Chloramines are chemical compounds derived from ammonia (NH₃) or organic amines in which one or more N–H bonds have been replaced by N–Cl bonds. They belong to the broader class of halamines and are encountered in both inorganic and organic forms.
Classification
Inorganic chloramines consist of three simple species:
- Monochloramine (NH₂Cl)
- Dichloramine (NHCl₂)
- Nitrogen trichloride (NCl₃)
These are produced by the reaction of ammonia with hypochlorous acid (HOCl) or elemental chlorine. Monochloramine, in particular, is widely employed as a disinfectant in municipal water treatment because it provides longer‑lasting antimicrobial activity than free chlorine while generating fewer regulated disinfection by‑products.
Organic chloramines contain the N–Cl functional group attached to an organic substituent. Examples include:
- N‑chloropiperidine
- Chloramine‑T (the sodium salt of N‑chlorophenylsulfonamide)
- N‑chloromethylamine (CH₃NHCl)
Organic chloramines are typically generated by treating secondary amines with sodium hypochlorite (bleach) or tert‑butyl hypochlorite, yielding the N‑chlorinated product and sodium hydroxide.
Chemical properties
Chloramines are generally less stable than their parent amines. In acidic media they can undergo homolytic cleavage (the Hofmann–Löffler reaction), while in basic conditions they tend to eliminate to form imines. Only a few chloramines are sufficiently stable for isolation; many decompose spontaneously, releasing nitrogen‑chlorine species.
Applications
- Water disinfection: Monochloramine is used as a secondary or primary disinfectant in drinking‑water distribution systems. It persists longer in pipes, reducing bacterial regrowth and minimizing formation of chlorination by‑products such as trihalomethanes.
- Swimming‑pool chemistry: Chloramines form unintentionally when free chlorine reacts with nitrogenous compounds (e.g., urea, sweat, urine) introduced by swimmers. Trichloramine (NCl₃) is responsible for the characteristic “chlorine smell” of pools and can cause eye, skin, and respiratory irritation.
- Organic synthesis: Certain organic chloramines serve as reagents for nitrogen‑halogen transfer reactions and in the preparation of N‑halogenated intermediates.
Health and safety considerations
Inhalation of volatile chloramines, especially trichloramine, may irritate the respiratory tract and eyes. In drinking water, monochloramine is regulated by agencies such as the U.S. Environmental Protection Agency (EPA), which sets maximum contaminant levels to protect public health. Proper monitoring and treatment (e.g., activated carbon filtration) are employed where chloramine‑treated water is supplied.
References
- Berliner, J. F. T. (1931). The Chemistry of Chloramines. American Water Works Association.
- Kovacic, P.; Lowery, M. K.; Field, K. W. (1970). “Chemistry of N‑bromamines and N‑chloramines.” Chemical Reviews.
- Lawrence, S. A. (2004). Amines: Synthesis, Properties and Applications. Cambridge University Press.
