Modulation and Tuning of UiO-66 for Lewis Acid Catalyzed Carbohydrate Conversion: Conversion of Unprotected Aldose Sugars to Polyhydroxyalkyl and <i>C</i>-Glycosyl Furans
Nima Ronaghi, Danny Shade, Hyun June Moon, Sean Najmi, Jacob W. Cleveland, Krista S. Walton, Stefan France, Christopher W. Jones
Abstract
Trifluoroacetic acid-modulated UiO-66 metal–organic frameworks (MOFs) are used to catalyze the reaction of unprotected aldose sugars with acetylacetone to polyhydroxyalkyl and C-glycosyl furans, known as the Garcia Gonzalez reaction. The effects of trifluoroacetic acid (TFA) modulation, linker substitution, and MOF activation temperature on the pore structure and catalytic activity are evaluated. Differing trends in activity and thermal stability are observed for MOFs with ligand substitutions vs ones without. Optimal MOF activation temperatures vary based on linker substitution, though both substituted and unsubstituted linkers give rise to catalysts with high activity. Catalytic tests using sugars of different sizes suggest catalysis occurs in the micropores and/or mesopores of the MOF, though deposition of carbonaceous species on the MOF limits catalyst recyclability. The MOF system leads to improved product yields and different ratios of cyclized to uncyclized products compared to a homogeneous zirconium salt catalyst under similar conditions, suggesting the MOF catalysts may offer synthetic utility.