DFT Study of Solvent Effects in Acid-Catalyzed Diels-Alder Cycloadditions of 2,5-Dimethylfuran and Maleic Anhydride.
Density functional theory electronic structure calculations were used to explore the mechanism for the Diels-Alder reaction between 2,5-dimethylfuran and maleic anhydride (MA). Reaction paths are reported for uncatalyzed and Lewis and Brønsted acid-catalyzed reactions in vacuum and in a broad range of solvents. The calculations show that, while the uncatalyzed Diels-Alder reaction is thermally feasible in vacuum, a Lewis acid (modeled as Na(+)) lowers the activation barrier by interacting with the dienophile (MA) and decreasing the HOMO-LUMO gap of the reactants. A Brønsted acid (modeled as a proton) can bind to a carbonyl oxygen in MA, changing the reaction mechanism from concerted to stepwise and eliminating the activation barrier. Solvation effects were studied with the SMD model. Electrostatic effects play the largest role in determining the solvation energy of the transition state, which tracks the net dipole moment at the transition state. For the uncatalyzed reaction, the dipole moment is largely determined by charge transfer between the reactants, but in the reactions with ionic catalysts, there is no simple relationship between solvation of the transition state and charge transfer between the reactants. Nonelectrostatic contributions to solvation of the reactants and transition state also make significant contributions to the activation energy.
Department of Physics and Astronomy, ‡Catalysis Center for Energy Innovation (CCEI), Department of Chemical and Biomolecular Engineering, and §Department of Chemistry and Biochemistry, University of Delaware , Newark, Delaware 19716, United States.
Taha
T
Salavati-fard
Department of Physics and Astronomy, ‡Catalysis Center for Energy Innovation (CCEI), Department of Chemical and Biomolecular Engineering, and §Department of Chemistry and Biochemistry, University of Delaware , Newark, Delaware 19716, United States.
Stavros
S
Caratzoulas
Department of Physics and Astronomy, ‡Catalysis Center for Energy Innovation (CCEI), Department of Chemical and Biomolecular Engineering, and §Department of Chemistry and Biochemistry, University of Delaware , Newark, Delaware 19716, United States.
Douglas J
DJ
Doren
D002384:Catalysis; D061565:Cycloaddition Reaction; D005663:Furans / Q000737:chemistry*; D058116:Lewis Acids / Q000737:chemistry*; D008299:Maleic Anhydrides / Q000737:chemistry*; D015394:Molecular Structure; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry*; D013816:Thermodynamics
D005663:Furans; D058116:Lewis Acids; D008299:Maleic Anhydrides; D012997:Solvents; C037555:2,5-dimethylfuran