Nitrosyl chloride

Nitrosyl chloride is the chemical compound with the formula NOCl. It is a yellow gas that is commonly encountered as a component of aqua regia, a mixture of 3 parts concentrated hydrochloric acid and 1 part of concentrated nitric acid. It is a strong electrophile and oxidizing agent. It is sometimes called Tilden's reagent, after William A. Tilden, who was the first to produce it as a pure compound.[1]

Nitrosyl chloride
Skeletal formula of nitrosyl chloride with measurements
Spacefill model of nitrosyl chloride
Names
IUPAC name
Nitrosyl chloride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.018.430
EC Number
  • 220-273-1
E number E919 (glazing agents, ...)
MeSH nitrosyl+chloride
RTECS number
  • QZ7883000
UNII
UN number 1069
  • InChI=1S/ClNO/c1-2-3 checkY
    Key: VPCDQGACGWYTMC-UHFFFAOYSA-N checkY
  • ClN=O
Properties
NOCl
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)
Reacts
Structure
Dihedral, digonal
Hybridisation sp2 at N
1.90 D
Thermochemistry
261.68 J K−1 mol−1
51.71 kJ mol−1
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
3
0
1
W
OX
Safety data sheet (SDS) inchem.org
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)
Infobox references

Structure and synthesis

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°.[2]

Production

Nitrosyl chloride can be produced in many ways.

HCl + NOHSO4 → H2SO4 + NOCl
  • A more convenient laboratory method involves the (reversible) dehydration of nitrous acid by HCl[4]
HNO2 + HCl → H2O + NOCl
Cl2 + 2 NO → 2 NOCl
  • By reduction of nitrogen dioxide with hydrogen chloride:[5]
2NO2 + 4 HCl → 2NOCl + 2H2O + Cl2

Occurrence in aqua regia

NOCl also arises from the combination of hydrochloric and nitric acids according to the following reaction:[6]

HNO3 + 3 HCl → 2[Cl] + 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.[7]

Reactions

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:

ClNO + AgSCN → AgCl + ONSCN

Similarly, it reacts with silver cyanide to give nitrosyl cyanide.[8]

Nitrosyl chloride is used to prepare metal nitrosyl complexes. With molybdenum hexacarbonyl, NOCl gives the dinitrosyldichloride complex:[9]

Mo(CO)6 + 2 NOCl → MoCl2(NO)2 + 6 CO

It dissolves platinum:[10]

Pt + 6 NOCl → (NO+)2[PtCl6]2- + 4 NO

Applications in organic synthesis

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.[11] The addition of NOCl follows the Markovnikov rule. Ketenes also add NOCl, giving nitrosyl derivatives:

H2C=C=O + NOCl → ONCH2C(O)Cl

Epoxides react with NOCl to give an α-chloronitritoalkyl derivatives. In the case of propylene oxide, the addition proceeds with high regiochemistry:[12]

It converts amides to N-nitroso derivatives.[13] NOCl converts some cyclic amines to the alkenes. For example, aziridine reacts with NOCl to give ethene, nitrous oxide and hydrogen chloride.

Industrial applications

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 cyclohexanone oxime is converted to caprolactam, a precursor to nylon-6.[3]

Safety

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

References
  1. Tilden, William A. (1874). "XXXII.—On aqua regia and the nitrosyl chlorides". J. Chem. Soc. 27: 630–636. doi:10.1039/JS8742700630.
  2. Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
  3. Ritz, Josef; Fuchs, Hugo; Kieczka, Heinz; Moran, William C. Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a05_031.
  4. Morton, J. R.; Wilcox, H. W.; Moellerf, Therald; Edwards, Delwin C. (1953). "Nitrosyl Chloride". In Bailar, John C. Jr (ed.). Inorganic Syntheses. Vol. 4. McGraw‐Hill. p. 48. doi:10.1002/9780470132357.ch16. ISBN 9780470132357.
  5. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 456. ISBN 978-0-08-037941-8.
  6. Beckham, L. J.; Fessler, W. A.; Kise, M. A. (1951). "Nitrosyl Chloride". Chemical Reviews. 48 (3): 319–396. doi:10.1021/cr60151a001. PMID 24541207.
  7. 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.
  8. Kirby, G. W. (1977). "Tilden Lecture. Electrophilic C-Nitroso Compounds". Chemical Society Reviews. 6: 1. doi:10.1039/CS9770600001.
  9. Johnson, B. F. G.; Al-Obadi, K. H. (1970). "Dihalogenodinitrosylmolybdenum and Dihalogenodinitrosyltungsten". Inorganic Syntheses. pp. 264–266. doi:10.1002/9780470132432.ch47. ISBN 9780470132432. {{cite book}}: |journal= ignored (help)
  10. Moravek, Richard T. (1986). "Nitrosyl Hexachloroplatinate(IV)". Inorganic Syntheses. Vol. 24. pp. 217–220. doi:10.1002/9780470132555.ch63. ISBN 9780470132555.
  11. Ohno, M.; Naruse, N.; Terasawa, I. (1969). "7-Cyanoheptanal". Org. Synth. 49: 27. doi:10.15227/orgsyn.049.0027.
  12. Malinovskii, M. S.; Medyantseva, N. M. (1953). "Olefin Oxides. IX. Condensation of Olefin Oxides with Nitrosyl Chloride". Zhurnal Obshchei Khimii. 23: 84-6. (translated from Russian)
  13. Van Leusen, A. M.; Strating, J. (1977). "p-Tolylsulfonyldiazomethane". Org. Synth. 57: 95. doi:10.15227/orgsyn.057.0095.
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