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IUPAC name
Other names
Azinous acid
Nitrinous acid
Molar mass 33.03 g/mol
Appearance White hygroscopic crystals
Odor Ammonia-like
Density 1.227 g /cm3 (at 20 °C)
Melting point 33 °C (91 °F; 306 K)
Boiling point 70 °C (158 °F; 343 K) (at 60 mm Hg; decomposes)
Solubility Soluble in liq. ammonia, ethanol, methanol
Poorly soluble in diethyl ether, carbon disulfide, chloroform, propanol,
Insoluble in acetone, benzene, petroleum ether, hydrogen sulfide
Vapor pressure 53 mm Hg at 32 °C
Acidity (pKa) 5.95
236.18 J·K−1·mol−1
−39.9 kJ·mol−1
Safety data sheet None
Flash point Explodes at 129 °C
Lethal dose or concentration (LD, LC):
408 mg/kg (oral, mouse)
9–70 mg/kg (intraperitoneal mouse, rat)
29 mg/kg (subcutaneous, rat)
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Hydroxylamine is a white crystalline solid, widely used as a reducing agent. It has the chemical formula NH2OH.

As pure hydroxylamine is unstable and explosive, its salts such as hydroxylammonium chloride are more often used. It can also be encountered as aqueous solution.



Hydroxylamine reacts with acids to give hydroxylammonium salts.

Reaction with copper(II) oxide gives nitrous oxide:

2 NH2OH + 4 CuO → 2 Cu2O + N2O + 3 H2O


Hydroxylamine is a white crystalline solid, hygroscopic and unstable when pure. It is very soluble in water and alcohol.


Freebase hydroxylamine can explode if heated at high temperatures.


Pure hydroxylamine is not sold by any entity. However, aqueous solutions are sold by many chemical entities, though they're not readily accessible to the amateur chemist.

Hydroxylammonium salts are also available.


Hydroxylamine can be prepared through various means:

The Raschig process is the most common route. It involves the reduction of ammonium nitrite with bisulfite (HSO3) and sulfur dioxide at 0 °C in water to hydroxylamido-N,N-disulfonate anion, which hydrolyzes to give hydroxylamine sulfate.

NH4NO2 + 2 SO2 + NH3 + H2O → 2 NH4+ + N(OH)(OSO2)22-
N(OH)(OSO2)22− + H2O → NH(OH)(OSO2)- + HSO4-
2 NH(OH)(OSO2) + 2 H2O → (NH3OH)2SO4 + SO42-

To obtain pure hydroxylamine, anhydrous ammonia is added:

(NH3OH)2SO4 + 2 NH3 → 2 NH2OH +(NH4)2SO4

Since free hydroxylamine quickly breaks down, the final product is either dissolved in water or reacted with a strong acid, like hydrochloric acid.

Other nitrites, such as nitrous acid or sodium nitrite can also be reduced with bisulfite to hydroxylamine.

Electrolytic reduction of nitric acid with sulfuric acid at 15-20 °C for 40 minutes at 24 A gives hydroxylamine:

HNO3 + 3 H2 → NH2OH + 2 H2O

Other acids, such as hydrochloric and phosphoric acids can also be used. The yield of this route is between 50-80%.[1]

Electrolysis of sodium nitrate in the presence of hydrogen chloride will also give hydroxylamine. A lead cathode and a coal anode are used as electrodes. The process takes 3 hours.[2]

Reaction of nitrogen dioxide or nitrous acid with tin(II) chloride will give hydroxylamine. The yield is 90%.[3]

Reduction of nitric oxide with tin(II) chloride in hydrochloric acid at 0 °C will also yield hydroxylamine.[4]

Hydroxylamine can also be made by heating nitromethane with concentrated hydrochloric acid. This gives hydroxylamine hydrochloride:

CH3NO2 + HCl → NH2OH·HCl + 2 H2O + CO




Hydroxylamine is an irritant to the respiratory tract, skin, eyes, and other mucous membranes. It is harmful if swallowed and may be absorbed through the skin. Hydroxylamine is considered a possible mutagen.

Hydroxylamine explodes upon heating, though the exact mechanism is not well understood. Ferrous and ferric salts accelerate its decomposition in aqueous solution.


Hydroxylamine is safe to store only as aqueous solution or in salt form. Do not store it in pure free base form.


Hydroxylamine can be neutralized by adding a ketone and then gently heating the resulting oxime, which reforms the ketone and releases nitrogen gas and water. It can also be neutralized by diluting it with water and carefully adding iron salts or other compounds that accelerate its decomposition.

Reduction of hydroxylamine with Zn/HCl yields ammonia.


  1. Schoch, E. P.; Pritchett, R. H.; Journal of the American Chemical Society; vol. 38; (1916); p. 2042
  2. Tafel, J.; Z. Anorg. Chem.; vol. 31; (1902); p. 321 - 324
  3. Raschig, F.; Z. Anorg. Chem.; vol. 155; (1926); p. 225
  4. https://pubs.acs.org/doi/10.1021/j150323a006

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