摘要
The aldehyde addition reaction is recognized as a key pathway in the formation of haloacetamides (HAMs) in drinking water. In particular, the reaction between monochloramine and chloroaldehydes has been reported to proceed rapidly. However, the measured concentrations of haloaldehydes (HALs) in chloraminated water are often much higher than those of HAMs. This discrepancy suggests that the role of the aldehyde pathway in HAM formation may have been overestimated. In this study, two commonly detected HALs [dichloroacetaldehyde (DCAL) and trichloroacetaldehyde (TCAL)] were selected as model compounds to investigate the transformation and formation among three classes of toxic disinfection byproducts (DBPs): HALs, HAMs, and haloacetonitriles (HANs), within a chloramination system. Theoretical calculations reveal that HALs can form HAMs via two distinct reaction pathways. Quantum-level computational analyses confirm the thermodynamic feasibility of both pathways for the studied Cl-HALs. Experimental investigations of the reaction kinetics between Cl-HALs and monochloramine, conducted at room temperature under light-shielded and catalyst-free conditions, showed that the concentrations of both DCAL and TCAL remained essentially unchanged throughout the reaction. HANs and HAMs in reaction solution were not detected. These results suggest that HALs exhibit negligible reactivity with monochloramine under ambient, uncatalyzed conditions, indicating strong kinetic hindrance in practical scenarios. In general, the reaction rate between HALs and monochloramine is not as high as that reported in the published literature (3.27–8.25 ×10 −3 h −1 ), which may help explain why much higher concentrations of HALs than HAMs were generally observed in chloraminated drinking water. This finding provides new insights into the transformation and formation of HALs, HAMs, and HANs in chloraminated drinking water systems.
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