Distinctive aldose isomerization characteristics and the coordination chemistry of metal chlorides in 1-butyl-3-methylimidazolium chloride

Article abstract of DOI:10.1021/cs5012684

The catalytic isomerization of aldoses to ketones is an important fundamental step for the transformation of cellulosic biomass to biobased chemicals and liquid fuels. The results of this work reveal for the first time the distinctive coordination chemistry features of four classes of metal chlorides, CrCl₃, VCl₃, FeCl₃, and PtCl₂ in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), that are well correlated to the drastically different catalytic performances of the metal chlorides in the isomerization of glucose. The relative bond strengths and the number of ligands to which the metal ions are coordinated by oxygen atoms of di fferent sources and by chloride were studied by probing model compounds with in situ far-infrared (FIR) and by reaction studies. The superior performance of CrCl₃ for this reaction is now distinguished from that of other metal chlorides, on the basis of its selective Cr(III) ene-diol coordination chemistry. We also offer new insights into the mechanism involved in the conversion of glucose to 5-hydroxymethylfurfural (5-HMF). In situ FIR is established as a powerful tool in the study of the coordination chemistry of metal complexes in ionic liquids. (Chemical Equation Presented).