Kinetic model for the dehydration of xylose to furfural from a boronate diester precursor

A comprehensive kinetic model describes the dehydration of xylose starting from the boronate diester-protected xylose (PBA₂X). The model incorporates (de)esterification of PBA₂X, partitioning, and xylose dehydration, and aims to evaluate the effects of the solvent system on these steps. The model explores the effect of the water contents in monophasic solvent systems, and that of ionic strength and mixing in biphasic aqueous-organic systems. At low water content, hydrolysis of PBA₂X is the rate-limiting step, while xylose dehydration is fast. Conversely, in a monophasic three-solvent system, where the water content is higher, complete hydrolysis of the diester is achieved quickly. Under biphasic conditions, xylose dehydration is fast at high ionic strengths, but the slower partitioning/hydrolysis of PBA₂X results in an overall slower furfural production. Furthermore, the observed different but high, constant xylose-to-furfural selectivities observed experimentally are tentatively ascribed to a higher order of parallel side-product formation.