The role of Beta zeolites in the selective single O-demethylation of alkyl-syringols to alkyl-methoxycatechols, a novel polymer building block class

Abstract

Syringyl moieties, the primary phenols in hardwood, represent a valuable resource for bio-based product development. Despite their potential, they are currently treated mostly as waste due to the lack of effective catalytic de/functionalization methods. A promising approach involves the single O-demethylation (ODM) of syringyl derivatives, yielding methoxy-catechol moieties (MC)—vicinal hydroxyphenols with a methoxy group—that offer broad yet underexplored applications. This study achieved selective ODM of 4-methylsyringol to 3-methoxy-5-methyl benzene-1,2-diol, or 4-methyl-6-methoxy catechol (MMC) using commercially available acidic Beta zeolites, and hot pressurized water as a green solvent system. Unlike other solid acid or homogeneous catalysts, Beta zeolites exhibited high MMC selectivity (>80 mol%) facilitated by their unique 3D 12-membered ring pore structure, allowing precise stepwise ODM of 4-methyl syringol (MSyr). Additionally, this study reports, for the first time, the application of MMC epoxy-thermosets via glycidylation. The resulting high-performance resin exhibited a glass transition temperature (T_g) of 126 °C, and excellent thermal resistance, with a 5% weight loss temperature (T_d5%) of 293 °C in air. This work introduces MMC as a renewable replacement to fossil-derived phenols as a novel polymer building block.