Abstract
Absolute rate constants for reactions of the dichlorine radical anion, Cl{sub 2}{sup {sm_bullet}{minus}}, with unsaturated alcohols and hydrocarbons have been measured at various temperatures. The alcohol reactions were measured in aqueous solutions and the hydrocarbon reactions in 1:1 aqueous acetonitirle (ACN) solutions. The rate constants for two alcohols and one hydrocarbon were also examined as a function of solvent composition. The room temperature rate constants varied between 10{sup 6} and 10{sup 9} M{sup {minus}1} s{sup {minus}1}. The pre-exponential factors, A, were about (1-5) {times} 10{sup 9} M{sup {minus}1} s{sup {minus}1} for the alcohols in aqueous solutions and about (0.1-1) {times} 10{sup 9} M{sup {minus}1} s{sup {minus}1} for the hydrocarbons in aqueous ACN solutions. The activation energies, E{sub a}, varied considerably, between 4 and 12 kJ mol{sup {minus}1} for the alcohols and between 2 and 8 kJ mol{sup {minus}1} for the hydrocarbons. The rate constants, k{sub 298}, decrease with increasing ionization potential (IP) of the unsaturated compound, in agreement with an electrophilic addition mechanism. The activation energies for the unsaturated alcohols decrease when the IP decreases from 9.7 to 9.1 eV but appear to level off at lower IP. Most alkenes studied had IP < 9.1 eV and showed little changemore » in E{sub a}. Upon addition of ACN to the aqueous solution, the values of log k{sub 298} decreased linearly by more than 1 order of magnitude with increasing ACN mole fraction. This decrease appears to result from a combination of changes in the activation energy and in the pre-exponential factor. The reason for these changes may lie in changes in the solvation shell of the Cl{sub 2}{sup {sm_bullet}{minus}} radical, which will affect the A factor, in combination with changes in solvation of Cl{sup {minus}}, which will affect the energetics of the reactions as well. 20 refs., 7 figs., 6 tabs.« less
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