High-Yield Synthesis of 1-Hydroxyhexane-2,5-dione via Hydrogenation/Hydrolysis of 5-Hydroxymethyl-furfural in Ionic Liquid-Assisted Multi-Phase Systems

Different multiphase (MP) systems comprising immiscible liquid water, a hydrocarbon, and an ionic liquid (IL) were investigated for the combined hydrogenation/hydrolysis of 5-hydroxymethylfurfural (HMF) to 1-hydroxyhexane-2,5-dione (HHD) in the presence of 5% Ru/C as a catalyst. Excellent control of selectivity was achieved using a water, isooctane, and methyltrioctylammonium chloride ([N8881][Cl]) liquid triphase: at 100 degrees C and 40 bar of H2, HHD was obtained as an exclusive product (98%), and it was isolated in an 85% yield at complete conversion of HMF. Both the reagents and the products were partitioned in the aqueous phase, while, by tuning the relative proportions of the MP components, the catalyst (Ru/C) could be perfectly segregated in the IL layer, where it could be recycled and reused up to six times without any loss of activity and selectivity, in a robust semi-continuous mode. Under such conditions, a reaction productivity of up to 9.7 mmol HHD (gcat center dot h)-1 was reached with negligible metal leaching (<0.67 ppb).

Automated summary

Various multiphase systems consisting of immiscible liquid water, a hydrocarbon, and an ionic liquid were studied for the hydrogenation/hydrolysis of 5-hydroxymethylfurfural. A liquid triphase system composed of water, isooctane, and methyltrioctylammonium chloride achieved excellent selectivity control with high yields of the desired product. By separating the reagents and catalyst in different phases, the catalyst could be effectively recycled and reused multiple times without any loss of activity or selectivity.