Solvent-free, selective and sustainable reaction protocol for an autoxidation of alkylbenzenes catalyzed by Co-NHPI (Cobalt-Nhydroxyphthalimide) under PTC (Phase Transfer Conditions) is described. A multigram scale preparation of acetophenone from ethylbenzene oxidation is demonstrated. The effect of catalyst [Cobalt, DDAB (Di-n-decyl-di-methyl ammonium bromide) and NHPI] concentrations, different types of catalysts, ef-fect of temperature and oxygen pressure as well as reaction kinetics related to present auto-oxidation of alkylbezenes is studied in details. Light microscope image shows that DDAB has Multi Lamellar Vesicles (MLVs) structures through which it protects NHPI at high temperatures. Thus efficient recovery and reuse of present ternary catalytic system (Co-NHPI/DDAB) is feasible.[a] Dr.
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.
A novel methodology for the solvent free autooxidation of methylbenzenes under mild conditions is disclosed. The new scheme is based on a combination of metallic salt (cobalt chloride) and a quaternary ammonium phase transfer catalyst (didecyldimethylammonium bromide) which together form a complex soluble catalyst in the organic phase. Major reaction parameters are studied and optimized and the procedure is applied for the conversion of several substituted toluenes to the corresponding benzoic acids in excellent isolated yields.
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