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The influence of the supporting electrolyte on electrode processes and homogeneous chemical reactions

The influence of the supporting electrolyte on electrode processes and homogeneous chemical reactions
The influence of the supporting electrolyte on electrode processes and homogeneous chemical reactions

The role of the supporting electrolyte in the electron transfer and coupled chemistry of several systems has been investigated using voltammetry at microdisc electrodes (radii 5 - 30 μm). It is shown that the interactions between electrolyte ions and charged intermediates have a significant effect on the thermodynamics and kinetics of these processes.

The reduction of CoII(salen) has been studied using gold microdisc electrodes in DMF containing several electrolytes (Bu4NBF4, NaBr, LiBr, LiClO4, CF3SO3Li), with concentrations in the range 0.1 - 100 mM. It is shown that the potential of the CoII(salen)/CoI(salen)- couple depends on the cation of the electrolyte and its concentration. Association constants for the ion pairs, determined by employing the commercially available simulation software, DigiSim, increase with decreasing crystallographic radius of the cation, thus, the data is interpreted in terms of formation of contact ion pairs between CoI(salen)- and the electrolyte cation.

It is demonstrated that the rates of the reaction of CoI(salen)- with alkyl halides (n-BuI, n-BuBr, EtBr) decrease with increasing electrolyte concentration and this is interpreted in terms of decreased nucleophillicity of CoI(salen)- due to ion pairing at high cation concentration. Rate constants for the reaction of RX with CoI(salen)- and Co(salen)-M+ are determined by simulation of experimental data. The choice and concentration of the supporting electrolyte was also found to influence the catalytic reduction of alkyl halides by CoII(salen), which occurs at more negative potentials. Catalysis of the reduction of 1,2-dibromobutane has also been studied at a range of concentrations of NaBr.

Au microdiscs are employed to study the influences of the supporting electrolyte on the voltammetry of a series of quinones (Q) in DMF. It is shown the anion radicals formed by transfer of one electron interact with all electrolyte cations studied and these interactions are stronger for op-quinones than p-quinones. Association constants for the ion pairs, determined using DigiSim, are found to increase in the order Bu4N+ < Na+ < Li+ in accordance with the formation of contact ion pairs. The reduction potential for the second electron transfer also appears to be influenced by ion pairing, although, in certain cases, the solubility of the product, QM2, determines the voltammetry.

University of Southampton
Thompson, Heather
Thompson, Heather

Thompson, Heather (1998) The influence of the supporting electrolyte on electrode processes and homogeneous chemical reactions. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The role of the supporting electrolyte in the electron transfer and coupled chemistry of several systems has been investigated using voltammetry at microdisc electrodes (radii 5 - 30 μm). It is shown that the interactions between electrolyte ions and charged intermediates have a significant effect on the thermodynamics and kinetics of these processes.

The reduction of CoII(salen) has been studied using gold microdisc electrodes in DMF containing several electrolytes (Bu4NBF4, NaBr, LiBr, LiClO4, CF3SO3Li), with concentrations in the range 0.1 - 100 mM. It is shown that the potential of the CoII(salen)/CoI(salen)- couple depends on the cation of the electrolyte and its concentration. Association constants for the ion pairs, determined by employing the commercially available simulation software, DigiSim, increase with decreasing crystallographic radius of the cation, thus, the data is interpreted in terms of formation of contact ion pairs between CoI(salen)- and the electrolyte cation.

It is demonstrated that the rates of the reaction of CoI(salen)- with alkyl halides (n-BuI, n-BuBr, EtBr) decrease with increasing electrolyte concentration and this is interpreted in terms of decreased nucleophillicity of CoI(salen)- due to ion pairing at high cation concentration. Rate constants for the reaction of RX with CoI(salen)- and Co(salen)-M+ are determined by simulation of experimental data. The choice and concentration of the supporting electrolyte was also found to influence the catalytic reduction of alkyl halides by CoII(salen), which occurs at more negative potentials. Catalysis of the reduction of 1,2-dibromobutane has also been studied at a range of concentrations of NaBr.

Au microdiscs are employed to study the influences of the supporting electrolyte on the voltammetry of a series of quinones (Q) in DMF. It is shown the anion radicals formed by transfer of one electron interact with all electrolyte cations studied and these interactions are stronger for op-quinones than p-quinones. Association constants for the ion pairs, determined using DigiSim, are found to increase in the order Bu4N+ < Na+ < Li+ in accordance with the formation of contact ion pairs. The reduction potential for the second electron transfer also appears to be influenced by ion pairing, although, in certain cases, the solubility of the product, QM2, determines the voltammetry.

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Published date: 1998

Identifiers

Local EPrints ID: 463418
URI: http://eprints.soton.ac.uk/id/eprint/463418
PURE UUID: 0da01ae6-81de-4225-862b-7cc6c63cf656

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Date deposited: 04 Jul 2022 20:51
Last modified: 04 Jul 2022 20:51

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Author: Heather Thompson

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