Selective Catalytic Oxidation of Ethylbenzene to Acetophenone: A Review of Catalyst Systems and Reaction Mechanisms

Abstract

Acetophenone is an important chemical intermediate often employed in the production chain of many pharmaceuticals, agrochemicals, food, and cosmetic products. It is industrially produced as a byproduct of the Hock process. However, a growing demand for acetophenone has necessitated consideration of alternative production routes. The oxidation of ethylbenzene to acetophenone (OEB-A) is one of the most considered alternatives due to the low cost and availability of ethylbenzene (EB). The EB is one of the products of refinery downstream processes that is obtained from the xylene/EB isomerization unit. Although the OEB-A reaction is considered inexpensive, it has not been of great interest due to the inert behavior of C−H bond, relatively low acetophenone selectivity, and cumbersome separation strategies for extracting acetophenone from other reaction byproducts. In this Review, we discuss the recent advances in the OEB-A reaction covering both homogeneous and heterogeneous systems. Advances in catalyst design and development including ligand design and coordination strategies and tuning of support properties have, over the years, proven to be effective in increasing acetophenone selectivity during the OEB-A process. Exploring a single-atom catalyst's definitive active centers and high atom efficiency in the OEB-A reaction has demonstrated high-throughput results, even though not well harnessed due to the challenges of controlled synthesis of single-atom metal catalyst. Solvent-free, the OEB-A reaction has demonstrated to be attractive due to its ease of product collection and environmental friendliness. Green synthesis strategies such as metal-free OEB-A reaction and CO 2 -assisted OEB-A reaction have been reviewed. The CO 2 assisted OEB-A reaction has not received the desired attention, even though considerable improvement in catalytic performance was reported. Considering the importance of carbon circular economy and the ready availability of CO 2 , the CO 2 assisted OEB-A reaction could be an interesting research focus in the near future.

Manipulation of Electronic Effect and Assembly Architecture to Invoke Oxidation of Ethylbenzene by Hierarchical Co3O4 Wreaths

“…4−6 Previous explorations have shown that homogeneous catalytic systems where catalysts can be fully dissolved in the reaction media can generally obtain good reaction results in the oxidation of EB to yield AP under mild reaction conditions, due to the enhanced interaction between catalytically active sites and substrates. 4,7,8 Despite these advantages, the features of easy separation and good recyclability strongly push scientists and engineers to put more emphasis on heterogeneous catalytic processes, which are more challenging to study and hence optimize compared with homogeneous ones. To this end, a wide range of solid catalysts have been explored for the selective oxidation of EB using different kinds of oxidants and solvents.…”

“…The selective oxidation of alkanes represents a crucial route for introducing oxygen-containing functional groups. − Typically, AP, obtained from the oxidation process of benzylic C–H of EB, serves as a popular chemical intermediate for the synthesis of value-added chemicals, such as resins, soaps, perfumes, flavorings, and plasticizers. − Previous explorations have shown that homogeneous catalytic systems where catalysts can be fully dissolved in the reaction media can generally obtain good reaction results in the oxidation of EB to yield AP under mild reaction conditions, due to the enhanced interaction between catalytically active sites and substrates. ,, Despite these advantages, the features of easy separation and good recyclability strongly push scientists and engineers to put more emphasis on heterogeneous catalytic processes, which are more challenging to study and hence optimize compared with homogeneous ones. To this end, a wide range of solid catalysts have been explored for the selective oxidation of EB using different kinds of oxidants and solvents. − Among them, some catalysts exhibited either good activity or AP selectivity, but the attainment of both high activity and selectivity in a sole catalyst is rather limited, especially with only oxygen as the oxidant and without the use of solvents.…”

Novel Cobalt(II)-Decorated 1D Covalent Organic Framework for Selective Oxidation of Ethylbenzene

“…In comparison, heterogeneous catalysis is regarded as a green and sustainable synthetic method, − which makes it a preferred option for EB oxidation. Due to variable oxidation states, many transition metals have been widely employed in catalyzed EB conversion . Among transition metals, cobalt­(II) is the one that has been extensively studied. , The catalytic activity can also be significantly improved through the synergistic interaction between different transition metal active centers .…”

Synthesis of a bistriazolyl-phenanthroline–Cu(ii) complex immobilized on nanomagnetic iron oxide as a novel green catalyst for synthesis of imidazoles via annulation reactions

“…15,16 Researchers have ingeniously coated the surface of these magnetic nanoparticles with diverse molecules, unlocking their potential in effective catalytic processes and driving significant advancements in chemical research. 17,18 The increasing focus on green chemistry aims to replace costly, hazardous, and polluting catalysts with environmentally friendly and highly stable heterogeneous catalysts. 19…”