Ionic liquid catalysts for dehydrochlorination: Stability, reaction mechanism, and catalyst optimization

The catalytic alkaline dehydrochlorination process, characterized by high atom economy, stands as a prevalent method in the synthesis of valuable alkene halides. Nonetheless, the efficacy of ionic liquids (ILs) as catalysts for dehydrochlorination is hindered by challenges such as swift deactivation attributed to decomposition and reduced selectivity without clear causative factors. This investigation employs a systematic approach, integrating Density Functional Theory (DFT) simulations with experimental methodologies, to delve into the mechanisms of IL-catalyzed dehydrochlorination, aiming to elucidate both stabilization strategies and catalytic pathways. The examination of thermal decomposition rates is rooted in a meticulous assessment of the energy barriers associated with decomposition and dissociation processes. The active role of free Cl − is established, albeit its acidification by HCl, which results in diminished catalytic activity. To counteract this acidifying influence, a novel active site denoted as [Cl-KCl] − is conceptually devised to mitigate such effects. Through the strategic implementation of cationic fixation, the IL-KCl combination catalyst is synthesized and empirically confirmed to demonstrate augmented acid resistance while upholding a consistent reaction selectivity of approximately 85 %. This contrasts starkly with the declining catalytic selectivity observed with IL in isolation, plummeting from 85% to 65%. Consequently, the IL-KCl combination catalyst emerges as a promising option for alkali catalyzed dehydrochlorination, offering enhanced stability and sustained high selectivity throughout the catalytic process.