Direct cleavage of sorbitol from oligosaccharides via a sequential hydrogenation-hydrolysis pathway

• Kinetics of the hydrolytic hydrogenation of trisaccharides to sorbitol was investigated.
• The study confirms the high kinetic selectivity of hydrogenation over hydrolysis.
• Kinetic analysis shows facilitated hydrolysis of reduced saccharides.
• A sequential hydrogenation-hydrolysis pathway contributes to sorbitol formation.

The production of sorbitol from polysaccharides is widely believed to proceed via hydrolysis to glucose and subsequent hydrogenation. Nevertheless, our previous study on the hydrolytic hydrogenation of cellobiose confirmed simultaneous hydrolysis and hydrogenation with a higher kinetic selectivity of hydrogenation over hydrolysis. Herein, kinetics of hydrogenolysis of trisaccharides with α-1,4 and β-1,4 glycosidic linkages were studied using Ru/C in combination with a molecular acid as catalyst system. Kinetic analysis emphasises a fast hydrogenation of the reducing end of trisaccharides followed by a facilitated cleavage of the terminal sorbitol unit. Considering the obtained reaction rate constants, hydrogenation compared to hydrolysis proceeds up to 24 and 15 times faster for maltotriose and cellotriose, respectively. Additionally, superior reaction rate constants and decreased activation energies for hydrolytic cleavage of sorbitol can be observed. Hence, a sequential hydrogenation-hydrolysis pathway clearly contributes to sorbitol formation based on oligosaccharides.

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