Homogeneous Liquid-Phase Oxidation of Ethylbenzene to Acetophenone in Continuous Flow Mode

Abstract

The oxidation of ethylbenzene with hydrogen peroxide and molecular oxygen catalyzed by cobalt and bromide ions in acetic acid as solvent was studied. The oxidation of ethylbenzene with hydrogen peroxide provided a mixture of ethylbenzene hydroperoxide, acetophenone, 1-phenylethanol, and 1-phenylethyl acetate. After rapid initial oxidation, the reaction rate decreased steadily so that full conversion of ethylbenzene and reaction intermediates to acetophenone could not be achieved. In contrast, no catalyst deactivation was observed for oxidations using atmospheric oxygen. Ethylbenzene was oxidized to acetophenone in 74% selectivity after a reaction time of 150 min at 80 °C. The reaction conditions were translated to a continuous flow process using a tubular gas–liquid reactor. At temperatures of 110 to 120 °C and an oxygen pressure of ∼12 bar, the reaction time necessary for complete oxidation of ethylbenzene was reduced to 6 to 7 min. The acetophenone was formed in 80 to 84% selectivity, and virtually pure acetophenone was isolated in 66% product yield without the need for chromatography. Increasing the reaction time to 16 min at a reaction temperature of 150 °C led to benzoic acid as the final product in 71% yield.

Liquid phase oxidation chemistry in continuous-flow microreactors

“…166 Kappe et al constructed a continuous-flow reactor for the preparation of acetophenone and benzoic acid from ethyl benzene. 167 The combination of CoBr2 (2.5 mol%) in combination with Mn(OAc)2 (2.5 mol %) in acetic acid was used as active catalytic system. The system is known in literature as the 'MC-system', and is one of the most active and selective catalytic systems available for aerobic, homogeneous liquid phase oxidations.…”

Catalytic Transformation of Biomass Derivatives to Value‐Added Chemicals and Fuels in Continuous Flow Microreactors

“…[286] Another challenge lies specifically in the precipitation of FDCA that is formed during the oxidation of HMF. The use of molecular O 2 for oxidation reactions in microreactors seems more promising for highly selective reactions, as in the occurrence of over oxidation reactions significantly more O 2 is required to achieve the same desired product yield.…”

Simple Copper Catalysts for the Aerobic Oxidation of Amines: Selectivity Control by the Counterion

“…Similarly, monitoring of the formation of imine 3aunder the catalysis of [Cu(CH 3 CN) 4 ](PF 6 )( abbreviated CuPF 6 )s howed that this catalyst system is more active than the CuI system (Figure 1a), thus suggesting that selectivity for 3a arises from its high Lewis acidity.T herefore,t oa ugment Lewis acidity,w e examined more polar solvents that would favor am ore dissociated ion pair. [20] The oxidation of less-activated aliphatic amines proceeded within standard reaction times and maintained excellent selectivity to provide valuable aliphatic nitriles possessing a-o rbbranching (products 2w,y), heteroatom substitution (products 2s,u), and readily oxidized C À Hb onds (product 2y). These results demonstrate that potent catalysts for selective amine oxidation can be generated from simple Cu salts,w hereby the counterion plays ac ritical role in controlling selectivity.T oe valuate their generality,w es urveyed arange of amines for the selective synthesis of either nitriles or imines.Inthe case of nitriles,abroad range of ortho-, meta-,a nd para-substituted benzylic amines were tolerated, including those bearing halogens (products 2d-f), electrondonating groups (products 2j,n), and electron-withdrawing groups (products 2i,m).…”