Immediate hydroxylation of arenes to phenols via V-containing all-silica ZSM-22 zeolite triggered non-radical mechanism

Yu Zhou,Yonghua Du,Zhipan Ma,Wei Zhang,Jun Wang,Shibo Xi,Ning Yan,Junjie Tang,Haimeng Wen,Kai Wang

doi:10.1038/s41467-018-05351-w

Abstract

Hydroxylation of arenes via activation of aromatic Csp2–H bond has attracted great attention for decades but remains a huge challenge. Herein, we achieve the ring hydroxylation of various arenes with stoichiometric hydrogen peroxide (H2O2) into the corresponding phenols on a robust heterogeneous catalyst series of V–Si–ZSM-22 (TON type vanadium silicalite zeolites) that is straightforward synthesized from an unusual ionic liquid involved dry-gel-conversion route. For benzene hydroxylation, the phenol yield is 30.8% (selectivity >99%). Ring hydroxylation of mono-/di-alkylbenzenes and halogenated aromatic hydrocarbons cause the yields up to 26.2% and selectivities above 90%. The reaction is completed within 30 s, the fastest occasion so far, resulting in ultra-high turnover frequencies (TOFs). Systematic characterization including 51V NMR and X-ray absorption fine structure (XAFS) analyses suggest that such high activity associates with the unique non-radical hydroxylation mechanism arising from the in situ created diperoxo V(IV) state.

Highlights

Hydroxylation of arenes via activation of aromatic Csp2–H bond has attracted great attention for decades but remains a huge challenge
V–Si–ZSM-22 was synthesized in an ionic liquid templated DGC process, in which the dry gel was prepared through the co-hydrolysis/condensation of tetraethylorthosilicate (TEOS) and ammonium metavanadate (NH4VO3) under mild acidic conditions[38,39]
Kinetic isotope effect (KIE, kH/kD) for the VSZ-5 catalyzed hydroxylation of benzene was determined by competitive hydroxylation of C6H6 and C6D6 with H2O2

Summary

Introduction

Hydroxylation of arenes via activation of aromatic Csp2–H bond has attracted great attention for decades but remains a huge challenge. Heterogeneous catalysts usually demonstrated inferior activities with lower TOF, with lower selectivity for the oxidation of substituted benzene derivatives[8,17,26]. This will raise more complexities in bringing insight into the heterogeneous reaction mechanism.

Methods

Results

Conclusion