TEMPO immobilized polymeric Janus dumbbell: Assembly and catalysis at liquid-liquid interface

Abstract

Pickering interfacial catalysts (PICs) have emerged as a promising solution for simultaneously enhancing and catalyzing liquid-liquid biphasic reactions. In this study, we successfully synthesized dumbbell-shaped Janus structured polymeric nanoparticles with one side anchored imidazolium-TEMPO (im-C4-TEMPO@JPP) as Pickering interfacial catalyst for the oxidation of alcohols using the Anelli-Montanari reaction system. In the Pickering emulsion system, the im-C4-TEMPO@JPPs particles are assembled at the W/O interface due to the hydrophilicity of imidazolium-TEMPO anchored lobe which enables excellent amphiphilic character of the polymeric Janus dumbbell. Moreover, the im-C4-TEMPO@JPPs particles reduce the interfacial tension from 27.82 to 18.43 mN/m. This excellent interfacial adsorption capacity of im-C4-TEMPO@JPPs strongly stabilizes the water/dichloromethane Pickering emulsion over two months (emulsion volume fraction >90 %), thus providing an efficient reaction platform for liquid-liquid biphasic reactions. As a result, the constructed Pickering emulsion system efficiently catalyzes the oxidation of cinnamyl alcohol to cinnamaldehyde under static conditions. After 1 hour of reaction, the conversion of cinnamyl alcohol achieved 97.1 % with a selectivity of 99 %, nearly the same level relative to stirring intensified biphasic reaction. Hence, this novel PIC effectively improves the efficiency and sustainability of liquid-liquid biphasic catalytic reactions.