Hydroxylamine
Properties
| State | Solid (white hygroscopic crystalline solid; free base unstable, usually supplied as hydrochloride salt) |
| Color | White |
| Solubility | Freely soluble in water; soluble in ethanol and methanol |
| Melting Point | 33°C (free base); 151°C (hydrochloride salt) |
| Boiling Point | 58°C (decomposes; free base) |
About Hydroxylamine
Hydroxylamine sits squarely in the middle of nitrogen's oxidation-state ladder — N(-I), one electron below ammonia and one above N2. That intermediate position is what makes it useful and what makes it dangerous: it can disproportionate to N2 and NH3 with enough enthalpy release to detonate, which is why nobody ships the free base. Bench chemists buy the hydrochloride or sulfate salt and generate the free amine in situ. The single largest commercial use is the nylon-6 supply chain: hydroxylamine condenses with cyclohexanone to give cyclohexanone oxime, which is then rearranged with oleum (Beckmann rearrangement) to caprolactam, the monomer for nylon-6. About 5 million tonnes of caprolactam are made this way each year. Smaller but interesting uses include cleaving Asn-Gly peptide bonds in protein chemistry (the Bornstein cleavage), reducing Cu(II) and Ag(I) in photographic developers, generating nitrile oxides for 1,3-dipolar cycloadditions, and stripping post-etch polymer residues off semiconductor wafers. In nature, ammonia-oxidizing bacteria oxidize NH3 to NO2- through an NH2OH intermediate using the enzyme hydroxylamine oxidoreductase — the second step of nitrification.
Where you'll encounter it
If you've ever made an oxime to characterize an unknown ketone, run a Beckmann rearrangement, or watched a photographic developer reduce silver halide to metallic Ag, hydroxylamine (or one of its salts) was doing the work. The nylon-6 in carpets, fishing line, and engineering plastics across the global market traces back through hydroxylamine: about 5 million tonnes per year of caprolactam monomer go through the cyclohexanone-oxime intermediate before Beckmann rearrangement with oleum opens it into the lactam ring. Semiconductor fabs use hydroxylamine-based photoresist strippers (the EKC265 family) to clean post-etch polymer residues off Si wafers without attacking the underlying copper or low-k dielectric. Older photography labs reaching for rapid silver-halide developers used hydroxylamine sulfate as the second-step reducing agent that converts AgX to metallic Ag in the gelatin emulsion.
Common Uses
- Cyclohexanone oxime synthesis feeding the Beckmann rearrangement to caprolactam (nylon-6)
- Oxime formation for ketone/aldehyde derivatization and characterization
- Asn-Gly peptide bond cleavage (Bornstein method) in protein sequencing
- Photoresist stripping and post-etch residue cleaning on Si wafers
- Reducing agent in silver-halide photographic developers and Cu(II) electroless plating baths
- Generation of nitrile oxides for 1,3-dipolar cycloaddition isoxazoline synthesis
Safety Information
GHS: Acute Tox. Cat 4, Skin Corr. 1B, Eye Dam. 1, STOT-RE 2, Self-react. Type C, Aquatic Acute 1. The free base is shock- and heat-sensitive and has caused fatal explosions at production scale (Concept Sciences 1999, Nissin 2000) — never isolate or concentrate above 50% aqueous. Salts (HCl, sulfate) are far safer to handle but still cause methemoglobinemia on systemic absorption and severe skin/eye burns. Causes hemolytic anemia on chronic exposure. Store cold (≤4 °C), dry, and away from metals (Fe, Cu catalyze decomposition). OSHA has no specific PEL but workplace exposure limits typically follow ACGIH guidance.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.