Unravelling the Mechanism of the Ru/C-Catalysed Isohexide and Ether Isomerization by Hydrogen Isotope Exchange

In this article we show that the catalytic isomerization of isohexide sugar alcohols as well as their respective ethers can occur by a hydride-based mechanism rather than a dehydrogenation/re-hydrogenation. C-H bonds in-position to hydroxy and ether groups are activated using Ru/C as solid catalyst at temperatures as high as 160 degrees C and above. Hydrogen isotope exchange experiments proved that a full hydride exchange and isomerization is possible for isohexides but unexpectedly also for their methyl ethers. This is of great importance as it proves the co-existence of the both mechanisms for reactions that were so far assumed to occur solely by a dehydrogenation/re-hydrogenation. Hence, this co-existence should be taken into account for kinetic investigations of such reaction systems especially in the conversion of biomass-based chemicals under hydrogenation conditions.