Copper on Calcium Carbonate and Marble Waste as Recyclable Catalysts for Ultrasound-Assisted One-Pot Synthesis of...

A simple heterogeneous copper catalyst was prepared by adsorbing Cu(II) ions from an aqueous CuSO₄ solution onto calcium carbonate (CaCO₃) and marble waste microfine dust from the Carrara production area. The resulting materials (CaCO₃-Cu and Carrara-Cu) were characterized by FTIR, PXRD, SEM-EDX, TGA, and zeta potential measurements, confirming copper uptake while preserving the carbonate framework. The catalytic activity of the materials was evaluated in the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Using glucose as a reducing agent, the reactions were performed in water under ultrasound irradiation at 30 °C, generating the active Cu(I) species in situ. A model three-component reaction between benzyl bromide, sodium azide, and phenylacetylene afforded the corresponding 1,4-disubstituted 1,2,3-triazole in 81% isolated yield after 1 h. The scope of the methodology was evaluated across a range of substituted aryl alkynes and benzyl bromides as reaction partners, affording the corresponding triazoles in moderate to good yields. The catalyst was recovered by simple filtration and reused in subsequent reaction cycles. The use of water as the reaction medium, mild operating conditions, catalyst recyclability, and the successful application of marble waste as a catalyst support make this methodology a practical and sustainable approach for the synthesis of 1,2,3-triazoles.