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

This study focuses on the detailed mechanism by which N-nitrosodimethylamine (NDMA) is photolyzed to form oxidized products, i.e., NO2− and NO3−, and reveals a key reactive species produced during the photolysis of NDMA. Under acidic conditions, NO2− formed from the photodecomposition of NDMA was more prevalent than NO3−. In this result, key species for the formation of NO2− are presumably N2O3 and N2O4 as termination products as well as NO and O2 as reactants. Conversely, under alkaline conditions, NO3− was more prevalent than NO2−. For this result, a key species for NO3− formation is presumably peroxynitrite (ONOO−). 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 × 108 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 ONOO− 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 NO2− and NO3−.

► This study reveals an unknown reactive species influencing the oxidized products. ► The detailed mechanistic study was performed with competition kinetics. ► The unknown reactive species having OH-like reactivity can be formed during photochemical decomposition of NDMA. ► This species would contribute to the formations of NO2− and NO3−.