OXIDATION. ANODIC Palladium acetate

The electrochemical Wacker-type oxidation of terminal olefins (111) by using palladium chloride or palladium acetate in the presence of a suitable oxidant leading to 2-alkanones (112) has been intensively studied. As recyclable double-mediatory systems (Scheme 43), quinone, ferric chloride, copper acetate, and triphenylamine have been used as co-oxidizing agents for regeneration of the Pd(II) catalyst [151]. The palladium-catalyzed anodic oxidation of... 

Methyl glyoxylate adducts of iV-Boc-protected allylic amines cyclize in the presence of a catalytic amount of palladium acetate and excess copper(II) acetate to 5-(l-alkenyl)-2-(methoxycarbonyl)oxazolidines (eq 5). These heterocycles are easily converted to unsaturatedIV-Boc protected /3-amino alcohols through anodic oxidation and mild hydrolysis. 

The reaction is considered to proceed by the elimination of H in the P position in complex [A], induced by the base (Scheme 1). NEt3 is probably more efficient than AcO in this reaction. The Pd(0) is then generated in higher concentrations from complex [A] in the presence of NEt3 and can be reoxidized to Pd(II) at the anode. Moreover, when acetate was used as base, acetic acid is formed from complex [A] concomitantly with the Pd(0) complex. It was been reported that Pd(0) undergoes oxidative addition with acetic acid to form a cationic palladium(II)hydride.[ll]... 

When a palladium(II)-hydroquinone system is used as the mediator4 in the anodic oxidation of 1,3-cyclohexadiene in acetic acid, either trans- or cis- 1,4-diacetoxy-2-cyclohexene is formed with rather high selectivity, though the possible formation of 1,2-diacetoxylated compound is not discussed. 

The mechanism of the Zn chloride-assisted, palladium-catalyzed reaction of allyl acetate (456) with carbonyl compounds (457) has been proposed [434]. The reaction involves electroreduction of a Pd(II) complex to a Pd(0) complex, oxidative addition of the allyl acetate to the Pd(0) complex, and Zn(II)/Pd(II) transmetallation leading to an allylzinc reagent, which would react with (457) to give homoallyl alcohols (458) and (459) (Scheme 157). Substituted -lactones are electrosynthesized by the Reformatsky reaction of ketones and ethyl a-bromobutyrate, using a sacrificial Zn anode in 35 92% yield [542]. The effect of cathode materials involving Zn, C, Pt, Ni, and so on, has been investigated for the electrochemical allylation of acetone [543]. 

They find that the anode potential determines the effect. The first reaction which occurs predominatingly at iron and palladium electrodes, requires the lowest potential. With platinized platinum electrodes the potential lies higher the oxidation action can exceed the evolution of oxygon and with a particularly high potential, which is obtained by prepolarizing the platinized anode,1 ethane is produced. With polished platinum and iridium anodes the potential is still higher than with prepolarized platinized platinum anodes. Thus the production of ethane predominates over the oxidation of acetic ester. 

The presence of both poisoning species and intermediate reaction products requires the development of new electrocatalysts able to break the C-C bond and to oxidize adsorbed CO at low temperatures [94]. Numerous studies have been carried out to develop more active electrocatalysts for ethanol eleetrooxidation. Besides Pt, other metals such as gold, rhodium, and palladium have been investigated as anode catalysts for ethanol eleetrooxidation and show certain activities [105]. On gold in an acid medium, the oxidation reaction leads mainly to the formation of acetaldehyde [94]. The oxidation of ethanol on rhodium proceeds mainly through the formation of acetic acid and CO. 

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