Ether Functional Groups Enable Oxidative Dehydrogenation of Aliphatic Secondary Alcohols in Water

Aerobic oxidative dehydrogenation (ODH) of secondary
alcohols is
catalyzed by both platinum and platinum–bismuth catalysts in
water. Symmetric 1,3-diether-2-alcohols are high-value glycerol-derived
products and ODH of these alcohols to form analogous ketones over
heterogeneous catalysts has not been reported previously. Reported
herein are initial turnover frequencies (TOFs, per surface Pt), apparent
activation energies, and apparent reaction orders for the ODH of several
glycerol-derived oxygenates over Pt and PtBi particles supported on
silica. Initial ODH rates were obtained from batch reactions (313–353
K, 0.01–2 M substrate). Apparent reaction orders were consistent
with a rate-determining step involving alcohol α C–H
bond activation over adjacent surface sites. Apparent activation energies
measured in the first order kinetic regime over Pt and PtBi catalysts
were similar for a range of substrates. Similar aliphatic alcohols
(e.g., 2-butanol, 3-pentanol, and 4-heptanol) were not measurably
converted under these conditions. Computational analysis of solvation
energy, solvated binding free energy, and the binding structure collectively
suggest that the experimentally observed reactivity of 1,3-dimethoxypropan-2-ol
and 1,3-diethoxypropan-2-ol results from their relatively weak binding
to the surface, whereas the lack of reactivity for 3-pentanol and
4-heptanol may result from them binding too strongly to the surface.
These findings suggest secondary alcohol ODH occurs via a similar
mechanism over Pt and PtBi particles and that the presence of ether
linkages increases the rate of ODH in water.