A laser flash photolysis kinetic study of reactions of the Cl2− radical anion with oxygenated hydrocarbons in aqueous solution
✍ Scribed by H.-W. Jacobi; F. Wicktor; H. Herrmann; R. Zellner
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 249 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0538-8066
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✦ Synopsis
A laser photolysis-long path laser absorption (LP-LPLA) experiment has been used to determine the rate constants for H-atom abstraction reactions of the dichloride radical anion (Cl 2 Ϫ ) in aqueous solution. From direct measurements of the decay of Cl 2 Ϫ in the presence of different reactants at pH ϭ 4 and I ϭ 0.1 M the following rate constants at T ϭ 298 K were derived: methanol, (5.1 Ϯ 0.3) • 10 4 M Ϫ1 s Ϫ1 ; ethanol, (1.2 Ϯ 0.2) • 10 5 M Ϫ1 s Ϫ1 ; 1-propanol, (1.01 Ϯ 0.07) • 10 5 M Ϫ1 s Ϫ1 ; 2-propanol, (1.9 Ϯ 0.3) • 10 5 M Ϫ1 s Ϫ1 ; tert.-butanol, (2.6 Ϯ 0.5) • 10 4 M Ϫ1 s Ϫ1 ; formaldehyde, (3.6 Ϯ 0.5) • 10 4 M Ϫ1 s Ϫ1 ; diethylether, (4.0 Ϯ 0.2) • 10 5 M Ϫ1 s Ϫ1 ; methyltert.-butylether, (7 Ϯ 1) • 10 4 M Ϫ1 s Ϫ1 ; tetrahydrofuran, (4.8 Ϯ 0.6) • 10 5 M Ϫ1 s Ϫ1 ; acetone, (1.41 Ϯ 0.09) • 10 3 M Ϫ1 s Ϫ1 . For the reactions of Cl 2 Ϫ with formic acid and acetic acid rate constants of (8.0 Ϯ 1.4) • 10 4 M Ϫ1 s Ϫ1 (pH ϭ 0, I ϭ 1.1 M and T ϭ 298 K) and (1.5 Ϯ 0.8) ⅐ 10 3 M Ϫ1 s Ϫ1 (pH ϭ 0.42, I ϭ 0.48 M and T ϭ 298 K), respectively, were derived.
A correlation between the rate constants at T ϭ 298 K for all oxygenated hydrocarbons and the bond dissociation energy (BDE) of the weakest C-H-bond of log k 2nd ϭ (32.9 Ϯ 8.9) Ϫ (0.073 Ϯ 0.022) • BDE/kJ mol Ϫ1 is derived.
From temperature-dependent measurements the following Arrhenius expressions were derived:
a Ϫ 10 Ϫ1 Ϫ1 k (Cl ϩ CH COOH) ϭ (2.7 Ϯ 0.5) • 10 • exp(Ϫ(4900 Ϯ 1300) K/T) M s , 2 3 Ϫ1 E ϭ (41 Ϯ 11) kJ mol a