Production
Ammonium bicarbonate is produced by combining carbon dioxide and ammonia:
CO2 + NH3 + H2O → (NH4)HCO3
Since ammonium bicarbonate is thermally unstable, the reaction solution is kept cold, which allows the precipitation of the product as white solid. About 100,000 tons were produced in this way in 1997.[3]
Ammonia gas passed into a strong aqueous solution of the sesquicarbonate (a 2:1:1 mixture of (NH4)HCO3, (NH4)2CO3, and H2O) converts it into normal ammonium carbonate ((NH4)2CO3), which can be obtained in the crystalline condition from a solution prepared at about 30 °C. This compound on exposure to air gives off ammonia and reverts to ammonium bicarbonate.
Salt of Hartshorn
Compositions containing ammonium carbonate have long been known. They were once produced commercially, formerly known as sal volatile or salt of hartshorn. It was obtained by the dry distillation of nitrogenous organic matter such as hair, horn, leather. In addition to ammonium bicarbonate, this material contains ammonium carbamate (NH4CO2NH2), and ammonium carbonate ((NH4)2CO3). It is sometimes called ammonium sesquicarbonate. It possesses a strong ammoniacal smell, and on digestion with alcohol, the carbamate is dissolved leaving a residue of ammonium bicarbonate.[3]
A similar decomposition takes place when the sesquicarbonate is exposed to air.
Uses
Ammonium bicarbonate is used in the food industry as a raising agent for flat baked goods, such as cookies and crackers, and in China in steamed buns and Chinese almond cookies. It was commonly used in the home before modern day baking powder was made available. In China it is called edible or food-grade "smelly powder". Many baking cookbooks (especially from Scandinavian countries) may still refer to it as hartshorn or hornsalt [4][5] (e.g., FI: "hirvensarvisuola", NO: "hjortetakksalt", DK: "hjortetakssalt", SE: "hjorthornssalt", "salt of hart's horn", DE: "Hirschhornsalz"). Although there is a slight smell of ammonia during baking, this quickly dissipates, leaving no taste. It is used in, for example, Swedish "drömmar" biscuits and Danish Christmas biscuits (Hjortetakssalt), and German Lebkuchen. In many cases it may be substituted with baking soda or baking powder or a combination of both, depending on the recipe composition and leavening requirements.[6] Compared to baking soda or potash, hartshorn has the advantage of producing more gas for the same amount of agent, and of not leaving any salty or soapy taste in the finished product, as it completely decomposes into water and gaseous products that evaporate during baking. It cannot be used for moist, bulky baked goods however, such as normal bread or cakes, since some ammonia will be trapped inside and will cause an unpleasant taste.
It is commonly used as an inexpensive nitrogen fertilizer in China, but is now being phased out in favor of urea for quality and stability. This compound is used as a component in the production of fire-extinguishing compounds, pharmaceuticals, dyes, pigments, and it is also a basic fertilizer being a source of ammonia. Ammonium bicarbonate is still widely used in the plastic and rubber industry, in the manufacture of ceramics, in chrome leather tanning, and for the synthesis of catalysts.[citation needed]
It is also used for buffering solutions to slightly alkaline pH during chemical purification, such as high-performance liquid chromatography. Because it entirely decomposes to volatile compounds this allows rapid recovery of the compound of interest by freeze-drying.
Ammonium bicarbonate is also a key component of the expectorant cough syrup "Senega and Ammonia".
E-Number: E503
Reactions
It dissolves in water to give a mildly alkaline solution. It is insoluble in acetone and alcohols.
Ammonium bicarbonate decomposes above about 36 °C into ammonia, carbon dioxide, and water in an endothermic process and so causes a drop in the temperature of the water:
NH4HCO3 → NH3 + H2O + CO2.
When treated with acids, carbon dioxide is also produced:
NH4HCO3 + HCl → NH4Cl + CO2 + H2O.
Reaction with base produces ammonia.
It reacts with sulfates of alkaline-earth metals to precipitating their carbonates:
CaSO4 + 2 NH4HCO3 → CaCO3 + (NH4)2SO4 + CO2 + H2O.
It also reacts with alkali metal halides, giving alkali metal bicarbonate and ammonium halide:
NH4HCO3 + NaCl → NH4Cl + NaHCO3;
NH4HCO3 + KI → NH4I + KHCO3;
NH4HCO3 + NaBr → NH4Br + NaHCO3.
Safety
Ammonium bicarbonate is an irritant to the skin, eyes and respiratory system. Short-term health effects may occur immediately or shortly after exposure to ammonium bicarbonate. Breathing ammonium bicarbonate can irritate the nose, throat and lungs causing coughing, wheezing and/or shortness of breath. Repeated exposure may cause bronchitis to develop with cough, and/or shortness of breath. Health effects can occur some time after exposure to ammonium bicarbonate and can last for months or years.
Where possible, operations should be enclosed and the use of local exhaust ventilation at the site of chemical release is recommended. If local exhaust ventilation or enclosure is not used, respirators are necessary. Wear protective work clothing. Change clothes and wash thoroughly immediately after exposure to ammonium bicarbonate.[7