| IUPAC name
| Other names
Nitrosyl hydrogen sulfate
Nitrosyl sulphuric acid
Nitrous sulfuric anhydride
|Molar mass||127.08 g/mol|
|Appearance||Pale yellow crystals|
|Density||1.612 g/cm3 (20 °C) (40% H2SO4 sol.)|
|Melting point||70 °C (158 °F; 343 K)|
|Solubility||Soluble in fuming nitric acid, conc. sulfuric acid|
|Safety data sheet||Sigma-Aldrich (40% sol. H2SO4)|
| Nitrating mixture|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Nitrosylsulfuric acid is used in organic chemistry to prepare diazonium salts from amines, for example in the Sandmeyer reaction. Related NO-delivery reagents include nitrosonium tetrafluoroborate and nitrosyl chloride.
Reduction of nitrosylsulfuric acid in sulfuric acid with metabisulfite, sulfite, nitrogen monoxide or various other reducing agents will yield a blue-purple, unstable solution called purple acid. If copper is present, a blue-purple copper(II)-nitrogen monoxide complex is formed instead.
Nitrosylsulfuric acid is a pale yellowish solid, that reacts with water and alcohols. It is very soluble in conc. sulfuric acid and fuming nitric acid. The compound can precipitate out as solid crystals from a solution of 30% conc. sulfuric acid, indicating that the hydrolysis is an equilibrium reaction.
Nitrosylsulfuric acid is sold by chemical suppliers. It is more commonly available as solution in sulfuric acid (usually 40-50%).
- HNO2 + H2SO4 → NOHSO4 + H2O
- HNO3 + SO2 → NOHSO4
The nitrosylsulfuric acid prepared this way, has a concentration of 45-50% in fuming nitric acid.
Nitrosylsulfuric acid is a side product of the lead chamber process, hence its name "chamber crystal".
- Synthesis of caprolactam
- Preparation of diazonium salts
Nitrosylsulfuric acid is corrosive and will react with water, releasing hazardous fumes. Proper protection must be worn when handling the compound.
Can be kept in concentrated sulfuric acid as solution.
Should be added to ice cold water or just crushed ice, followed by neutralization with a base.
- Coleman, G. H., Lillis, G. A., Goheen, G. E., Herrmann, C. V., & Booth, H. S. (2007). Nitrosyl Chloride. Inorganic Syntheses, 55–59
- J. Am. Chem. Soc. 1925, 47, 1, 143–147