title: Isotope Fractionation Associated with the Photochemical Dechlorination of Chloroanilines.
abstract: Isotope fractionation associated with the photochemical transformation of organic contaminants is not well understood and can arise not only from bond cleavage reactions but also from photophysical processes. In this work, we investigated the photolytic dechlorination of 2-Cl- and 3-Cl-aniline to aminophenols to obtain insights into the impact of the substituent position on the apparent (13)C and (15)N kinetic isotope effects (AKIEs). Laboratory experiments were performed in aerated aqueous solutions at an irradiation wavelength of 254 nm over the pH range 2.0 to 7.0 in the absence and presence of Cs(+) used as an excited singlet state quencher. Photolysis of 2-Cl-anilinium cations exhibits normal C and inverse N isotope fractionation, while neutral 2-Cl-aniline species shows inverse C and normal N isotope fractionation. In contrast, the photolysis of 3-Cl-aniline was almost insensitive to C isotope composition and the moderate N isotope fractionation points to rate-limiting photophysical processes. (13)C- and (15)N-AKIE-values of 2-Cl-aniline decreased in the presence of Cs(+), whereas those for 3-Cl-aniline were not systematically affected by Cs(+). Our current and previous work illustrates that photolytic dechlorinations of 2-Cl-, 3-Cl-, and 4-Cl-aniline isomers are each accompanied by distinctly different and highly variable C and N isotope fractionation due to spin selective isotope effects.
authors.affiliation: †Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland.|‡Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich, CH-8092 Zürich, Switzerland.
authors.forename: Marco
authors.initials: M
authors.lastname: Ratti
authors.affiliation: †Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland.
authors.forename: Silvio
authors.initials: S
authors.lastname: Canonica
authors.affiliation: ‡Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich, CH-8092 Zürich, Switzerland.
authors.forename: Kristopher
authors.initials: K
authors.lastname: McNeill
authors.affiliation: †Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland.
authors.forename: Jakov
authors.initials: J
authors.lastname: Bolotin
authors.affiliation: †Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland.|‡Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich, CH-8092 Zürich, Switzerland.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Hofstetter
mesh_terms: D000814:Aniline Compounds / Q000737:chemistry*; D002247:Carbon Isotopes; D005591:Chemical Fractionation; D054879:Halogenation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009587:Nitrogen Isotopes; D055668:Photochemical Processes; D010782:Photolysis
chemical_list: D000814:Aniline Compounds; D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; C023650:aniline