Fremy's salt

Fremy's salt, discovered in 1845 by Edmond Fremy (1814 - 1894), is a chemical compound and a strong oxidizing agent. The formal name is disodium nitrosodisulfonic acid or NO(SO3Na)2 but Fremy's salt refers equally well to the potassium salt potassium nitrosodisulfonate.

Properties and reactions
The nitroso compound is a persistent organic radical like TEMPO. It is especially useful in oxidations of phenols to hydroquinones in the Teuber reaction.

Preparation
The salt can be prepared from sodium nitrite, sodium bicarbonate and sulfur dioxide to disodium hydroxylaminedisulfonate and carbon dioxide followed by one-electron oxidation by electrolysis in a basic solution.