Single-Walled Zeolitic Nanotube-Poly(oxazoline) Nanocomposites as Heterogeneous Catalysts for Acid-Base Cascade...

Zeolites with a unique, 1-dimensional form factor were recently discovered - zeolite nanotubes (ZNTs). Here we describe the synthesis and characterization of NaH-ZNT-poly(oxazoline) composites targeting liquid-phase acid-base cascade catalysis. NaH-ZNT, a one-dimensional zeolite analogue with mesoporosity (3-4 nm) associated with nanotubes and inherent Brønsted acid sites associated with the microporous zeolite domains, is functionalized with poly(oxazoline)-based triblock copolymers with varying molecular weights (3-17 kDa). The composites are characterized using N₂ sorption, STEM, FTIR, and elemental analysis, confirming successful grafting and preservation of the zeolite nanotube structure. The composites' catalytic performance is evaluated through separate acid and base reactions, followed by a combined cascade of a deacetalization-Knoevenagel condensation for the synthesis of chalcone compounds. High initial reaction rates are demonstrated, but modest overall cascade product formation rates are observed, attributed to interactions between Brønsted acid sites and base amine groups that occur in the polymer-grafted systems. Physical mixtures of NaH-ZNT-SH and poly(oxazoline)s, lacking covalent linkages between ZNT and the polymer, support this supposition. This work demonstrates the potential of NaH-ZNT-poly(oxazoline) composites for liquid-phase cascade catalysis for synthesizing compounds of potential medicinal interest, highlighting the benefits of the grafting-to approach as well as the need for further optimization of the catalytic performance.