Monochloramine
[CAS# 10599-90-3]

Identification

• Classification: Pharmaceutical intermediate >> Heterocyclic compound intermediate >> Pyrimidine compound >> Amine
• Name: Monochloramine
• Synonyms: Chlorinated Water (Chloramine); Hsdb 4293
• Molecular Formula: ClH₂N
• Molecular Weight: 51.48
• CAS Registry Number: 10599-90-3
• EC Number: 234-217-9
• SMILES: NCl

Properties

• Density: 1.2±0.1 g/cm³ Calc.^*
• Melting point: -66 ºC (Expl.)
• Index of refraction: 1.394 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS05;GHS07;GHS08 DangerGHS05
• Hazard Statements: H290-H314-H315-H319-H335-H372-H412
• Precautionary Statements: P234-P260-P261-P264-P264+P265-P270-P271-P273-P280-P301+P330+P331-P302+P352-P302+P361+P354-P304+P340-P305+P351+P338-P305+P354+P338-P316-P319-P321-P332+P317-P337+P317-P362+P364-P363-P390-P403+P233-P405-P406-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin corrosion	Skin Corr.	1A	H314
Specific target organ toxicity - repeated exposure	STOT RE	1	H372
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Specific target organ toxicity - single exposure	STOT SE	3	H335
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315

Discovory and Applicatios

Monochloramine is an inorganic chemical compound with the formula NH2Cl, consisting of one chlorine atom bonded to an amino group. Its discovery is closely connected to the development of water disinfection practices in the late nineteenth and early twentieth centuries. During this period, scientists and public health officials were searching for reliable methods to control waterborne diseases such as typhoid fever and cholera. Chlorine was identified as a powerful disinfectant, but early applications revealed drawbacks, including strong taste, odor, and the formation of undesirable byproducts. Research into alternative chlorination chemistry led to the identification and controlled use of chloramines, with monochloramine becoming the most important member of this group.

Monochloramine was first recognized as a distinct chemical species through studies of ammonia and chlorine reactions in aqueous solutions. Chemists observed that when chlorine is added to water containing ammonia under carefully controlled conditions, a series of chloramine compounds can form, including monochloramine, dichloramine, and nitrogen trichloride. Among these, monochloramine was found to be the most stable and least irritating. This stability made it suitable for practical use, as it persists longer in water systems compared with free chlorine. By the early twentieth century, water engineers had begun to understand how adjusting the chlorine-to-ammonia ratio could favor the formation of monochloramine.

The primary application of monochloramine has been in drinking water disinfection. Its adoption expanded significantly in the mid twentieth century as large municipal water systems sought disinfectants that could maintain residual activity throughout extensive distribution networks. Monochloramine travels farther in pipes than free chlorine before decomposing, which helps protect water quality at the point of use. This characteristic is especially important in large cities where water may spend many hours or days in the distribution system. The use of monochloramine also reduces the formation of certain chlorinated disinfection byproducts compared with chlorine alone, an advantage that became increasingly important as regulatory standards for drinking water quality evolved.

In addition to municipal drinking water treatment, monochloramine has been applied in industrial water systems. Cooling towers, heat exchangers, and process water loops are vulnerable to biofouling caused by bacteria and algae. Monochloramine provides effective microbial control while being less aggressive toward metals and some polymers than free chlorine. This has made it useful in power plants, refineries, and manufacturing facilities where material compatibility and long-term system integrity are critical.

Monochloramine has also played a role in scientific and medical contexts. In laboratory research, it has been used as a reagent to study oxidative and chlorination reactions involving nitrogen-containing compounds. Its relatively mild reactivity compared with other chlorinating agents allows controlled experimentation. In biological and environmental studies, monochloramine has been examined for its interactions with proteins, cell membranes, and microbial cells, contributing to a deeper understanding of disinfectant mechanisms and microbial inactivation.

Despite its benefits, the application of monochloramine has required careful management. Its disinfecting action is slower than that of free chlorine, which means it is typically used after initial treatment steps that reduce microbial loads. Engineers and chemists have developed operational guidelines to ensure that monochloramine concentrations remain effective while minimizing the formation of unwanted secondary chloramines. These efforts reflect a broader trend in water treatment toward balancing efficacy, safety, and aesthetic quality.

Overall, monochloramine represents an important milestone in the history of applied chemistry and public health. Its discovery emerged from fundamental studies of simple inorganic reactions, while its widespread use reflects the translation of chemical knowledge into practical infrastructure. By improving the stability and distribution of disinfectant residuals in water systems, monochloramine has contributed significantly to the reliability of modern drinking water supplies and to the prevention of waterborne disease on a large scale.

References

2025. Impacts of orthophosphate addition on chloramine decay and biofilm development in a model drinking water distribution system. Water Research.
DOI: 10.1016/j.watres.2025.123712

2025. Long-term impacts of free chlorine and monochloramine on the development of drinking water biofilm. Water Research.
DOI: 10.1016/j.watres.2025.123566

2025. Formation mechanisms of carcinogenic N-nitrosamines from dissolved organic matter derived from nitrogen-containing microplastics during chloramine disinfection. Water Research.
DOI: 10.1016/j.watres.2025.123696