title: Isotope fractionation associated with the direct photolysis of 4-chloroaniline.
abstract: Compound-specific isotope analysis is a useful approach to track transformations of many organic soil and water pollutants. Applications of CSIA to characterize photochemical processes, however, have hardly been explored. In this work, we systematically studied C and N isotope fractionation associated with the direct photolysis of 4-Cl-aniline used as a model compound for organic micropollutants that are known to degrade via photochemical processes. Laboratory experiments were carried out at an irradiation wavelength of 254 nm over the pH range 2.0 to 9.0 as well as in the presence of Cs(+) as a quencher of excited singlet 4-Cl-aniline at pH 7.0 and 9.0. We observed considerable variation of C and N isotope enrichment factors, ϵC and ϵN, between -1.2 ± 0.2‰ to -2.7 ± 0.2‰ for C and -0.6 ± 0.2‰ to -9.1 ± 1.6‰ for N, respectively, which could not be explained by the speciation of 4-Cl-aniline alone. In the presence of 1 M Cs(+), we found a marked increase of apparent (13)C-kinetic isotope effects ((13)C-AKIE) and decrease of 4-Cl-aniline fluorescence lifetimes. Our data suggest that variations of C and N isotope fractionation originate from heterolytic dechlorination of excited triplet and singlet states of 4-Cl-aniline. Linear correlations of (13)C-AKIE vs (15)N-AKIE were distinctly different for these two reaction pathways and may be explored further for the identification of photolytic aromatic dechlorination reactions.
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: ‡Institute of Biogeochemistry and Pollutant Dynamics (IBP), ETH Zürich, CH-8092 Zürich, Switzerland.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Erickson
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 / Q000737:chemistry; D005591:Chemical Fractionation; D004785:Environmental Pollutants / Q000737:chemistry; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009587:Nitrogen Isotopes / Q000737:chemistry; D010782:Photolysis
chemical_list: D000814:Aniline Compounds; D002247:Carbon Isotopes; D004785:Environmental Pollutants; D009587:Nitrogen Isotopes; C004658:4-chloroaniline