Electrochemistry in tetrahydrofuran and at low temperature: protocol, procedures and methods

Abstract

This review describes the protocol, procedures and methods for electrochemical studies in THF and at low temperature that have been developed in the course of the last 5 years in our laboratory. Electrochemical studies in THF benefit from a large accessible potential window. In practice, it is however necessary to avoid the presence of humidity in the electrochemical cell. A specific reference electrode had to be designed for those measurements. Microelectrodes, the voltammetric response of which is negligibly affected by the resistivity of the medium, were preferred to macroelectrodes. Moreover, a methodology has been developed for the quantitative analysis of both voltammetric and chronoamperometric curves obtained for the microelectrodes. The fitting of chronoamperometric measurements using the Shoup and Szabo's expression allows us to estimate the diffusion coefficient of the substrate. The modelling of the cyclic voltammograms measured over a large range of scan rates allows the confirmation of the diffusion coefficient of the substrate D A , the determination of the diffusion coefficient of the electrogenerated molecule D B , of the formal potential E 0 f , of the transfer coefficient a and of the standard heterogeneous rate constant for the electron transfer k 0 . Typically, systems are investigated at temperatures ranging from room temperature to 192 K. Parameters obtained at various temperatures are used to extract, through Arrhenius plots, the activation energies both for the diffusion coefficient E A (D) and for the electron transfer reaction E A (k 0 ).

Modeling Diffusion Effects for a Stepwise Two-Electron Reduction Process at a Microelectrode: Study of the Reduction of para-Quaterphenyl in Tetrahydrofuran and Inference of Fast Comproportionation of the Dianion with the Neutral Parent Molecule

“…In contrast, D PQ -is singly charged and will coordinate to only one. 20,33 This theory is consistent with the observation that D PQ -is greater than D PQ 2-. The rate constant k PQ/PQ -0 is five times greater than k PQ -/PQ 2-0 .…”

“…The setup, protocol and procedures used for electrochemical studies in super dry THF have been detailed in a recent publication. 20 Electrochemical measurements were performed using a PGSTAT20 potentiostat (Eco-Chemie, Utrecht, Netherlands). The electrochemical cell used was an airtight standard three-electrode cell.…”

“…The third area is that of voltammetry in solvents of very low polarity such as tetrahydrofuran (THF). 19,20 If A is neutral, species B and C are anions and dianions, respectively, and are likely to be involved in ion pairing with cations contained in the supporting electrolyte. 19 In both types of medium considered above, RTILs and nonpolar solvents, the preferred voltammetric method is one involving microelectrodes: the tiny currents minimize ohmic distortion in the voltammogram.…”

Electrosynthetic C−O Bond Activation in Alcohols and Alcohol Derivatives

“…A landmark series of studies detailing homolytic C(O)O−C bond cleavage in aromatic esters was conducted by Lam and Markó, [101] complemented by electroanalytical studies by others. [ 102 , 103 ] While examining a more practical alternative to the Barton–McCombie reaction,[ 10 , 104 ] Lam and Markó studied the electrochemical behavior of aliphatic benzoates at low potentials in aprotic media, [105] demonstrating an E r C i mechanism for their one‐electron reduction. While only a small difference in the reduction potentials was found for a series of aliphatic benzoates ( E 1/2 ≈−2.3 V vs. SCE), [24] the rate of decomposition of the anion‐radical (C i step) strongly depended on the stability of C‐radical formed upon C(O)O−C bond cleavage.…”

Electrosynthetic C−O Bond Activation in Alcohols and Alcohol Derivatives

“…[100] Electrochemical reductive CÀ O bond activa- A landmark series of studies detailing homolytic C(O)OÀ C bond cleavage in aromatic esters was conducted by Lam and Markó, [101] complemented by electroanalytical studies by others. [102,103] While examining a more practical alternative to the Barton-McCombie reaction, [10,104] Lam and Markó studied the electrochemical behavior of aliphatic benzoates at low potentials in aprotic media, [105] demonstrating an E r C i mechanism for their one-electron reduction. While only a small difference in the reduction potentials was found for a series of aliphatic benzoates (E 1/2 � À 2.3 V vs. SCE), [24] the rate of decomposition of the anion-radical (C i step) strongly depended on the stability of C-radical formed upon C(O)OÀ C bond cleavage.…”