Lead tetraacetate alkane oxidation

Carboxylic acids are oxidized by lead tetraacetate. Decarboxylation occurs and the product may be an alkene, alkane or acetate ester, or under modified conditions a halide. A free radical mechanism operates and the product composition depends on the fate of the radical intermediate.267 The reaction is catalyzed by cupric salts, which function by oxidizing the intermediate radical to a carbocation (Step 3b in the mechanism). Cu(II) is more reactive than Pb(OAc)4 in this step. 

A substantial improvement in yield (84-96%) was achieved by using the O-trimethylsilyl derivatives of the above alcohols. DIB was superior in these oxidations to lead tetraacetate. It is noted that l-silyloxy-bicyclo[n.l.O]alkanes (n = 4-7) on treatment with iodosylbenzene-tetrabutylammonium fluoride were converted into mixtures of cyclic unsaturated ketones (Section 5.2.1). 

Another widely used decarboxylation procedure involves the use of lead tetraacetate. Depending on the nature of the substrate and the reaction conditions, this reagent may transform a carboxylic acid into an alkane or alkene, or into the respective acetoxy derivative (Scheme 2.144). The most favorable conditions for alkane formation utilize a good hydrogen donor as the solvent. Usually this transformation is carried out as a photochemically induced oxidative decarboxylation in chloroform solution, as is exemplified in the conversion of cyclobutanecarboxylic acid in cyclobutane.In contrast, the predominant formation of alkenes occurs in the presence of co-oxidants such as copper acetate. ... 

Because oxidative decarboxylation of carboxylic acids by lead tetraacetate depends on the reaction conditions, the co-reagents, and the structures of the acids, a variety of products such as acetate esters, alkanes, alkenes, and alkyl hahdes can be obtained. Mixed lead(IV) carboxylates are involved as intermediates as a result of their thermal or photolytic decomposition decarboxylation occurs and alkyl radicals are formed. Oxidation of alkyl radicals by lead(IV) species gives carbocations a variety of products is then obtained from the intermediate alkyl radicals and the carbocations. Decarboxylation of primary and secondary acids usually affords acetate esters as the main products (Scheme 13.41) [63]. 

Nitroalkanes react with lead tetraacetate to afford a-acetoxynitroalkanes, but no yields were reported. The reaction is accelerated by addition of base, but not a ected by radical initiators. These a-acetoxynitroalkanes can also be obtained by oxidation of the corresponding a-acetoxynitroso alkanes by hydrogen peroxide-sodium nitrite (see section 7.1.2.5). 7... 

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