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

Recent strides towards greater sustainability in materials and energy production have led to a resurgence in the study and utilisation 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.