Palladium on charcoal

The addition of N-bromosuccinimide (1.1equiv) to a dichlo-romethane solution containing the alkene (1 equiv) and cyana-mide (4 equiv). The solution was maintained at room temperature (3 days) and then washed with water, dried, and concentrated in vacuo. Treatment of the bromocyanamide [intermediate] with 1% palladium on charcoal in methanol (1h) led to reduction of the for-madine. Addition of base to the reaction mixture (50% aqueous KOH, reflux 6h) followed by extraction with ether gave monoamine. (Yield is 48-64% final amine from alkenes analogous to safrole)... 

More conveniently, compound (13) was directly condensed with barbituric acid (14) in acetic acid (28) or in the presence of an acid catalyst in an organic solvent (29). The same a2o dye intermediate (13) and alloxantin give riboflavin in the presence of palladium on charcoal in alcohoHc hydrochloric acid under nitrogen. This reaction may involve the reduction of the a2o group to the (9-phenylenediamine by the alloxantin, which is dehydrogenated to alloxan (see Urea) (30). 

Later, a completely different and more convenient synthesis of riboflavin and analogues was developed (34). It consists of the nitrosative cyclization of 6-(A/-D-ribityl-3,4-xyhdino)uracil (18), obtained from the condensation of A/-D-ribityl-3,4-xyhdine (11) and 6-chlorouracil (19), with excess sodium nitrite in acetic acid, or the cyclization of (18) with potassium nitrate in acetic in the presence of sulfuric acid, to give riboflavin-5-oxide (20) in high yield. Reduction with sodium dithionite gives (1). In another synthesis, 5-nitro-6-(A/-D-ribityl-3,4-xyhdino) uracil (21), prepared in situ from the condensation of 6-chloro-5-nitrouracil (22) with A/-D-ribityl-3,4-xyhdine (11), was hydrogenated over palladium on charcoal in acetic acid. The filtrate included 5-amino-6-(A/-D-ribityl-3,4-xyhdino)uracil (23) and was maintained at room temperature to precipitate (1) by autoxidation (35). These two pathways are suitable for the preparation of riboflavin analogues possessing several substituents (Fig. 4). 

Pyrazine 1,4-dioxides are available by the direct self-condensation of 1,2-hydroxyaminooximes (70JOC2790). 1,2-Nitrooximes are obtained by the isomerization of alkene initrogen trioxide adducts, which are reduced with palladium on charcoal to the hydroxyaminooximes which undergo acid-catalyzed auto-condensation to the pyrazine 1,4-dioxides (Scheme 19). 

Aryl tetrazolyl ethers (519) are reduced by palladium on charcoal to give the arene and the tetrazolinone (520) (77AHC(2D323) this reaction is used for the removal of phenolic functionality. 

The synthesis of indazoles from their 4,5,6,7-tetrahydroderivatives (439) by means of sulfur or, better, by catalytic dehydrogenation over palladium on charcoal (67HC(22)l) can also be included here. 

B. 2,2,7,7,12,12,17,17-Octemfi<%Z-21,22,23,24-t tfstainless-steel shaking autoclave is charged with 4.0 g. (0.0092 mole) of the tetraoxaquaterene from Part A, 200 ml. of ethanol, and 400 mg. of 5% palladium on charcoal catalyst (Note 6). The autoclave is filled with hydrogen at an initial pressure of 170 atm. and heated with shaking for 4 hours at 105 . Catalyst and a white solid are removed by filtration (Note 7), the solid is dissolved in 100 ml. of warm chloroform, the solution is filtered, the chloroform is evaporated, and the white solid which is obtained is dried under reduced pressure at 60° (Note 8). The tetraoxaperhydroquaterene is obtained as a white solid, m.p. 204-209 (Note 9), in a yield of 2.85-2.97 g. (69-72%). 

Catalyst obtained from Engelhard Industries was used. The submitters used 200 mg. of Fluka 10% palladium on charcoal catalyst with 5 g. of starting material in 250 ml. of ethanol and obtained a total yield of 2.3 g. (46%), m.p. 208-211°. 

A route to phenol has been developed starting from cyclohexane, which is first oxidised to a mixture of cyclohexanol and cyclohexanone. In one process the oxidation is carried out in the liquid phase using cobalt naphthenate as catalyst. The cyclohexanone present may be converted to cyclohexanol, in this case the desired intermediate, by catalytic hydrogenation. The cyclohexanol is converted to phenol by a catalytic process using selenium or with palladium on charcoal. The hydrogen produced in this process may be used in the conversion of cyclohexanone to cyclohexanol. It also may be used in the conversion of benzene to cyclohexane in processes where benzene is used as the precursor of the cyclohexane. 

A suitable catalyst is 10% palladium-on-charcoal, such as is supplied by Baker and Company, Inc., 113 Astor Street, Newark 5, New Jersey. 

Snyder and Smith prepared diethyl acetamidomalonate in 40% yield by reduction of diethyl isonitrosomalonate in ethanol over palladium on charcoal followed by direct acetylation of diethyl aminomalonate in the filtrate with acetic anhydride. Ghosh and Dutta used zinc dust instead of palladium. A modification using Raney nickel is described by Akabori et al. Shaw and Nolan reported a 98% yield by conversion of diethyl oximino-malonate-sodium acetate complex. 

Diethyl isonitrosomalonate has been reduced catalytically, over palladium on charcoal, Raney nickel, and chemically by aluminum amalgam or hydrogen sulfide. ... 

Normally, the hydrogenation of a readily hydrogenated double bond occurs over palladium-on-charcoal in ethanol at room temperature and atmospheric pressure. The more difficultly reduced olefins require elevated reaction temperatures and/or pressures for the reaction to proceed at a reasonable rate. The saturation of an 8(14)-double bond is virtually impossible under normal hydrogenation conditions. In order to remove unsaturation at this position it is necessary to first isomerize the double bond to the readily hydrogenated 14 position by treatment with dry hydrogen chloride in chloro-form. ° ... 

Five to ten grams of the benzyl ether is hydrogenolyzed over 1-1.5 g of 5% palladium-on-charcoal in 75-100 ml of ethanol at room temperature and atmospheric pressure. Filtration and evaporation of the filtrate to dryness gives very good yields of the alcohol. ... 

A solution of 4,4-dimethyl-5a-androst-l-en-3-one (128, 14 mg) in cyclohexane (3 ml) is stirred in a microhydrogenation apparatus in the presence of 10 % palladium-on-charcoal (15 mg) at atmospheric pressure and room temperature. The uptake of one eq of deuterium (1.15 ml) is complete in about 1 min and no more deuterium is consumed. After 5 min the catalyst is removed by filtration, and the solvent evaporated under reduced pressure. The resulting l<, 2< -d2-4,4-dimethyl-5a-androstan-3-one (129, 13 mg, 93%), mp 120-122°, exhibits 87% isotopic purity and 13% d species. ... 

Displacement of aromatic halogen in 2,4-diiodo-estradiol with tritiated Raney nickel yields 2,4-ditritiated estradiol. Aromatic halogen can also be replaced by heating the substrate with zinc in acetic acid-OD or by deuteration with palladium-on-charcoal in a mixture of dioxane-deuterium oxide-triethylamine, but examples are lacking for the application of these reactions in the steroid field. Deuteration of the bridge-head position in norbornane is readily accomplished in high isotopic purity by treatment of the... 

Reduction of 17a-EthynyI to 17a-Ethyl °° A solution of 5 g of 17a-ethynyl-androst-5-ene-3j9,17j5-diol in 170 ml of absolute alcohol is hydrogenated at atmospheric pressure and room temperature using 0.5 g of 5 % palladium-on-charcoal catalyst. Hydrogen absorption is complete in about 8 min with the absorption of 2 moles. After removal of the catalyst by filtration, the solvent is evaporated under reduced pressure and the residue is crystallized from ethyl acetate. Three crops of 17a-ethylandrost-5-ene-3) ,17j9-diol are obtained 3.05 g, mp 197-200° 1.59 g, mp 198.6-200.6° and 0.34 g, mp 196-199° (total yield 5.02 g, 90%). A sample prepared for analysis by recrystallization from ethyl acetate melts at 200.6-202.4° [aj, —70° (diox.). 

The intermediacy of dipolar species such as 186 has been demonstrated by reaction of enamines with 2-hydroxy-1-aldehydes of the aromatic series (129). The enamine (113) reacts in benzene solution at room temperature with 2-hydroxy-1-naphthaldehyde to give the crystalline adduct (188) in 91 % yield. Oxidation with chromium trioxide-pyridine of 188 gave 189 with p elimination of the morpholine moiety. Palladium on charcoal dehydrogenation of 189 gave the known 1,2-benzoxanthone (129). 

Indolizine (18) combines with dimethyl acetylenedicarboxylate in the presence of palladium on charcoal yielding two products, (19) and (20), which may be formed as indicated. 

The zwitterion (22) obtained from 1-phenacylpyridinium bromide (21) and dimethyl acetylenedicarboxylate in the presence of palladium on charcoal yields the indolizine (23) possibly through the route shown. 

Phenacylpyridinium bromide (155) with aqueous sodium carbonate yields the chloroform soluble zwitterion (156) which, with dimethyl acetylenedicarboxylate in the presence of palladium on charcoal, cyclized to the indolizine (157) in ca. 20% yield. In a similar way the pyrazine (158) gave a mixture of (159) and (160) through loss of the benzoyl group. The last compound was also ob-... 

Reduction of quinazoline oxides to quinazolines, catalytically (Raney nickel, palladium on charcoal) or with iron and ferrous sulfate in 85% alcohol can be extended to the preparation of benz-substituted quinazolines. ... 

A different type of tautomeric relationship exists between compounds of types 323 and 324. Both types of structure can be isolated, pyridones (324, Z = N—Me) and pyrones (324, Z = 0) being formed when 323 (Z = N—Me or 0) is heated with palladium on charcoal in ethylene glycol. Similar isomerizations in the quinol-4-one series have been reported."... 

Perhaps the most reliable method for the reductive cyclization of a nitro ester to a hydroxamic acid is that which involves treatment with sodium horohydride in the presence of palladium on charcoal. Although under these conditions aromatic nitro compounds are reduced to amines, o-nitro esters such as 53, in which the ester group is suitably oriented with respect to the nitro group, give good yields of cyclic hydroxamic acids (54). Coutts and his co-... 

Simple l,2,3,4-tetrahydro-)3-carbolines have been aromatized in this manner. Palladium black at 160-170° or at higher temperature, palladium-maleic acid in aqueous solution, and platinum/oxygen have been used for the purpose. Palladium-on-charcoal in a high-boiling solvent has been used also to aromatize 5,6,7,8-tetrahydro-j3-carbohnes and 6,7,8,9-tetrahydro-3-carbo-hne. ... 

Debenzylation of the benzyloxy groups in 156 and 158 to 157 and 159 respectively was achieved, without affecting the aromaticity of the system, by catalytic hydrogenolysis in the presence of palladium-on-charcoal (86TL3127 89JHC991) (Scheme 61). 

The first example of an indolo[2,3-a]carbazole derivative reported with a reasonably estabhshed structure was the mono N-methylated system 9, prepared via dehydrogenation with palladium on charcoal of the octahydro derivative 10, available via reaction of the aminocarbazole 11 with 2-hydroxycyclohexanone in the presence of a trace amount of anihnium bromide (Scheme 1). An approach toward the parent compound 1 using the same method has also been attempted, although without success (56JCS4783). The utility of this route is impaired by the complexity of the starting material, which requires multistep preparation, and the harsh conditions of the final step. 

An alternative route was later reported by Hall and Plant, who obtained 2 as well as the methyl derivative 110 in low yields, via the reaction of 5-aminotetrahydro-carbazoles with 2-chlorocyclohexanone, followed by dehydrogenation with palladium on charcoal of the intermediate octahydro derivatives 109 or 111 (53JCS116). The octahydro compounds 109 and 111 have also been reported as products from the reactions of suitable 1,3-phenylenediamines and 2-hydroxycyclohexanone in the presence of a catalytic amount of hydrochloric acid (53JCS4114). 

Preparation of the substituted piperazine required for sul-falene (114) starts with bromination of 2-aminopiperazine to give the dihalide (150). Displacement of halogen by sodium methoxide proceeds regioselectively at the more reactive 3 position to give 151. Hydrogenolysis over palladium on charcoal gives the desired intermediate (152). 

A 250-ml flask is charged with 28 g (0.20 mole) of 2-acetyIcyclohexanone and 25 g (0.22 mole) of 30% hydrogen peroxide in 100 ml of /-butyl alcohol. The solution is refluxed for 3 hours, cooled, and a pinch of palladium on charcoal (10%) is cautiously added. The mixture is refluxed for an additional hour to decompose excess peroxide. The cooled mixture is then filtered through celite, and the volume is reduced by removal of /-butyl alcohol and water at reduced pressure. Distillation of the residue affords about 85% of cyclopentanecarboxylic acid, bp 59-6271 rnm, 123727 mm, 215-21671 atm. 

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