Dimethylaluminum complexes bearing bidentate phenoxy-amine ligands (LRAlMe2) were prepared in high yields and characterized by spectroscopic methods and elemental analysis. Efficient aluminum catalysts for glucose dehydration to 5-hydroxymethylfurfural (HMF) were generated through modification of the (aminomethyl)phenolate ligand. LRAlMe2 where R is an aryl substituent on the amino moiety of the (aminomethyl)phenolate ligand are efficient catalysts for glucose dehydration to HMF in ionic liquid solvents. In [EMIM]Br and [BMIM]Br, the reaction proceeds at 120 °C to very high conversion in 2 hours to produce HMF with 60-63% selectivity and in 58-60% yield. These complexes efficiently catalyze glucose isomerization to fructose at ≥120 °C. Nevertheless, HMF yield is determined by HMF selectivity of fructose dehydration, with HMF loss to humin formation being the competing side reaction. These results indicate that additional studies of ancillary ligand effects on aluminum catalyzed glucose dehydration are needed to improve knowledge of structure-function relationships that are key to increasing the efficiency of aluminum catalysts for dehydration of glucose (and ultimately cellulose) to HMF.

Catalytic dehydration of glucose and fructose into 5-hydroxymethylfurfural by aluminum complexes bearing bidentate (aminomethyl)phenolate ligands

254th National Meeting (2017)

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