chemistry

Hydroxylamine

Hydroxylamine is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Hydroxylamine rather than just read about it. In short: Hydroxylamine (also known as hydroxyammonia) is an inorganic compound with the chemical formula NH2OH. The compound exists as hygroscopic colorless crystals.

Key takeaways

Hydroxylamine belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hydroxylamine to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hydroxylamine from memory before moving on to harder problems.

Reference excerpt

Hydroxylamine (also known as hydroxyammonia) is an inorganic compound with the chemical formula NH2OH. The compound exists as hygroscopic colorless crystals. Hydroxylamine is almost always provided and used as either 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. The crystal structure of hydroxylamine was first determined in 1955 under the direction of Nobel laureate William Lipscomb, although the positions of the hydrogen atoms were not localized at that time due to methodological limitations. In 2026, under the direction of M. A. Navasardyan, a high-precision crystal structure of hydroxylamine with unambiguous anisotropic refinement of all hydrogen atoms was successfully obtained, which also revealed the first observation of a cyclic hydroxylamine dimer (NH₂OH)₂.

History 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. 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). The coordination complex ZnCl2(NH2OH)2 (zinc dichloride di(hydroxylamine)), known as Crismer's salt, releases hydroxylamine upon heating.

Structure 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.

Production 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 NH2OH is mainly produced as its sulfuric acid salt, hydroxylammonium sulfate ([NH3OH]2[SO4]), by the hydrogenation of nitric oxide over platinum catalysts in the presence of sulfuric acid.

2 NO + 3 H2 + H2SO4 → [NH3OH]2[SO4]

Raschig process 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 Julius Tafel discovered that hydroxylamine hydrochloride or sulfate salts can be produced by electrolytic reduction of nitric acid with HCl or H2SO4 respectively:

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

Isolation of hydroxylamine 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:

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:

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

Reactions 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. NH2OH reacts with chlorosulfonic acid to give hydroxylamine-O-sulfonic acid:

HO−S(=O)2−Cl + NH2OH → NH2−O−S(=O)2−OH + HCl In aqueous solution, hydroxylamine is predicted to coexist with a tautomer, the amine oxide H3N+−O− (ammonia oxide). The solvated ammonia oxide form has variously been estimated to be less stable by 0.9–3.5 kcal·mol−1. It is absent from the gas phase, where the predicted stability gap is 27.6 kcal·mol−1.

Functional group

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

R−NH−OH (Zn, HCl) → R−NH2 + ZnO Oximes such as dimethylglyoxime are also employed as ligands.

Synthesis 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:

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:

Hydrogenation of an oxime Amine oxide pyrolysis (the Cope reaction) or rearrangement

Uses

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

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Hydroxylamine

Start with the simplest possible case. Write down what Hydroxylamine claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hydroxylamine before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hydroxylamine ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hydroxylamine

In research: Hydroxylamine appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hydroxylamine in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hydroxylamine is common in secondary-school and first-year university syllabi. It links to neighbouring topics Functional groups, Hydroxylamines, Inorganic amines, so understanding it makes those chapters shorter.
In everyday life: Look for Hydroxylamine outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Hydroxylamine in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hydroxylamine means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hydroxylamine out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hydroxylamine in simple terms?

Hydroxylamine (also known as hydroxyammonia) is an inorganic compound with the chemical formula NH2OH. The compound exists as hygroscopic colorless crystals.

Why does Hydroxylamine matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hydroxylamine?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hydroxylamine.