Reduction catalytic hydrogen transfer

This encompasses all reduction methods other than hydrogenation and includes hydride equivalents and one-electron reductions. Catalytic hydrogen transfer is included under hydrogenation (see Section 3.6.3). 

Catalytic hydrogenation transfers the elements of molecular hydrogen through a series of complexes and intermediates. Diimide, HN=NH, an unstable hydrogen donor that can be generated in situ, finds specialized application in the reduction of carbon-carbon double bonds. Simple alkenes are reduced efficiently by diimide, but other easily reduced functional groups, such as nitro and cyano are unaffected. The mechanism of the reaction is pictured as a concerted transfer of hydrogen via a nonpolar cyclic TS. 

S. Ram u. R. E. Ehrenkaufer, Synthesis 1988,91 - -95 . .Ammonium Formate in Organic Synthesis, a Versatile Agent in Catalytic Hydrogen-Transfer Reductions". 

The possibility of using of aliphatic alcohols as hydrogen donors for the catalytic transfer reduction of nitro group over MgO was examined. Catalytic hydrogen transfer was found to be effective and selective method for reduction of nitrobenzene, A-nitrotoluene, A-chloronitrobenzene, 4-nitro-m-xylene, 3-nitro-styrene, 3-nitrobenzaldehyde, 1-nitropropane, and 1-nitrobutane. Conversion of starting nitro compound into desired product depended on the alcohol used as a donor. Adsorption of reactant and catalyst deactivation were studied by esr. New aspects of a role of one-electron donor sites in hydrogen transfer over MgD were demonstrated. 

The Kp values for the reactions of hydrogen transfer between primary and secondary alcohols and nitro compounds were calculated using Van Krevelen and Chermin procedure (ref. 4). Similarly as the simple reduction with hydrogen the catalytic hydrogen transfer from alcohols to nitro derivatives is strongly favored thermodynamically. For all studied reactions with primary alcohols the K... 

Strong centres, forming anion radical even from nitrobenzene molecule are poisoned irreversibly, however, their presence is not necessity for the preservation of catalytic activity. Taking into consideration that regenerated MgO which is not able to ionize nitrobenzene molecule is still active in its reduction by hydrogen transfer and that only a few from reduced nitro compounds form ion radicals on catalyst surface one can ascertain that ion radicals formation is not necessary step in nitroarenes (or nitroparaffins) activation. Probably, one-electron donor sites take part only in activation of alcohol what was demonstrated by us earlier. 

Hydrogen peroxide, Hydrogen, Palladium catalyst, 4471 3-Methyl-2-penten-4-yn-l-ol, 2378 l,Ll-Tris(azidomethyl)ethane, 1931 Tris(hydroxymethyl)nitromethane, 1658 See CATALYTIC NITRO REDUCTION PROCESSES, HYDROGEN TRANSFER... 

The selective and rapid reduction of nitro compounds is an active area of research, particularly when other potentially reducible moieties are present in the molecules. Anhydrous ammonium formate has been developed as a catalytic hydrogen transfer agent for selectively reducing nitro groups in the presence of acid, ester, amide, halogen and nitrile groups (equation 13). ... 

In the absence of a laboratory or industrial pressure vessel, catalytic hydrogen transfer is a viable alternative. Here, the nitro compound is stirred in a solvent with a catalyst, commonly 1% platinum on carbon, in the presence of a hydrogen donor such as hydrazine, sodium formate (sodium methanoate) or methylcyclohexene (Scheme 7.6). In the case of hydrazine, interaction at the catalyst surface produces the reductant, hydrogen, and nitrogen. Toluene is the by-product when methylcyclohexene is used. 

Nitriles are reduced completely to methyl groups by an active donor such as p-menthene under conditions normally used for catalytic hydrogen transfer. Reduction proceeds satisfactorily when the cyano group is bound to an aromatic of heterocyclic ring [equation (a)] but is slightly more difficult in the case of aliphatic nitriles [equation... 

Ammonium Formate in Organic Synthesis A Versatile Agent in Catalytic Hydrogen Transfer Reductions"... 

Uses In analytical chemistry reagent for carbon monoxide absorp. processes as metal precipitant or as reductant in catalytic hydrogen transfer reactions buffer Manuf./Distrib. Alfa Aesar http //www.alfa.com-, Cater Chems. http //www.caterchem.com, GFS http //www.gfschemicals.com-, Honeywell Perf. Polymers http //www.honeywellppc.com, http //www.honeywell-plastics.com, Integra http //www.integrachem. com J.T. Baker http //www.jtbaker.com,... 

Finally the formation of the aldehyde 58 during the catalytic reaction could be due to an internal hydrogen transfer from the alcoholic group to nitrogen. Catalytic hydrogen transfer reduction of nitroarenes by alcohols is a known reaction. 

Transfer hydrogenation is particularly good for the reduction of ketones and imines that are somewhat more difficult to reduce with Hj than are C—C bonds. BSckvall and co-workers have shown how RuCl fPPhj) is effective at 80°C with added base as catalyst promoter. The role of die base is no doubt to form the isopropoxide ion. which presumably coordinates to Ru and by elimination forms a hydride and acetone. Noyori and co-workers have has a remarkable asymmetric catalytic hydrogen transfer that goes without direct coordination of the C=0 bond to the metal. Instead, the metal donates a hydride to the C=0 carbon while the adjacent RU-NH2R group donates a proton to the C=0 oxygen. 

Amides are very weak nucleophiles, far too weak to attack alkyl halides, so they must first be converted to their conjugate bases. By this method, unsubstituted amides can be converted to N-substituted, or N-substituted to N,N-disubstituted, amides. Esters of sulfuric or sulfonic acids can also be substrates. Tertiary substrates give elimination. O-Alkylation is at times a side reaction. Both amides and sulfonamides have been alkylated under phase-transfer conditions. Lactams can be alkylated using similar procedures. Ethyl pyroglutamate (5-carboethoxy 2-pyrrolidinone) and related lactams were converted to N-alkyl derivatives via treatment with NaH (short contact time) followed by addition of the halide. 2-Pyrrolidinone derivatives can be alkylated using a similar procedure. Lactams can be reductively alkylated using aldehydes under catalytic hydrogenation... 

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