Nitrosylsulfuric acid

Nitrosylsulfuric acid is the chemical compound with the formula HSO₄NO. It is a colourless solid that is used industrially in the production of caprolactam,^[3] and was formerly part of the lead chamber process for producing sulfuric acid. The compound is the mixed anhydride of sulfuric acid and nitrous acid.

Nitrosylsulfuric acid

Names
IUPAC name Nitrosylsulfuric acid
Other names nitrosonium bisulfate, chamber crystals
Identifiers
CAS Number	7782-78-7 Y
3D model (JSmol)	Interactive image
ChemSpider	74147 Y
ECHA InfoCard	100.029.058
PubChem CID	82157
UNII	40K942UPM8 Y
CompTox Dashboard (EPA)	DTXSID30889380
InChI InChI=1S/HNO5S/c2-1-6-7(3,4)5/h(H,3,4,5) Y Key: VQTGUFBGYOIUFS-UHFFFAOYSA-N Y InChI=1/HNO5S/c2-1-6-7(3,4)5/h(H,3,4,5) Key: VQTGUFBGYOIUFS-UHFFFAOYAM
SMILES O=NOS(=O)(=O)O
Properties
Chemical formula	HSO4NO
Molar mass	127.08 g/mol
Appearance	Pale yellow crystals[1]
Density	1.865 g/mL in 40% sulfuric acid soln [2]
Melting point	70 °C (158 °F; 343 K)[1]
Boiling point	Decomposes
Solubility in water	Decomposes
Solubility	Soluble in H2SO4[1]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Oxidizer
Related compounds
Other anions	NOCl
Other cations	NaHSO4
Related compounds	NOBF4
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

In organic chemistry, it is used as a reagent for nitrosating, as a diazotizing agent, and as an oxidizing agent.^[1]

Synthesis and reactions

A typical procedure entails dissolving sodium nitrite in cold sulfuric acid:^[4][5]

HNO₂ + H₂SO₄ → HSO₄NO + H₂O

It can also be prepared by the reaction of nitric acid and sulfur dioxide.^[6]

HSO₄NO is used in organic chemistry to prepare diazonium salts from amines, for example in the Sandmeyer reaction. Related NO-delivery reagents include nitrosonium tetrafluoroborate [NO]⁺[BF₄]⁻ and nitrosyl chloride.

In industry, the nitrosodecarboxylation reaction between nitrosylsulfuric acid and cyclohexanecarboxylic acid is used to generate caprolactam:^[3] This is known as the Snia Viscosa process

Safety

Nitrosylsulfuric acid is a hazardous material and precautions are indicated.^[1]