Abstract:
The neonicotinoid nitenpyram (NPM) is a multifunctional nitroenamine [(R1N)(R2N)C=CHNO2]
pesticide. As a nitroalkene, it is structurally similar to other emerging contaminants such as the
pharmaceuticals ranitidine and nizatidine. Because ozone is a common atmospheric oxidant,
such compounds may be oxidized on contact with air to form new products that have different
toxicity compared to the parent compounds. Here we show that oxidation of thin solid films of
NPM by gas-phase ozone produces unexpected products, the majority of which do not contain
oxygen, despite the highly oxidizing reactant. A further surprising finding is the formation of
gas-phase nitrous acid (HONO), a species known to be a major photolytic source of the highly
reactive hydroxyl radical in air. The results of application of a kinetic multilayer model show that
reaction was not restricted to the surface layers but, at sufficiently high ozone concentrations,
occurred throughout the film. The rate constant derived for the O3−NPM reaction is 1 ×
10−18
cm
3
⋅s
−1
, and the diffusion coefficient of ozone in the thin film is 9 × 10−10
cm
2
⋅s
−1
. These
findings highlight the unique chemistry of multifunctional nitroenamines and demonstrate that
known chemical mechanisms for individual moieties in such compounds cannot be extrapolated
from simple alkenes. This is critical for guiding assessments of the environmental fates and
impacts of pesticides and pharmaceuticals, and for providing guidance in designing better future
alternatives.
