Reaction rates of electrons in liquid methanol and ethanol: effects of pressure

Abstract

The value of the rate constant kl for the reaction e-s,lv + RO-s,lv + H, [I], at 295 K and 1 bar is 51.4 X lo5 s-1 in methanol and 5 8 X 104 s-1 in ethanol. The respective volumes of activation averaged between 1 bar and 2 kbar are AVl* 2 -21 and 5 -22 cm3 mol-1. A high concentration of potassium hydroxide (1 M) or water (5 M) decreases the apparent value of kl somewhat but has little or no effect on the value of AV,". The effect of pressure on the rate constant of e-s,lv + S + product, [2], was also measured for a series of solutes that displays a wide range of reactivity. Experimental values of AV2* depend on the relative contributions of the effects of solvent density on the reactant diffusion rates, the concentrations of the actual reacting species, and the relative energies of the reactant and intermediate states. For reactions whose rates are near the diffusion controlled limit, k2 = 10'0 M-1 s-1 in methanol and ethanol, the values of AV2' are positive and similar to those for the diffusion of simple ions. AV* (e-s,!v diffusion) = 4 cml mol-1 in methanol and 6 cml mol-1 in ethanol. Cadmium chlor~de IS apparently not completely dissociated in alcohols, and k(e-s,lv + CdC12) < k(e-s,lv + CdCl+) < k(e-,,lv + Cd2+). For a series of compounds with lower rate constants there is a correlation between log k2 and AVz*, the latter being negative for very low values of k2. The products of electron capture by benzene, toluene, ethyl acetate, and possibly acetonitrile appear to be stabilized by protonation: e-,,,I,. + S = S-,,lv, 13, -31,; S-s,lv + ROH + SH + ,I,,[4]. The results indicate that the decomposition of e-s,lv in a pure alcohol occurs by protonatlon of the electron site, e-s,lv + ROH -t H + RO-,,,,, 14'1, rather than by electron transfer to an alcohol molecule followed by decomposition of the anion. [Traduit par le journal]

Electron behavior in mixed solvents: optical spectra and reactivities in water/alkane diols

“…Electron capture by toluene, and probably by allyl alcohol, is stabilized by protonation (26,27): [4] S-, + ROH + i~ + RO-, Reaction [4] involves the rotation of solvent dipoles adjacent to the reaction site as the charge center changes from S-to RO-; the reaction rate should correlate with the dielectric relaxation For personal use only. (14,15).…”

Solvent effects on the reactivity of solvated electrons with ions in isobutanol/water mixed solvents

“…Possible exceptions are e; + ROH + H + RO; and e; + ROH;, + H + ROH in water and alcohols, where a proton from a solvating -OH or -OH; group might transfer to the site of the electron (3). Proton transfer to the "cavity" of the electron site might avoid the work needed to create a new site for the H atom if the electron were to transfer first, followed by decomposition of the transient ROH-or ROH2.…”

Ultrafast Reactivity of IR-Excited Electron in Aqueous Ionic Solutions

“…We have focused our attention on (i) the prevailing trajectory of IR prehydrated electrons, and (ii) the role of early branchings between reactive (eq 1a) and nonreactive (eq 1b) channels. Due to the low C 37 value of aqueous Cd 2+ , the computed kinetic model investigates a prehydration one-electron reduction of Cd 2+ . This ultrafast redox channel would be triggered by an electron photodetachment from excited aqueous chloride ions with a probability P Reac (eq 3).…”

“…In polar solutions, intermolecular electron transfer faster than the picosecond solvation process has been investigated by fluorescence up-conversion − but up to now competitive nonreactive electron dynamics (electron solvation) and ultrafast presolvation radical reactions in water have not be investigated at very short times. Nanosecond and picosecond pulse radiolysis studies have suggested that ultrafast radical reaction (univalent reduction of a solute) would involve hot electrons or short-lived precursors of hydrated electron. − These indirect investigations determine the subnanosecond G value of solvated electrons for different electron scavenger concentrations. The pulse radiolysis experiments treat the data by determining empirical relationships between the rate constant of an electron transfer and the C 37 value, − or stochastic analysis of competitive electron solvation and electron capture .…”

“…Nanosecond and picosecond pulse radiolysis studies have suggested that ultrafast radical reaction (univalent reduction of a solute) would involve hot electrons or short-lived precursors of hydrated electron. − These indirect investigations determine the subnanosecond G value of solvated electrons for different electron scavenger concentrations. The pulse radiolysis experiments treat the data by determining empirical relationships between the rate constant of an electron transfer and the C 37 value, − or stochastic analysis of competitive electron solvation and electron capture . The investigations of ultrafast electron transfers at the macroscopic level do not permit one (i) to understand in detail presolvation intermolecular charge transfer, and (ii) to determine the exact nature of early branching between short-lived nonreactive and reactive electronic configurations.…”