Laser based spectroscopic and kinetic investigations of reactions of the Cl atom with oxygenated hydrocarbons in aqueous solution

Abstract

A time-resolved laser photolysis broadband diode array experiment has been used to measure the absorption spectrum of the chlorine atom in aqueous solution formed after excimer laser photolysis of chloroacetone and hypochlorous acid at λ = 248 nm. Laser photolysis-long path laser absorption at λ = 325 nm (He/Cd) was then applied to determine the rate coefficients for the reactions of the chlorine atom at T = 298 K with methanol, k1 = (1.0 ± 0.1)·109 M−1 s−1; ethanol, k2 = (2.2 ± 0.3)·109 M−1 s−1; 1-propanol, k3 = (2.2 ± 0.4)·109 M−1 s−1; 2-propanol, k4 = (3.2 ± 0.7)·109 M−1 s−1; tert-butanol, k5 = (1.5 ± 0.1)·109 M−1 s−1; diethyl ether, k6 = (1.3 ± 0.1)·109 M−1 s−1; methyl-tert-butyl ether, k7 = (1.3 ± 0.1)·109 M−1 s−1; tetrahydrofuran, k8 = (2.6 ± 0.4)·109 M−1 s−1; acetone, k9 = (7.8 ± 0.7)·107 M−1 s−1; formic acid, k10 = (2.8 ± 0.3)·109 M−1 s−1; acetic acid, k11 = (1.0 ± 0.2)·108 M−1 s−1; 2-butanol, k12 = (5.0 ± 0.6)·109 M−1 s−1; 2-butanone, k13 = (2.4 ± 0.3)·108 M−1 s−1; hydrated formaldehyde, k14 = (1.4 ± 0.3)·109 M−1 s−1; propionic acid, k15 = (1.2 ± 0.3)·109 M−1 s−1; isobutyric acid, k16 = (1.7 ± 0.3)·109 M−1 s−1; trichloromethane, k17 = (2.3 ± 0.5)·108 M−1 s−1 and dichloromethane, k18 = (9.3 ± 0.3)·106 M−1 s−1. A correlation between the rate constants at T = 298 K for all oxygenated hydrocarbons and the bond dissociation energy of the weakest C–H bond oflog kH/l mol−1 s−1 = (29 ± 9) − (5 ± 2)·10−2 BDE/kJ mol−1(n = 18, r = 0.88) is derived. From temperature dependent measurements (temperature range from 288 to 328 K) the following Arrhenius expressions were derived:k1 (Cl + CH3OH) = (7.9 ± 0.3)·1014 exp[−(4.1 ± 0.7)·103 K/T] l mol−1 s−1Ea = 34 ± 6 kJ mol−1k2 (Cl + CH3CH2OH) = (4.6 ± 0.4)·1012 exp[−(2.7 ± 0.9)·103 K/T] l mol−1 s−1Ea = 19 ± 7 kJ mol−1k3 (Cl + CH3CH2CH2OH) = (5.0 ± 0.4)·1012 exp[−(2.3 ± 0.8)·103 K/T] l mol−1 s−1Ea = 19 ± 7 kJ mol−1k4 (Cl + CH3CH(OH) CH3) = (2.8 ± 0.3)·1013 exp[−(3.3 ± 1.2)·103 K/T] l mol−1 s−1Ea = 23 ± 8 kJ mol−1k10 (Cl + HCOOH) = (8.9 ± 1.4)·1012 exp[−(2.8 ± 1.1)·103 K/T] l mol−1 s−1Ea = 20 ± 6 kJ mol−1k11 (Cl + CH3COOH) = (1.3 ± 0.1)·1015 exp[−(4.9 ± 1.4)·103 K/T] l mol−1 s−1Ea = 41 ± 11 kJ mol−1k14 (Cl + HCHO) = (4.7 ± 0.3)·1013 exp[−(3.9 ± 0.9)·103 K/T] l mol−1 s−1Ea = 26 ± 6 kJ mol−1k15 (Cl + CH3CH2COOH) = (6.4 ± 0.6)·1016 exp[−(9.8 ± 2.2)·103 K/T] l mol−1 s−1Ea = 44 ± 10 kJ mol−1k16 (Cl + CH3CH(CH3) COOH) = (5.7 ± 0.3)·1013 exp[−(3.8 ± 0.6)·103 K/T] l mol−1 s−1Ea = 26 ± 4 kJ mol−1A regression for the measured activation energies as a function of the bond dissociation energies (BDE) of the weakest C–H bond yields Ea = (0.8 ± 0.3) BDE/kJ mol−1 − (300 ± 100). The effects of ionic strength (Ieff) on the reactions of chlorine atom with methanol and hydrated formaldehyde were also investigated. A decrease of the rate constant with increasing Ieff was found. All the errors stated throughout this work are statistical errors for a confidence interval of 95%.