Selective Conversion of 5‐Hydroxymethylfuraldehyde Using Cp*Ir Catalysts in Aqueous Formate Buffer Solution

Abstract

The highly selective hydrogenation/hydrolytic ring-opening reaction of 5-hydroxymethylfuraldehyde (5-HMF) was catalyzed by homogeneous Cp*Ir(III) half-sandwich complexes to produce 1-hydroxy-2,5-hexanedione (HHD). Adjustment of pH was found to regulate the distribution of products and reaction selectivity, and full conversion of 5-HMF to HHD with 99 % selectivity was achieved at pH 2.5. A mechanistic study revealed that the hydrolysis/ring-opening reaction of 2,5-bis-(hydroxymethyl)furan is the important intermediate reaction step. In addition, an isolated yield of 85 % for HHD was obtained in a 10 g-scale experiment, and the reaction with fructose as the starting material also led to a 98 % GC yield (71.9 % to fructose) of HHD owing to the excellent tolerance of the catalyst under acidic conditions.

Cyclopentanone Derivatives from 5‐Hydroxymethylfurfural via 1‐Hydroxyhexane‐2,5‐dione as Intermediate

“…However, these methods require high H 2 pressures and selectivities vary from 57 % to 81 %. Higher HHD selectivities are obtained in processes catalyzed by homogeneous catalysts . In particular, Cp*Ir III half‐sandwich complexes have appeared to be most promising …”

pH‐Regulated Aqueous Catalytic Hydrogenation of Biomass Carbohydrate Derivatives by Using Semisandwich Iridium Complexes

“…Initially, we investigated the influence of electronic effect of substituents on TOF at different pH values. Two of the most active catalysts in our previous work, [Cp*Ir‐(di‐OMe‐bpy)(OH 2 )][SO 4 ] (di‐OMe‐bpy=4,4′‐dimethoxyl‐2,2′‐bipyridine) (catalyst 1) and [Cp*Ir‐(di‐OH‐bpy)(OH 2 )][SO 4 ] (di‐OH‐bpy=4,4′‐dihydroxyl‐2,2′‐bipyridine) (catalyst 2), were used to perform our experiments. Furfural, which is the typical product of dehydration of pentose, is hydrogenated under 1 MPa H 2 at 120 °C for one hour over 0.0083 mol % catalyst 1.…”

“…If we used hydroxyl as the substitute (catalyst 2), the highest TOF was 7340 h −1 at pH 5.0. We previously found that electron‐donating groups on the catalyst promoted the catalytic activity significantly . A small amount of GVL was observed if pH<1.5.…”

“…In addition, our group have reported that water‐soluble semisandwich iridium complexes can efficiently convert levulinic acid (LA) into GVL under mild conditions (120 °C and 1.01 MPa) in pure aqueous system . In addition, pH was recently demonstrated to effectively regulate the catalytic efficiency and distribution of products of hydrogenation/ring‐opening reaction of 5‐(hydroxymethyl)furfural (5‐HMF) catalyzed by a semisandwich iridium catalyst …”

Highly Selective Conversion of HMF to 1‐hydroxy‐ 2,5‐hexanedione on Pd/MIL‐101(Cr)

“…There were several reports on the conversion of HMF to HHD. Supported Pd, Pt and Au catalysts were proved to be effective for this conversion . Mentech and their group reported this conversion with 60% yield of HHD using Pt/C by the addition of oxalic acid for the first time .…”