Using Mechanochemistry to Activate Poly(vinyl chloride) as a Mechanotunable Brønsted-Acid-Releasing Reagent for Organic Synthesis

Mechanical force has the potential to activate thermodynamically and chemically stable molecules, enabling unique reactions to proceed with lower activation energies compared to those of conventional thermal activation pathways. However, the practical utility of such force-driven transformations in synthetic chemistry remains to be demonstrated. In this study, we developed a mechanochemical strategy for the facile activation of poly(vinyl chloride) (PVC), a stable plastic material, as a convenient and practical hydrochloric acid (HCl)-releasing reagent. Although HCl can be generated from PVC via thermal decomposition processes, elevated temperatures (>250 °C) are required, which restrict their practical applications in chemical synthesis. In contrast, our mechanochemical approach leverages the mechanical energy generated via ball milling to induce the homolytic cleavage of the polymer chains, producing HCl under mild conditions. Preliminary calculations support that our proposed force-induced mechanoradical-related mechanism generates HCl with lower activation energies than thermal activation. Inspired by this finding, we demonstrate the applicability of PVC as a mechanotunable Brønsted-acid-releasing reagent to facilitate direct S N 1-type substitution reactions of allylic and benzylic alcohols with electron-rich (hetero)aromatics, amines, and alcohols as nucleophiles under mild, solvent-free, and moisture-tolerant mechanochemical conditions. Moreover, these reactions proceeded efficiently using PVC-based plastic waste, such as PVC tubing. Beyond the immediate utility of this protocol, this work can be expected to inspire the development of mechanochemical approaches to activate stable, abundant commodity plastic materials for their valorization as chemical reagents in the synthesis of high-value molecules.