Palladium-barium sulfate

Catalytic hydrogenation of dimethyl 3-methyl-3//-3-benzazepine-2,4-dicarboxylate (10) to the 1,2,4,5-tetrahydro derivative with hydrogen and a palladium-barium sulfate catalyst, followed by treatment of the reaction mixture with iodomethane in refluxing methanol, yields a mixture of the 2,4-dicarboxylic acid 11 and the methiodide salt 12.24... 

The palladium-barium sulfate is prepared by the method described by Houben.2 The barium sulfate should be freshly precipitated material. 

Palladium-barium sulfate Hydrogenation of ethylene derivatives... 

Preparation of the palladium-barium sulfate catalyst has been described by Mozingo.456... 

Under suitable conditions it is possible to isolate the A-substituted hydroxylamines that are formed as intermediates in the reduction of nitro compounds. For this purpose it is essential in the reduction of aromatic nitro compounds to work with neutral or nearly neutral solutions suitable reducing agents are hydrogen and platinum oxide catalysts in glacial acetic acid,82,83 zinc dust in ammonium chloride solution,84 aluminum amalgam,85 and ammonium sulfide.86 Aliphatic nitro compounds may be reduced as their alkali salts (nitronates) by diborane in tetrahydrofuran, then giving A-alkylhydroxyl-amines 87 for instance, A-cyclohexylhydroxylamine is thus obtained from nitrocyclohexane in 53% yield. However, aliphatic nitro compounds are converted into A-alkylhydroxylamines more simply by catalytic hydrogenation in the presence of palladium-barium sulfate unlike aromatic nitro compounds, aliphatic nitro compounds require an acid medium for reduction to hydroxylamines an oxalic acid medium has proved the most suitable. 

Catalytic hydrogenation of oximes to amines requires conditions resembling those for catalytic hydrogenation of nitro compounds and nitriles.20d The catalyst should be as active as possible, e.g., Raney nickel101 (if necessary, platinized), platinum oxide,102 palladium-charcoal,103 palladium-barium sulfate,104 or rhodium-alumina.105 This rhodium catalyst also serves for reduction of an amidoxime to the amidine.106 Hydrogenation may be effected under pressure, but the temperature should be kept as low as possible to avoid formation of secondary amines. 

The alkyne is then hydrogenated to the cis-alkene. This is accomplished by using palladium, barium sulfate and quinoline the hydrogen adds on the same side of the triple bond. The reaction is ... 

Catalyst—Continued palladium-barium sulfate, 21, 85, 110 piperidine benzoate, 25, 42 poison, for use in Rosenmund reduc-... 

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