Insights into C-C Bond Cleavage Mechanisms in Dichloroacetonitrile Formation during Chlorination of Long-Chain Primary Amines, Amino Acids, and Dipeptides.
Environ Sci Technol
; 57(47): 18834-18845, 2023 Nov 28.
Article
em En
| MEDLINE
| ID: mdl-37183372
ABSTRACT
Dichloroacetonitrile (DCAN) as one of the potentially prioritized regulated DBPs has drawn great attention; however, understanding its formation, especially the C-C bond cleavage mechanisms, is limited. In this study, DCAN formation mechanisms from long-chain primary amines, amino acids, and dipeptides during chlorination were investigated by a combined computational and experimental approach. The results indicate that nitriles initially generate for all of the above precursors, then they undergo ß-C-hydroxylation or/and α-C-chlorination processes, and finally, DCAN is produced through the Cα-Cß bond cleavage. For the first time, the underlying mechanism of the C-C bond cleavage was unraveled to be electron transfer from the O- anion into its attached C atom in the chlorinated nitriles, leading to the strongly polarized Cα-Cß bond heterocleavage and DCAN- formation. Moreover, DCAN molar yields of precursors studied in the present work were found to be determined by their groups at the γ-site of the amino group, where the carbonyl group including -CO2-, -COR, and -CONHR, the aromatic group, and the -OH group can all dramatically facilitate DCAN formation by skipping over or promoting the time-consuming ß-C-hydroxylation process and featuring relatively lower activation free energies in the C-C bond cleavage. Importantly, 4-amino-2-hydroxybutyric acid was revealed to possess the highest DCAN yield among all the known aliphatic long-chain precursors to date during chlorination. Additionally, enonitriles, (chloro-)isocyanates, and nitriles can be generated during DCAN formation and should be of concern due to their high toxicities.
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Base de dados:
MEDLINE
Assunto principal:
Poluentes Químicos da Água
/
Purificação da Água
Idioma:
En
Ano de publicação:
2023
Tipo de documento:
Article
País de afiliação:
China