hydroxylamine

Hydroxylamine
IUPAC name	Hydroxylamine
Other names	Azanol Oxammonium
Identifiers
CAS number	7803-49-8 Y
PubChem	787
RTECS number	NC2975000
Properties
Molecular formula	NH2OH
Molar mass	33.030 g/mol
Appearance	white needles or flakes
Density	1.21 g/cm3 (20 °C) [1]
Melting point	33 °C
Boiling point	58 ºC decomp.
Solubility in water	soluble in cold water, decomposes in hot water
Solubility	very soluble in liquid ammonia, alcohol
Acidity (pKa)	5.94
Structure
Dipole moment	0.67553 D
Thermochemistry
Std enthalpy of formation ΔfHo298	−39.9 kJ/mol
Hazards
MSDS	ICSC 0661
EU Index	612-122-00-7 (solution, >55%) 612-122-01-4 (solution, <55%)
EU classification	Explosive (E) Carc. Cat. 3 Toxic (T) Harmful (Xn) Irritant (Xi) Dangerous for the environment (N)
R-phrases	R2, R21/22, R37/38, R40, R41, R43, R48/22, R50
S-phrases	(S2), S26, S36/37/39, S61
NFPA 704	0 2 3
Flash point	129 ºC explodes
Autoignition temperature	265 ºC
LD50	408 mg/kg (oral, mouse); 59–70 mg/kg (intraperitoneal mouse, rat); 29 mg/kg (subcutaneous, rat)[2]
Related compounds
Related hydroxylammonium salts	Hydroxylammonium chloride Hydroxylammonium nitrate Hydroxylammonium sulfate
Related compounds	Ammonia Hydrazine
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Hydroxylamine is a reactive chemical with formula NH₂OH. It can be considered a hybrid of ammonia and water due to parallels it shares with each. At room temperature pure NH₂OH is ordinarily a white, unstable crystalline, hygroscopic compound;^[3] however it is almost always encountered as an aqueous solution.

Hydroxylamine tends to be explosive, and the nature of the hazard is not entirely understood. At least two factories dealing in hydroxylamine have been destroyed since 1999 with loss of life.^[4] 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.

NH₂OH is an intermediate in biological nitrification. The oxidation of NH₃ is mediated by hydroxylamine oxidoreductase (HAO).

Production

NH₂OH can be synthesized via several routes.

The first 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

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.^[3]

Another route is to make hydroxylammonium salts which can then be converted to hydroxylamine.

(NH₃OH)Cl + NaOBu → NH₂OH + NaCl + BuOH^[3]

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

HNO₂ + 2 HSO₃⁻ → N(OH)(OSO₂)₂²⁻ + H₂O → NH(OH)(OSO₂)⁻ + HSO₄⁻

NH(OH)(OSO₂)⁻ + H₃O⁺ (100 °C/1 h) → NH₃(OH)⁺ + HSO₄⁻

Reactions

Hydroxylamine reacts with electrophiles, such as an alkylating agents, which can attach at either the O or N position.

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. Oximes, e.g., dimethylglyoxime, are also employed as ligands.

NH₂OH reacts with chlorosulfuric 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, can be checked by iodometric titration.

Hydroxylamine (NH₂OH), or hydroxylamines (R-NHOH) can be reduced to amines.^[5]

NH₂OH (Zn/HCl) → NH₃

R-NHOH (Zn/HCl) → R-NH₂

Uses

Hydroxylamine and its salts are commonly used as reducing agents in a myriad of 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.^[6]

The nitrate salt, hydroxylammonium nitrate, is being researched as a rocket propellant, both in water solution as a monopropellant and in its solid form as a solid propellant.

This has also been used in the past by biologists to introduce random mutations by switching base pairs from A to G, 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.

Safety

Hydroxylamine may explode on heating. 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.^[7]

See also

• Amine

References

External links

• Calorimetric studies of hydroxylamine decomposition
• Chemical company BASF info
• MSDS
• MSDS
• Deadly detonation of hydroxylamine at Concept Sciences facility