Copper-Containing Catalysts for Azide–Alkyne Cycloaddition in Supercritical CO2

Abstract

Background: Chemical industry has increased the investment into and innovation capacity to supply chemicals from safe and sustainable sources, which will be essential to offering new solutions and supporting the green transition of the global economy and society. In this sense, the use of green solvents and reusable heterogeneous catalysts has emerged as a promising sustainable process strategy for engineering, chemistry and the environment. In this work, different homogeneous (copper bromide, CuBr and copper(II) acetate, Cu (CH3COO)2·H2O) and heterogeneous (Cu Wire, Cu Plate, Cu/β-SiC, pre-treated Cu Wire and pre-treated Cu Plate) copper catalysts were tested for the copper(I)-catalyzed alkyne–azide cycloaddition (CuAAC) reaction. In addition, the influence of different reaction media was analyzed, comparing the use of an organic solvent such as toluene and a green solvent such as supercritical CO2 (scCO2). Methods: Characterization of the catalysts includes by X-ray diffraction (XRD), Scan Electron Microscopy (SEM), Atomic absorption spectrophotometry (AA) and Temperature Programmed Reduction (TPR). Parameters such as catalyst loading, reaction time, reusability and leaching of the catalysts were studied to obtain more information on the CuAAC reaction in scCO2. Results: The pre-treated copper plate achieved a 57% increase in reaction yield compared to the non pre-treated copper plate. However, the recovery and reuse of the pre-treated copper plate showed a severe deterioration and a considerable change in its surface. Cu Wire (without pre-treatment) achieved yields of up to 94.2% after reusing it for five cycles. Conclusions: These results suggest the possibility to exploit the combination of heterogeneous catalysts and scCO2 and justify further research to highlight green solvents and simultaneously address the challenges of reaction, purification and recycling.

Modulating the coordination microenvironment of uranyl compounds to enhance photocatalytic CO2 reduction

“…48,57 Finally, Cu 2+ undergoes comproportionation with the adjacent unreacted Cu 0 and returns to the original state of Cu + . 58,59…”

“…48,57 Finally, Cu 2+ undergoes comproportionation with the adjacent unreacted Cu 0 and returns to the original state of Cu + . 58,59 The UCu2 photocatalytic CO 2 reduction pathway involves the following reactions:…”

A New Insight Into The Huisgen Reaction: Heterogeneous Copper Catalyzed Azide‐Alkyne Cycloaddition for the Synthesis of 1,4‐Disubstituted Triazole (From 2018–2023)

“… [37,38] Various copper based catalysts have been employed for the synthesis of 1,2,3‐triazoles, including CuSO 4 , CuI, Cu 2 O, (PPh 3 ) 3 CuBr, CuFe 2 O 4 nanoparticles, Cu−Fe bimetals, imidazole‐Cu(II), Cu/C, Cu/SiO 2 , and polymer‐modified Cu/Cu 2 O [39–41] . Typically, Cu + salts or the reduction of Cu 2+ ions are utilized as homogeneous catalysts in the regioselective alkyne‐azide cycloaddition (AAC) reaction [42] . However, the instability and low solubility of simple copper(I) salts in many reaction solvents, particularly organic ones, present a considerable obstacle [43] .…”

“…[39][40][41] Typically, Cu + salts or the reduction of Cu 2 + ions are utilized as homogeneous catalysts in the regioselective alkyne-azide cycloaddition (AAC) reaction. [42] However, the instability and low solubility of simple copper(I) salts in many reaction solvents, particularly organic ones, present a considerable obstacle. [43] Instead, the active copper species are frequently produced insitu using copper(II) salts and a reducing agent such as sodium ascorbate.…”