Nitrogen trichloride

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Nitrogen trichloride

Nitrogen, N   Chlorine, Cl
Names
Other names Trichloramine Agene Nitrogen(III) chloride Trichloroazane Trichlorine nitride

Properties
Chemical formula	NCl3
Molar mass	120.36 g·mol−1
Appearance	yellow oily liquid
Odor	chlorine-like
Density	1.653 g/mL
Melting point	−40 °C (−40 °F; 233 K)
Boiling point	71 °C (160 °F; 344 K)
Solubility in water	immiscible slowly decomposes
Solubility	soluble in benzene, chloroform, CCl4, CS2, PCl3
Structure
Crystal structure	orthorhombic (below −40 °C)
Molecular shape	trigonal pyramidal
Dipole moment	0.6 D
Thermochemistry
Std enthalpy of formation (ΔfH⦵298)	232 kJ/mol
Hazards
NFPA 704 (fire diamond)	2 0 4 OX
Autoignition temperature	93 °C (199 °F; 366 K)
Related compounds
Other anions	Nitrogen trifluoride Nitrogen tribromide Nitrogen triiodide
Other cations	Phosphorus trichloride Arsenic trichloride
Related chloramines	Monochloramine Dichloramine
Related compounds	Nitrosyl chloride

Nitrogen trichloride, also known as trichloramine, is the chemical compound with the formula NCl₃. This yellow, oily, and explosive liquid is most commonly encountered as a product of chemical reactions between ammonia-derivatives and chlorine (for example, in swimming pools). Alongside monochloramine and dichloramine, trichloramine is responsible for the distinctive 'chlorine smell' associated with swimming pools, where the compound is readily formed as a product from hypochlorous acid reacting with ammonia and other nitrogenous substances in the water, such as urea from urine.

Preparation and structure

The compound is prepared by treatment of ammonium salts, such as sal ammoniac with a chlorine source.

Intermediates in this conversion include monochloramine and dichloramine, NH₂Cl and NHCl₂, respectively.

Like ammonia, NCl₃ is a pyramidal molecule. The N-Cl distances are 1.76 Å, and the Cl-N-Cl angles are 107°.

Reactions and uses

The chemistry of NCl₃ has been well explored. It is moderately polar with a dipole moment of 0.6 D. The nitrogen center is basic but much less so than ammonia. It is hydrolyzed by hot water to release ammonia and hypochlorous acid.

${\displaystyle {\text{NCl}}_3^{}+3{\text{H}}_2^{}\text{O}⟶{\text{NH}}_3^{}+3\text{HOCl}}$

${\displaystyle {\text{NCl}}_3^{}}$ explodes to give ${\displaystyle {\text{N}}_2^{}}$ and chlorine gas.

${\displaystyle 2{\text{NCl}}_3^{}⟶{\text{N}}_2^{}+3{\text{Cl}}_2^{}}$

This reaction is inhibited for dilute gases.

Nitrogen trichloride can form in small amounts when public water supplies are disinfected with monochloramine, and in swimming pools by disinfecting chlorine reacting with urea in urine and sweat from bathers.

Nitrogen trichloride, trademarked as Agene, was at one time used to bleach flour, but this practice was banned in the United States in 1949 due to safety concerns.

Safety

Nitrogen trichloride can irritate mucous membranes—it is a lachrymatory agent, but has never been used as such. The pure substance (rarely encountered) is a dangerous explosive, being sensitive to light, heat, even moderate shock, and organic compounds. Pierre Louis Dulong first prepared it in 1812, and lost several fingers and an eye in two explosions. In 1813, an NCl₃ explosion blinded Sir Humphry Davy temporarily, inducing him to hire Michael Faraday as a co-worker. They were both injured in another NCl₃ explosion shortly thereafter.