Organocatalytic upgrading of furfural and 5-hydroxymethyl furfural to C10 and C12 furoins with quantitative yield and atom-efficiency

• Published in: International journal of molecular sciences Vol. 16; no. 4; pp. 7143 - 7158
• Main Authors: Zang, Hongjun, Chen, Eugene Y X
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 30.03.2015; MDPI
• Subjects: 09 BIOMASS FUELS; 5-hydroxymethyl furfural (HMF); BASIC BIOLOGICAL SCIENCES; Biofuels; biomass; biorefining; Catalysis; Catalysts; Chemical compounds; Chemical reactions; Chemistry Techniques, Synthetic - methods; Furaldehyde - analogs & derivatives; Furaldehyde - chemistry; furfural; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; ionic liquid; Ionic Liquids - chemistry; Molecular Structure; N-heterocyclic carbene; Organic chemicals; organocatalysis; umpolung coupling
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms16047143

There is increasing interest in the upgrading of C5 furfural (FF) and C6 5-hydroxymethyl furfural (HMF) into C10 and C12 furoins as higher energy-density intermediates for renewable chemicals, materials, and biofuels. This work utilizes the organocatalytic approach, using the in situ generated N,S-heterocyclic carbene catalyst derived from thiazolium ionic liquids (ILs), to achieve highly efficient self-coupling reactions of FF and HMF. Specifically, variations of the thiazolium IL structure have led to the most active and efficient catalyst system of the current series, which is derived from a new thiazolium IL carrying the electron-donating acetate group at the 5-ring position. For FF coupling by this IL (0.1 mol %, 60 °C, 1 h), when combined with Et3N, furoin was obtained in >99% yield. A 97% yield of the C12 furoin was also achieved from the HMF coupling by this catalyst system (10 mol % loading, 120 °C, 3 h). On the other hand, the thiazolium IL bearing the electron-withdrawing group at the 5-ring position is the least active and efficient catalyst. The mechanistic aspects of the coupling reaction by the thiazolium catalyst system have also been examined and a mechanism has been proposed.