Frémy's salt

Frémy's Salt

Structural formula of Frémy's salt

Frémy's salt, also known as potassium nitrosodisulfonate, is an inorganic compound with the formula KSO₃NO. It is a bright yellow, water-soluble salt that is used as a radical in various chemical reactions. Frémy's salt is named after the French chemist Edmond Frémy, who first synthesized it in the 19th century.

Structure and Properties

Frémy's salt is composed of the nitrosodisulfonate anion, [ON(SO₃)₂]_, and a potassium cation, K_. The anion is a stable radical, which is unusual for inorganic compounds. The stability of the radical is attributed to the delocalization of the unpaired electron over the sulfur and oxygen atoms in the anion.

The compound is typically encountered as a dihydrate, KSO₃NO·2H₂O. It is highly soluble in water, forming a yellow solution. The radical nature of Frémy's salt makes it a useful reagent in organic synthesis and as a standard in electron paramagnetic resonance (EPR) spectroscopy.

Applications

Frémy's salt is primarily used as an oxidizing agent in organic chemistry. It is particularly effective in the oxidation of phenols to quinones. This reaction is useful in the synthesis of various organic compounds, including dyes and pharmaceuticals.

In addition to its role as an oxidant, Frémy's salt is used as a standard in EPR spectroscopy due to its stable radical nature. It provides a reliable reference signal for calibrating EPR instruments.

Synthesis

Frémy's salt can be synthesized by the oxidation of potassium sulfite with nitrosyl chloride (NOCl) in an aqueous solution. The reaction proceeds as follows:

2 K₂SO₃ + 2 NOCl _ 2 KSO₃NO + 2 KCl

The resulting solution is then evaporated to yield the crystalline salt.

Safety and Handling

Frémy's salt should be handled with care, as it is a strong oxidizing agent. It can cause irritation to the skin and eyes, and appropriate protective equipment should be used when handling the compound. It should be stored in a cool, dry place, away from reducing agents and organic materials.

Related Pages

• Radical (chemistry)
• Oxidizing agent
• Electron paramagnetic resonance
• Phenol
• Quinone

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