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.

Structure and synthesis

The molecule is bent. A double bond exists between N and O and a single bond between N and Cl. The O–N–Cl angle is 113°.

Production

Since nitrosyl chloride is chemically simple and thermally stable, it can be produced in many ways.
NOCl also arises from the combination of hydrochloric and nitric acids according to the following reaction:
In nitric acid, NOCl is readily oxidized into nitrogen dioxide. The presence of NOCl in aqua regia was described by Edmund Davy in 1831.

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:
In a related reaction, sulfuric acid gives nitrosylsulfuric acid, the mixed acid anhydride of nitrous and sulfuric acid:
NOCl reacts with silver thiocyanate to give silver chloride and the pseudohalogen nitrosyl thiocyanate:
Similarly, it reacts with silver cyanide to give nitrosyl cyanide.
Nitrosyl chloride is used to prepare metal nitrosyl complexes. With molybdenum hexacarbonyl, NOCl gives the dinitrosyldichloride complex:

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. The addition of NOCl follows the Markovnikov rule. Ketenes also add NOCl, giving nitrosyl derivatives:
Epoxides react with NOCl to give an α-chloronitritoalkyl derivatives. In the case of propylene oxide, the addition proceeds with high regiochemistry:
It converts amides to N-nitroso derivatives. 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 oxide is converted to caprolactam, a precursor to Nylon-6.

Safety

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