Solvated Electron Chemistry

Early work on the chemical interactions of solvated electrons arose due to an interest in effects caused by ionizing radiation. A further interest is in 

TABLE V. Kinetics Studies of Scavengers Using Photoemission at the Hg/Electrolyte Interface 

N2O product reactions with aqueous CH3OH, C2H5OH Disintegration rate of NO3  

OH- radical reaction rates with isopropyl, butyl and amyl alcohols, phenol, aniline 

CgHsCl and C6H5Br scavengers in DMF acetone radical anion formation Reduction and oxidation of CO2 reduction intermediates Hydroxyalkyl radical kinetics Reduction and oxidation of (CH3)2COH- radicals 

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II. SOLVATED ELECTRON CHEMISTRY FOR ENVIRONMENTAL REMEDIATION BACKGROUND AND FUNDAMENTALS... 

Solutions of alkali metals in liquid ammonia are used in organic chemistry as reducing agents. The deep blue solutions effectively contain solvated electrons (p. 126), for example... 

Background alkali metal chemistry. The alkali metals have the lowest ionization potentials of any group in the periodic table and hence their chemistry is dominated by the M+ oxidation state. However, it has been known for some time that a solution of an alkali metal (except lithium) in an amine or ether forms not only M+ ions and solvated electrons but also alkali anions of type M (Matalon, Golden Ottolenghi, 1969 Lok, Tehan Dye, 1972). That is, although an alkali metal atom very readily loses its single s-shell electron ... 

Ferradini, C., Jay-Gerin, J.-P., Eds. Excess Electrons in Dielectric Media. Ann Arbor CRC Press, 1991 Pikaev, A.K. The Solvated Electron in Radiation Chemistry. Israel Program for Scientific Translations Jerusalem, 1971. 

The solution chemistry that can be studied by photoemission techniques is largely that instigated by solvated electrons. It therefore has much in common... 

Current interest in the hydrated electron has sparked increased activity in the entire field of solvated electrons. If Conant and Hall had the hydrated electron at their disposal, they might have refrained from writing that 44Much important chemistry has been obscured by our slavish devotion to water. Now, because of the interconversion of hydrogen atoms and hydrated electrons in alkaline solutions and because the hydrated electron is a primary product in many photochemical processes, intensified studies on aqueous systems at the experimental and theoretical levels may be predicted. 

Jhe development of chemistry in the 20th century has been dominated and motivated by the electronic theory of the chemical bond and the role of electrons in chemical reactivity. The electronic structure of the chemical bond could be deduced by more or less direct methods, such as electronic excitation spectra, dipole moments, or paramagnetism but there was no direct indication for the transfer of electrons in chemical reactions. Using isotopic techniques it has been possible to demonstrate bond cleavage and atom transfer reactions, but it is impossible to label an electron and trace its transfer from one molecule to another. It was not until the discovery of the radiolytically produced solvated electron that electron transfer processes could be examined directly and unambiguously. 

An additional product of these studies was the characterization of many reduced species which have never before been produced or investigated. It may be concluded that the discovery of the solvated electron with its characteristic spectrum of absorption is one of the great achievements in chemistry of the last few decades—not only because it demonstrated the existence of a most elementary chemical species, but also because it firmly establishes the role of electron transfer in chemical reactivity. 

Earlier work (6) using this method yielded a second-order rate constant of 24.7 1.5 M""1 sec."1 for the reaction of dilute solutions of cesium with water in ethylenediamine. On the basis of optical absorption spectra (7) and other evidence (8, II), it was assumed that this reaction was that of the solvated electron as well as loosely bound electrostatic aggregates of electrons and cations with water. This permitted correlation with the results of aqueous radiation chemistry. 

The Electron Excess Center. In their earlier paper Schulte-Frohlinde and Eiben (57) had assigned the line A to the O ion and the other line to the stabilized electron subsequently they have reversed this assignment, and are therefore in agreement with other authors. However, the line with g = 2.0006 has been interpreted in different ways, although all interpretations relate it to the radiation-produced electron. Thus Schulte-Frohlinde and Eiben (57, 58) consider the species responsible for this line to be a stabilized free electron, while Ershov et al. (16) and Henriksen (23) identify it with a solvated electron or a po-laron in the same sense as these two terms are used in the radiation chemistry of water and aqueous solutions. According to the above authors, this species is not found in pure ice because of Reaction 30, whereas in alkaline systems such a reaction should not occur. (Henriksen does not offer any explanation about the specific role of alkali hydroxide in stabilizing the solvated electron. ) Both of these hypotheses can be shown to be incorrect. Thus, if Reaction 30 occurred to any extent in pure ice, one should be able to detect H atoms in neutral ice with a yield of at least as high as the maximum yield of the solvated electrons, viz.. 

A. K. Pikaev, Solvated Electron in Radiation Chemistry. Nauka, Moscow, 1969 (in Russian). 

Schuchmann MN, von Sonntag C (1982) Flydroxyl radical induced oxidation of diethyl ether in oxygenated aqueous solution. A product and pulse radiolysis study. J Phys Chem 86 1995-2000 Schuchmann MN, Schuchmann H-P, Knolle W, von Sonntag J, Naumov S, Wang W-F, von Sonntag C (2000) Free-radical chemistry of thiourea in aqueous solution, induced by OFI radical, FI atom, a-hydroxyalkyl radicals, photoexcited maleimide, and the solvated electron. Nukleonika 45 55-62... 

Pulse radiolysis is a powerful tool for the creation and kinetic investigation of highly reactive species. It was introduced to the field of radiation chemistry at the end of the 1950s and became popular in the early 1960s. Although the objects of this modern technique were, at first, limited to solvated electrons and related intermediates, it was soon applied to a variety of organic and inorganic substances. As early as 1964, ionic intermediates produced by electron pulses in vinyl monomers were reported for the first time. Since then, the pulse radiolysis method has achieved considerable success in the field of polymer science. 

The chemistry of gold is more diversified than that of silver. Six oxidation states, from -I to III and V, occur in its chemistry. Gold(-I) and Auv have no counterparts in the chemistry of silver. Solvated electrons in liquid ammonia can reduce gold to give the Au" ion which is stable in liquid ammonia (E° = -2.15 V). In the series of binary compounds MAu (M = Na, K, Rb, Cs), the metallic character decreases from Na to Cs. CsAu is a semiconductor with the CsCl structure and is best described as an ionic compound, Cs+Au . The electron affinity of gold (—222.7 kJ mol"1) is comparable to that of iodine (-295.3 kJ mol-1). Gold in the oxidation state -I is also found in the oxides (M+ Au O2 (M = Rb, Cs) these, too, have semiconducting properties.1... 

The free electron has been described as the simplest free radical, base and reducing agent (Dainton, 1967), a concept which assumes considerable importance with the discovery of solvated electrons as major reactants in radiation chemistry. The existence and reactions of this chemical entity have implications beyond the field of radiation chemistry since it may well be an intermediate in other reactions such as electron transfer and electrochemical reductions. 

A solvated electron may be regarded as the simplest radical anion. The chemistry of solvated electron reactions is qualitatively similar to radical anion reactions but the physical properties of electron solutions are very complicated [167]. They are not suitable as a model of radical anions. 

Kevan L. (1989) Solvated electron structure. In Kroh J (ed.). Early Developments in Radiation Chemistry. Royal Society of Chemistry, Cambridge, England, pp. 257-271. 

EJ Hart and M Anbar have detailed the characteristics and the chemistry of the solvated electron in water, otherwise known as the hydrated electron and denoted by e] y or e. A number of reviews on the solvated electron are also available.In this article, we will recall briefly the main steps of the discovery and the principal properties of the solvated electron. We will then depict its reactivity and focus on recent results concerning the effect of metal cations pairing with the solvated electron. At last, we will present results on the solvation dynamics of electron. Due to the development of ultrashort laser pulses, great strides have been made towards the understanding of the solvation and short-time reactivity of the electron, mainly in water but also in polar solvents. However, due to the vast and still increasing literature on the solvated electron, we do not pretend for this review to be exhaustive. 

The solvated electron is a transient chemical species which exists in many solvents. The domain of existence of the solvated electron starts with the solvation time of the precursor and ends with the time required to complete reactions with other molecules or ions present in the medium. Due to the importance of water in physics, chemistry and biochemistry, the solvated electron in water has attracted much interest in order to determine its structure and excited states. The solvated electrons in other solvents are less quantitatively known, and much remains to be done, particularly with the theory. Likewise, although ultrafast dynamics of the excess electron in liquid water and in a few alcohols have been extensively studied over the past two decades, many questions concerning the mechanisms of localization, thermalization, and solvation of the electron still remain. Indeed, most interpretations of those dynamics correspond to phenomenological and macroscopic approaches leading to many kinetic schemes but providing little insight into microscopic and structural aspects of the electron dynamics. Such information can only be obtained by comparisons between experiments and theoretical models. For that, developments of quantum and molecular dynamics simulations are necessary to get a more detailed picture of the electron solvation process and to unravel the structure of the solvated electron in many solvents. 

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