The Non-Aqueous Sol-Gel Mediated Microencapsulation of Deep Eutectic Solvents: Characterization and Application

In last decade, deep eutectic solvents (DESs) have surfaced as promising alternatives to conventional solvents in synthesis. DESs exhibit low volatilities, high thermal stabilities, impressive solubilization capacities for various metal oxides and electrolytes and high biodegradability. In addition, they can be easily modified and fine-tuned to serve specific objectives. On the other hand, DESs usually comprise high viscosities that limit their applicability in catalysis, especially in large-scale industries.

The main objective of this research is to microencapsulate DESs via a non-aqueous sol-gel technique using formic acid as both a reagent and a catalyst. Particularly, proline-based DESs, which may be used as catalysts in various organic reactions such as Aldol, Michael and Mannich reactions. This technique eliminates most of the drawbacks that originate from the high viscosity of DESs by turning them into easily handleable and dispersible solids. Typically, DESs are encapsulated using oil in oil (O/O) emulsions as templates for the interfacial polymerization between formic acid and suitable silanes. This produces porous silica shells that surround the DESs droplets and separate them from the outer environment. The microencapsulated DESs may then be used as catalysts in various organic reactions and as hosts for different enzymes, organocatalysts, organometallic catalysts and drugs.

Several DESs were successfully encapsulated using the non-aqueous sol-gel technique. The capsules were analyzed using SEM, TEM, solid NMR, IR and TGA techniques and then tested in catalysis. For example Choline chloride: L-tartaric acid (1:0.5) DES was used for the one-pot synthesis of α-aminophosphonates. Whereas, proline: formic acid (1:2) DES was employed in Aldol condensations and Michael additions. The preparation and characterization of these microencapsulated DESs will be presented.