Solvent‐Free Aerobic Oxidation of Ethylbenzene Promoted by NHPI/Co(II) Catalytic System: The Key Role of Ionic Liquids

Abstract

The synergistic action between imidazolium based ionic liquid (IL) [bmim][OcOSO3] and Co(II)/N‐hydroxyphthalimide (NHPI) systems in the catalytic aerobic oxidation of ethylbenzene under solvent‐free conditions have been here demonstrated by reaching a 35 % conversion with 83 % of selectivity in acetophenone at 80 °C. This highly performing catalytic system have been selected after screening several different IL and Co(II) salt combinations, and making sure that the complete solubilization of the polar NHPI in the lipophilic medium, without thus requiring any chemical modification of the organic catalyst, could be attained. This solubilizing effect can be ascribed to a direct interaction between [bmim][OcOSO3] IL and NHPI as revealed by a detailed NMR investigation which also allowed to exclude the formation of higher IL aggregates in the form of micelles or vesicles.

N-Hydroxyphthalimide on a Polystyrene Support Coated with Co(II)-Containing Ionic Liquid as a New Catalytic System for Solvent-Free Ethylbenzene Oxidation

“…The relatively lower selectivities toward hydroperoxide production, in favor of ketone production, obtained for these SCILL/SILP systems may result from the higher CoCl 2 concentration in the IL layer, which promotes better contact between the co-catalyst and the EBOOH oxidation product. Selectivities comparable to those reported here for acetophenone production (~70%) were reported for the oxidation of ethylbenzene with dioxygen (0.1 MPa) in the presence of stearate and a Co(II) acetylacetonate catalyst, which had high solubility in the reaction mixture at 80 • C [42]. For comparison, as part of this study, the ethylbenzene oxidation reaction was carried out using PS-NHPI-3 and CoCl 2 in benzonitrile, and the products obtained were acetophenone (S AP = 66.7%), 1-phenylethanol (S PEOH = 26.2%), and ethylbenzene hydroperoxide (S EBOOH = 7.1%).…”

N-Hydroxyphthalimide Supported on Silica Coated with Ionic Liquids Containing CoCl2 (SCILLs) as New Catalytic System for Solvent-Free Ethylbenzene Oxidation

“…The influence of the type of ionic liquid on activity of the system and a possibility of recovery and reuse was determined. In the previous work [38] it was proved that selected ionic liquid, used in catalytic amounts, can positively influence the hydrocarbons oxidation process using NHPI/Co(II) system without solvent additive.…”

“…Therefore, it is difficult to explicitly determine, whether the observed effect results from the presence of IL dissolved in the system or supported onto the surface of silica.Asopposed to [bmim][OcOSO 3 ], [bmim][Cl] and [bmim][CF 3 SO 3 ] poorly dissolve in ethylbenzene. Additionally, in the previous work[38] we ascertained that the addition of catalytic amounts of [bmim][CF 3 SO 3 ] to the process of ethylbenzene oxidation catalyzed by Co(II) or NHPI/Co(II), in both cases influenced the decrease in conversion of substrate. However, in the studies presented in this paper, it was observed that there was a slight increase in conversion, which was related to the process of coating SiOCONHPI with a layer of [bmim][CF 3 SO 3 ] containing CoCl 2 , what would indicate a positive influence of IL bonded with silica on the whole process.…”

Transition Metal Salts of Carboxylated Multiwalled Carbon Nanotubes in Combination with N-hydroxyphthalimide as Catalytic Systems for Hydrocarbon Oxidation

“…The conversion increased depending on the metal salt used in the series, Mn (II) < Co (II) < Cu (II), from 13% to 27%. For comparison, when ethylbenzene was oxidized under similar conditions in the presence of a homogeneous Co(acac) 2 (0.1 mol%), the conversion of 14.9% and the selectivity of acetophenone 74.9% were achieved [ 21 ].…”