|Jmol-3D images||Image 1
|Molar mass||33.03 g mol−1|
|Appearance||Vivid white, opaque crystals|
|Density||1.21 g cm−3 (at 20 °C)|
33 °C, 306 K, 91 °F
58 °C, 331 K, 136 °F (decomposes)
|Trigonal at N|
|Molecular shape||Tetrahedral at N|
|Dipole moment||0.67553 D|
|Std enthalpy of
|−39.9 kJ mol−1|
|236.18 J K−1 mol−1|
|Specific heat capacity, C||46.47 J K−1 mol−1|
|EU classification||E Xn Xi N|
|R-phrases||R2, R21/22, R37/38, R40, R41, R43, R48/22, R50|
|S-phrases||(S2), S26, S36/37/39, S61|
|Flash point||129 °C|
|LD50||408 mg/kg (oral, mouse); 59–70 mg/kg (intraperitoneal mouse, rat); 29 mg/kg (subcutaneous, rat)|
|Related hydroxylammonium salts||Hydroxylammonium chloride
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Hydroxylamine is an inorganic compound with the formula NH2OH. The pure material is a white, unstable crystalline, hygroscopic compound. 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).
NH2OH can be produced via several routes. The main route is via Raschig synthesis: aqueous ammonium nitrite is reduced by HSO4− and SO2 at 0 °C to yield a hydroxylamido-N,N-disulfate anion:
- NH4NO2 + 2 SO2 + NH3 + H2O → 2 NH4+ + N(OH)(OSO2)22−
This anion is then hydrolyzed to give (NH3OH)2SO4:
- N(OH)(OSO2)22− + H2O → NH(OH)(OSO2)− + HSO4−
- 2 NH(OH)(OSO2)− + 2 H2O → (NH3OH)2SO4 + SO2−
Solid NH2OH can be collected by treatment with liquid ammonia. Ammonium sulfate, (NH4)2SO4, a side-product insoluble in liquid ammonia, is removed by filtration; the liquid ammonia is evaporated to give the desired product.
The net reaction is: 2NO−
2 + 4SO2 + 6H2O + 6NH3 → 4SO2−
4 + 6NH+
4 + 2NH2OH
Hydroxylammonium salts can then be converted to hydroxylamine by neutralization:
- (NH3OH)Cl + NaOBu → NH2OH + NaCl + BuOH
- HNO2 + 2 HSO3− → N(OH)(OSO2)22− + H2O → NH(OH)(OSO2)− + HSO4−
- NH(OH)(OSO2)− + H3O+ (100 °C/1 h) → NH3(OH)+ + HSO4−
- R-X + NH2OH → R-ONH2 + HX
- R-X + NH2OH → R-NHOH + HX
The reaction of NH2OH with an aldehyde or ketone produces an oxime.
- R2C=O + NH2OH∙HCl , NaOH → R2C=NOH + NaCl + H2O
This reaction is useful in the purification of ketones and aldehydes: if hydroxylamine is added to an aldehyde or ketone in solution, an oxime forms, which generally precipitates from solution; heating the precipitate with an inorganic acid then restores the original aldehyde or ketone.
NH2OH reacts with chlorosulfonic acid to give hydroxylamine-O-sulfonic acid, a useful reagent for the synthesis of caprolactam.
- HOSO2Cl + NH2OH → NH2OSO2OH + HCl
The hydroxylamine-O-sulfonic acid, which should be stored at 0 °C to prevent decomposition, can be checked by iodometric titration.[clarification needed]
- NH2OH (Zn/HCl) → NH3
- R-NHOH (Zn/HCl) → R-NH2
Hydroxylamine explodes with heat:
- 4 NH2OH + O2 → 2 N2 + 6 H2O
Hydroxylamine and its salts are commonly used as reducing agents in myriad organic and inorganic reactions. They can also act as antioxidants for fatty acids. Some non-chemical uses include removal of hair from animal hides and photography developing solutions.
This has also been used in the past by biologists to introduce random mutations by switching base pairs from G to A, or from C to T. This is to probe functional areas of genes to elucidate what happens if their functions are broken. Nowadays other mutagens are used. Hydroxylamine can also be used to highly selectively cleave asparaginyl-glycine peptide bonds in peptides and proteins. It also bonds to and permanently disables (poisons) heme-containing enzymes. It is used as an irreversible inhibitor of the oxygen-evolving complex of photosynthesis on account of its similar structure to water.
In the semiconductor industry, hydroxylamine is often a component in the "resist stripper", which removes photoresist after lithography.
Hydroxylamine may explode on heating. The nature of the explosive hazard is not well understood. At least two factories dealing in hydroxylamine have been destroyed since 1999 with loss of life. It is known, however, that ferrous and ferric iron salts accelerate the decomposition of 50% NH2OH solutions. Hydroxylamine and its derivatives are more safely handled in the form of salts.
It is an irritant to the respiratory tract, skin, eyes, and other mucous membranes. It may be absorbed through the skin, is harmful if swallowed, and is a possible mutagen.
Substituted derivatives of hydroxylamine are known. If the hydroxyl hydrogen is substituted, this is called an O-hydroxylamine, if one of the amine hydrogens is substituted, this is called an N-hydroxylamine. Similarly to ordinary amines, one can distinguish primary, secondary and tertiary hydroxylamines, the latter two referring to compounds where two or three hydrogens are substituted, respectively. Examples of compounds containing a hydroxylamine functional group are N-tert-butyl-hydroxylamine or the glycosidic bond in calicheamicin. N,O-Dimethylhydroxylamine is a coupling agent, used to synthesize Weinreb amides.
Possible Deep-Space "Origin of Life"
In 2013, astrophysicists reported that the signature of hydroxylamine may have been detected in a star-forming field 1000 light years from earth. The scientists speculate that rocky bodies passing through such fields and later impacting distant planets may provide the basic building-blocks of life.
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- Cisneros, L. O.; Rogers, W. J.; Mannan, M. S.; Li, X.; Koseki, H. (2003). "Effect of Iron Ion in the Thermal Decomposition of 50 mass% Hydroxylamine/Water Solutions". J. Chem. Eng Data 48 (5): 1164–1169. doi:10.1021/je030121p.
- MSDS Sigma-Aldrich
- "Have Astronomers Found Chemical Precursor to Life In Gas Clouds?". www.livescience.com. 11 January 2013.
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- Schupf Computational Chemistry Lab
- M. W. Rathke A. A. Millard "Boranes in Functionalization of Olefins to Amines: 3-Pinanamine" Organic Syntheses, Coll. Vol. 6, p. 943; Vol. 58, p. 32. (preparation of hydroxylamine-O-sulfonic acid).