Accelerated Non-Enzymatic Fatty Acid Esterification during Microdroplet Collision: A Method for Enhanced Sustainability

Accelerated non-enzymatic and metal-free “reaction and extraction” of sugar esters at the interface of two immiscible liquid microdroplets is demonstrated. The bimolecular reaction occurs by collision of microdroplets originating from two home-built electrospray sonic ion sources, carrying sugar molecules in water and long-chain fatty acids in toluene, respectively. Our method shows that the rate of reaction is enhanced ∼10⁷ times in comparison to the bulk, initiated by ultrasonic activation. Such a high rate of reaction in the microdroplets can be attributed to factors such as surface activity, concentration enhancement, partial solvation, and temperature-assisted dehydration of the species occurring in microdroplets. We provide evidence for an interfacial nucleophilic addition–elimination reaction mechanism. This method of synthesis is extended to 18 similar reactions. Microdroplet synthesis offers a sustainable method for biphasic reactions, eliminating the need for phase transfer reagents and activating agents such as acids/bases, metals, or enzymes.