A sustainable system for maleic acid synthesis from biomass-derived sugar

BACKGROUND The preparation of maleic acid from the oxidation of renewable furfural has attracted significant attention, but research regarding the direct transformation of biomass-derived sugar to maleic acid is rare. The research regarding the direct transformation of xylose to maleic acid would further promote its industrial applications. RESULTS The direct synthesis of maleic acid from xylose was investigated based on a sustainable system of deep eutectic solvents (DESs). Four DESs were screened to evaluate their abilities for the dehydration of xylose. Hydrogen peroxide (H2O2) was then loaded to realize the oxidation of furfural without the separation of intermediates. A good maleic acid yield of 20.8%, along with 5.0% of fumaric acid, based on the xylose content were obtained under the initial xylose loading of 50 mM, a tin(IV) chloride (SnCl4)-xylose molar ratio of 4:1, in a monophase choline chloride (ChCl)-formic acid (Fa) (molar ratio of 1:6) system at 120 degrees C for 2 h. Then, 4 mL of H2O2 per mmol furfural was loaded for a further 10 min at 120 degrees C. CONCLUSION This ChCl-Fa-SnCl4-H2O2 system possesses a higher oxidation selectivity to maleic acid with no furanone and succinic acid. Moreover, it was interesting that ChCl and SnCl4 could be recovered through natural recrystallization. (c) 2019 Society of Chemical Industry