The ammonium carbonate is an inorganic salt nitrogen, ammoniacal specifically, the chemical formula (NH 4) 2 CO 3. It is made by synthetic methods, among which the sublimation of a mixture of ammonium sulfate and calcium carbonate stands out: (NH 4) 2 SO 4 (s) + CaCO 3 (s) => (NH 4) 2 CO 3 (s) + CaSO 4 (s).
Generally, the ammonium and calcium carbonate salts are heated in a vessel to produce the ammonium carbonate. The industrial method that produces tons of this salt consists of passing carbon dioxide through an absorption column containing a solution of ammonium in water, followed by distillation.
Vapors containing ammonia, carbon dioxide and water condense to form ammonium carbonate crystals: 2NH 3 (g) + H 2 O (l) + CO 2 (g) → (NH 4) 2 CO 3 (s). In the reaction, carbonic acid, H 2 CO 3, is produced after dissolving carbon dioxide in water, and it is this acid that gives up its two protons, H +, to two ammonia molecules.
Physical and chemical properties
It is a white, crystalline, colorless solid with strong ammonia odors and flavors. It melts at 58ºC, decomposing into ammonia, water and carbon dioxide: exactly the previous chemical equation but in the opposite direction.
However, this decomposition occurs in two steps: first a molecule of NH 3 is released, producing ammonium bicarbonate (NH 4 HCO 3); and second, if heating continues, the carbonate is disproportionate releasing even more gaseous ammonia.
It is a solid very soluble in water and less soluble in alcohols. It forms hydrogen bonds with water, and when 5 grams is dissolved in 100 grams of water, it generates a basic solution with a pH around 8.6.
Its high affinity for water makes it a hygroscopic solid (absorbs moisture), and therefore it is difficult to find it in its anhydrous form. In fact, its monohydrated form, (NH 4) 2 CO 3 · H 2 O), is the most common of all and explains how salt carries ammonia gas, which causes odor.
In air it decomposes to generate ammonium bicarbonate and ammonium carbonate (NH 4 NH 2 CO 2).
Chemical structure
The upper image illustrates the chemical structure of ammonium carbonate. In the middle is the anion CO 3 2–, the flat triangle with a black center and red spheres; and on its two sides, the NH 4 + ammonium cations with tetrahedral geometries.
The geometry of the ammonium ion is explained by the sp 3 hybridization of the nitrogen atom, arranging the hydrogen atoms (the white spheres) around it in the form of a tetrahedron. Among the three ions, interactions are established by hydrogen bonds (H 3 N-H- O-CO 2 2–).
Thanks to its geometry, a single CO 3 2– anion can form up to three hydrogen bonds; while NH 4 + cations may not be able to form their corresponding four hydrogen bonds due to electrostatic repulsions between their positive charges.
The result of all these interactions is the crystallization of an orthorhombic system. Why is it so hygroscopic and soluble in water? The answer is in the same paragraph above: hydrogen bonds.
These interactions are responsible for the rapid absorption of water from the anhydrous salt to form (NH 4) 2 CO 3 · H 2 O). This results in changes in the spatial arrangement of the ions, and consequently, in the crystal structure.
Structural curiosities
As simple as (NH 4) 2 CO 3 looks, it is so sensitive to countless transformations that its structure is a mystery subject to the true composition of the solid. This structure also varies according to the pressures that affect the crystals.
Some authors have found that ions are arranged as hydrogen-bonded coplanar chains (that is, a chain with a sequence NH 4 + -CO 3 2– -…) in which water molecules probably serve as linkers to others. chains.
Furthermore, transcending the terrestrial sky, what are these crystals like in space or interstellar conditions? What are their compositions in terms of the stabilities of the carbonate species? There are studies that confirm the great stability of these crystals trapped in planetary ice masses and comets.
This allows them to act as carbon, nitrogen and hydrogen reserves, which, receiving solar radiation, can be transformed into organic material such as amino acids.
In other words, these frozen ammonia blocks could be carriers of "the wheel that starts the machinery of life" in the cosmos. For these reasons, his interest in the field of astrobiology and biochemistry is growing.
Applications
It is used as a leavening agent, since when heated it produces carbon dioxide and ammonium gases. Ammonium carbonate is, if you will, a precursor to modern baking powders and can be used to bake cookies and flatbreads.
However, it is not recommended for baking cakes. Due to the thickness of the cakes, the ammonium gases are trapped inside and produce an unpleasant taste.
It is used as an expectorant, that is, it relieves cough by decongesting the bronchial tubes. It has fungicidal action, being used for this reason in agriculture. It is also a regulator of acidity present in food and is used in the organic synthesis of urea under high pressure conditions, and of hydantoins.
Risks
Ammonium carbonate is highly toxic. Produces acute irritation of the oral cavity in humans on contact.
In addition, if it is ingested it causes gastric irritation. A similar action is observed in eyes exposed to ammonium carbonate.
Inhalation of the gases from the decomposition of salt can irritate the nose, throat and lungs, causing coughing and respiratory distress.
Acute exposure of fasting dogs to ammonium carbonate at a dose of 40 mg / kg of body weight causes vomiting and diarrhea. Higher doses of ammonium carbonate (200 mg / kg body weight) are often lethal. A heart damage is indicated as the cause of death.
If heated to very high temperatures and in oxygen-enriched air, it releases toxic NO 2 gases.
References
- PubChem. (2018). Ammonium Carbonate. Retrieved on March 25, 2018, from PubChem: pubchem.ncbi.nlm.nih.gov
- Organic Chemistry Portal. ((2009-2018)). Bucherer-Bergs Reaction. Retrieved on March 25, 2018, from Organic Chemistry Portal: www.organic-chemistry.org
- Kiyama, Ryo; Yanagimoto, Takao (1951) Chemical reactions under ultra high pressure: urea synthesis from solid ammonium carbonate. The Review of Physical Chemistry of Japan, 21: 32-40
- Fortes, AD, Wood, IG, Alfè, D., Hernández, ER, Gutmann, MJ, & Sparkes, HA (2014). Structure, hydrogen bonding and thermal expansion of ammonium carbonate monohydrate. Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials, 70 (Pt6), 948–962.
- Wikipedia. (2018). Ammonium carbonate. Retrieved on March 25, 2018, from Wikipedia: en.wikipedia.org
- The Chemical Company. (2018). The Chemical Company. Retrieved on March 25, 2018, from The Chemical Company: thechemco.com