischer-Tropsch. The synthesis of methane by the catalytic reduction of carbon monoxide and hydrogen over nickel and cobalt catalysts at atmospheric pressure was reported in 1902 (11). 

Manufacture. The manufacture of 1,4-cyclohexanedimethanol can be accompHshed by the catalytic reduction under pressure of dimethyl terephthalate ia a methanol solution (47,65). This glycol also may be prepared by the depolymerization and catalytic reduction of linear polyesters that have alkylene terephthalates as primary constituents. Poly(ethylene terephthalate) may be hydrogenated ia the presence of methanol under pressure and heat to give good yields of the glycol (see Polyesters) (66,67). 

In the former USSR, there reportedly are two technologies in use one is old anthrahydroquinone autoxidation technology and the other is closed-loop isopropyl alcohol oxidation technology. Production faciUties include several smaller, 100-150-t/yr isopropyl alcohol oxidation plants and a larger, 15,000-t/yr plant, which reportedly is being expanded to 30,000-t/yr. Differences in this technology as compared to the Shell Chemical Co. process are the use of oxygen-enriched air in the oxidation step and, catalytic reduction of the coproduct acetone back to isopropyl alcohol per equation 21. 

Other routes for hydroxybenzaldehydes are the electrolytic or catalytic reduction of hydroxybenzoic acids (65,66) and the electrolytic or catalytic oxidation of cresols (67,68). (see Salicylic acid and related compounds). Sahcylaldehyde is available in drums and bulk quantities. The normal specification is a freezing point minimum of 1.4°C. 4-Hydroxybenzaldehyde is available in fiber dmms, and has a normal specification requirement of a 114°C initial melting point. More refined analytical methods are used where the appHcation requires more stringent specifications. 

Reduction. Most ketones are readily reduced to the corresponding secondary alcohol by a variety of hydrogenation processes. The most commonly used catalysts are palladium, platinum, and nickel For example, 4-methyl-2-pentanol (methyl isobutyl carbinol) is commercially produced by the catalytic reduction of 4-methyl-2-pentanone (methyl isobutyl ketone) over nickel. 

Reduction. Heterogeneous catalytic reduction processes provide effective routes for the production of maleic anhydride derivatives such as succinic anhydride [108-30-5] (26), succinates, y-butyrolactone [96-48-0] (27), tetrahydrofuran [109-99-9] (29), and 1,4-butanediol [110-63-4] (28). The technology for production of 1,4-butanediol from maleic anhydride has been reviewed (92,93). 

Naphthalenediol. This diol can be prepared by the chemical or catalytic reduction of 1,4-naphthoquinone. Both the diol and quinone are of interest because of their relation to the vitamin K family. Carboxylation of 1,4-naphthalenediol with CO2—K2CO2 followed by neutralization gives... 

Process Licensors. Some of the well-known nitric acid technology licensors are fisted in Table 3. Espindesa, Grande Paroisse, Humphreys and Glasgow, Rhfyne Poulenc, Uhde, and Weatherly are all reported to be licensors of weak acid technology. Most weak acid plant licensors offer extended absorption for NO abatement. Espindesa, Rhfyne Poulenc, Weatherly, and Uhde are also reported (53,57) to offer selective catalytic reduction (SCR) technology. 

Glycohc acid [79-14-1], HOOCCH2OH, mol wt 76.05, can be obtained by the electrolytic reduction of oxaUc acid or the catalytic reduction of oxaUc acid with hydrogen in the presence of a mthenium catalyst. Because of its acidity it is used as a cleaning agent for metal surface treatments and for boiler cleaning. It also serves as an ingredient in cosmetics (qv). 

The most common oxidatiou states and corresponding electronic configurations of rhodium are +1 which is usually square planar although some five coordinate complexes are known, and +3 (t7 ) which is usually octahedral. Dimeric rhodium carboxylates are +2 (t/) complexes. Compounds iu oxidatiou states —1 to +6 (t5 ) exist. Significant iudustrial appHcatious iuclude rhodium-catalyzed carbouylatiou of methanol to acetic acid and acetic anhydride, and hydroformylation of propene to -butyraldehyde. Enantioselective catalytic reduction has also been demonstrated. 

Aromatic amines can be produced by reduction of the corresponding nitro compound, the ammonolysis of an aromatic haUde or phenol, and by direct amination of the aromatic ring. At present, the catalytic reduction of nitrobenzene is the predominant process for manufacture of aniline. To a smaller extent aniline is also produced by ammonolysis of phenol. 

The predominant process for manufacture of aniline is the catalytic reduction of nitroben2ene [98-95-3] ixh. hydrogen. The reduction is carried out in the vapor phase (50—55) or Hquid phase (56—60). A fixed-bed reactor is commonly used for the vapor-phase process and the reactor is operated under pressure. A number of catalysts have been cited and include copper, copper on siHca, copper oxide, sulfides of nickel, molybdenum, tungsten, and palladium—vanadium on alumina or Htbium—aluminum spinels. Catalysts cited for the Hquid-phase processes include nickel, copper or cobalt supported on a suitable inert carrier, and palladium or platinum or their mixtures supported on carbon. 

Aminophenols are either made by reduction of nitrophenols or by substitution. Reduction is accompHshed with iron or hydrogen in the presence of a catalyst. Catalytic reduction is the method of choice for the production of 2- and 4-aminophenol (see Amines BY reduction). Electrolytic reduction is also under industrial consideration and substitution reactions provide the major source of 3-aminophenol. 

Catalytic Reduction. Catalytic reduction usually takes place in solution, emulsion, or suspension in autoclaves or pressurized vessels after the catalyst is added, the vessel is pressurized with hydrogen (32,33). Water and methanol are the preferred solvents. In water the addition of alkaU hydroxide (34), alkah carbonate (35), or acid (36) has been recommended. 

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