Abstract

This communication presents a novel and sustainable approach to organic synthesis based on the sonophotocatalytic dimerization of coniferyl alcohol. The sonophotocatalytic approach synergistically integrates ultrasonic cavitation with light-induced activation, significantly enhancing reaction efficiency and selectivity compared to conventional methods, which require multi-step procedures. Under optimized conditions, a chitosan-lignin-based hybrid catalyst and/​or a ZnO catalyst functionalized with Cu achieved 100% conversion of coniferyl alcohol with a high selectivity toward dimeric products – racemic dehydrodiconirefyl alcohol (DHCA), demonstrating remarkable stability over time-on-stream of 24 hours. For the first time, coniferyl alcohol dimers were successfully synthesized using low-powered ultrasound (at an ambient temperature and pressure) instead of the harsher conditions typically required in traditional dimerization reactions, such as high temperatures, elevated pressures, and the use of oxidizing agents or toxic catalysts. For the first time, the correlation between acoustic fields, energy distribution and catalytic properties were studied and described. As a consequence, it was proved that the control of selectivity can be achieved by changing the power energy of sonication. The hybrid catalyst combines the renewable nature of lignin and/​or the sonophotocatalytic properties of ZnO, as well as the catalytic activity of copper. The dimeric products obtained possess considerable value for pharmaceutical and chemical applications. This methodology represents a paradigm shift toward sustainable organic synthesis, valorizing lignocellulosic waste, as well as the production of valuable chemicals through environmentally benign catalytic processes. The approach aligns with circular economy principles and offers an alternative for the synthesis of coniferyl alcohol dimers using conventional multi-steps synthesis.