An efficient aerobic oxidation of isobutane to t-butyl alcohol by N-hydroxyphthalimide combined with Co(II) species

Highly selective aerobic oxidation of isobutane to t-butyl alcohol was successfully achieved by the use of a radical catalyst, N-hydroxyphthalimide (NHPI) in the presence of Co(II) salt under relatively mild conditions. The oxidation of isobutane by NHPI combined with Co(acac)(2) under a pressure of air (10 atm) in benzonitrile at 100 degrees C gave t-butyl alcohol in high yield (84%) along with acetone (13%). The reaction is thought to proceed via hydrogen abstraction from isobutane by the phthalimidooxyl radical (PINO), which seems to be a key active species. The formation of acetone can be explained by a partial beta-scission of the t-butoxy radical, generated from the redox decomposition of t-butyl hydroperoxide by cobalt ion. Alkyl-substituted butanes and pentanes were difficult to be oxidized selectively under these conditions because of easy degradation to smaller fragments of the resulting alkoxyl radical intermediates.