Kinetic investigation of sorbitol and xylitol dehydration catalyzed by silicotungstic acid in water

Low‐Temperature Continuous‐Flow Dehydration of Xylose Over Water‐Tolerant Niobia–Titania Heterogeneous Catalysts

“…If these data confirmt hat the xylose conversion process is favored by hight emperatures, two justifications can be found for the observed selectivity trend. [139,140] Interception of the 2,5-anhydroxylose supports that, at least under our experimental conditions, the dehydration of xylose occurs through a" cyclic intermediates rearrangement" mechanism (Scheme 2), [141,142] which was suggestedt ob ee nergetically more favorable compared with a" dehydrationo fa cyclic intermediates" mechanism. On the other hand, it is known that xylose dehydration is faster than furfural loss reactions (e.g.,r esinification) at high temperatures, which is called "entropy effect".…”

“…[138] Analogous findings have been reported for the two-fold dehydration reactionofs orbitol to isosorbide via 1,4-sorbitan. [139,140] Interception of the 2,5-anhydroxylose supports that, at least under our experimental conditions, the dehydration of xylose occurs through a" cyclic intermediates rearrangement" mechanism (Scheme 2), [141,142] which was suggestedt ob ee nergetically more favorable compared with a" dehydrationo fa cyclic intermediates" mechanism. [143,144] Nonetheless, we cannot rule out ac ontribution to the mechanism based on xylose-xylulose isomerization followed by dehydration,owing to the combined action of Lewis and Brønsted acid sites (Scheme 3).…”

Role of acid sites and selectivity correlation in solvent free liquid phase dehydration of sorbitol to isosorbide

“…Based on the literature and characterization data [34,42,43], possible mechanism is outline for sorbitol dehydration using Brönsted and Lewis acid catalyst (Scheme 2). The mechanism for dehydration of sorbitol by Brönsted acid (H + ) can explained by preferential protonation of the hydroxyl group at C 1 or C 6 position in the sorbitol (Scheme 2) and then cyclic dehydration of these carbons with C 4 or C 3 produces 1,4-sorbitan or 3,6-sorbitan [34].…”

“…S4 and S5). Simplified reaction scheme for sorbitol dehydration with rate constant and corresponding rate equations.Oltmanns et al[42], Li et al[44] and Yamaguchi et al[45] also proposed kinetic model for dehydration of sorbitol assuming first order reaction for all the steps. The experiment data of both catalysts MSA and TS at different temperatures (140,150,160 and 170  C) were fitted to the above kinetic model for the estimation of the three rate constants.…”

Nitrogen-functionalized Isohexides in Asymmetric Induction

“…1). Double dehydration of d-mannitol and d-glucitol have afforded isomannide and isosorbide in a wide range of acidic conditions such as formic acid/HF, [6] pyridinium chloride, [7] H 2 SO 4 , [8] Amberlyst or Dowex resins, [9] metal phosphates (of tin, zirconium, titanium, niobium), [10] zeolites, [11] silicotungstic acid [12] and so on. Simple metallic or bifunctional catalysts also efficiently performed the dehydration of these polyols.…”