Abstract
The classical stoichiometric oxidation of alcohols is an important tool in contemporary organic chemistry. However, it still requires huge modifications in order to comply with the principles of green chemistry. The use of toxic chemicals, hazardous organic solvents, and the large amounts of toxic wastes that result from the reactions are a few examples of the problems that must be solved. Nanogold alone or conjugated with palladium were supported on different carriers (SiO2, C) and investigated in order to evaluate their catalytic potential for environmentally friendly alcohol oxidation under solvent-free and base-free conditions in the presence H2O2 as a clean oxidant. We tested different levels of Au loading (0.1–1.2% wt.) and different active catalytic site forms (monometallic Au or bimetallic Au–Pd sites). This provided new insights on how the structure of the Au-dispersions affected their catalytic performance. Importantly, the examination of the catalytic performance of the resulting catalysts was oriented toward a broad scope of alcohols, including those that are the most resistant to oxidation—the primary aliphatic alcohols. Surprisingly, the studies proved that Au/SiO2 at a level of Au loading as low as 0.1% wt. appeared to be efficient and prospective catalytic system for the green oxidation of alcohol. Most importantly, the results revealed that 0.1% Au/SiO2 might be the catalyst of choice with a wide scope of utility in the green oxidation of various structurally different alcohols as well as the non-activated aliphatic ones.
Highlights
Large amounts of alcohols can be obtained from natural and renewable sources
The powder X-ray diffraction (XRD) experiments of the catalysts were performed on a (Panalytical, Almelo, The Netherlands) that was equipped with a pixel detector using Cu Kα radiation at 40 kV and 30 mA
Taking into account the fact that different preparation methods can lead to different structural properties of the catalysts, we used the same technique to prepare all of the catalysts that were examined [14]
Summary
Large amounts of alcohols can be obtained from natural and renewable sources. They are attractive starting materials for the chemical industry. The oxidation of alcohols into their corresponding carbonyl compounds is one of the most important organic transformations because of the high value of these products in the manufacture of fine chemicals, pharmaceuticals, and special materials [1]. The classical methods of alcohol oxidation involve the use of stoichiometric amounts of toxic oxidants (such as chromates and permanganates), harmful organic solvents, and vigorous reaction conditions [2]. With the intensively growing environmental concerns and more stringent ecological standards in industry, there is an emerging quest to develop economic and efficient “green” processes for alcohol oxidation. The catalytic oxidation of alcohols that have a reusable catalytic system and environmentally benign oxidants such as O2 and H2O2 have received considerable attention owing to its low environmental impact, especially when compared to stoichiometric oxidation [3]
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