CuMgAl layered double hydroxide-catalyzed oxidative coupling of 2,6-di-tert-butylphenol to tetra-tert-butylbiphenyldiquinone

Abstract

Tetra-tert-butylbiphenyldiquinone (TBDPQ) is a valuable electron-transport material, yet its selective synthesis from hindered phenols remains challenging. Herein, a CuMgAl layered double hydroxide (CuMgAl-LDH) catalyst prepared by co-precipitation is reported for the oxidative coupling of 2,6-di-tert-butylphenol (2,6B) to TBDPQ using molecular oxygen. Characterization by XRD, TEM, and XPS confirms uniform incorporation of Cu²⁺ into the LDH framework, forming well-dispersed HO–Cu²⁺–OH active sites. Under optimized conditions (5 g 2,6B, 60 g n-octanol, 1 g catalyst, 180 °C, 0.55 MPa O₂, and 1 h), 97.3% conversion and 83.3% TBDPQ selectivity are achieved, with minimal C–O coupling by-products. The product is easily isolated by centrifugation and crystallization, yielding 93.4% purity. The catalyst outperforms homogeneous copper salts in selectivity and recyclability, offering a green and efficient route to TBDPQ. A plausible mechanism involves Cu²⁺-mediated phenoxy radical formation followed by Claisen-type C–C coupling.