Kinetics and mechanisms of the reactions of hydroxyl radicals and hydrated electrons with nitrosamines and nitramines in water

Absolute rate constants for hydroxyl radical, •OH, and hydrated electron, eaq-, 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 eaq- and •OH reactions, respectively, were as follows: methylethylnitrosamine, (1.67 ± 0.06) × 1010 and (4.95 ± 0.21) × 108; diethylnitrosamine, (1.61 ± 0.06) × 1010 and (6.99 ± 0.28) × 108; dimethylnitramine, (1.91 ± 0.07) × 1010 and (5.44 ± 0.20) × 108; methylethylnitramine, (1.83 ± 0.15) × 1010 and (7.60 ± 0.43) × 108; and diethylnitramine, (1.76 ± 0.07) × 1010 and (8.67 ± 0.48) × 108, 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.