Universal kinetic solvent effects in acid-catalyzed reactions of biomass-derived oxygenates

The rates of Brønsted-acid-catalyzed reactions of ethyl tert -butyl ether, tert -butanol, levoglucosan, 1,2-propanediol, fructose, cellobiose, and xylitol were measured in solvent mixtures of water with three polar aprotic cosolvents: γ-valerolactone; 1,4-dioxane; and tetrahydrofuran. As the water c...

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Bibliographic Details
Published in:Energy & environmental science 2018-01, Vol.11 (3), p.617-628
Main Authors: Walker, Theodore W, Chew, Alex K, Li, Huixiang, Demir, Benginur, Zhang, Z. Conrad, Huber, George W, Van Lehn, Reid C, Dumesic, James A
Format: Article
Language:English
Subjects:
Acids
Butanol
Catalysis
Cellobiose
Chemical bonds
Chemical reactions
Computer simulation
Dehydration
Fructose
Hydrogen bonding
Hydroxyl groups
INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Levoglucosan
Moisture content
Molecular dynamics
Rate constants
Solvent effect
Solvents
Tert-butanol
Tetrahydrofuran
Water chemistry
Water content
Xylitol
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Summary:The rates of Brønsted-acid-catalyzed reactions of ethyl tert -butyl ether, tert -butanol, levoglucosan, 1,2-propanediol, fructose, cellobiose, and xylitol were measured in solvent mixtures of water with three polar aprotic cosolvents: γ-valerolactone; 1,4-dioxane; and tetrahydrofuran. As the water content of the solvent environment decreases, reactants with more hydroxyl groups have higher catalytic turnover rates for both hydrolysis and dehydration reactions. We present classical molecular dynamics simulations to explain these solvent effects in terms of three simulation-derived observables: (1) the extent of water enrichment in the local solvent domain of the reactant; (2) the average hydrogen bonding lifetime between water molecules and the reactant; and (3) the fraction of the reactant accessible surface area occupied by hydroxyl groups, all as a function of solvent composition. We develop a model, constituted by linear combinations of these three observables, that predicts experimentally determined rate constants as a function of solvent composition for the entire set of acid-catalyzed reactions. Experiments and molecular simulations are combined to understand organic solvent effects, enabling prediction of acid-catalyzed reaction rates for biomass conversion.
ISSN:1754-5692
1754-5706
DOI:10.1039/c7ee03432f