Hydroxylammonium sulfate, (NH₃OH)₂SO₄, is the sulfuric acid salt of hydroxylamine. It is primarily used as an easily-handled form of hydroxylamine, which is explosive when pure.

Synthesis

Hydroxylammonium sulfate can be obtained by the acid-base reaction of hydroxylamine with sulfuric acid:

2NH₂OH(aq) + H₂SO₄(aq) → (NH₃OH)₂SO₄(aq)

Applications

Hydroxylammonium sulfate is used in organic synthesis to convert aldehydes and ketones to oximes, carboxylic acids and their derivatives (e.g. esters) to hydroxamic acids, isocyanates to N-hydroxyureas and nitriles to amidoximes. Hydroxylammonium sulfate is also used to generate hydroxylamine-O-sulfonic acid from oleum or chlorosulfuric acid.

Hydroxylammonium sulfate is used in the production of anti-skinning agents, pharmaceuticals, rubber, textiles, plastics and detergents. It is a radical scavenger that terminates radical polymerization reactions and serves as an antioxidant in natural rubber. (NH₃OH)₂SO₄ is a starting material for some insecticides, herbicides and growth regulators. It is used in photography as a stabiliser for colour developers and as an additive in photographic emulsions in colour film.

Decomposition

At 120 °C, hydroxylammonium sulfate begins to decompose to sulfur trioxide, nitrous oxide, water, and ammonia:

2(NH₃OH)₂SO₄ → 2SO₃ + N₂O + 2NH₃ + 5H₂O

The reaction is exothermic above 138 °C, and is most exothermic at 177 °C. Metals (especially copper, its alloys and its salts) catalyse the decomposition of hydroxylammonium sulfate.

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