A laser flash photolysis kinetic study of reactions of the Cl-2(-) radicalanion with oxygenated hydrocarbons in aqueous solution

A laser photolysis-long path laser absorption (LP-LPLA) experiment has been used to determine the rate constants for H-atom abstraction reactions of t he dichloride radical anion (Cl-2(-)) in aqueous solution. From direct meas urements of the decay of Cl-2(-) in the presence of different reactants at pH = 4 and I = 0. 1 M the following rate constants at T = 298 K were derive d: methanol, (5.1 +/- 0.3) 10(4) M-1 S-1; ethanol, (1.2 +/- 0.2) 10(5) M-1 s(-1); 1-propanol, (1.01 +/- 0.07) 10(5) M-1 s(-1); 2-propanol, (1.9 +/- 0. 3) 105 M-1 S-1; tert.-butanol, (2.6 +/- 0.5) 104 M-1 s(-1); formaldehyde, ( 3.6 +/- 0.5) 10(4) M-1 s(-1); diethylether, (4.0 +/- 0.2) 10(5) M-1 s(-1); methyltert.-butylether, (7 +/- 1) 10(4) M-1 s(-1); tetrahydrofuran, (4.8 +/ - 0.6) 105 M-1 s(-1); acetone, (1.41 +/- 0.09) 10(3) M-1 s(-1). For the rea ctions of Cl-2(-) with formic acid and acetic acid rate constants of (8.0 /-: 1.4) 10(4) M-1 s(-1) (pH = 0, I = 1.1 M and T= 298 K) and (1.5 +/- 0.8) 10(3) M-1 s(-1) (pH = 0.42, I = 0.48 M and T= 298 K), respectively, were d erived. A correlation between the rate constants at T = 298 K for all oxygenated hy drocarbons and the bond dissociation energy (BDE) of the weakest C-H-bond o f log k(2nd) = (32.9 +/- 8.9) (0.073 +/- 0.022) BDE/kJ mol(-1) is derived. From temperature-dependent measurements the following Arrhenius expressions were derived: k(Cl-2(-) + HCOOH) = (2.00 +/- 0.05) . 10(10 .) exp(-(4500 +/- 200) K/T) M- 1 s(-1), E-a = (37 +/- 2) kJ mol(-1) k(Cl-2(-) + CH3COOH) = (2.7 +/- 0.5) .10(10) . exp(-(4900 +/- 1300) k/T) M- 1 s(-1), E-a= (41 +/- 11) kJ mol(-1).