Abstract
The oxidation of ethylbenzene using dioxygen was carried out applying a new catalytic system—heterogeneous N-hydroxyphthalimide (PS-NHPI) coated with an ionic liquid containing CoCl2. The catalytic system represents a combination of solid catalyst with ionic liquid layer (SCILL) and supported ionic liquid phase (SILP) techniques, wherein the resulting system utilizes CoCl2 dissolved in the 1-ethyl-3-methylimidazolium octyl sulphate ([emim)][OcOSO3]) ionic liquid phase that is layered onto the solid catalyst support. PS-NHPI was obtained by immobilizing N-hydroxyphthalimide on chloromethyl polystyrene resins by ester bonds. It was observed that novel SCILL/SILP systems significantly improved the selectivity toward acetophenone. We also demonstrate that these systems can be separated from the reaction mixture and recycled without appreciably reducing its activity and selectivity.
Highlights
Hydrocarbon oxidations represent an important family of reactions in organic synthesis, and they play a key role in the chemical industry
@[emim][OcOSO3 ], which embody a combination of SCILL and SILP techniques, were used for ethylbenzene oxidation reactions
The obtained heterogeneous catalysts were characterized by Scanning electron microscopy (SEM), FT-Infrared spectra (IR), and elemental analysis, and were covered with the ionic liquid, [emim][OcOSO3 ], which contained dissolved CoCl2
Summary
Hydrocarbon oxidations represent an important family of reactions in organic synthesis, and they play a key role in the chemical industry. For environmental and economic reasons, it is advantageous to use dioxygen or air as the oxidizing agent for such transformations, which is made possible by using catalytic systems containing often transition metal compounds, e.g., Co and Mn [1,2]. The high activity of N-hydroxyphthalimide (NHPI) in this type of reaction has been demonstrated repeatedly in the literature [3,4,5]. This compound’s activity is related to the fact that, during turnover, it generates the phthalimide-N-oxyl (PINO) radical, which effectively abstracts the hydrogen atom from the hydrocarbon being oxidized (Scheme 1). Azobisisobutyronitrile (AIBN) was used in the oxidation of cumene to its hydroperoxide using dioxygen at 60 ◦ C, aided by
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