Two-Phase Azo-Coupling Reactions Driven by Phase-Boundary Potential Across the Liquid|Liquid Interface

Phase-boundary-potential-driven azo coupling has been demonstrated for the reaction between hydrophilic arenediazonium ions and lipophilic coupling components in 1,2-dichloroethane (DCE)|water (W) two-phase systems. Instead of using phase-transfer catalysts, hydrophilic arenediazonium ions are driven into the DCE phase by externally controlling the potential drop across the polarized DCE|W interface. The diffusion-controlled transfer of arenediazonium ions across the interface is followed by azo-coupling reactions with coupling components in the DCE phase. The rate of the azo coupling in DCE has been accurately determined by using potential-step chronoamperometry for the transfer for four arenediazonium ions having different lipophilicity in the presence of one of four aromatic coupling components in DCE. No appreciable contribution of the adsorbed reactants to the overall azo-coupling process is detected. An electrochemical approach using liquid|liquid two-phase systems is advantageous in determining the rate of two-phase chemical reactions and is promising for elucidating the mechanism of phase-transfer catalysis.