Effect of Mixed-Solvent Environments on the Selectivity of Acid-Catalyzed Dehydration Reactions

Alex K. Chew, Theodore W. Walker, Zhizhang Shen, Benginur Demir, Liam Witteman, Jack Euclide, George W. Huber, James A. Dumesic, Reid C. Van Lehn

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


The composition of the liquid phase can alter the rates of individual reaction steps and thus alter the selectivity of acid-catalyzed reactions, but these solvent effects are difficult to anticipate for design purposes. Herein, we report the kinetics and selectivity of Brønsted acid-catalyzed 1,2-propanediol dehydration in pure water and in aqueous mixtures of the polar aprotic cosolvents γ-valerolactone, 1,4-dioxane, tetrahydrofuran, N-methyl-2-pyrrolidone, tetramethylene sulfoxide, and dimethyl sulfoxide at 433 K. We find that the major product of 1,2-propanediol dehydration is propanal in most mixed-solvent environments with selectivities between 1 and 68 mol %. In contrast, 1,2-propanediol dehydration in aqueous mixtures of dimethyl sulfoxide affords acetone as the major product with up to 48% selectivity with minimal propanal formation. We use classical molecular dynamics simulations to probe these solvent effects by computing the difference between the solvation free energies of 1,2-propanediol and propanal in aqueous mixtures of polar aprotic cosolvents and in pure water. We find that the difference in the solvation free energies is correlated with the rates of propanal formation in all mixed-solvent environments, indicating that the solvent-mediated stabilization of the product state relative to the reactant state translates to increased selectivity toward the same product. Similar agreement between simulated solvation free energies and experimental reaction rates/selectivities is established for the acid-catalyzed dehydration of cis- and trans-1,2-cyclohexanediol and 1,3-cyclohexanediol. Finally, analysis of the solvation environment around 1,2-propanediol shows that dimethyl sulfoxide uniquely competes against water to solvate reactive hydroxyl groups, which causes a change in reaction mechanism in this solvent system that leads to the formation of acetone rather than propanal. These results represent a step toward the computationally efficient screening of solvent systems for acid-catalyzed, liquid-phase processes.

Original languageEnglish (US)
Pages (from-to)1679-1691
Number of pages13
JournalACS Catalysis
Issue number3
StatePublished - Feb 7 2020
Externally publishedYes


  • acid catalysis
  • biomass conversion
  • classical molecular dynamics
  • selectivity
  • solvent effects

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry


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