Formation of (halo)acetamides and (halo)acetonitriles from the reaction of monochloramine and (halo)acetaldehydes in water

haloacetamides;haloacetonitriles;chloramination;disinfection by-products;monochloramine;oxidative amidation;carbinolamine;carbinolamine oxidation;chloroacetonitrile;bromoacetonitrile;acetonitrile;N-haloacetamides;N,2-dichloroacetamide;N-chloroacetamide;2-bromo-N-chloroacetamide;kinetics;drinking water

Kimura Hara, Susana

关键词: haloacetamides;    haloacetonitriles;    chloramination;    disinfection by-products;    monochloramine;    oxidative amidation;    carbinolamine;    carbinolamine oxidation;    chloroacetonitrile;    bromoacetonitrile;    acetonitrile;    N-haloacetamides;    N,2-dichloroacetamide;    N-chloroacetamide;    2-bromo-N-chloroacetamide;    kinetics;    drinking water;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/44797/Susana_Kimura%20Hara.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Chloramination is increasingly being used in the United States as a secondary disinfectant as a result of tighter regulations on selected disinfection by-products (DBPs) that include four trihalomethanes and five haloacetic acids. However, recent research suggests that unregulated nitrogen-containing DBPs formed by combined chlorine, such as haloacetonitriles and haloacetamides, might be more toxic than regulated DBPs. Monochloramine has been shown to react with aldehydes, common DBPs formed from ozone and free chlorine disinfection, to form carbinolamines that slowly dehydrate to imines which undergo fast decomposition to nitriles. It is also known that nitriles can hydrolyze to its corresponding amides. However, in this study the formation rate of amides was found to be significantly higher and independent of nitrile hydrolysis. The formation pathways of acetonitrile and two haloacetonitriles (chloro- and bromo-) and three haloacetamides (N,2-dichloroacetamide, 2-bromo-N-chloroacetamide, and N-chloroacetamide) from the reaction of monochloramine with acetaldehyde and two haloacetaldehydes (chloro- and bromo-) were investigated. Chloroacetaldehyde and monochloramine were found to quickly react to form and reach equilibrium with the carbinolamine 2-chloro-1-(chloroamino)ethanol. 2-chloro-1-(chloroamino)ethanol then decomposed through two concurrent pathways 1) slow dehydration to 1-chloro-2-(chloroimino)ethane, which in turn decomposed quickly to chloroacetonitrile, and 2) oxidation by monochloramine to form the previously unreported DBP N,2-dichloroacetamide. Similar pathway was found to take place for the formation of bromoacetonitrile and 2-bromo-N-chloroacetamide from the reaction between bromoacetaldehyde and monochloramine, and acetonitrile and N-chloroacetamide formation from the reaction of acetaldehyde and monochloramine. These parallel reactions are acid/base catalyzed, and therefore, the influence of pH on (halo)acetonitrile and (halo)acetamide formation was investigated. A kinetic model was proposed.