RATES OF PHOTOCHEMICAL AND THERMAL DECARBOXYLATION OF ACIDS BY LEAD .4. TETRAACETATE

The rates of the photochemical and thermal decarboxylation of aliphatic acids by lead (IV) tetraacete have been examined by a competition method. Photochemically, pivalic (tertiary) acid decarboxylates at 30° approximately 100 times, and isobutyric (secondary) acid 20 times, faster than n-butyric (primary) acid. The competitive decarboxylations of acids by lead(IV) carried out thermally at 80-100° show a smaller spread in reactivity. The thermal procedure is complicated by further oxidation of the olefinic products by PbIV. Rates of decarboxylation are related to the multibond cleavage of the Pb-carboxylate linkages directly into alkyl radicals and carbon dioxide. The mechanism of the reduction of PbIV is compared to the homolytic decarboxylations of the analogous CoIII, MnIII and CeIV carboxylates. © 1969.