Direct Production of 5‐Hydroxymethylfurfural via Catalytic Conversion of Simple and Complex Sugars over Phosphated TiO2

Abstract A water–THF biphasic system containing N ‐methyl‐2‐pyrrolidone (NMP) was found to enable the efficient synthesis of 5‐hydroxymethylfurfural (HMF) from a variety of sugars (simple to complex) using phosphated TiO 2 as a catalyst. Fructose and glucose were selectively converted to HMF resulting in 98 % and 90 % yield, respectively, at 175 °C. Cellobiose and sucrose also gave rise to high HMF yields of 94 % and 98 %, respectively, at 180 °C. Other sugar variants such as starch (potato and rice) and cellulose were also investigated. The yields of HMF from starch (80–85 %) were high, whereas cellulose resulted in a modest yield of 33 %. Direct transformation of cellulose to HMF in significant yield (86 %) was assisted by mechanocatalytic depolymerization—ball milling of acid‐impregnated cellulose. This effectively reduced cellulose crystallinity and particle size, forming soluble cello‐oligomers; this is responsible for the enhanced substrate–catalytic sites contact and subsequent rate of HMF formation. During catalyst recyclability, P–TiO 2 was observed to be reusable for four cycles without any loss in activity. We also investigated the conversion of the cello‐oligomers to HMF in a continuous flow reactor. Good HMF yield (53 %) was achieved using a water–methyl isobutyl ketone+NMP biphasic system.