Zeolite-catalyzed isomerization of tetroses in aqueous medium

The isomerization of erythrose (ERO) was studied in water over commercially available large-pore zeolites such as, e.g. H-Y, H-USY and H-beta. Among the employed zeolites, H-USY(6) was found to efficiently isomerize the sugar yielding 45 % erythrulose (ERU), 42 % ERO and 3 % of the epimer threose (THO) (corresponding to the equilibrium mixture), i.e. total tetrose yield 90 %, after reaction for 5-7 h at 120 °C.

Changing the solvent from water to methanol decreased the yield of ERU markedly to 18 %, and gave only a total yield of tetroses of 27 % which is significantly lower than obtained in water. Hence, the results demonstrate water to be a preferred solvent compared to lower alcohols for zeolite-catalyzed tetrose isomerization, which is opposite to what previously have been found for analogous pentose and hexose isomerization.

A reuse study revealed further that H-USY(6) could be applied in at least five reaction runs with essentially unchanged activity and without significant aluminium leaching from the catalyst. The use of benign reaction conditions and an industrially pertinent solid catalyst in combination with water establishes a new, green tetrose isomerization protocol