Ammonium Compounds
Authors: Weston Charles W. 
Published: August 2004

Abstract

There are a considerable number of stable crystalline salts of the ammonium ion,

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. Several are of commercial importance because of large‐scale consumption in fertilizer and industrial markets. These salts are often isomorphous and have similar solubility in water. Compounds in which the ammonium ion is combined with a large, uninegative anion are usually the most stable. Ammonium salts containing a small, highly charged anion generally dissociate easily into ammonia and the free acid. Both normal or neutral ammonium acetate, NH
4
C
2
H
3
O
2
, and the acid salt are known. The normal salt, CH
3
COONH
4
, is a white, deliquescent, crystalline solid that results from exact neutralization of acetic acid using ammonia. It is quite soluble in water or ethanol. Ammonium bicarbonate, also known as ammonium hydrogen carbonate or ammonium acid carbonate, is easily formed. It is produced as both food and standard grade. Normal ammonium carbonate, a crystalline solid, is the principal ingredient of smelling salts because of its characteristic strong ammonia odor. Diammonium citrate, (NH
4
)
2
C
6
H
6
O
7
, is made by neutralization of citric acid. The crystalline or granular product is used as a chemical reagent and as a diuretic. Ammonium chloride, NH
4
Cl, ammonium bromide, NH
4
Br, and ammonium iodide, NH
4
I, are crystalline, ionic compounds that exhibit high vapor pressures at elevated temperatures and sublime readily. Aqueous solutions of ammonium halides are acidic. A process based on metathesis or double decomposition is generally preferred for manufacture of ammonium chloride. Several commercial grades are available. Ammonium chloride is used as a nitrogen source for fertilization of rice, wheat, and other crops in Japan, China, India, and Southeast Asia. Ammonium chloride serves as an electrolyte in the manufacture of drycell batteries, is also used to make quarrying explosives. Ammonium bromide and iodide are manufactured either by the reaction of ammonia with the corresponding hydrohalic acid or by the reaction of ammonia with elemental bromine or iodine. Ammonium bromide is used to manufacture chemical intermediates, and in photographic chemicals. Ammonium nitrate, NH
4
NO
3
, a white, crystalline salt that is highly soluble in water, is the most commercially important ammonium compound both in terms of production volume and usage. It is the principal component of most industrial explosives and nonmilitary blasting compositions; however, it is used primarily as a nitrogen fertilizer. One disadvantage of nitrogen fertilizers, and ammonium nitrate in particular, is that the nitrate ion is more prone to leach through the soil profile and enter the groundwater. The presence of nitrate in groundwater became an important environmental issue in the 1980s. Ammonium nitrate is considered a very stable salt, but when heated to temperatures from 200 to 230°C, exothermic decomposition occurs. The reaction is rapid, but can be controlled. Above 230°C, exothermic elimination of N
2
and NO
2
begin, and a final violent exothermic reaction occurs with great rapidity when ammonium nitrate detonates. When used in blasting, ammonium nitrate is mixed with fuel oil and sometimes sensitizers such as powdered aluminum. Modern commercial processes for ammonium nitrate rely almost exclusively on the neutralization of nitric acid with ammonia. Ammonium nitrate can be considered a safety material if treated and handled properly. Potential hazards include those associated with fire, decomposition accompanied by generation of toxic fumes, and explosion. Many plants outside of North America prill or granulate a mixture of ammonium nitrate and calcium carbonate. Production of this mixture, often called calcium ammonium nitrate, essentially removes any explosion hazard. Ammonium sulfate, (NH
4
)
2
SO
4
, a white, soluble, crystalline salt, is produced from the direct neutralization of sulfuric acid with ammonia. Used as a fertilizer, it is valued both for its nitrogen content and for its readily available sulfur content. Ammonium sulfide and ammonium hydrosulfide are used by the textile industry.