School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland.
Environ Sci Process Impacts. 2018 Oct 17;20(10):1479-1487. doi: 10.1039/c8em00335a.
N-Nitrosamines are an important class of potent human carcinogens and mutagens that can be present in water and wastewater. For instance, N-nitrosamines can be formed by reaction of nitrosating agents such as NO+ or N2O3 formed from nitrite under acidic conditions with secondary amine precursors by an acid-catalysed nitrosation pathway. This study investigates the catalytic effect of cationic and anionic micelles on the nitrosation of secondary aliphatic amines in the presence of nitrite at different pH values. The results of this study demonstrate that the nitrosation of hydrophobic secondary amines (e.g., dipropylamine and dibutylamine) by nitrite was significantly enhanced in the presence of micelles of the cationic surfactant cetyltrimethylammonium chloride whereas anionic micelles formed by sodium dodecylsulfate did not significantly enhance the formation of N-nitrosamines. Rate enhancements of up to 100-fold were observed for the formation of N-nitrosodibutylamine in the presence of cetyltrimethylammonium chloride. The magnitude of the catalytic effect of cationic micelles on the nitrosation reaction depended mainly of the hydrophobicity of the amine precursors (i.e., alkyl chain length), the stability and the charge of the micelles and pH. One important enhancement factor is the lowering of the pKa of the precursor alkylammonium ion due to the electrical potential at the micelle-water interface by up to ∼2.5 pH units. These results suggest that cationic micelle-forming surfactants might play a role in the formation of N-nitrosamines in wastewater, consumer products and in industrial processes using high concentrations of cationic surfactants.
亚硝胺是一类重要的强致癌和致突变物质，存在于水和废水中。例如，亚硝胺可以通过酸性条件下亚硝酸根形成的亚硝酰离子（如 NO+或 N2O3）与仲胺前体之间的酸催化亚硝化途径反应生成。本研究考察了阳离子和阴离子胶束在不同 pH 值下亚硝酸根存在时对仲脂肪胺亚硝化的催化作用。研究结果表明，在阳离子表面活性剂十六烷基三甲基氯化铵胶束的存在下，亚硝酰根显著增强了疏水性仲胺（如二丙基胺和二丁基胺）的亚硝化作用，而十二烷基硫酸钠形成的阴离子胶束则没有显著增强 N-亚硝胺的形成。在十六烷基三甲基氯化铵存在下，N-亚硝二丁基胺的形成速率提高了 100 倍。阳离子胶束对亚硝化反应的催化作用的大小主要取决于胺前体的疏水性（即烷基链长度）、胶束的稳定性和电荷以及 pH 值。一个重要的增强因子是由于胶束-水界面的电势，前体烷基铵离子的 pKa 值降低了约 2.5 pH 单位。这些结果表明，在使用高浓度阳离子表面活性剂的废水、消费品和工业过程中，阳离子胶束形成的表面活性剂可能在 N-亚硝胺的形成中发挥作用。
