Organocatalytic upgrading of the key biorefining building block by a catalytic ionic liquid and N-heterocyclic carbenes

The present study of rapid degradation of the key biorefining building block 5-hydroxymethylfurfural (HMF) in an ionic liquid (IL), 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc), has led to highly selective and efficient upgrading of HMF to 5,5′-di(hydroxymethyl)furoin (DHMF), a promising C12 kerosene/jet fuel intermediate. This HMF upgrading reaction is carried out under industrially favourable conditions (i.e., ambient atmosphere and 60–80 °C), catalyzed by N-heterocyclic carbenes (NHCs), and complete within 1 h; this process selectively produces DHMF with yields up to 98% (by HPLC or NMR) or 87% (unoptimized, isolated yield). Mechanistic studies have yielded four lines of evidence that support the proposed carbene catalytic cycle for this upgrading transformation catalyzed by the acetate IL and NHCs.