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 similar to 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.