Nitrosyl chloride

Nitrosyl chloride is the chemical compound with the formula NOCl. It is a yellow gas that is most commonly encountered as a decomposition product of aqua regia, a mixture of hydrochloric acid and nitric acid. It is a strong electrophile and oxidizing agent. It is sometimes called Tilden's reagent.

Nitrosyl chloride
Skeletal formula of nitrosyl chloride with measurements
Spacefill model of nitrosyl chloride
Preferred IUPAC name
Nitrosyl chloride[citation needed]
3D model (JSmol)
ECHA InfoCard 100.018.430
EC Number
  • 220-273-1
E number E919 (glazing agents, ...)
MeSH nitrosyl+chloride
RTECS number
  • QZ7883000
UN number 1069
Molar mass 65.459 g mol−1
Appearance Yellow gas
Density 2.872 mg mL−1
Melting point −59.4 °C (−74.9 °F; 213.8 K)
Boiling point −5.55 °C (22.01 °F; 267.60 K)
Dihedral, digonal
Hybridisation sp2 at N
1.90 D
261.68 J K−1 mol−1
51.71 kJ mol−1
Safety data sheet
NFPA 704 (fire diamond)
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Structure and synthesisEdit

The molecule is bent. A double bond exists between N and O (distance = 1.16 Å) and a single bond between N and Cl (distance = 1.96 Å). The O–N–Cl angle is 113°.[1]


Since nitrosyl chloride is chemically simple and thermally stable, it can be produced in many ways.

  • A more convenient laboratory method involves the (reversible) dehydration of nitrous acid by HCl[3]
HNO2 + HCl → H2O + NOCl
Pd + HNO3 + 3 HCl → PdCl2 + 2 H2O + NOCl
  • NOCl forms by the direct combination of chlorine and nitric oxide; This reaction reverses above 100 °C.
Cl2 + 2 NO → 2NOCl
  • Another method of producing nitrosyl chloride is by direct union of the elements at 400 °C, although there is some regression as above.
N2 + O2 + Cl2 → 2 NOCl ⇌ 2 NO + Cl2

Occurrence in aqua regiaEdit

NOCl also arises from the combination of hydrochloric and nitric acids according to the following reaction:[4]

HNO3 + 3 HCl → Cl2 + 2 H2O + NOCl

In nitric acid, NOCl is readily oxidized into nitrogen dioxide. The presence of NOCl in aqua regia was described by Edmund Davy in 1831.[5]


NOCl behaves as an electrophile and an oxidant in most of its reactions. With halide acceptors, for example antimony pentachloride, converts to nitrosonium salts:

NOCl + SbCl5 → [NO]+[SbCl6]

In a related reaction, sulfuric acid gives nitrosylsulfuric acid, the mixed acid anhydride of nitrous and sulfuric acid:

ClNO + H2SO4 → ONHSO4 + HCl

NOCl reacts with silver thiocyanate to give silver chloride and the pseudohalogen nitrosyl thiocyanate:


Nitrosyl chloride is used to prepare metal nitrosyl complexes. With molybdenum hexacarbonyl, NOCl gives the dinitrosyldichloride complex:[6]

Mo(CO)6 + 2 NOCl → MoCl2(NO)2 + 6 CO

Applications in organic synthesisEdit

Aside from its role in the production of caprolactam, NOCl finds some other uses in organic synthesis. It adds to alkenes to afford α-chloro oximes.[7] The addition of NOCl follows the Markovnikov rule. Ketenes also add NOCl, giving nitrosyl derivatives:

H2C=C=O + NOCl → ONCH2C(O)Cl

Propylene oxide reacts with NOCl to give an α-chloronitritoakyl derivative:

It converts amides to N-nitroso derivatives.[8] NOCl converts some cyclic amines to the alkenes. For example, aziridine reacts with NOCl to give ethene, nitrous oxide and hydrogen chloride.

Industrial applicationsEdit

NOCl and cyclohexane react photochemically to give cyclohexanone oxime hydrochloride. This process exploits the tendency of NOCl to undergo photodissociation into NO and Cl radicals. The oxide is converted to caprolactam, a precursor to Nylon-6.[2]


Nitrosyl chloride is very toxic and irritating to the lungs, eyes, and skin.


  1. ^ Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
  2. ^ a b Ritz, Josef; Fuchs, Hugo; Kieczka, Heinz; Moran, William C. (2002). "Caprolactam". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a05_031.
  3. ^ Morton, J. R.; Wilcox, H. W. (1953). "Nitrosyl Chloride". Inorganic Syntheses. 48: 52. doi:10.1002/9780470132357.ch16.
  4. ^ Beckham, L. J.; Fessler, W. A.; Kise, M. A. (1951). "Nitrosyl Chloride". Chemical Reviews. 48 (3): 319–396. doi:10.1021/cr60151a001.
  5. ^ Edmund Davy (1830–1837). "On a New Combination of Chlorine and Nitrous Gas". Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London. 3: 27–29. JSTOR 110250.
  6. ^ Johnson, B. F. G.; Al-Obadi, K. H. (1970). "Dihalogenodinitrosylmolybdenum and Dihalogenodinitrosyltungsten". Inorg. Synth. 12: 264–266. doi:10.1002/9780470132432.ch47.
  7. ^ Ohno, M.; Naruse, N.; Terasawa, I. (1969). "7-cyanoheptanal". 49: 27. doi:10.15227/orgsyn.049.0027. Cite journal requires |journal= (help)
  8. ^ Van Leusen, A. M.; Strating, J. (1977). "p-Tolylsulfonyldiazomethane". Org. Synth. 57: 95. doi:10.15227/orgsyn.057.0095.

External linksEdit