Pulse radiolytic induced transient electrical conductance in liquid solutions. Part 4.—The radiolysis of methanol, ethanol, 1-propanol and 2-propanol

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]

Section: Eflect Of Pressure On K2supporting

confidence: 91%

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

Bolton¹,

Robinson²,

Freeman³

1976

“…If, as seein most likely, reaction 3 occurs (22), then it has a rate constant greater than 2 X lo7 M-I s-I (assuming tl/z = 20 ns) even at 147 K ; this value is in good agree~n e n t with the values determined by Fowles (22 For personal use only.…”

Section: Resultssupporting

confidence: 65%

The pulse radiolysis of 1-propanol at 147 to 300 K

Gilles¹,

Boyd²

1976

Using -20 ns electron pulses the spectra and kinetics of the electron and an absorption in the uv in I-propanol have been determined at temperatvres from 147 to 300 K. The uv absorptio~~ is attributed to the hydroxy propyl radical,CH3CH2CHOH; it is formed within -20 ns over this temperature range and disappears by second order kinetics. The results for the formation of the solvated electron are in agreement with those of Baxendale and Wardman. The temperature dependence of both the radical-radical reaction and the reaction of the solvated electron with N 2 0 is very nearly the same as that of TItl.

“…By assunling the product to have about the same value for the alcohols one obtains u, =: 0.003 cm2/V s in methanol and 0.001, in ethanol at 298 K (Table I). These values are five-fold larger than those estimated (18) from results of Fowles (19) and data from Conway (20). Thus the electron mobility in an alcohol at 298 K appears to be several-fold larger than that of the alkoxide ion.…”

Section: Decay Of Esol-spectrummentioning

confidence: 57%

Radiolysis of Liquid Di-n-propyl Ether: Alcohol Formation and Solvated Electrons

VERMEER¹,

Freeman²

1974

In they radiolysis of pure di-11-propyl ether at 296 K, G(n-propanol) = 2.5 + 0.1. The propanol yield was reduced by the addition of an electron scavenger (SF,) or proton scavenger (C3H7NH2), but was not affected by the addition of hydrogen chloride or propylene. In the absence of additives the geminate neutralization reaction [7] R 2 0 H + + e,,,,-+ ROH + R gave 1.8 G units of alcohol. The charge scavenging reactions of SF, and C3H7NH2 were consistent with the nonhomogeneous kinetics model reported earlier. The optical absorbance of solvated electrons in di-tz-propyl ether increased with wavelength up to 1.6 y, the practical limit of the detector, at all temperatures in the liquid range, including the liquid supercooled to 140 K (f.p. = 151 K). The kinetics of electron reactions could be measured by observing theabsorption at 0.9 y. The optical absorbance observed as a function of time r at all temperatures was consistent with the kinetics model and had the general form: absorbance = b(t-'I2 + c)e-", where b is a proportionality constant, c is related to the free ion yield and k is a first order decay constant that describes the decay of the solvated electron free ions. At 273 K, k(e,,,,-+ SF,) = 4.5 x 10" M -' s-' and the activation energy is 3.2 + 0.3 kcal/mol.Le rendement en 12-propanol, G(n-propanol) = 2.5 0.1, provenant de I'irradiation gamma du di-n-propyle ether a 296 K, diminue par I'addition d'un capteur d'electrons (SF,) ou de protons (C3H,NH,), mais n'est pas influence par I'addition d'acide chlorhydrique ou de propylene.Dans I'ether pur, la neutralisation [7] R,OH+ + e,,,,--> ROH + R a un rendement en alcool de 1.8 unite G. Les reactions decapture de charges dces au SF, et C,H7NH2 sont compatibles avec un modele de cinitique nonhomogene propose precedemment. L'absorption optique pour I'electron solvate dans le di-n-propyle ether liquide augmente en fonction de la longueur d'onde jusqu'i 1.6 y, la limite pratique du spectrophotometre, et ce mtme dans le liquide surfondu a 140 K (la temperature de fusion est 151 K). La cinetique des reactions de I'electron est suivie par ]'observation a 0.9 y de son absorption optique. La variation de celle-ci en fonction du temps r est en accord avec le modele de cinetique non homogene, et est de la forme: