Seeking new chemo-catalytic routes to produce glyceric
acid using
renewable biomass-based sugar as feedstock is of significance but
remains a big challenge due to a quite low yield (<5%). Herein,
we prepare an MgO catalyst with an oxygen vacancy and explore a simple
but robust MgO–NaBF4 system, achieving the selective
production of glyceric acid from fructose with a high yield of 78.8%
in an O2 atmosphere via chemo-catalysis at mild conditions
(373 K), eliminating the use of strong inorganic alkalis and severe
reaction conditions. As far as we know, this has the highest value
among the state-of-the-art chemo-catalytic strategies. Evidenced by
the isotope-probe experiment and theoretical calculation, it was revealed
that MgO and NaBF4 exhibited pronounced cooperative effects.
The hydroxyl group exposed on the MgO surface first facilitated the
adsorption of fructose. With the assistance of MgO, B(OH)4
– from NaBF4 hydrolysis preferentially
combined with β-d-fructofuranose, as evidenced by 11B and 13C NMR spectroscopy, due to its strong
electron-withdrawing ability, producing a complex which could easily
undergo ring-opening reaction with an attack of OH– derived from the alkaline MgO. More importantly, the oxygen vacancies
on the MgO surface subsequently assisted the C3–C4 cleavage
in fructose by MgO species to produce a glyceraldehyde intermediate
and activated O2 to oxidize glyceraldehyde, yielding glyceric
acid. The conjunction of B(OH)4
– with
a glyceraldehyde intermediate or glyceric acid could also hinder its
over-oxidation. The insights in this work might provide new chemo-catalytic
approaches for glyceric acid production from renewable biomass.