Re-Examining the Role of Dichloramine in High-Yield N‑Nitrosodimethylamine Formation from N,N‑Dimethyl-α-arylamines
journal contributionposted on 22.01.2018, 00:00 by Meredith E. Huang, Shiyang Huang, Daniel L. McCurry
N-Nitrosodimethylamine (NDMA) is a potent carcinogen associated with chloramination of wastewater and wastewater-impacted drinking waters. Substantial effort has been expended to identify the precursors and mechanisms leading to NDMA formation. One of the major discoveries has been that molecules in the N,N-dimethyl-α-arylamine class, including the common pharmaceutical ranitidine, form NDMA in high yield during chloramination. Simultaneously, it was hypothesized that these precursors react with monochloramine, the dominant species in most chloramine mixtures, to form NDMA. This monochloramine hypothesis contradicts past mechanistic work with simple secondary amines, as well as practical experience showing that minimization of dichloramine reduces the level of NDMA formation during wastewater reuse and drinking water treatment. In this work, we address the contradiction between practical experience and model precursor studies by showing that N,N-dimethyl-α-arylamines form NDMA chiefly via reactions with dichloramine, rather than monochloramine. We experimentally demonstrate substantially higher NDMA yields from dichloramination than from monochloramination of four N,N-dimethyl-α-arylamine compounds, including ranitidine, and computationally rationalize declining NDMA yields at large dichloramine doses, which may explain past results reporting low NDMA yields from dichloramination of ranitidine. These results provide support for NDMA control strategies currently under evaluation at wastewater reuse facilities.