Sustainable Highly Selective Toluene Oxidation to Benzaldehyde

Abstract

Thanks to the well-recognized role of benzaldehyde in industry, nowadays the research of new and sustainable approaches to selectively synthesize such an interesting product is receiving great attention from the chemists’ community. In this paper, a V-based catalytic biphasic system is adopted to perform toluene oxidation to benzaldehyde. Importantly, to pursue sustainability, organic solvents have been avoided, so toluene is used as substrate and co-solvent, together with water. Also, the use of hydrophobic ionic liquids has been explored. To perform oxidation, NH4VO3 catalyst, H2O2, and a safe and inexpensive co-catalyst are used. Among the tested co-catalysts, KF and O2 were found to be the best choice, to guarantee good yields, in mild reaction conditions. In fact, with such a sustainable method, up to 30% of benzaldehyde can be obtained at 60 °C and, more interestingly, the oxidative system can be recharged, raising-up the yield. The entire process results highly selective, since no traces of benzyl alcohol or benzoic acid are detected. Hence, it constitutes a very appealing synthetic route, even suitable to be easily scaled-up at an industrial level.

Selective Oxidation of Styrene on Nanostructured Cerium Vanadate Catalyst

“…The conventional industrial synthesis process of benzaldehyde is chlorination of toluene and hydrolysis of benzyl chloride, which uses strong acid and generates chlorinated toxic side products. The benzaldehyde selectivity is thus low because of the generation of side products …”

“…The benzaldehyde selectivity is thus low because of the generation of side products. 9 In the past few years, efforts have been made to synthesize benzaldehyde in an alternative pathway, which is environmentally friendly than that of the conventional process. 10,11 In our previous work, we reported the synthesis of benzaldehyde through direct oxidation of toluene by C−H activation with a mixed metal oxide as catalyst.…”

A Stoichiometric Solvent-Free Protocol for Acetylation Reactions

“…Indeed, earth-abundant transition metals ( Zhu et al, 2018 ; Jain et al, 2019 ), solvent-free conditions ( Rajabi and Luque, 2014 ; Behera and Patra, 2021 ), and safe acylating reagents ( Singha and Ray, 2016 ; Temperini et al, 2017 ; Pantawane et al, 2021 ) have been employed. Among transition metal complexes, vanadium covers a chief role as an environment-friendly catalyst for several organic transformations, including oxidation and halogenation reactions ( Conte and Floris, 2010 ; Galloni et al, 2013 ; Floris et al, 2017 ; Coletti et al, 2018 ; Sabuzi et al, 2019 ; Sabuzi et al, 2021 ; Valentini et al, 2021 ). Moreover, various inorganic and organic vanadium (IV) complexes have been studied as catalysts in acetylation of alcohols, thiols, and amines, with high excess of acetic anhydride, eventually adding organic solvents ( Chen et al, 2001 ; Oskooie et al, 2008 ; Taghavi et al, 2011 ).…”

Stimuli-Responsive Polymer Stabilized Iron Oxide Nanoparticle as Green Catalyst for Styrene Oxidation Reaction

“…For example, styrene oxidation provides styrene oxide and benzaldehyde that are used as intermediates in a broad range of industrial products, such as perfumery, dyes, and adhesives. − Hydrolysis of benzyl alcohol and chlorination of toluene are the two traditional industrial processes that are used for synthesizing benzaldehyde. However, in these processes, a wide range of toxic chlorinated side products are produced, and strong acids are used during the reactions which cause environmental harm . Hence, in order to eradicate the disadvantages of conventional processes and make them more environmentally friendly, scientists from around the world have developed alternative pathways, including the styrene oxidation reaction. , Styrene is a carcinogenic and toxic material, and an oxidative elimination reaction of styrene can produce valuable chemicals like benzaldehyde.…”

“…However, in these processes, a wide range of toxic chlorinated side products are produced, and strong acids are used during the reactions which cause environmental harm. 6 Hence, in order to eradicate the disadvantages of conventional processes and make them more environmentally friendly, scientists from around the world have developed alternative pathways, including the styrene oxidation reaction. 7,8 Styrene is a carcinogenic and toxic material, and an oxidative elimination reaction of styrene can produce valuable chemicals like benzaldehyde.…”