Solvent-free synthesis of MDC via sulfonic acid-functional ionic liquids-catalyzed MPC condensation

Methyl diphenylmethane dicarbamate (MDC) is a key intermediate in the non-phosgene synthesis of diphenylmethane diisocyanate (MDI), which serves as an essential raw material for polyurethane production. In this work, six triethylamine-based sulfonic acid-functionalized ionic liquids (TEA-SAILs) were synthesized and employed as catalysts for the condensation reaction of methyl phenyl carbamate (MPC) to MDC under solvent-free conditions. Among the synthesized TEA-SAILs, [TEA PS][HSO 4 ], possessing the highest acidity, exhibited excellent catalytic activity with an MDC yield of up to 84.2% and a selectivity of 93.5% under mild conditions, which compares favorably with numerous reported catalytic systems. The plausible reaction pathway for the MPC condensation catalyzed by [TEA PS][HSO 4 ] was proposed based on In-situ FT-IR experiments and DFT calculations, suggesting a nucleophilic substitution mechanism. [TEA PS][HSO 4 ] demonstrates remarkable reusability and can be efficiently recovered via simple heterogeneous separation. TEA-SAIL not only enhances reaction efficiency but also substantially reduces the required reactor volume, aligning with the principles of green and sustainable chemical manufacturing. Download: Download high-res image (196KB) Download: Download full-size image