Two-phase flow electrosynthesis: Comparing N-octyl-2-pyrrolidone-aqueous and acetonitrile-aqueous three-phase boundary reactions

Stuart MacDonald, John D Watkins, Steven D Bull, Iwan R Davies, Yonfeng Gu, Kamran Yunus, Adrian C Fisher, Philip C Bulman Page, Yohan Chan, Claire Elliott, Frank Marken

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23 Citations (Scopus)

Abstract

A microfluidic double channel device is employed to study reactions at flowing liquid-liquid junctions in contact with a boron-doped diamond (BDD) working electrode. The rectangular flow cell is calibrated for both single-phase liquid flow and biphasic liquid-liquid flow for the case of (i) the immiscible N-octyl-2-pyrroIidone (NOP)-aqueous electrolyte system and (ii) the immiscible acetonitrile-aqueoys electrolyte system. The influence of flow speed and liquid viscosity on the position of the phase boundary and mass transport-controlled limiting currents are examined. In contrast to the NOP-aqueous electrolyte case, the acetonitrile-aqueous electrolyte system is shown to behave close to ideal without 'undercutting' of the organic phase under the aqueous phase. The limiting current for three-phase boundary reactions is only weakly dependent on flow rate but directly proportional to the concentration and the diffusion coefficient in the organic phase. Acetonitrile as a commonly employed synthetic solvent is shown here to allow effective three-phase boundary processes to occur due to a lower viscosity enabling faster diffusion. N-butylferrocene is shown to be oxidised at the acetonitrile-aqueous electrolyte interface about 12 times faster when compared with the same process at the NOP-aqueous electrolyte interface. Conditions suitable for clean two-phase electrosynthetic processes without intentionally added supporting electrolyte in the organic phase are proposed. Copyright 2008 John Wiley Sons, Ltd.
Original languageEnglish
Pages (from-to)52-58
Number of pages7
JournalJournal of Physical Organic Chemistry
Volume22
Issue number1
DOIs
Publication statusPublished - 2009

Keywords

  • microfluidic
  • voltammetry
  • green chemistry
  • phase transfer catalysis
  • ion transfer
  • phase boundary
  • electrosynthesis
  • ion extraction
  • electrochemistry

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