The structure and reactivity of the organic-water interface has gained considerable attention due to the substantial rate accelerations that have been observed for some organic reactions in water. “On water” catalysis refers to rate increases seen in systems with an organic-water interface formed in emulsions (liquid-liquid) or suspensions (solid-liquid), whereby water is believed to be the primary source of catalysis. The mechanistic elucidation of this phenomenon and its application at industrial scale, has the potential to advance technology in fields like petroleum chemistry, pharmaceutics, food processing, organic synthesis and heterogeneous catalysis. However, currently there is no consensus on the mechanism behind this type of catalysis. Some researchers claim that size and chemical structure of the organic-water interface are at play, while others indicate that proton transfer (PT) and H-bonding across the interface are required for catalysis. Herein, we have intended to use toluene emulsion droplets (0.1 to 2 um in diameter) dispersed in water as model systems to investigate “on water” catalysis. These droplets can be detected individually by electrochemistry when redox species are trapped inside the droplets. The emulsions were prepared by sonication of water and toluene-ferrocene (Fc) solution containing an ionic liquid to provide conductivity to the droplet. Upon collision with the electrode held at a potential to oxidize Fc, each droplet produces a spike of current from which the diameter of the droplet can be measured. Initial focus will be to prove that the Fc inside the toluene droplet can act as a rely of electrons for a species outside (cysteine) that cannot be solubilized in the droplet. For this system, the effect of the water pH, the presence of bases and hydrogen bonding reagents inside and outside the toluene droplet, as well as the surfactant charge will be studied. Other systems to study, will be trapping hydrophobic quinones in the droplet and studying their response in the presence of hydrogen bonding and PT reagents inside and outside the droplet. Emulsion will also be prepared with fluorocarbonated solvents instead of water so that its effect can be evaluated. Quinones were selected because their redox potential is very sensitive to PT and hydrogen bonding reagents.

Study of electrochemical reactions across oil-water interface by single particle collision

254th National Meeting (2017)

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