Aqueous conditions palladium® reduction

For aliphatic aldehydes and ketones, reduction to the alcohol can be carried out under mild conditions over platinum or the more-active forms of Raney nickel. Ruthenium is also an excellent catalyst for reduction of aliphatic aldehydes and can be used to advantage with aqueous solutions. Palladium is not very active for hydrogenation of aliphatic carbonyl compounds, but is effective for the reduction of aromatic aldehydes and ketones excellent yields of the alcohols can be obtained if the reaction is interrupted after absorption of one mole of hydrogen. Prolonged reaction, particularly at elevated temperatures or in the presence of acid, leads to hydrogenolysis and can therefore be used as a method for the reduction of aromatic ketones to methylene compounds. 

The reaction is used for the chain extension of aldoses in the synthesis of new or unusual sugars In this case the starting material l arabinose is an abundant natural product and possesses the correct configurations at its three chirality centers for elaboration to the relatively rare l enantiomers of glucose and mannose After cyanohydrin formation the cyano groups are converted to aldehyde functions by hydrogenation m aqueous solution Under these conditions —C=N is reduced to —CH=NH and hydrolyzes rapidly to —CH=0 Use of a poisoned palladium on barium sulfate catalyst prevents further reduction to the alditols... 

Nitropyridazines are reduced catalytically either over platinum, Raney nickel or palladium-charcoal catalyst. When an N-oxide function is present, palladium-charcoal in neutral solution is used in order to obtain the corresponding amino N-oxide. On the other hand, when hydrogenation is carried out in aqueous or alcoholic hydrochloric acid and palladium-charcoal or Raney nickel are used for the reduction of the nitro group, deoxygenation of the N- oxide takes place simultaneously. Halonitropyridazines and their N- oxides are reduced, dehalogenated and deoxygenated to aminopyridazines or to aminopyridazine N- oxides under analogous conditions. 

The hydrogenation of 5a-cholestanone (58) in methanolic hydrobromic acid over platinum gives 3j5-methoxycholestane ° (61). This compound is also obtained from the palladium oxide reduction of (58) in methanol in the absence of acid. Hydrogenation of 5 -cholestanone also gives the 3j5-methoxy product under these conditions. Reduced palladium oxides are quite effective for the conversion of ketones to ethers. The use of aqueous ethanol as the solvent reduces the yield of ether. Ketals are formed on attempted homogeneous hydrogenation of a 3-keto group in methanol. ... 

Palladium, platinum, and Raney nickel 7,126) all have been used successfully under mild conditions for hydrogenation of the azido function. In especially sensitive molecules, subambient temperature may prove advantageous. Reduction of methyl 3, 5-dihydroxy-4 -methoxy-7-(3-azido-3-carboxypropoxy)flavanone (32) in aqueous alkali proved capricious, The major product (33) was contaminated by several other products when reagents were mixed and hydrogenated at room temperature or above, but by the... 

Under vigorous conditions (100°C and 1000 psig) in 25% aqueous sulfuric acid, the yield of cyclohexanol plus cyclohexanone from dimethyl-aniline was 90, 75, and 13% over 5% palladium-, 5% rhodium-, and 5% platinum-on-carbon, respectively (33). The decreasing yield parallels the decreasing tendency for migration. Reductive hydrolysis is favored by substitution on the nitrogen atom attributed in part to the relative difficulty of hydrogenating hindered enamines. 

Spongy Palladium is readily obtained by heating ammonium chlor-palladite, (NH4)2PdCl4, in hydrogen. It is then in a particularly suitable condition for exhibiting catalytic activity. Graham 2 prepared it by ignition of the cyanide, and Berry 8 by reduction of the chloride with sodium formate in hot aqueous solution. 

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