Sonophotocatalytic dimerization of coniferyl alcohol - The influence of energy distribution during sonication

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 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 high selectivity toward the dimeric product racemic dehydrodiconiferyl alcohol (DHCA), demonstrating remarkable stability over a 24-hour time-on-stream. For the first time, coniferyl alcohol dimers were successfully synthesized using low-powered ultrasound (at 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. The correlations between acoustic fields and catalytic properties were studied, and described. Consequently, it was demonstrated that selectivity can be controlled by modulating the sonication energy input. 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 for coniferyl alcohol dimers using conventional multi-step synthesis.