Superior Performance of NHPI Cocatalyst in the Autoxidation of Methylbenzenes under Solvent-Free Phase Transfer Conditions

Abstract

The novel three-way catalytic system Co(II)/QX/NHPI (QX = lipophilic ammonium salt) is presented as a highly potent promoter for the autoxidation of methylbenzenes to benzoic acids in the absence of a solvent. The key feature of the scheme is the phase transfer of Co(II) and NHPI into the organic phase partially via a hydrogen-bond mechanism. With certain QXs the latter interaction also stabilizes NHPI and prevents its degradation (which is a crucial drawback of this reagent). Ammonium salts that have a tendency to self-assemble in giant multilamellar vesicle (onion) structures, such as DDAB, are particularly effective in this system.