(720d) Regio- and Stereo- Selective Synthesis of Hexane-Tetrols and -Triols from Methyl Glycosides over Supported Metal Catalysts
AIChE Annual Meeting
2019
2019 AIChE Annual Meeting
Catalysis and Reaction Engineering Division
Catalysis for Biomass Upgrading III: Novel Conversion Strategies
Thursday, November 14, 2019 - 4:24pm to 4:42pm
Partially
reduced C6 polyols are potentially valuable precursors to polymers,
surfactants, and solvents [1]. Sugars are a renewable feedstock for the
production of C6 polyols, but typical catalytic hydrogenolysis
processes are unselective towards C-OH bond cleavage at different positions and
do not preserve the sugars stereocenters. In contrast, Tomishige and co-workers recently reported on
the selective cleavage of cis-vicinal OH groups of a variety of methyl
glycosides over a ReOx-Pd/CeO2 catalyst [2]. This
reaction step produces dideoxy sugars in which the chirality of the remaining
C-OH groups is preserved.
Here, we demonstrate the regio- and stereo-
selective synthesis of hexane-tetrols and hexane-triols from methyl glycosides over
supported metal catalysts (Scheme 1). First, the above method
is used to synthesize dideoxy sugars from sugar feedstocks. Next, these intermediates
are hydrolyzed and hydrogenated to produce hexane-tetrols and hexane-triols. The
reaction mechanism proceeds through initial methoxy bond hydrolysis to form a mixture
of intermediates. Different reaction intermediates are formed depending on the structure of the
feedstock. Hydrogenation of these intermediates over Pt/SiO2 produces
the final hexane-tetrols and -triols. 2,3-Dideoxy substrates are more reactive
than 3,4-dideoxy substrates due to the electron withdrawing nature of the C2-OH
group. 3,4-Dideoxy substrates also undergo aldose-ketose isomerization
at higher temperatures which decreases the stereoselectivity due to scrambling
of the C2-OH stereocenter. Stereoselectivity can be increased by introducing
an acid catalyst to facilitate hydrolysis at lower temperature.
![](https://www.aiche.org/sites/default/files/aiche-proceedings/conferences/269951/papers/562732/Paper_562732_abstract_142415_0.png)
Scheme
1. Reaction network
for synthesis of hexane-tetrols
and triols from methyl glycosides with cis-vicinal OH groups.
This
work demonstrates a novel catalytic route to produce valuable chemical
precursors from sugars, and provides insight into controlling stereoselectivity
in biomass conversion reactions.
References.
1. Corma, A, et al. Chem. Rev. 2007,107 (6), 2411-2502. 2. Tamura, M., et al. Angew.
Chem. Int. Ed, 2018, 57 (27), 8058-8062.