Kinetics and Mechanisms of the Reactions of Hydroxyl Radicals and Hydrated Electrons with Nitrosamines and Nitramines in Water

Abstract

Absolute rate constants for hydroxyl radical, *OH, and hydrated electron, e(aq)(-), reactions with low-molecular-weight nitrosamines and nitramines in water at room temperature were measured using the techniques of electron pulse radiolysis and transient absorption spectroscopy. The bimolecular rate constants obtained, k (M(-1) s(-1)), for e(aq)(-) and *OH reactions, respectively, were as follows: methylethylnitrosamine, (1.67 +/- 0.06) x 10(10) and (4.95 +/- 0.21) x 10(8); diethylnitrosamine, (1.61 +/- 0.06) x 10(10) and (6.99 +/- 0.28) x 10(8); dimethylnitramine, (1.91 +/- 0.07) x 10(10) and (5.44 +/- 0.20) x 10(8); methylethylnitramine, (1.83 +/- 0.15) x 10(10) and (7.60 +/- 0.43) x 10(8); and diethylnitramine, (1.76 +/- 0.07) x 10(10) and (8.67 +/- 0.48) x 10(8), respectively. MNP/DMPO spin-trapping experiments demonstrated that hydroxyl radical reaction with these compounds occurs by hydrogen atom abstraction from an alkyl group, while the reaction of the hydrated electron was to form a transient radical anion. The latter adduct formation implies that the excess electron could subsequently be transferred to regenerate the parent chemical, which would significantly reduce the effectiveness of any free-radical-based remediation effort on nitrosamine/nitramine-contaminated waters.

Free Radical Chemistry of Advanced Oxidation Process Removal of Nitrosamines in Waters

“…In these data a consistent trend was observed, in which the reaction rate constant became faster as the nitrosamine complexity increased. This is to be expected, as previous electron paramagnetic spin trap measurements for NDMA have shown that this oxidation reaction consists of hydrogen atom abstraction from the molecule (15,18). In the more complex nitrosamines, thermodynamic considerations suggest that the hydroxyl radical reaction would also be a hydrogen atom abstraction, but mainly from one of the methylene (-CH 2 -) groups.…”

“…Nitrosamines were either commercially purchased (Sigma-Aldrich, > 99%) or synthesized from the corresponding amine using standard methodologies (15). All sample solutions were prepared in water filtered through a Millipore Milli-Q system constantly illuminated by a UV lamp to maintain total organic carbon levels below 13 μg/L, as measured by an on-line analyzer.…”

Tropospheric Aqueous‐Phase Free‐Radical Chemistry: Radical Sources, Spectra, Reaction Kinetics and Prediction Tools

“…Amines are currently heavily discussed in atmospheric chemistry due to their abundance in marine [44,45] and small, newly formed [46] particles. Furthermore, the reactions of OH with some derivatives such as nitrosamines and nitramines have been newly investigated by Mezyk et al [47] Aromatics A number of new rate constants is available for mostly deactivated aromatic benzene, phenol and benzoic acid derivatives from the studies of Monod et al, [28] Zona et al, [48] Kwon et al, [49] Einschlag et al, [50] Elovitz et al, [51] Makarov et al, [52] Elovitz et al, [51] and Geeta et al [53] All reported data do refer to room temperature rate constants only with 23 new determinations and 12 remeasurements, and for four major differences in the rate constants are observed (Table 7).…”

Mechanism and Kinetics of the Reaction of Nitrosamines with OH Radical: A Theoretical Study

“…S2-S4 in the Supporting Information. The reaction of the radicals (6), (8), and (10) with O 2 resulting in formation of peroxy radical intermediates (20), (21), and (22) in the barrierless reaction. Table I summarizes the enthalpy of formation of the peroxy radicals and compared with available literature data of the enthalpies of formation of the corresponding cycloalkyl peroxy radicals [52].…”

“…Tuazon et al studied the reaction of NDMA and dimethylnitramine (DMN) with the OH radical using the FTIR technique, and it is found that the rate constant for the degradation of NDMA is (2.4 ± 0.4) × 10 −12 cm 3 molecule −1 s −1 and for DMN; the rate constant is (4.5 ± 0.5) × 10 −12 cm 3 molecule −1 s −1 . Zabarnick et al used the laser photolysis technique to study the reaction between NDMA and OH and found a rate constant of (3.6 ± 0.1) × 10 −12 cm 3 molecule −1 s −1 at 296 K. Mezyk et al studied the absolute rate constants for the reaction of nitrosamines with the hydroxyl radical and hydrated electron. They reported that the rate constants increase with increasing in the complexity of alkyl substitution for the nitrosamines with the hydroxyl radical reaction.…”