Hydrogenation palladium/carbon

Reduction of the halogen substituent has been carried out by different procedures such as catalytic hydrogenation using palladium-carbon or Raney nickel, red phosphorus and hydroiodic acid, and zinc and sulfuric acid (66AHQ6)347). 3-Deuteropyrazole has been... 

A mixture of 2.0 g (0.064 mol) of 2-fluoromethyl-3-(o-tolyl)-6-nitro-4(3H)-qulnazolinone, Oi g of 5% palladium-carbon and 100 ml of acetic acid is shaken for 30 minutes in hydrogen gas. The initial pressure of hydrogen gas is adjusted to 46 lb and the mixture is heated with an infrared lamp during the reaction. After 30 minutes of this reaction, the pressure of hydrogen gas decreases to 6 lb. After the mixture is cooled, the mixture is filtered to remove the catalyst. The filtrate is evaporated to remove acetic acid, and the residue is dissolved in chloroform. The chloroform solution is washed with 5% aqueous sodium hydroxide and water, successively. Then, the solution is dried and evaporated to remove solvent. The oily residue thus obtained is dissolved in 2 ml of chloroform, and the chloroform solution is passed through a column of 200 g of silica gel. The silica gel column is eluted with ethyl acetate-benzene (1 1). Then, the eluate is evaporated to remove solvent. The crude crystal obtained is washed with isopropylether and recrystallized from isopropanol. 0.95 g of 2-fluoromethyl-3-(o-tolyl)-6-amino-4(3H)-quinazolinone Is obtained. Yield 52.5% MP 195°-196°C. 

A mixture of 53.5 g (0.5 mol) of cyclopentylideneacetonitrile dissolved in 50 cc of absolute ethanol and 0.5 g of a palladium-carbon catalyst is hydrogenated with hydrogen at a pressure of about 40 lb for about 3 hours. An additional amount of 0.8 g of palladium-carbon catalyst is then added and the hydrogenation continued for about 4 hours during which time the reduction is substantially completed and the cyclopentylideneacetonitrile is converted to cyclopentylacetonitrile. The reaction mixture is filtered to remove the catalyst and the alcohol is evaporated in vacuo. 

Then 21.89 g of the hydrochloride salt was dissolved in 600 ml of 80% aqueous ethanol. With the addition of a palladium carbon catalyst, this solution was hydrogenated at room temperature under a hydrogen pressure of about 1.1 atmospheres. After 2 mols hydrogen had been absorbed, the catalyst was filtered off and the filtrate was evaporated in vacuo until crystallization occurred. Then the crystals were dissolved by heating in the smallest possible quantity of water and after cooling, the crystallized substance was filtered off, washed with water and dried in vacuo. The yield was 6.80 g, i.e., 39% of the theoretically possible yield. The resultant product recrystallized from water melted at 203° to 204°C. 

Figure 6.38. Potential energy diagram for the hydrogenation of ethylene to the ethyl (C2H5) intermediate on a palladium(m) surface. The zero of energy has been set at that of an adsorbed H atom, (a) Situation at low coverage ethylene adsorbed in the relatively stable di-cr bonded mode, in which the two carbon atoms bind to two metal atoms. In the three-centered transition state, hydrogen and carbon bind to the same metal atom, which leads to a considerable increase in the energy...

Formic acid at 98% had to be used as a solvent during a catalytic hydrogenation by using the palladium/carbon system. When the solvent came into contact with the catalyst there was a release of hydrogen. Does this accident result from the acid decomposition catalysed by palladium In this case the decomposition... 

The most widely used method for adding the elements of hydrogen to carbon-carbon double bonds is catalytic hydrogenation. Except for very sterically hindered alkenes, this reaction usually proceeds rapidly and cleanly. The most common catalysts are various forms of transition metals, particularly platinum, palladium, rhodium, ruthenium, and nickel. Both the metals as finely dispersed solids or adsorbed on inert supports such as carbon or alumina (heterogeneous catalysts) and certain soluble complexes of these metals (homogeneous catalysts) exhibit catalytic activity. Depending upon conditions and catalyst, other functional groups are also subject to reduction under these conditions. 

The surface areas of the iridium and palladium catalysts were determined by chemisorption of hydrogen and carbon monoxide, respectively, the monolayer volume being determined from an adsorption isotherm taken at 20°C. 

The catalytic cycle proposed for the cyclization-hydrosilylation with the cationic palladium catalyst is classified into the type D in Scheme 2. The reaction consists of an olefin insertion into palladium-silicon bond and the metathesis between palladium-carbon and hydrogen-silicon bond, regenerating the silylpalladium intermediate and releasing the product where migratory insertion of the pendant olefin into the alkylpalladium is involved before the metathesis (Scheme 26).83a... 

Add a 1 M excess of nitroethylene dropwise to liquid 5-benzyloxyindole (or other indole) on a steam bath over two hours. Cool, filter and recrystallize from methylene chloride-petroleum ether. Hydrogenate at two atmospheres over 10% palladium-carbon... 

Keywords Asymmetric Hydrogenation m Carbon Dioxide m Carbonylation m Dimethylformamide Enantioselectivity m Formic Acid m Homogeneous Hydrogenation n Palladium Catalysts Radical Reactions m Ruthenium Catalysts m Supercritical Fluids m Solvent Replacement... 

The intermediate Jt-allyl complex is formally the palladium(II) complex of an allylic anion that can be represented by the two mesomeric forms shown in Scheme 17.2. It is important to note that this is not a fast equilibrium between two cr-allyl complexes but a stable species where palladium is simultaneously bound to both carbon-1 and carbon-3. All eight atoms of the Jt-allyl moiety are almost in the same plane. All three carbon atoms have sp2 character and the rotation between the Cl-C2 and C2-C3 bonds is blocked. As a consequence of the hindered rotation, four dia-stereomeric Jt-allyl complexes are possible. For example, in Scheme 17.2 both R and R are syn to the hydrogen on carbon-2, therefore this complex is called the syn,syn diastereomer. 

Hydrogenation of the Condensation Product. The above product can be hydrogenated by using 10% palladium carbon catalyst and the methods in the reductions chapter. 

A solution of the above octene (50 g) in 100 ml of ethanol is shaken under 2-3 atmospheres of hydrogen in the presence of 0.6 g of 10% palladium-carbon catalyst, until no more hydrogen... 

An improved route to milnacipran (2) and derivatives is described in Scheme 14.5. In this approach, lactone 20 was opened with lithium diethylamide to provide amide alcohol 25, which was readily transformed into azide 26. Hydrogenation on palladium-carbon directly led to the desired target in 86% yield over the three steps. 

Iodine at the N-alkylcarbazole 3-position has been reductively removed with lithium aluminium hydride - and hydrogen-Raney nickel, and bromine at the same position has been removed with lithium-tcrt-butanol. Hydrogen-nickel at 600 psi has also been used to hydrogenolyze carbazole carbon-bromine bonds, and hydrogen-palladium/charcoal at 200°C to remove a 1-chlorine. ... 

Methyl-5-hepten-2-one is converted into linalool in excellent yield by base-catalyzed ethynylation with acetylene to dehydrolinalool [45]. This is followed by selective hydrogenation of the triple bond to a double bond in the presence of a palladium carbon catalyst. 

The first step in the cycle, analogous to the cross-coupling reactions, is the oxidative addition of an aryl (vinyl) halide or sulfonate onto the low oxidation state metal, usually palladium(O). The second step is the coordination of the olefin followed by its insertion into the palladium-carbon bond (carbopalladation). In most cases palladium is preferentially attached to the sterically less hindered end of the carbon-carbon double bond. The product is released from the palladium in a / -hydrogen elimination and the active form of the catalyst is regenerated by the loss of HX in a reductive elimination step. To facilitate the process an equivalent amount of base is usually added to the reaction mixture. 

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