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
IUPAC name
Nitrosylsulfuric acid
Other names
nitrosonium bisulfate, chamber crystals
3D model (JSmol)
ECHA InfoCard 100.029.058
  • InChI=1S/HNO5S/c2-1-6-7(3,4)5/h(H,3,4,5) Y
  • InChI=1/HNO5S/c2-1-6-7(3,4)5/h(H,3,4,5)
  • O=NOS(=O)(=O)O
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 Soluble in H2SO4[1]
Occupational safety and health (OHS/OSH):
Main hazards
Related compounds
Other anions
Other cations
Related compounds
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]


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


  1. George A. Olah, G. K. Surya Prakash, Qi Wang, Xing-Ya Li (2001). "Nitrosylsulfuric Acid". Encyclopedia of Reagents for Organic Synthesis. E-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn060. ISBN 978-0471936237.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. "Nitrosylsulfuric acid solution". Merck.
  3. Ritz, J.; Fuchs, H.; Kieczka, H.; Moran, W. C. (2002). "Caprolactam". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a05_031. ISBN 978-3527306732.
  4. Hodgson, H. H.; Mahadevan, A. P.; Ward, E. R. (1955). "1,4-Dinitronaphthalene". Organic Syntheses.; Collective Volume, vol. 3, p. 341 (diazodization followed by treatment with nitrite)
  5. Sandin, R. B.; Cairns, T. L. (1943). "1,2,3-Triiodo-5-nitrobenzene". Organic Syntheses.; Collective Volume, vol. 2, p. 604 (diazodization followed by treatment with iodide)
  6. Coleman, G. H.; Lillis, G. A.; Goheen, G. E. (1939). Nitrosyl Chloride. Inorganic Syntheses. Vol. 1. pp. 55–59. doi:10.1002/9780470132326.ch20. ISBN 9780470132326. This procedure generates the nitrosylsulfuric acid as an intermediate en route to NOCl.
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