# What is the mechanism of the reaction of a ketone with sodium nitrite/ hydrogen chloride?

What is the mechanism of reaction of a ketone with $$\ce{NaNO2/HCl}$$? Can $$\ce{NaNO2/HCl}$$ be considered as freshly prepared $$\ce{HONO}$$ here? I am confused about how the reaction will proceed.

• Consider also production of nitrosyl chloride – Poutnik Apr 23 '19 at 10:25
• I know how Sodium nitrite reacts with amines. I was just curious about how it would react with a carbonyl group. – Arshiya Apr 23 '19 at 13:30

$$\ce{NaNO2/HCl}$$ is as you suggest a source of $$\ce{HONO}$$. This will be protonated by $$\ce{HCl}$$ to give the nitrosonium ion $$\ce{NO+}$$ (in equilibrium with nitrosyl chloride). This strongly electrophilic species will react with the enol of the ketone to nitrosate the alpha position. This nitroso compound then rearranges to give the alpha oxime.

Image from: Emilia Iglesias and Isabel Brandariz, A further study of acetylacetone nitrosation. Org. Biomol. Chem. 2013, 11, 1059-1064. DOI: 10.1039/C2OB26073E; available as pdf from pdfs.semanticscholar.org.

• Slightly weird diagram ... two methyl groups disappeared – orthocresol Apr 23 '19 at 11:14
• I noticed that, think they were meant to be hydrogens – Waylander Apr 23 '19 at 11:37
• – user55119 Apr 23 '19 at 14:35