Ethanol trapped electrons

FIGURE 6.4 A typical trapped electron absorption spectrum in ethanol at 4 K and the corresponding solvated electron spectrum at 77 K. The irradiation is at 4 K in both cases. Reproduced from Hase et a1. (1972a), with permission from Am. Inst. Phys.O... 

In turn, such a long-term accumulation of the trapped electrons indicates that the rate of withdrawal of the photogenerated electrons in reaction with water and ethanol in the absence of any additional electron transfer mediator proceeds with a small rate [11, 14]. 

The trapped electrons were formed simply by depositing alkali metal atoms on ice or solid alcohols at 77°K. Studies were made of the reactions between sodium or potassium atoms and ice (HgO or D2O), methanol, ethanol, isopropyl alcohol, t-butyl alcohol or dodecanol. The reactions of caesium, rubidium and lithium with ice were also investigated. The deposits were highly coloured and the optical and e.s.r. spectra showed that the electron was no longer associated with the alkali metal ion but had been transferred completely to the solid matrix. 

Minteer and co-workers have also exploited the broad substrate specificity of PQQ-dependent alcohol dehydrogenase and aldehyde dehydrogenase from Gluconobacter species trapped within Nahon to oxidize either ethanol or glycerol at a fuel cell anode [Arechederra et al., 2007]. Although the alcohol dehydrogenase incorporates a series of heme electron transfer centers, it is unlikely that many enzyme molecules trapped within the mediator-free Nahon polymer are electronically engaged at the electrode. 

Fig. 6. The time dependence [12] of the concentration of anion radicals of (a) biphenyl and (b) of triphenylethylene in vitreous ethanol containing 0.15 M of biphenyl + various amounts of triphenylethylene. T — 77 K. The solid lines are theoretical curves calculated using eqn. (7) of Chap. 5 and the values of ve = I0132s 1, ae = 1.90A, a = 13.1 M-1. n(oo) is the concentration of triphenylethylene anion radical in a sample containing 0.15 M of PhaEt and no Ph2 in which, by the time t = 10 6s, all the electrons have been trapped by the molecules of Ph3Et.

In view of the possibility that existing bands may simply be smeared out at room temperature by the thermal disorder in the liquid and the resulting fluctuations in the structure of the electron trap, Arai and Sauer (4) have determined the absorption spectrum of the solvated electron in ethanol at —78° C. No structure was observed, so that evidence is lacking for a transition to a second level, Is - 3p, even at the lower temperature. The absorption maximum was, however, found to be shifted from 7000 A. at 23 ° C. to 5800 A. at — 78 ° C. It is interesting to note that the half-width of the band remained the same, about 1.5 e.v., at the lower temperature. 

A typical example is seen for 1-hydroxyethyl radical trapped in a y-irra-diated ethanol matrix at 77 K [16]. As is shown in Fig. 2, the cw ESR spectrum of the radical is composed of five lines due to hyperfine interactions with one a proton and three P protons of a methyl group. The hyperfine interaction depends on the location of the P protons with respect to the p. orbital of the unpaired electron. However, the observed hyperfine coupling constant is the same for all the p protons because of the quick rotation of the methyl group in the time scale of the cw ESR measurement. On the other hand, the ESE-detected ESR spectrum is composed of four lines due to the hyperfine interactions with... 

From the correlations depicted in Sec. 4.1, information is also obtained on hole scavenging, temperature effects, e solvation, etc. Among many other applications of PAT in fast radiolysis, the aggregation of alcohol molecules in an alkane and the solvation of e in such a system is notheworthy. The ethanol molecules remain dispersed in the alkane at low alcohol concentration (C), as reflected by the small change in I3. With increasing C, the alcohol molecules aggregate and trap the electrons which can then solvate I3 decreases very rapidly. The variations of I3 also parallel those of the electron yield [120, 121]. 

Shields, L. Electron Trapping in Rigid Ethanol-Methyl-2-Tetrahydrofuran Mixtures. J. Phys. Chem. 69, 3186 (1965). 

This direct conversion of benzene to phenol is of great practical importance [58c]. The surface oxygen radical anion, 0 , formed through a reaction of N7O with electrons trapped on the surface of MgO, reacts with methane at 298 K [59], The partial oxidation of ethane to ethanol and acetaldehyde over iron phosphate catalyst (573-773 K) by using nitrous oxide as an oxidant has been reported [60],... 

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