A Comparative study of various methods for the synthesis of o-methyl eugenol via methylation reaction

Abstract:

The synthesis of o-methyl eugenol (methyl eugenol) from eugenol via O-methylation reactions has garnered significant attention in green chemistry literature, with conventional thermal, microwave-assisted, and light-assisted methods emerging as versatile strategies for sustainable production. Eugenol extraction from clove sources typically involves hydrodistillation (70-90% yield), followed by purification through vacuum distillation or chromatography to attain analytical purity. Conventional thermal methylation employs dimethyl carbonate (DMC) with K₂CO₃  under reflux (140°C, 3 h), achieving 90-96% yields of methyl eugenol post-workup, supplanting toxic reagents like dimethyl sulfate for industrial viability. Microwave-assisted protocols enable rapid, solvent-free conversion using dimethyl sulfate, K₂CO₃ and alkali bases,  phase-transfer catalyst (20-50 s irradiation), selectively affording methyl eugenol or its isoeugenol isomer via distillation purification.Light-assisted approaches, Dimethyl carbonate was used as a safer alternative to toxic methylating agents, along with mild bases and suitable catalysts to promote the reaction efficiently, offering mild alternatives adaptable to eugenol substrates. The final product was confirmed using analytical techniques such as IR, and NMR. This review synthesizes these methodologies, underscoring thermal processes for scalability, microwave for expedition, and photochemistry for eco-compatibility. Despite advances, dedicated reviews remain scarce, highlighting opportunities for optimized, catalyst-driven innovations in flavor-fragrance synthesis while adhering to green principles—reagent minimization, energy efficiency, and waste reduction—to meet pharmaceutical and perfumery demands.