Hydroxylamine

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"Aminol" redirects here; not to be confused with hemiaminal.
Hydroxylamine
Stereo, skeletal formula of hydroxylamine with all explicit hydrogens added
Stereo, skeletal formula of hydroxylamine with all explicit hydrogens added
Stereo, skeletal formula of hydroxylamine with all explicit hydrogens added and assorted dimensions
Stereo, skeletal formula of hydroxylamine with all explicit hydrogens added and assorted dimensions
Names
IUPAC name
Azinous acid
Preferred IUPAC name
Hydroxylamine (only preselected[1])
Other names
  • Aminol
  • Azanol
  • Hydroxyammonia
  • Hydroxyamine
  • Hydroxyazane
  • Hydroxylazane
  • Nitrinous acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard Lua error in Module:Wikidata at line 880: attempt to index field 'wikibase' (a nil value). Lua error in Module:Wikidata at line 880: attempt to index field 'wikibase' (a nil value).Lua error in Module:EditAtWikidata at line 29: attempt to index field 'wikibase' (a nil value).
EC Number
  • 232-259-2
E number Lua error in Module:Wikidata at line 880: attempt to index field 'wikibase' (a nil value).
478
KEGG
MeSH Hydroxylamine
RTECS number
  • NC2975000
UNII
  • {{#property:P3117}}Lua error in Module:EditAtWikidata at line 29: attempt to index field 'wikibase' (a nil value).
  • InChI=1S/H3NO/c1-2/h2H,1H2 checkY
    Key: AVXURJPOCDRRFD-UHFFFAOYSA-N checkY
  • InChI=1/H3NO/c1-2/h2H,1H2
    Key: AVXURJPOCDRRFD-UHFFFAOYAD
  • NO
Properties
NH2OH
Molar mass 33.030 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) /22 mm Hg (decomposes)
Soluble
log P −0.758
Acidity (pKa) 6.03 ([NH3OH]+)
Basicity (pKb) 7.97
Structure
Tricoordinated at N, dicoordinated at O
Trigonal pyramidal at N, bent at O
0.67553 D
Thermochemistry
46.47 J/(K·mol)
236.18 J/(K·mol)
−39.9 kJ/mol
Hazards
GHS labelling:
GHS01: ExplosiveGHS05: CorrosiveGHS07: Exclamation markGHS08: Health hazardGHS09: Environmental hazard
Danger
H200, H290, H302, H312, H315, H317, H318, H335, H351, H373, H400
P201, P202, P234, P260, P261, P264, P270, P271, P272, P273, P280, P281, P301+P312, P302+P352, P304+P340, P305+P351+P338, P308+P313, P310, P312, P314, P321, P322, P330, P332+P313, P333+P313, P362, P363, P372, P373, P380, P390, P391, P401, P403+P233, P404, P405, P501
NFPA 704 (fire diamond)

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2
1
3
Flash point 129 °C (264 °F; 402 K)
265 °C (509 °F; 538 K)
Lethal dose or concentration (LD, LC):
408 mg/kg (oral, mouse); 59–70 mg/kg (intraperitoneal mouse, rat); 29 mg/kg (subcutaneous, rat)[3]
Safety data sheet (SDS) ICSC 0661
Related compounds
Related hydroxylammonium salts
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Hydroxylamine (also known as hydroxyammonia) is an inorganic compound with the chemical formula NH2OH. The compound exists as hygroscopic colorless crystals.[4] Hydroxylamine is almost always provided and used as an aqueous solution or more often as one of its salts such as hydroxylammonium sulfate, a water-soluble solid.

Hydroxylamine and its salts are consumed almost exclusively to produce Nylon-6. The oxidation of NH3 to hydroxylamine is a step in biological nitrification.[5]

History

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Hydroxylamine was first prepared as hydroxylammonium chloride in 1865 by the German chemist Wilhelm Clemens Lossen (1838-1906); he reacted tin and hydrochloric acid in the presence of ethyl nitrate.[6] It was first prepared in pure form in 1891 by the Dutch chemist Lobry de Bruyn and by the French chemist Léon Maurice Crismer (1858-1944).[7][8] The coordination complex ZnCl2(NH2OH)2 (zinc dichloride di(hydroxylamine)), known as Crismer's salt, releases hydroxylamine upon heating.[9]

Structure

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Hydroxylamine and its N-substituted derivatives are pyramidal at nitrogen, with bond angles very similar to those of amines. The most stable conformation of hydroxylamine has the NOH anti to the lone pair on nitrogen, seeming to minimize the repulsion between the nitrogen and oxygen lone pairs. [10]

Production

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Hydroxylamine or its salts (salts containing hydroxylammonium cations [NH3OH]+) can be produced via several routes but only two are commercially viable. It is also produced naturally as discussed in a section on biochemistry.

From nitric oxide

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NH2OH is mainly produced as its sulfuric acid salt, hydroxylammonium sulfate ([NH3OH][SO4]), by the hydrogenation of nitric oxide over platinum catalysts in the presence of sulfuric acid.[11]

2 NO + 3 H2 + H2SO4 → [NH3OH]2[SO4]

Raschig process

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Another route to NH2OH is the Raschig process: aqueous ammonium nitrite is reduced by HSO−3 and SO2 at 0 °C to yield a hydroxylamido-N,N-disulfonate anion:

[NH4]+[NO2]− + 2 SO2 + NH3 + H2O → [NH4]2[HON(SO3)2]

This ammonium hydroxylamine disulfonate anion is then hydrolyzed to give hydroxylammonium sulfate:

[NH4]2[HON(SO3)2] + 2 H2O → [HONH3]2SO4

Other methods

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Julius Tafel discovered that hydroxylamine hydrochloride or sulfate salts can be produced by electrolytic reduction of nitric acid with HCl or H2SO4 respectively:[12][13]

HNO3 + 3 H2 → NH2OH + 2 H2O

Hydroxylamine can also be produced by the reduction of nitrous acid or potassium nitrite with bisulfite:

HNO2 + 2 HSO−3 → N(OH)(OSO−2)2 + H2O → NH(OH)(OSO−2) + HSO−4
NH(OH)(OSO−2) + [H3O]+ → [NH3OH]+ + HSO−4 (100 °C, 1 h)

Hydrochloric acid disproportionates nitromethane to hydroxylamine hydrochloride and carbon monoxide via the hydroxamic acid.[citation needed]

A direct lab synthesis of hydroxylamine from molecular nitrogen in water plasma was demonstrated in 2024.[14]

Isolation of hydroxylamine

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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.[4] The net reaction is:

2 NO−2 + 4 SO2 + 6 H2O + 6 NH3 → 4 SO2−4 + 6 [NH4]+ + 2 NH2OH

Base, such as sodium butoxide, can be used to free the hydroxylamine from hydroxylammonium chloride:[4]

[NH3OH]Cl + NaO(CH2)3CH3 → NH2OH + NaCl + CH3(CH2)3OH

Reactions

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Hydroxylamine is a base with a pKa of 6.03:

NH3OH+ ⇌ NH2OH + H+

Hydroxylamine reacts with alkylating agents usually at the nitrogen atom:

R−X + NH2OH → R−NH−OH + HX

The reaction of NH2OH with an aldehyde or ketone produces an oxime.

R2C=O + NH2OH → R2C=N−OH + H2O

This reaction can be 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 aqueous acid then restores the original aldehyde or ketone.[15]

NH2OH reacts with chlorosulfonic acid to give hydroxylamine-O-sulfonic acid:[16]

HO−S(=O)2−Cl + NH2OH → NH2−O−S(=O)2−OH + HCl

It isomerizes to the amine oxide H3N+−O−.[17]

Functional group

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See also: Hydroxamic acid
File:Hydroxylamine-group-2D.png
Secondary N,N-hydroxylamine schema

Hydroxylamine derivatives substituted in place of the hydroxyl or amine hydrogen are (respectively) called O- or N‑hydroxyl­amines. In general N‑hydroxyl­amines are more common. Examples are N‑tert‑butyl­hydroxyl­amine or the glycosidic bond in calicheamicin. N,O‑Dimethyl­hydroxylamine is a precursor to Weinreb amides.

Similarly to amines, one can distinguish hydroxylamines by their degree of substitution: primary, secondary and tertiary. When stored exposed to air for weeks, secondary hydroxylamines degrade to nitrones.[18]

N‑organyl­hydroxyl­amines, R−NH−OH, where R is an organyl group, can be reduced to amines R−NH2:[19]

R−NH−OH (Zn, HCl) → R−NH2 + ZnO

Oximes such as dimethylglyoxime are also employed as ligands.

Synthesis

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The hydrolysis of N-substituted oximes, hydroxamic acids, and nitrones easily provides hydroxylamines.

Alkylating of hydroxylamine or N-alkylhydroxylamines proceeds usually at nitrogen. One challenge is dialkylation when only monoalkylation is desired.

RNHOH + R'X → RR'NOH + HX

For O-alkylation of hydroxylamines, strong base such as sodium hydride is required to first deprotonate the OH group:[20]

RNHOH + NaH → RNHONa + H2
RNHONa + R'X → RNHOR' + NaX

Amine oxidation with benzoyl peroxide is a common method to synthesize hydroxylamines. Care must be taken to prevent over-oxidation to a nitrone. Other methods include:

Uses

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File:Beckmann-rearangement (cropped).png
Conversion of cyclohexanone to caprolactam involving the Beckmann rearrangement.

Approximately 95% of hydroxylamine is used in the synthesis of cyclohexanone oxime, a precursor to Nylon 6.[11] The treatment of this oxime with acid induces the Beckmann rearrangement to give caprolactam.[21] The latter can then undergo a ring-opening polymerization to yield Nylon 6.[22]

Laboratory uses

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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.

High concentrations of hydroxylamine are used by biologists to introduce mutations by acting as a DNA nucleobase amine-hydroxylating agent.[23] In is thought to mainly act via hydroxylation of cytidine to hydroxyaminocytidine, which is misread as thymidine, thereby inducing C:G to T:A transition mutations.[24] But high concentrations or over-reaction of hydroxylamine in vitro are seemingly able to modify other regions of the DNA & lead to other types of mutations.[24] This may be due to the ability of hydroxylamine to undergo uncontrolled free radical chemistry in the presence of trace metals and oxygen, in fact in the absence of its free radical effects Ernst Freese noted hydroxylamine was unable to induce reversion mutations of its C:G to T:A transition effect and even considered hydroxylamine to be the most specific mutagen known.[25] Practically, it has been largely surpassed by more potent mutagens such as EMS, ENU, or nitrosoguanidine, but being a very small mutagenic compound with high specificity, it found some specialized uses such as mutation of DNA packed within bacteriophage capsids,[26] and mutation of purified DNA in vitro.[27]

File:Celanese synthesis of paracetamol.svg
This route also involves the Beckmann Rearrangement, like the conversion from cyclohexanone to caprolactam.

An alternative industrial synthesis of paracetamol developed by Hoechst–Celanese involves the conversion of ketone to a ketoxime with hydroxylamine.

Some non-chemical uses include removal of hair from animal hides and photographic developing solutions.[2] In the semiconductor industry, hydroxylamine is often a component in the "resist stripper", which removes photoresist after lithography.

Hydroxylamine can also be used to better characterize the nature of a post-translational modification onto proteins. For example, poly(ADP-Ribose) chains are sensitive to hydroxylamine when attached to glutamic or aspartic acids but not sensitive when attached to serines.[28] Similarly, Ubiquitin molecules bound to serines or threonines residues are sensitive to hydroxylamine, but those bound to lysine (isopeptide bond) are resistant.[29]

Biochemistry

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In biological nitrification, the oxidation of NH3 to hydroxylamine is mediated by the ammonia monooxygenase (AMO).[5] Hydroxylamine oxidoreductase (HAO) further oxidizes hydroxylamine to nitrite.[30]

Cytochrome P460, an enzyme found in the ammonia-oxidizing bacteria Nitrosomonas europea, can convert hydroxylamine to nitrous oxide, a potent greenhouse gas.[31]

Hydroxylamine can also be used to highly selectively cleave asparaginyl-glycine peptide bonds in peptides and proteins.[32] 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.

Safety and environmental concerns

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Hydroxylamine is a skin irritant but is of low toxicity.

A detonator can easily explode aqueous solutions concentrated above 80% by weight, and even 50% solution might prove detonable if tested in bulk.[33][34] In air, the combustion is rapid and complete:

4 NH2OH + O2 → 2 N2 + 6 H2O

Absent air, pure hydroxylamine requires stronger heating and the detonation does not complete combustion:

3 NH2OH → N2 + NH3 + 3 H2O

At least two factories dealing in hydroxylamine have been destroyed since 1999 with loss of life.[35] It is known, however, that ferrous and ferric iron salts accelerate the decomposition of 50% NH2OH solutions.[36] 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.[37]

See also

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References

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  4. ^ a b c Greenwood and Earnshaw. Chemistry of the Elements. 2nd Edition. Reed Educational and Professional Publishing Ltd. pp. 431–432. 1997.
  5. ^ a b Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
  6. ^ W. C. Lossen (1865) "Ueber das Hydroxylamine" (On hydroxylamine), Zeitschrift für Chemie, 8 : 551-553. From p. 551: "Ich schlage vor, dieselbe Hydroxylamin oder Oxyammoniak zu nennen." (I propose to call it hydroxylamine or oxyammonia.)
  7. ^ C. A. Lobry de Bruyn (1891) "Sur l'hydroxylamine libre" (On free hydroxylamine), Recueil des travaux chimiques des Pays-Bas, 10 : 100-112.
  8. ^ L. Crismer (1891) "Préparation de l'hydroxylamine cristallisée" (Preparation of crystalized hydroxylamine), Bulletin de la Société chimique de Paris, series 3, 6 : 793-795.
  9. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
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  15. ^ Ralph Lloyd Shriner, Reynold C. Fuson, and Daniel Y. Curtin, The Systematic Identification of Organic Compounds: A Laboratory Manual, 5th ed. (New York: Wiley, 1964), chapter 6.
  16. ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
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  19. ^ Smith, Michael and Jerry March. March's advanced organic chemistry : reactions, mechanisms, and structure. New York. Wiley. p. 1554. 2001.
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  35. ^ Japan Science and Technology Agency Failure Knowledge Database Archived 2007-12-20 at the Wayback Machine.
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  37. ^ MSDS Sigma-Aldrich

Further reading

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  • Hydroxylamine[permanent dead link]
  • Walters, Michael A. and Andrew B. Hoem. "Hydroxylamine." e-Encyclopedia of Reagents for Organic Synthesis. 2001.
  • 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).
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