Rational Designed Polymer as a Metal-Free Catalyst for Hydroxylation of Benzene to Phenol with Dioxygen
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Rational Designed Polymer as a Metal‑Free Catalyst for Hydroxylation of Benzene to Phenol with Dioxygen Weitao Wang1 · Yaoyao Wei1 · Xulu Jiang1 · Zhen‑Hong He1 · Cunshe Zhang2 · Zhao‑Tie Liu1,3 Received: 23 July 2020 / Accepted: 4 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Direct hydroxylation of benzene to phenol with dioxygen is a green route for synthesis of phenol. The higher bonding energies of C–H in benzene and O–O in dioxygen make metal-free catalysis a challenge. A novel metal-free catalyst of quinone-cylcohexanone-formaldehyde polymer was rationally designed and prepared. The polymer was characterized with FT-IR, XRD, Raman, SEM, 13C NMR and XPS. Abundant oxygen functional groups of cyclic ketonic, quinone carbonyl and hydroquinone were found on the surface of polymer. The catalytic performances for hydroxylation of benzene to phenol with dioxygen over the metal-free catalyst were investigated and a phenol yielding of 11.4% was achieved. Moreover, the reaction mechanism was proposed. Graphic Abstract
Keywords Green chemistry · Catalysis · Aerobic oxidation · Liquid-phase oxidation · Partial oxidation · Hydroxylation · Benzene · Metal-free catalysis
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10562-020-03392-9) contains supplementary material, which is available to authorized users. * Weitao Wang [email protected] * Zhao‑Tie Liu [email protected] 1
Shaanxi Key Laboratory of Chemical Additives for Industry, College of Chemistry & Chemical Engineering, Shaanxi University of Science & Technology, Xi’an, Shaanxi 710021, China
2
Shaanxi Key Laboratory of Petroleum Fine Chemicals, Shaanxi Provincial Research and Design Institute of Petroleum and Chemical Industry, Xi’an, Shaanxi 710054, China
3
School of Chemistry & Chemical Engineering, Shaanxi Normal University, Xi’an, Shaanxi 710119, China
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1 Introduction Phenol is an important intermediate in chemical industry [1] and it is industrially prepared by an isopropyl benzene process in three steps. However, this synthetic method has some disadvantages, such as long process flow, by-product of acetone and waste water containing phenol [2]. The direct hydroxylation of benzene to phenol with O2 is a green route for preparation of phenol due to its high atomic economy, low cost and easy availability of O2. Oxygen is widely used as an oxidant for hydroxylation of benzene to phenol. However, direct hydroxylation of benzene to phenol is still a challenge due to the higher bonding energies of C–H and O–O in benzene and O2 [3–5]. Rational designed catalyst with specific active sites is a key to explore the catalytic system for direct hydroxylation of benzene to phenol with dioxygen. Redox transition metals as the active center for benzene hydroxylation reaction are widely reported, mainly the V, Cu, Fe, Pd, polyoxometalate based catalysts [6–14]. With molecular oxygen as the oxidant, metal-based catalysts usually gav
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