(541d) Rational Tailoring of Solvent Recipes for Acid-Catalyzed Dehydration of Biomass-Derived Lactones

Non-covalent interactions of organic solvents and their mixtures in water are observed to affect the rates of acid catalysed reactions of biomass-derived platform chemicals. Because of the differential stabilization of acidic protons in different solvents, mixtures of organic solvents with water are proposed, wherein on increasing the fraction of the organic phase, the aqueous phase is observed to preferentially cluster around the reactant with increased hydrogen bonding interactions. Moreover, acid catalysed reactions conducted in zeolites, also show an additional positive confinement effect, for which the stabilization of the transition state by the zeolite pores, leads to a lowering of activation energy. Our group has carried out simulations in explicit solvent environments using Car–Parrinello Molecular Dynamics (CPMD) and density functional theory (DFT) simulations and compare the two implicit and explicit solvation model to explain the reactivity of biomass-derived platform lactones in water and tetrahydrofuran (THF).

In this study, effect of organic solvents and their mixtures with water on the dehydration reaction of Mevalonolactone (MVL) are elucidated using ab initio molecular dynamics (AIMD)-metadynamics simulations. The activation free energy barrier for the dehydration of MVL is observed to be higher by around 45 kJ/mol in water as compared to THF due to possible changes in the rate determining step; C-H bond activation in water as compared to C-O bond activation in THF. In mixtures of water and THF, the presence of organic phase is observed to facilitate a water enriched confined space around the reactant, which helps in reducing the activation barrier, compared to pure water and THF. While in the confined pores of zeolite, water molecules are observed to facilitate the abstraction of the proton from the zeolite framework, forming a hydronium ion cluster inside the pore. The nature and size of the hydronium ion formed has consequential significance on reaction kinetics.