Fabrication of copper silicate microspheres using rice husk ash and its application for dearomatization of phenol derivatives

In the present study, tubular copper silicate microspheres (CuSi-NTMs) were hydrothermally synthesized using high-silicon rice husk ash (RHA) as the raw material. Structural characterization reveals CuSi-NTMs have abundant mesopores, with a larger pore volume (0.367 cm³ g^-1) and specific surface area (375 m² g^-1) than the precursor RHA, facilitating active component dispersion. As expected, CuSi-NTMs exhibited superior catalytic performance in the dearomatization reaction between phenol derivatives and azodicarboxylates compared to other copper-based catalysts, achieving a 98% yield. The steric hindrance and electronic effects of phenolic substituents were also investigated. An ionic catalytic mechanism for CuSi-NTMs has been proposed. Cu(ii) coordinates with the phenolic hydroxyl group to activate its para-position. Then, the activated phenol undergoes a Michael addition with the N[double bond, length as m-dash]N group and deprotonates, resulting in the formation of cyclohexadienone derivatives. Additionally, preparative scale synthesis of cyclohexadieneone has been demonstrated.