An Efficient Aerobic Oxidation of Isobutane to t-Butyl Alcohol by N-Hydroxyphthalimide Combined with Co(II) Species

Abstract

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 °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 β-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.

Innovation of Hydrocarbon Oxidation with Molecular Oxygen and Related Reactions

“…Further oxidation of the resulting alcohols to ketones may be suppressed by the cyano group with its strong electronwithdrawing character. Other alkanes also gave oxyalkylated adducts in good yields (Equation 46). …”

“…[46] 2-Methylbutane was converted into the carbon-carbon bond cleaved products, acetone and acetic acid, rather than the alcohols, as principal products. These cleaved products seem to be formed via bscission of an alkoxy radical derived from the decomposition of a hydroperoxide by Co ions.…”

Chemo- and regioselective oxygenation of C(sp3)–H bonds in aliphatic alcohols using a covalently bound directing activator and atmospheric oxygen

“…For example, exposing 1i to condition A afforded 2i and C–C bond-cleaved products ( Scheme 2 ). 18 As the presence of these decomposition products may be explained by the formation of hydroperoxide intermediates, we carried out a screening of the reductants in order to ensure optimal in situ reduction conditions for such problematic species. We found that Me 2 S provided the best results, as this additive was not susceptible to oxidation using the Co/O 2 catalytic system in the absence of substrates 1 .…”

“…Trapping 6 with molecular oxygen, the resulting alkyl peroxy radical 7 is quenched by a hydroperoxy radical generated in the initiation step to produce alkyl peroxide 8 , or through intramolecular hydrogen abstraction from DA, generating 9 . In the case of tertiary C–H oxygenation, undesired decomposition pathway from 8 (see Scheme 2 ) 18 is suppressed by in situ reduction with Me 2 S to produce the corresponding tertiary alcohols. In the case of methylene oxygenation, the corresponding ketone is produced either through β-elimination from alkylperoxy species 8 or 9 , or oxidation of the secondary alcohol generated from 8 with Me 2 S.…”

Metal‐Free, Selective Alkane Functionalizations

“…The role of the metal co-catalyst in the generation of the active species from NHPI is not yet clear; the involvement of the metal-oxygen complex in the generation of the PINO-radical from NHPI was recently suggested. [99,100] The direct radical carbonylation of alkanes usually requires drastic reaction conditions (several thousands atmospheres of pressure) or the use of peroxides. [105] The NHPI-catalyzed alkane carboxylation with CO under oxygen occurs at much lower pressures (15 atm) [103] and involves selective H-abstraction with the PINO radical (Eq.…”