Electrochemically Driven Ion Insertion Processes across Liquid|Liquid Boundaries:  Neutral versus Ionic Redox Liquids

Abstract

The oxidation and rereduction of the redox liquids para-N,N,N′,N′-tetrahexylphenylenediamine (THPD) and para-N,N,N′-trihexylphenylenediamine (TriHPD) associated with anion and proton insertion and expulsion are studied as a function of the proton concentration in aqueous NaClO 4 electrolyte. Voltammetric, in situ UV/vis-spectroelectrochemical, and quartz crystal microbalance techniques are employed. The biphasic acidbase equilibria of the redox liquids involving protonation and simultaneous anion transfer from the aqueous phase are shown to exhibit only small deviation from ideal behavior and well-defined biphasic dissociation constants, pK A,biphasic have been determined. However, the protonation of the bulk redox liquids is shown to be dominated by intermolecular rather than intramolecular factors. In particular, the ability of THPD to undergo bulk protonation by HClO 4 is higher (pK A2,biphasic ) 5.1) compared to that of TriHPD (pK A2,biphasic ) 3.9); this is opposite to the behavior predicted on the basis of the estimated values for the aqueous protonation equilibrium constants, pK A2 ) 7.5 ( 0.5 and pK A2 ) 8.8 ( 0.5 for THPD and TriHPD, respectively. Further, the electrochemically driven deprotonation occurs irrespective of protonation constants at essentially the same potential for both materials. The three-phase junction electrode|redox liquid|aqueous electrolyte for the initiation of the anion and proton insertion-electrochemical reactions is shown to be the key to processes observed for neutral redox liquids, whereas ionic redox liquids show reactivity independent of the three-phase junction due to sufficient ionic bulk conductivity.

Quantification of the chiral recognition in electrochemically driven ion transfer across the interface water/chiral liquid

“…These experiments are similar to those of Compton and coworkers [13][14][15][16], who used immobilized droplets of redox active liquids and studied the simultaneous electron and ion transfer at the three-phase junction. This method overcomes certain limitations of the classical electrochemical technique that needs the use of a four-electrode potentiostat and necessarily uses supporting electrolytes in both liquid phases [17].…”

Lipophilicity of Peptide Anions: An Experimental Data Set for Lipophilicity Calculations

“…18 Using a chiral organic solvent as a matrix for dmfc, we have shown that even quantification between the energies of transfer of the D and L forms of some amino acids can be achieved. 18 A similar approach for monitoring the simultaneous electron and ion transfer in the case of the oxidation of electroactive ionic liquids has been published by Compton et al 21,22 The "thinfilm" method developed by Shi and Anson [23][24][25][26][27][28] and applied mainly for studying the kinetic of interfacial electron-transfer reactions fundamentally differs from our technique. Extended comments regarding the principal differences between our approach and Anson's can be found in a recent paper.…”

A Comparison of the Solvation Properties of 2-Nitrophenyloctyl Ether, Nitrobenzene, and n-Octanol as Assessed by Ion Transfer Experiments

“…[33][34][35][36][37] Whereas Compton and his group used three-phased electrodes to study the electrochemistry of electroactive liquids, 32,[38][39][40] Scholz and co-workers [28][29][30][31][33][34][35][36][37] developed the technique of determining the Gibbs energies of ion transfer with the help of solutions of electroactive compounds in droplets of organic solvents immobilized on electrode surfaces.…”