RESUMO
The oxidative cleavage of alkenes to carboxylic acids with 40% w/v aqueous hydrogen peroxide catalyzed by methyltrioctylammonium tetrakis(oxodiperoxotungsto)phosphate(3-) (Ia) is reported to occur in high yields and selectivities under two-phase conditions in the absence of organic solvents. On the basis of a study of the reaction, two main reaction pathways leading to acids have been recognized, the first one involving the perhydrolysis and the second one the hydrolysis of the epoxide initially formed. The "perhydrolytic" reaction pathway appears to play a primary role in the oxidation of medium- and long-chain alkenes to acids, while it intervenes to a rather limited extent in the oxidation of arylalkenes and C(5)-C(7) cycloalkenes. The occurrence of this pathway has been proved by the isolation of the intermediate beta-hydroperoxy alcohols and their transformation into acids with H(2)O(2) and Ia. The course of this transformation, involving an initial oxidation (to alpha-oxo hydroperoxide) or decomposition (to carbonyl compounds) of the beta-hydroperoxy alcohol intermediate, is described. The primary oxidation products, alpha-hydroperoxy ketones, have been isolated in the case of internal beta-hydroperoxy alcohols, whereas their presence has been evidenced with terminal beta-hydroperoxy alcohols bearing a secondary hydroxy group. Hydrogen peroxide concentration appears to exert a remarkable influence on medium acidity, and its effects on the reaction efficiency are shown.
