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A laser flash photolysis kinetic study of reactions of the Cl 2 − radical anion with oxygenated hydrocarbons in aqueous solution
Author(s) -
Jacobi H.W.,
Wicktor F.,
Herrmann H.,
Zellner R.
Publication year - 1999
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1999)31:3<169::aid-kin2>3.0.co;2-k
Subject(s) - chemistry , reaction rate constant , aqueous solution , methanol , formic acid , tetrahydrofuran , flash photolysis , formaldehyde , photodissociation , photochemistry , medicinal chemistry , organic chemistry , kinetics , solvent , physics , quantum mechanics
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 − ) in aqueous solution. From direct measurements 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 derived: 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)·10 5 M −1 s −1 ; tert.‐butanol, (2.6 ± 0.5)·10 4 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 ; methyl‐tert.‐butylether, (7 ± 1)·10 4 M −1 s −1 ; tetrahydrofuran, (4.8 ± 0.6)·10 5 M −1 s −1 ; acetone, (1.41 ± 0.09)·10 3 M −1 s −1 . For the reactions 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 derived. A correlation between the rate constants at T = 298 K for all oxygenated hydrocarbons and the bond dissociation energy (BDE) of the weakest C‐H‐bond of 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 −1k (Cl 2 − + CH 3 COOH) = (2.7 ± 0.5)·10 10 ·exp(−(4900 ± 1300) K/ T ) M −1 s −1 ,E a = (41 ± 11) kJ mol −1k (Cl 2 − + CH 3 OH) = (5.1 ± 0.9)·10 12 ·exp(−(5500 ± 1500) K/ T ) M −1 s −1 ,E a = (46 ± 13) kJ mol −1k (Cl 2 − + CH 2 (OH) 2 ) = (7.9 ± 0.7)·10 10 ·exp(−(4400 ± 700) K/ T ) M −1 s −1 ,E a = (36 ± 5) kJ mol −1Finally, in measurements at different ionic strengths ( I ) a decrease of the rate constant with increasing I has been observed in the reactions of Cl 2 − with methanol and hydrated formaldehyde. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 169–181, 1999