The formation of reactive species having hydroxyl radical-like reactivity from UV photolysis of N-nitrosodimethylamine (NDMA): Kinetics and mechanism

摘要

This study focuses on the detailed mechanism by which N-nitrosodimethylamine (NDMA) is photolyzed to form oxidized products, i.e., NO_2~- and NO_3~-, and reveals a key reactive species produced during the photolysis of NDMA Under acidic conditions, NO_2~- formed from the photodecomposition of NDMA was more prevalent than NOf. In this result, key species for the formation of NO_2~- are presumably N_2O_3 and N_2O_4 as termination products as well as NO and O_2 as reactants. Conversely, under alkaline conditions, NO_3~- was more prevalent than NO_2~-. For this result, a key species for NO_3~- formation is presumably peroxynitrite (ONOCT). A detailed mechanistic study was performed with a competition reaction (or kinetics) between NDMA and p-nitrosodimethylaniline (PNDA) probe for hydroxyl radical (OH). It is fortuitous that the second-order rate constant for NDMA with an unknown reactive species (URS) was 5.13 × 10~8 M~(-1) s~(-1), which was similar to its published value for the reaction of NDMA+ ·OH. Our study results showed that a key reactive species generated during NDMA photo-decomposition had hydroxyl radical-like reactivity and in particular, under alkaline conditions, it is most likely ONOC~- as a source of nitrate ion. Therefore, for the first time, we experimentally report that an URS having ·OH-like reactivity can be formed during photochemical NDMA decomposition. This URS could contribute to the formations of NO_2~- and NO_3~-.