Title: Hydroxylamine
CAS Registry Number: 7803-49-8
Molecular Formula: H3NO
Molecular Weight: 33.03
Percent Composition: H 9.15%, N 42.41%, O 48.44%
Line Formula: NH2OH
Literature References: Prepn as the hydrochloride: W. L. Semon, Org. Synth. coll. vol. I, 318 (1932). Prepn: Hurd, Inorg. Synth. 1, 87 (1939); Benson et al., J. Am. Chem. Soc. 78, 4202 (1956). Crystal structure: Meyers, Lipscomb, Acta Crystallogr. 5, 583 (1955). Toxicity data: Riemann, Acta Pharmacol. Toxicol. 6, 285 (1950); R. P. Smith, W. R. Layne, J. Pharmacol. Exp. Ther. 165, 30 (1969). Mutagenic action: Phillips, Brown in Prog. Nucleic Acid Res. Mol. Biol. 7, 349-368 (1967). Reviews: Mason, "Hydroxylamine" in Mellor's vol. VIII, supplement 2, Nitrogen (part 2), 115-157 (1967); Jones in Comprehensive Inorganic Chemistry vol. 2, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 265-276.
Properties: Unstable, large white flakes or needles, mp 33°, bp22 58°. d40 1.2255; d440 1.204. pK (20°) 7.97. Very sol in water, liq ammonia and methanol. The soly in the higher alcohols decreases with increasing mol wt. Sparingly sol in ether, benzene, carbon disulfide, chloroform. Very hygroscopic. Dec by hot water. Undergoes rapid decompn at room temps esp in the presence of atm moisture and CO2. Detonates in test tube heated with flame. LD50 i.p. in mice: 1.83 mmol/kg (Smith, Layne).
Melting point: mp 33°
Boiling point: bp22 58°
pKa: pK (20°) 7.97
Density: d40 1.2255; d440 1.204
Toxicity data: LD50 i.p. in mice: 1.83 mmol/kg (Smith, Layne)
Derivative Type: Hydrochloride
CAS Registry Number: 5470-11-1
Additional Names: Oxammonium hydrochloride
Molecular Formula: H3NO.HCl
Molecular Weight: 69.49
Percent Composition: H 5.80%, N 20.16%, O 23.02%, Cl 51.02%
Properties: Monoclinic columnar crystals; slowly dec when moist. d17 1.67. mp about 151°. One gram dissolves in about 1 ml water (83 g in 100 ml water at 17°); 19 ml alcohol; 8 ml methanol. Sol in glycerol, propylene glycol. Insol in cold ether. pH of 0.2 molar aq soln 3.2. Keep well closed. LD50 orally in mice: 408 mg/kg (Riemann).
Melting point: mp about 151°
Density: d17 1.67
Toxicity data: LD50 orally in mice: 408 mg/kg (Riemann)
Derivative Type: Sulfate
CAS Registry Number: 10039-54-0
Additional Names: Oxammonium sulfate
Molecular Formula: (H3NO)2.H2SO4
Molecular Weight: 164.14
Percent Composition: H 4.91%, N 17.07%, O 58.48%, S 19.54%
Properties: Crystals, mp about 170°. Freely sol in water.
Melting point: mp about 170°
CAUTION: Skin irritant. May cause methemoglobinemia, sulfhemoglobinemia, cyanosis, convulsions, hypotension and coma. See Clinical Toxicology of Commercial Products, R. E. Gosselin et al., Eds. (Williams & Wilkins, Baltimore, 5th ed., 1984) Section II, p 117.
Use: As reducing agent in photography; in synthetic and analytical chemistry; to purify aldehydes and ketones. As antioxidant for fatty acids and soaps. As dehairing agent for hides.
Hydroxylupanine Hydroxymercurichlorophenols Hydroxypethidine Hydroxyphenamate Hydroxyproline

Stereo, skeletal formula of hydroxylamine with all explicit hydrogens added Spacefill model of hydroxylamine
Stereo, skeletal formula of hydroxylamine with all explicit hydrogens added and assorted dimensions
CAS number 7803-49-8 YesY
PubChem 787
ChemSpider 766 YesY
EC number 232-259-2
KEGG C00192 YesY
MeSH Hydroxylamine
ChEBI CHEBI:15429 YesY
RTECS number NC2975000
Gmelin Reference 478
3DMet B01184
Jmol-3D images Image 1
Image 2
Molecular formula H3NO
Molar mass 33.03 g mol−1
Appearance Vivid white, opaque crystals
Density 1.21 g cm−3 (at 20 °C)[2]
Melting point 33 °C; 91 °F; 306 K
Boiling point 58 °C; 136 °F; 331 K (decomposes)
log P −0.758
Acidity (pKa) 5.95
Basicity (pKb) 8.05
Trigonal at N
Molecular shape Tetrahedral at N
Dipole moment 0.67553 D
heat capacity C
46.47 J K−1 mol−1
Std molar
entropy So298
236.18 J K−1 mol−1
Std enthalpy of
formation ΔfHo298
−39.9 kJ mol−1
EU Index 612-122-00-7
EU classification E Harmful Xn Irritant Xi Dangerous for the Environment (Nature) N
R-phrases R2, R21/22, R37/38, R40, R41, R43, R48/22, R50
S-phrases (S2), S26, S36/37/39, S61
NFPA 704
NFPA 704.svg
Flash point 129 °C; 264 °F; 402 K
Autoignition temperature 265 °C; 509 °F; 538 K
LD50 408 mg/kg (oral, mouse); 59–70 mg/kg (intraperitoneal mouse, rat); 29 mg/kg (subcutaneous, rat)[3]
Related compounds
Related hydroxylammonium salts Hydroxylammonium chloride
Hydroxylammonium nitrate
Hydroxylammonium sulfate
Related compounds Ammonia


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Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Hydroxylamine is an inorganic compound with the formula NH2OH. The pure material is a white, unstable crystalline, hygroscopic compound.[4] However, hydroxylamine is almost always provided and used as an aqueous solution. It is used to prepare oximes, an important functional group. It is also an intermediate in biological nitrification. The oxidation of NH3 is mediated by the enzyme hydroxylamine oxidoreductase (HAO).