Intermediate Stabilization by Quaternary Ammonium Salts for One-Pot Synthesis of 5-Methoxymethylfurfural

The high production cost and inherent instability of 5-hydroxymethylfurfural (HMF) present major bottlenecks for the scalable synthesis of 5-methoxymethylfurfural (MMF), a promising biobased fuel additive and platform chemical. To address this, we propose a novel and cost-effective one-pot strategy that incorporates quaternary ammonium salts as stabilizers within a dimethyl carbonate (DMC)−methanol solvent system catalyzed by Amberlyst-15. This approach effectively suppresses the degradation of the HMF intermediate during the tandem conversion of fructose, achieving an MMF yield of 77.2% under the optimized conditions. Mechanistic investigations by Fourier transform infrared and 1H nuclear magnetic resonance spectroscopy confirm that the quaternary ammonium stabilizers coordinate with the hydroxyl and aldehyde groups of HMF through electrostatic interactions, thereby shielding it from hydration and enhancing etherification selectivity. Thus, it achieves the necessary intermediate stabilization without the economic and separation penalties of conventional DMSO or ionic liquid systems, providing a practical foundation for developing an economically viable route to MMF production.