Inhibitory effect of alkyl groups on N -nitrosamine formation from secondary and tertiary alkylamines with monochloramine

N -nitrosamines are contaminants of emerging concern, and controlling these chemicals in potable water and recycled water for potable reuse has become important for protecting public health. This study aimed to evaluate the influence of the alkyl chain lengths of N -nitrosamine precursors (secondary and tertiary amines) on the formation of N -nitrosamines via chloramination. The molar conversion efficiency from dimethylamine, an N -nitrosodimethylamine (NDMA) precursor, to NDMA (0.67%) was greater than that from diethylamine, an N -nitrosodiethylamine (NDEA) precursor, to NDEA (0.38%). Similarly, the molar conversion efficiency from trimethylamine to NDMA (0.92%) was greater than from triethylamine to NDEA (0.33%). Interestingly, a considerable difference in molar conversion efficiencies were observed for tertiary amines with the N, N -dialkyl- α -arylamine structure: the molar conversion efficiencies from N, N -dimethylbenzylamine and N, N -diethylbenzylamine to NDMA and NDEA were 50.2% and 1.7%, respectively. These results indicate that amines with ethyl groups have lower potentials for producing the corresponding N -nitrosamines than those with methyl groups. These differences in yields between amines with methyl and ethyl groups can be explained by the difference in electron density in the nitrogen atom of the amine, which influences the protonation of the amine and stabilization of intermediate species. These findings could be useful for enhancing source control of water and wastewater by regulating runoff or industrial wastewater containing high concentrations of specific N -nitrosamine precursors.