A novel green catalytic strategy for hydration of α-pinene by a natural deep eutectic solvent

Abstract

Hydration of α-pinene catalyzed by a natural deep eutectic solvent (NADES) prepared by oxalic acid dihydrate (OA·2H2O) and betaine (Bet), 2.7OA·2H2O/Bet, has been studied to develop a more economical and green process for one-step hydration method. It has been found that a homogeneous ternary DES system could be established with OA·2H2O and Bet in a simple, convenient, and atomic economy way. Fourier transform infrared spectrum (FT-IR), proton nuclear magnetic resonance (1H NMR), thermogravimetry (TG), and differential scanning calorimetry (DSC) have been applied to confirm the formation of hydrogen bonding between OA, H2O, and Bet. With the consideration of catalytic activity, selectivity, and ability to recycle, 2.7OA·2H2O/Bet has been screened out to be a promising catalyst for hydration of α-pinene due to its appropriate acidic properties and solubility. In this catalytic system of hydration, water, as one of the reactants, both assisted in the formation of DES and acted as the dispersing agent. Correspondingly, an “emulsifying reaction at the reaction temperature and solid-liquid separation below room temperature” characteristic of this specific catalytic hydration of α-pinene has been achieved.