Mixed solvents, electrochemical reaction

The first controversial point in this mechanism is the nature of the reaction planes where the precursor formation and the ET reaction take place. Samec assumed that the ET step occurs across an ion-free layer composed of oriented solvent molecules [1]. By contrast, Girault and Schiffrin considered a mixed solvent region where electrochemical potentials are dependent on the position of the reactants at the interface [60]. From a general perspective, the phenomenological ET rate constant can be expressed in terms of... 

Electrochemical properties of samarium(ii) iodide are very sensitive to the nature of solvents. Reduction potential increases by replacing THE with a more polar solvent, such as DME or CH3CN. Addition of HMPA to a THE solution of samarium(ii) iodide leads to a substantial increase in the electron-donating nature of samarium(ii). The principal samarium(ii) species in a mixed solvent of THE and HMPA is an ionic cluster of [Sm(HMPA)4(THE)2] 2I in HMPA-THF (4 1) or [Sm(HMPA)6] 2I in HMPA-THE (>10 1). The reactivity order of the samarium(ii) complexes is [Sm(HMPA)6] 2I > [Sm(HMPA)4(THF)2] 2P > Sml2 in the reaction with 1-iodobutane. 

In previous chapters, we dealt with various electrochemical processes in non-aque-ous solutions, by paying attention to solvent effects on them. Many electrochemical reactions that are not possible in aqueous solutions become possible by use of suitable non-aqueous or mixed solvents. However, in order for the solvents to display their advantages, they must be sufficiently pure. Impurities in the solvents often have a negative influence. Usually commercially available solvents are classified into several grades of purity. Some of the highest-grade solvents are pure enough for immediate use, but all others need purification before use. In this chapter, the effects of solvent impurities on electrochemical measurements are briefly reviewed in Section 10.1, popular methods used in solvent purification and tests of impurities are outlined in Sections 10.2 and 10.3, respectively, and, finally, practical purification procedures are described for 25 electrochemically important solvents in Section 10.4. 

Galus, Z., in Advances in Electrochemical Science and Engineering, Vol. 2 (Eds H. Gerischer, C.W. Tobias), VCH, Weinheim, 1994, pp. 217-295. Thermodynamics and kinetics of electrode reactions in non-aqueous and mixed solvents. 

HP he study of the behavior of electrolytes in mixed solvents is currently arousing considerable interest because of its practical and fundamental implications (1). Among the simpler binary solvent mixtures, those where water is one component are obviously of primary importance. We have recently compared the effects of small quantities of water on the thermodynamic properties of selected 1 1 electrolytes in sulfolane, acetonitrile, propylene carbonate, and dimethylsulfoxide (DMSO). These four compounds belong to the dipolar aprotic (DPA) class of solvents that has received a great deal of attention (2) because of their wide use as media for physical separations and chemical and electrochemical reactions. We interpreted our vapor pressure, calorimetry, and NMR results in terms of preferential solvation of small cations and anions by water and obtained... 

Sections 2 and 3 are concerned mainly with electrochemical reactions in single solvents, and electrode reactions occurring in mixed solvents are covered in Secs. 5-7. The chapter concludes with suggestions for future work. 

Mixtures of two solvents have frequently been used as a reaction medium. Such mixed solvents have also been applied in electrochemical analysis. Very often, water was one of the components of such binary mixtures. One should add here that even in experiments carried out in single solvents, especially with a relatively low donor number, water that has not been carefully removed could cause changes in thermodynamic and kinetic parameters of the electrochemical reaction under study. 

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