Mechanistic Study on Deoxydehydration and Hydrogenation of Methyl Glycosides to Dideoxy Sugars over a ReO x-Pd/CeO2Catalyst

Ji Cao, Masazumi Tamura, Ryu Hosaka, Akira Nakayama, Jun Ya Hasegawa, Yoshinao Nakagawa, Keiichi Tomishige

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Abstract

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 ReOx-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 ReOx/CeO2 as the active site of the ReOx-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.

Original languageEnglish
Pages (from-to)12040-12051
Number of pages12
JournalACS Catalysis
Volume10
Issue number20
DOIs
Publication statusPublished - 2020 Oct 16
Externally publishedYes

Keywords

  • deoxydehydration
  • heterogeneous catalysis
  • methyl glycoside
  • rhenium
  • sugar conversion

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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