Microwave‐Assisted Synthesis of 5‐Hydroxymethylfurfural Using Imidazole‐Based Ionic Liquid Catalyst

ABSTRACT A series of sulfonic acid‐functionalized ionic liquids (ILs) bearing different counter anions was synthesized using imidazole (IM) or 1‐methylimidazole (MIM) as the cation, functioning effectively as Brønsted acid catalysts. Synthesized ILs exhibit distinct characteristic properties, which offer advantages in various aspects. Microwave‐assisted fructose dehydration was examined for a series of ILs in IPA (isopropyl alcohol), which has a low‐boiling point (LBP) and is a reaction medium. Of the tested series of ILs, 1‐methylimidazole‐based IL having p ‐TsOH ( p ‐toluene sulfonic acid) anion showed excellent performance for fructose dehydration as well as the characteristic “smart” property of solidification at room temperature, which contributed to the ease of separation. Additionally, an intensification study was conducted to investigate the impact of reaction parameters. Reactions under optimized conditions of 120°C in IPA as a reaction medium and 120 s reaction time yielded a maximum of 62% for HMF and 95% fructose conversion. The [Benz‐SO 3 H MIM] + [OTs] − was successfully recycled and reused due to its “smart” properties, showing consistent performance in terms of yield and conversion across five recycle runs. The use of “smart” ILs for 5‐hydroxymethylfurfural (5‐HMF) synthesis facilitates easy product separation with higher yield. It provides an added advantage of ease of recycling and separation, thereby contributing to a reduction in the overall production cost at a larger scale.