Hollow, mesoporous, eutectic Zn1−xMgxO nano-spheres as solid acid–base catalysts for the highly regio-selective O-methylation of 1,2-diphenols

Abstract

The highly regio-selective O-methylation of catechol with dimethyl carbonate (DMC), catalyzed by a solid acid–base catalyst, is an environmentally friendly chemical process for industrial production of guaiacol. However, a guaiacol yield below 84% and high reaction temperature above 280 °C limit its industrial application. Here, hollow, mesoporous Zn_1−xMg_xO nano-spheres with a eutectic structure, denoted as Zn_1−xMg_xO HMNSs (x = 0.012–0.089), are facilely fabricated via the calcination of Mg²⁺/Zn²⁺ ion-adsorbing carbon spheres at 500 °C in air. In the O-methylation of catechol with DMC at 180 °C, Zn_1−xMg_xO HMNSs (x = 0.052) afford guaiacol in 95.5% yield with a complete catechol conversion. Furthermore, 89.0–95.3% mono-ether yields with high 1,2-diphenol conversions (94.5–100%) are also obtained for the other 1,2-diphenols bearing –CH₃ and –Br groups. Moreover, a plausible mechanism for highly selective O-methylation of catechol with DMC is proposed, in which the single-site activation and double-site activation of phenolic hydroxyls by the basic oxygen of Mg–O afford guaiacol and veratrole, respectively.