Surfactant-Dependent Partitioning of Organics in Aqueous–Organic Reaction Systems

Performing organic reactions in water provides environmental and toxicity advantages compared to in organic solvents, but such strategies are still evolving, limited by current understanding of these multiphasic systems. Here, a fluorescence lifetime imaging microscopy (FLIM) technique characterizes surfactant-dependent partitioning of organics in a system that mimics the early, zinc-related steps of a Negishi-like cross-coupling reaction in water, under synthetically relevant high concentrations of substrate (0.18 M), where large emulsion droplets (5–20 um) form an organic phase. Brij-30 resulted in the highest degree of partitioning of organics in the aqueous phase, which was not predictable from simple hydrophilic–lipophilic balances (HLB). The ionic surfactant CTAC suppressed reactivity of the metallic zinc surface with both neutral (TMEDA) and anionic (carboxylate) reactants, presumably through competitive chloride binding and concurrent cetrimonium coating, a finding that may contribute to the reduced performance of ionic surfactant in the bench-scale coupling reaction.