Nitrosyl chloride

Nitrosyl chloride is the chemical compound 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. The related nitrosyl halides nitrosyl fluoride, NOF, and nitrosyl bromide, NOBr, are also known.

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Structure and synthesis

Although its formula is written NOCl, the structure is better represented ONCl. A double bond exists between N and O (distance = 1.16 Å) and a single bond between N and Cl (distance = 1.69 Å). The O-N-Cl angle is 113°.^[1]

NOCl can be prepared by the direct combination of chlorine and nitric oxide. Alternatively, nitrosylsulfuric acid and HCl also affords the compound:

HCl + NOHSO₄ → NOCl + H₂SO₄

It also arises from the combination of hydrochloric and nitric acids according to the following reaction:^[2]

HNO₃ + 3 HCl → Cl₂ + 2 H₂O + NOCl

Although this mixture was used for dissolving gold for a long time the first description of the gas was done by Edmund Davy in 1831.^[3]

Reactions

• NOCl reacts with halide acceptors to give the nitrosyl cation, [NO]⁺. This species is available as NOBF₄.
• NOCl reacts with water to release HCl.
• Heating NOCl above 100 C gives back Cl₂ and NO.
• In organic synthesis, NOCl is often employed. It adds to alkenes to afford α-chloro oximes.^[4]

Safety

NOCl is toxic and irritating to the lungs.

References

1. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
2. ^ L. J. Beckham, W. A. Fessler, M. A. Kise (1951). "Nitrosyl Chloride". Chemical Reviews 48: 319-396. doi:10.1021/cr60151a001.
3. ^ Edmund Davy (1830 - 1837). "Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London, Vol. 3.": 27-29.
4. ^ Ohno, M,; Naruse, N.; Terasawa, I. " 7-cyanoheptanal" Organic Syntheses, Collected Volume 5, page.266 (1973). (addition of NOCl to cyclooctene)