Sustainable Mechanochemical Oxidation Of Benzylic Alcohols

The aim of this work is to develop a new sustainable protocol for oxidizing alcohols into carbonylic compounds through a mechanochemical catalysed reaction. Selective oxidations are pivotal reactions in the chemical industry; however, they produce large amounts of waste and perform poorly in terms of green metrics 1. Mechanochemistry is a tool used by chemists to achieve more sustainable chemical processes2 and to facilitate catalytic activation of reactions 3. In this work, preliminary studies have shown that p-OH-benzyl alcohol can be selectively oxidised into the corresponding aldehyde using a mechanochemical protocol with different copper-supported catalysts and TEMPO. The reaction proceeds in 3 hours achieving approximately 80% conversion (Figure 1). The procedure is straightforward: first, the solid alcohol is placed in the milling vial along with TEMPO and a copper-supported catalysts and then the mixture is subjected to ball milling. After that, the aldehyde can be easily extracted with a small amount of solvent. Compared to the solution-phase synthesis, this method requires less time and energy and generates no byproducts. In addition, the green assessment 4,5 reveals that the mechanochemical route exhibits improved metrics compared to the solution-phase synthesis using the same reagents.