Recent Advances in Copper Catalyzed Alcohol Oxidation in Homogeneous Medium

Abstract

The development of sustainable processes and products through innovative catalytic materials and procedures that allow a better use of resources is undoubtedly one of the most significant issues facing researchers nowadays. Environmental and economically advanced catalytic processes for selective oxidation of alcohols are currently focused on designing new catalysts able to activate green oxidants (dioxygen or peroxides) and applying unconventional conditions of sustainable significance, like the use of microwave irradiation as an alternative energy source. This short review aims to provide an overview of the recently (2015–2020) discovered homogeneous aerobic and peroxidative oxidations of primary and secondary alcohols catalyzed by copper complexes, highlighting new catalysts with potential application in sustainable organic synthesis, with significance in academia and industry.

Green Procedure for Aerobic Oxidation of Benzylic Alcohols with Palladium Supported on Iota-Carrageenan in Ethanol

“…As such, it constitutes a "green route" for alcohol oxidation that can be performed in variety of organic solvents [8,9]. Over the years, many homogeneous catalysts have been suggested for this purpose, among them systems with copper [10] and iron [11] or transition-metal complexes [12,13] based mainly on palladium or ruthenium [14,15]. Yet if the intention is to develop an environmentally friendly, simple and inexpensive industrial protocol, homogeneous systems suffer a huge drawback: separation of the metal from the reaction mixture at the end of the reaction is a complicated process in such systems, and the catalyst cannot be recycled.…”

The superiority of cuprous chloride to iodide in the selective aerobic oxidation of benzylic alcohols at ambient temperature

“…[ 4–14 ] Being inspired by the enzymatic chemistry of galactose oxidase, which is a copper‐containing protein catalysing aerobic oxidation of primary alcohols into aldehydes, [ 15,16 ] copper‐based catalytic systems, particularly cuprous systems, have been investigated in tremendous enthusiasm in the past decades. [ 5,17–31 ] In such systems, the basic combination is Cu(I) salt and a radical compound like TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl). Addition of some N‐containing compounds, for example, 2,2′‐bipyridine (BPY) and N ‐methyl imidazole (NMI), could greatly improve the catalytic efficiency of the cuprous systems.…”

Synthesis of Novel Aqua ƞ4-NNNO/Cu(II) Complexes as Rapid and Selective Oxidative Catalysts for O-Catechol: Fluorescence, Spectral, Chromotropism and Thermal Analyses

“…Copper complexes containing Schiff bases have been applied in catalytic oxidation of various types of chemical compounds including hydrocarbons [35], cyclooctene and benzylic alcohols [36][37][38]. However, the conversion rates and ease of experimental conditions were not optimum when compared to the process we report in the current work, where complete conversion of o-catechol to o-benzoquinone has been achieved in a very short time and under mild reaction conditions.…”

“…Increasing the temperature of catalytic conversion reaction from room temperature to 50 °C allowed an increase in the conversion rate and at the same time a reduction in reaction time by half (Trial 6), while the TOF was increased further by a factor of 10 at 70 It is worth mentioning that plenty of sustainable catalytic oxidation reactions have been performed in the presence of molecular oxygen and hydrogen peroxide as oxidants [31]. However, peroxide is largely used for having higher oxidation potential than oxygen [31][32][33][34][35][36][37][38]. Initially the catalytic oxidation of o-catechol to o-benzoquinone was perused using UV-Vis spectroscopy, in which in the recorded absorbance values at 358 nm of the o-benzoquinone were time dependent, measured every one minute for 20 min using complex 3 (Figure 11).…”