We found that nonprotected methyl glycosides with cis-vicinal OH groups could be converted to the corresponding methyl dideoxy glycosides by deoxydehydration and consecutive hydrogenation (DODH + HG) over a ReO x –Pd/CeO2 catalyst with gaseous H2. In the study, the reactivity of the methyl glycosides in DODH was clearly lower than that of simple cyclic vicinal diols, such as cis-1,2-cyclohexanediol and cis-1,2-cyclopentanediol, and the reactivity of the methyl glycosides was also different. Herein, we investigated the reactivity difference based on kinetic studies and density-functional theory (DFT) calculations. The kinetic studies suggest that the reactivity difference between the methyl glycosides and the simple diols is derived from the OH group of methyl glycosides except the cis-vicinal diols, and that the reactivity difference among the methyl glycosides will be associated with the configuration of the substituents adjacent to the cis-vicinal diols, while the reaction mechanism of DODH is suggested to be basically similar judging from almost the same reaction orders with respect to the substrate concentration and H2 pressure in all substrates. The adsorption and transition states of methyl α -l- rhamnopyranoside and methyl α-l-fucopyranoside, which have a large reactivity difference (methyl α-l-rhamnopyranoside≫ methyl α-l-fucopyranoside), were estimated by DFT calculations with ReO x /CeO2 as the active site of the ReO x –Pd/CeO2 catalyst, showing that the main difference is the activation energy in DODH of these substrates (65 kJ mol–1 for methyl α-l-rhamnopyranoside and 77 kJ mol–1 for methyl α-l-fucopyranoside), which was also supported by the results of Arrhenius plots (63 and 73 kJ mol–1 for methyl α-l-rhamnopyranoside and methyl α-l-fucopyranoside, respectively). The activation energy was influenced by the torsional angle of the substituents adjacent to the cis-vicinal OH groups, which is derived from the interaction of the OH group adjacent to the cis-vicinal OH groups and the surface hydroxy groups on CeO2.

The detailed structures of monomeric ReO x catalysts supported on the CeO 2 surface and the reaction mechanism of the deoxydehydration (DODH) reaction were investigated by density functional theory calculations. After examining various ReO x H y structures over CeO 2 without substrate adsorption, the stable structure under the experimental condition at 400 K was determined to be the Re VII O 2 species. The reaction mechanism of DODH was then investigated for the conversion of 1,4-anhydroerythritol to 2,5-dihydrofuran as a model reaction. Through the investigations of several reaction pathways, an oxygen vacancy-assisted mechanism, in which the starting structure is the Re IV O species and the oxidation state of the Re atom changes between +IV and +VI during the reaction, was postulated to be the most plausible pathway, considering the energies of the intermediates and the barrier height for the cleavage of the two C−O bonds.