Extraction of Natural Products using Deep Eutectic Solvents

Abstract

Extraction of natural products from their biological sources have received great attention recently. Organic solvents and thermal and mechanical methods have been widely used to extract and isolate such compounds. In this study Deep Eutectic Solvents (DESs) have been tested for the extraction process. The first part of this study involved the transfer of chosen molecular solutes, dissolved in alkanes, into the DESs. The studied solutes were butanoic acid, 1-pentanol, ethyl acetate, 2- pentanone, phenol, benzyl alcohol and cyclohexanol. The thermodynamics of their transfers were quantified by determining the partition coefficients with DESs. The largest partition coefficients were observed by the liquids with the lowest surface tensions and this is thought to arise because the enthalpy of hole formation controls the thermodynamics of solute transfer. Accordingly, it was shown that the size of the solute has an effect on the partition coefficient with smaller solutes partitioning preferably into the DES. It was found that solutes capable of strongly hydrogen bonding partitioned much better into the DES as the enthalpy of transfer was negative. The second stage of the work focused on the phase behaviour of the solutes transferred to the DESs. Solid (glucose and phenol) and liquid (1-pentanol) hydrogen bonding compounds are mixed with a DES and the heterogeneity and homogeneity of such mixtures are determined using Dynamic Light Scattering (DLS) and Pulsed Field Gradient NMR (PFG-NMR). The study showed that solids interacts strongly with DESs while with liquids this interaction is weaker. It was found that solid solutes form a homogeneous solution with the DES whereas liquid solutes form heterogeneous nanophases because of the weaker solute−solvent interactions and density difference. The final part of the project involved the extraction of a variety of phenolic compounds from olive oil using DESs under different conditions. The studied phenolics were tyrosol, pcoumaric acid, vanilic acid, ferulic acid and apigenin. The results showed that such compounds iii are partition better to the DES compared to conventional solvents, and the extraction efficiency can be enhanced by several factors. Thermodynamics of the transfer and green metrics are also discussed in this part guided by the 12 principles of green chemistry.