The Role Played by Ionic Liquids in Carbohydrates Conversion into 5-Hydroxymethylfurfural: A Recent Overview

Abstract

Obtaining industrially relevant products from abundant, cheap, renewable, and low-impacting sources such as lignocellulosic biomass, is a key step in reducing consumption of raw fossil materials and, consequently, the environmental footprint of such processes. In this regard, a molecule that is similar to 5-hydroxymethylfurfural (5-HMF) plays a pivotal role, since it can be produced from lignocellulosic biomass and gives synthetic access to a broad range of industrially important products and polymers. Recently, ionic liquids (ILs) have emerged as suitable solvents for the conversion of biomass and carbohydrates into 5-HMF. Herein, we provide a bird’s-eye view on recent achievements about the use of ILs for the obtainment of 5-HMF, covering works that were published over the last five years. In particular, we first examine reactions involving homogeneous catalysis as well as task-specific ionic liquids. Then, an overview of the literature addressing the use of heterogeneous catalysts, including enzymes, is presented. Whenever possible, the role of ILs and catalysts driving the formation of 5-HMF is discussed, also comparing with the same reactions that are performed in conventional solvents.

Highly Efficient and Selective Preparation of 5-Hydroxymethylfurfural from Concentrated Carbohydrates Using Deep Eutectic Solvents

“…Next, the catalytic performances of DESs were evaluated in the presence of TsOH, which is an effective Brønsted acid for fructose dehydration . As shown in Figure b,c, negligible HMF yields are obtained in TEABF 4 and TEAOtf, possibly due to the reduced coordination capacity of the anions . Although Brønsted acid is an effective catalyst for fructose dehydration, acidic TEAHSO 4 results in a poor yield (31%).…”

“…32 As shown in Figure 2b,c, negligible HMF yields are obtained in TEABF 4 and TEAOtf, possibly due to the reduced coordination capacity of the anions. 33 Although Brønsted acid is an effective catalyst for fructose dehydration, acidic TEAHSO 4 results in a poor yield (31%). This phenomenon might be explained by the increased side reactions caused by the excessive acid concentration.…”