Heterogeneous Base‐Catalyzed Conversion of Glycolaldehyde to Aldotetroses: Mechanistic and Kinetic Insight

Abstract

Recent strides towards greater sustainability in materials and energy production have led to a resurgence in the study and utilization of carbohydrates. Opposite to C6 and C5 carbohydrates, C4 carbohydrates (tetroses) are much less accessible from biological sources. A promising approach for the production of C4 carbohydrates is the cracking of C6 carbohydrates to C2 fragments, and the subsequent combination of two C2 fragments to tetroses. Here, we show that the suitable choice of reaction conditions can kinetically stabilize the rare aldotetroses threose (THR) and erythrose (ERY). The latter approach yields THR and ERY at high selectivity under benign conditions, using commercial resins with tertiary amine groups as the catalyst. Isotope incorporation into GA in D2O solvent is introduced as a reference reaction to probe the competitive formation of aldotetroses and deuterated GA from a low‐populated, not directly detected enediol intermediate that is formed in the rate‐determining step. Reaction progress tracked in situ by NMR and ex situ by chromatography validates that the overall conversion is of first order with respect to GA due to the slow initial enolization. Cyclization of the aldotetroses slows their further conversion to thermodynamically more stable erythrulose and C6 sugars.

Deactivation and Reductive Regeneration of Sn-Beta for Liquid-Phase Biomass Conversion

“…However, heating in the presence of Brønsted/Lewis acids leads to GADMA formation. 41,47 Therefore, GADMA can be regarded as "unconverted" GA reactant. Consistent with previous studies, we did not detect substantial amounts of intermediate tetroses, implying that GADMA hydrolysis is the rate-determining step.…”

“…The free aldehyde form of GA is seldom present in solution, as hydrates tend to prevail in water, whereas the hemiacetal form (GAHA) dominates when the solvent is an alcohol. However, heating in the presence of Brønsted/Lewis acids leads to GADMA formation. , Therefore, GADMA can be regarded as “unconverted” GA reactant. Consistent with previous studies, we did not detect substantial amounts of intermediate tetroses, implying that GADMA hydrolysis is the rate-determining step .…”

Tailoring the Formation of Functionalized Furans from Glucose in Water with Nature-Sourced Catalysts and In Situ NMR

“…Carbohydrates, especially glucose monomers, are ubiquitous products of natural CO 2 sequestration that hold great potential as sustainable building blocks for a future sustainable society [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. While many dehydration [ 9 , 10 , 11 , 12 , 13 ] or isomerization [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ] reactions seek to upgrade glucose to flexibly usable precursors either without modification of the carbon chain or by its cleavage, unlocking the full potential of carbohydrates as building blocks often requires extending their carbon chain [ 3 , 21 , 22 , 23 ]. Carbon chain extension hinges on C-C bond formation usually at the anomeric carbon, where the Knoevenagel reaction between an aldose and activated methylene groups offers a promising approach for selectively extending carbohydrate chains in water [ 24 , 25 , 26 , 27 ].…”

Probing the Role of Individual OH Sites in Carbohydrate Conversion Suggests Strategies for Increasing Product Selectivity and Avoiding Humins

“…Pathway usage and product yields can be easier optimized for smaller carbohydrates (C2–C4) than for the naturally abundant C5 and C6 carbohydrates − due to the presence of fewer functional groups and the absence or limited ability to form cyclic structures in smaller carbohydrates. In contrast, C5 and especially C6 carbohydrates are naturally abundant and are more easily accessible in pure, cheap form.…”