title: Chlorination of Amino Acids: Reaction Pathways and Reaction Rates.
abstract: Chlorination of amino acids can result in the formation of organic monochloramines or organic dichloramines, depending on the chlorine to amino acid ratio (Cl:AA). After formation, organic chloramines degrade into aldehydes, nitriles and N-chloraldimines. In this paper, the formation of organic chloramines from chlorination of lysine, tyrosine and valine were investigated. Chlorination of tyrosine and lysine demonstrated that the presence of a reactive secondary group can increase the Cl:AA ratio required for the formation of N,N-dichloramines, and potentially alter the reaction pathways between chlorine and amino acids, resulting in the formation of unexpected byproducts. In a detailed investigation, we report rate constants for all reactions in the chlorination of valine, for the first time, using experimental results and modeling. At Cl:AA = 2.8, the chlorine was found to first react quickly with valine (5.4 × 104M-1s-1) to form N-monochlorovaline, with a slower subsequent reaction with N-monochlorovaline to form N,N-dichlorovaline (4.9 × 102M-1s-1), although some N-monochlorovaline degraded into isobutyraldehyde (1.0 × 10-4s-1). The N,N-dichlorovaline then competitively degraded into isobutyronitrile (1.3 × 10-4s-1) and N-chloroisobutyraldimine (1.2 × 10-4s-1). In conventional drinking water disinfection, N-chloroisobutyraldimine can potentially be formed in concentrations higher than its odor threshold concentration, resulting in aesthetic challenges and an unknown health risk.
authors.affiliation: Curtin Water Quality Research Centre, Department of Chemistry, Curtin University , GPO Box U1987 Perth, Western Australia Australia 6845.
authors.forename: Zuo Tong
authors.identifier: http://orcid.org/0000-0002-8473-5762
authors.initials: ZT
authors.lastname: How
authors.affiliation: Curtin Water Quality Research Centre, Department of Chemistry, Curtin University , GPO Box U1987 Perth, Western Australia Australia 6845.
authors.forename: Kathryn L
authors.identifier: http://orcid.org/0000-0002-3743-0640
authors.initials: KL
authors.lastname: Linge
authors.affiliation: Curtin Water Quality Research Centre, Department of Chemistry, Curtin University , GPO Box U1987 Perth, Western Australia Australia 6845.
authors.forename: Francesco
authors.initials: F
authors.lastname: Busetti
authors.affiliation: Curtin Water Quality Research Centre, Department of Chemistry, Curtin University , GPO Box U1987 Perth, Western Australia Australia 6845.
authors.forename: Cynthia A
authors.identifier: http://orcid.org/0000-0003-4761-7350
authors.initials: CA
authors.lastname: Joll
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002700:Chloramines / Q000737:chemistry; D002713:Chlorine / Q000737:chemistry; D004203:Disinfection; D054879:Halogenation; D018508:Water Purification
chemical_list: D000596:Amino Acids; D002700:Chloramines; D002713:Chlorine