What Is Hydroxylamine?
Hydroxylamine is an inorganic compound with the chemical formula NH2OH.
It is an intermediate in the nitrification process in biosynthesis and is oxidized by hydroxylamine oxidase to produce nitrite. Hydroxylamine is commonly handled in aqueous solution and as salts, including hydrochloride and sulfate.
Uses of Hydroxylamine
Hydroxylamine and its salts serve as reducing agents in various organic and inorganic chemical reactions. They are used in synthesizing oximes and caprolactam, a raw material for nylon. Additionally, they function as analytical reagents, enzyme reactivators, de-hairing agents for animal skins, photographic developers, semiconductor cleaners, and raw materials for pharmaceuticals and agrochemicals. Hydroxylamine is also used in tobacco sweeteners, soaps, and as antioxidants and stabilizers for fatty acids. Moreover, it plays a significant role in the nitrogen cycle and wastewater treatment, serving as a biological intermediate in nitrification and anaerobic ammonia oxidation.
Properties of Hydroxylamine
Hydroxylamine is a colorless, needle-like crystal, highly deliquescent and volatile. It has a melting point of 91.4 °F (33 °C) and decomposes at 136.4 °F (58 °C). The molar mass of hydroxylamine is 33.030 g/mol, and its density at 68 °F (20 °C) is 1.21 g/cm³.
Hydroxylamine is an unstable substance, gradually decomposing even at room temperature. This decomposition is hastened by moisture and CO2. It can explode when heated or exposed to ultraviolet light, transforming into substances like ammonia (NH3), nitrogen (N2), and nitrous oxide (N2O).
It is soluble in water, liquid ammonia, and methanol, but insoluble in ether, benzene, and chloroform.
Structure of Hydroxylamine
Hydroxylamine’s structure resembles a combination of water and ammonia. Consequently, liquid hydroxylamine, similar to water, dissolves many inorganic salts.
Other Information About Hydroxylamine
1. Synthesis of Hydroxylamine
Hydroxylamine can be synthesized using the Raschig method: reduction of an aqueous solution of ammonium nitrite at 0 °C with HSO4-/SO2 yields hydroxylamide-N,N-disulfate. Upon hydrolysis, this yields the sulfate salt, (NH3OH)2SO4.
Treating this sulfate with liquid ammonia yields solid hydroxylamine. Ammonia can be removed under reduced pressure, leaving behind ammonium sulfate, which is insoluble in liquid ammonia. Other synthetic methods include the production of hydroxylammonium salts and the reduction of nitrite or sodium nitrite by sulfite ions, yielding hydroxylammonium salts.
2. Reaction of Hydroxylamine
Hydroxylamine reacts with ketones and aldehydes to form oximes and with chlorosulfuric acid to produce hydroxylamine-O-sulfonic acid. It also reacts with electrophilic reagents like alkylating agents, where both nitrogen and oxygen atoms are subject to electrophilic attack.
3. Synthesis of Caprolactam With Hydroxylamine
Approximately 95% of hydroxylamine is utilized in synthesizing cyclohexanone oxime, a precursor to Nylon 6. Cyclohexanone is converted to cyclohexanone oxime using hydroxylamine sulfate. This oxime undergoes Beckmann rearrangement when treated with acid, forming caprolactam, from which Nylon 6 is synthesized through ring-opening polymerization.