Formation of Reactive Species Enhanced by H₂O₂Addition in the Photodecomposition of N-Nitrosodimethylamine (NDMA)

Abstract

This study noted that the actual mechanism of N-nitrosodimethylamine (NDMA) photodecomposition in the presence of H 2 O 2 is missing from the previous works. This study investigated a key unknown reactive species (URS) enhanced by the addition of H 2 O 2 during the photolysis of NDMA with H 2 O 2 , not hydroxyl radicals. In order to provide experimental evidences in support of URS formation, we have mainly used p-nitrosodimethylaniline, methanol, and benzoic acid as well-known probes of •OH in this study. Both loss of PNDA and formation of hydroxybenzoic acids were dependent on NDMA concentrations during the photolysis in a constant concentration of H 2 O 2 . In particular, competition kinetics showed that the relative reactivity of an URS was at least identical with •OH-like reactivity. In addition, the decay of NDMA was estimated to be about 65% by the direct UV light and about 35% by the reactive species or URS generated through the photolysis of NDMA and H 2 O 2 . Therefore, our data suggest that a highly oxidizing URS is formed in the photolysis of NDMA with H 2 O 2 , which could be peroxynitrite (ONOO -) as a potent oxidant by itself as well as a source of •OH.

Mechanistic Insight into the Degradation of Nitrosamines via Aqueous-Phase UV Photolysis or a UV-Based Advanced Oxidation Process: Quantum Mechanical Calculations

“…This latter pathway involves several barrierless reactions, and is dominant over the pathway involving the addition of molecular oxygen. The formation of N -methylidenemethylamine was also postulated in a previous report [ 18 , 19 ].…”

“…However, some of the pathways involved in the formation of transformation products are still unknown. UV-induced NDMA degradation was also studied and identified previously unknown reactive species in the NDMA degradation pathways [ 17 , 18 , 19 ]. The HO • -induced NDMA degradation mechanisms were studied in an ozone-based AOP, and general reaction mechanisms were proposed [ 20 , 21 ].…”

Predicting the Organic Compound Degradation in Aqueous-Phase Ultraviolet (Uv) and Uv-Based Advanced Oxidation Processes

“…The formation of N-methylidenemethylamine was also postulated in a previous report [26]. kcal/mol) and CH3NNO(CH2)2 • CH2 (−23.9 kcal/mol) are very similar to those that were observed for typical molecular oxygen addition to C-centered radicals.…”

“…However, some of the pathways involved in the formation of transformation products are still unknown. UV-induced NDMA degradation was also studied and identified previously unknown reactive species in the NDMA degradation pathways [25,26]. The HO • -induced NDMA degradation mechanisms were studied in an ozone-based AOP, and general reaction mechanisms were proposed [27,28].…”

“…Previous studies suggested that the formation of nitrate was a result of the presence of peroxynitrite (ONOO -) but Kwon et al showed this is not possible due to the pKa value of peroxynitrite relative to the acidic conditions in the study. Rather a new mechanism for the creation of nitrate is proposed[25,26]. The initial pathways through which NDMA degrades by UV photolysis are well understood and some of the subsequent reactions involving the products of the initial pathways have been identified.…”