Modulation and Tuning of UiO-66 for Lewis Acid Catalyzed Carbohydrate Conversion: Conversion of Unprotected Aldose Sugars to Polyhydroxyalkyl and C-Glycosyl Furans

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.

Computational Mechanism of Methyl Levulinate Conversion to γ-Valerolactone on UiO-66 Metal Organic Frameworks

“…Other MOFs with similar Zr 6 O 8 nodes (MOF-808, DUT-52, and ZrF) can also catalyze this reaction with high conversion and moderate-to-good selectivity, as well as some Hf-based analogues . The improved catalytic activity obtained by MOF tuning is general and can be extrapolated to other processes, as recently demonstrated in UiO-66-catalyzed carbohydrate conversion …”

“…19 The improved catalytic activity obtained by MOF tuning is general and can be extrapolated to other processes, as recently demonstrated in UiO-66-catalyzed carbohydrate conversion. 20 These promising results encourage further mechanistic understanding for catalyst optimization. Here is where computational chemistry comes into play to provide quantum mechanical insight at the atomic level of detail.…”

“… 19 The improved catalytic activity obtained by MOF tuning is general and can be extrapolated to other processes, as recently demonstrated in UiO-66-catalyzed carbohydrate conversion. 20 …”

Synergistic Lewis acid and Pd active sites of metal–organic frameworks for highly efficient carbonylation of methyl nitrite to dimethyl carbonate

“…Since TFA in UiO-66 could be removed by activating at a higher temperature to form unsaturated Zr 6 , 42,43 NH 3 -TPD was employed to investigate the Lewis acid sites in UiO-66 x -250. As shown in Fig.…”

Selective Conversion of Malononitrile and Unprotected Carbohydrates to Bicyclic Polyhydroxyalkyl Dihydrofurans Using Magnesium Oxide as a Recyclable Catalyst

“…Our groups recently reported success in the synthesis of polyhydroxyalkyl and C -glycosyl furans from simple carbohydrates and a 1,3-dicarbonyl through the Garcia Gonzalez reaction, − , which gives products with great promise as precursors for platform chemicals, value-added chemicals, pharmaceutical intermediates, and materials. − First, using ZrCl 4 as an efficient homogeneous Lewis acid catalyst, we followed that report with the subsequent development of zirconium terephthalate-based metal–organic frameworks (MOFs) as heterogeneous catalysts for the same transformation …”