How many atoms are in urea

urea

Structural formula
General
Surname urea
other names
  • Carbonic acid diamide
  • Carbamide
  • UREA (INCI)
  • Carbonyl diamide
  • Carbonic acid diamide
  • Diaminomethanal
  • Piagran (brand name)
  • E927b
Molecular formula CH4N2O
CAS number 57-13-6
PubChem1176
ATC code
Brief description

colorless and odorless, crystalline solid[1]

properties
Molar mass 60.06 g mol−1
Physical state

firmly

density

1.32 g cm−3[2]

Melting point

132.5-134.5 ° C (Decomposition)[2]

Vapor pressure

0.2 Pa (75 ° C) [2]

pKs-Value
solubility

very good in water:

safety instructions
LD50

8471 mg kg−1 (Mouse, perorally) [6]

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions.
Template: Infobox chemical / molecular formula search available

urea (Latin and English urea), chemically carbonic acid diamide, is an organic compound that is produced by many living things as an end product of the metabolism of nitrogen compounds (e.g. amino acids) in the so-called urea cycle and excreted in the urine. Pure urea is a white, crystalline, non-toxic and hygienically harmless solid that should not be confused with uric acid.

history

Urea was first synthesized in 1828 by Friedrich Wöhler by reacting potassium cyanate and ammonium sulfate. Urea is considered to be the first organic compound to be synthesized from inorganic raw materials.

That contradicted the then widespread notion that organic substances basically only from living things through the so-called "Vis vitalis" (Life force) could be produced. To be precise, as early as 1824, F. Wöhler provided evidence by hydrolysing dicyan to oxalic acid that the synthesis of organic molecules does not require “life force”.[7]

Physiological importance

Urea is formed in the protein and amino acid metabolism and is one of the substances that require urine. In mammals, turtles, some fish and adult amphibians, it is the most important form of excretion of the nitrogen contained in proteins. Birds and most reptiles produce uric acid instead; Tadpoles, most types of fish and other aquatic animals excrete nitrogen as ammonia.

Ammonia is produced when amino acids are broken down and, in correspondingly high concentrations, has a toxic effect on cells. In order to counteract an increase in the ammonia concentration, it is converted into non-toxic urea via the urea cycle and excreted via the kidneys.

Diseases such as acute or chronic kidney failure, as well as diabetic impaired kidney function, can lead to increased urea levels in the serum / plasma (normal value: 10-50 mg / dl).

Disturbances and peculiarities

A high protein intake leads to increased urea levels even with normal kidney function, which makes it a poor kidney parameter. In (pre-) terminal renal insufficiency, the urea concentration in the serum is better suited to assess the severity of the uremia than the serum creatinine concentration.

Applications

Due to its high nitrogen content of 46.62%, urea is the most important nitrogen fertilizer worldwide.

Urea is also often used as a moisture factor in cosmetics because of its high water-binding capacity. In pharmacy, urea is known as a keratolytic. This property is used in various recipes. For example, it has a highly concentrated effect (40%) in pastes together with an antifungal agent (antifungal agent) against nail fungus (onychomycosis), whereby the urea softens the nail so that the infected nail substance can be removed piece by piece. It is also used as a moisturizer in ointments to combat atopic eczema and lichen diseases.

Cigarette manufacturers add urea to tobacco so that the nicotine can be better absorbed by increasing the pH value in the lungs. This increases the effect of supposedly lighter cigarettes.

Urea can also be used as a substitute for road salt, but this is not economical because of its higher price. In Vienna, its use in this regard - which leads to over-fertilization of the soil - is prohibited[8].

Urea is used to reduce nitrogen oxides in the exhaust gas from power plants and internal combustion engines. The SNCR process (selective non-catalytic reduction) is used in power plants, primarily in smaller systems. In the so-called SCR process (selective catalytic reduction), which is used in power plants and increasingly also in vehicle technology, urea or ammonia is injected into the hot exhaust gas flow. The urea decomposes into ammonia, which reduces the nitrogen oxides in a downstream catalytic converter. In automotive engineering, an aqueous solution with a 32.5% urea content is used, which is known under the trade name AdBlue. The consumption of urea solution is about 2 to 8% of the fuel consumption.

Urea is added to food as a stabilizer. In the EU it is labeled as a food additive E 927b only approved for chewing gum with no added sugar.

Urea plays a role as a protein supplier in dairy cattle feeding.

The addition of urea in higher concentrations to aqueous solutions leads to a denaturation of proteins, so urea acts as a denaturant or as a chaotropic compound. However, small concentrations of urea can have the opposite effect, namely increase the hydrophobic effect and thus stabilize the protein structure.[9]

properties

When heated above the melting point, urea condenses with the elimination of ammonia (NH3) to biuret:


Urea reacts with the enzyme urease to form carbon dioxide and ammonia.

Industrial manufacture

Urea is produced industrially in large quantities (2004: 127 million t worldwide) and is used e.g. B. as nitrogen fertilizer or as NOx- Reducing agents in the SNCR process. The first production plant was commissioned by BASF in 1922. The ammonium carbamate formed in a high-pressure reactor in the first step at 150 bar was then thermally split into urea in decomposers. Excess ammonia was used to make ammonium sulfate and ammonium nitrate as fertilizer. At the end of the 1920s, the process was improved and excess ammonia was returned to the production process. Various total cycle processes developed from this. All processes have in common that the ammonium carbamate formed exothermically in a reactor at high pressure is endothermically converted into urea in subsequent decomposition stages at low pressure and excess gases are returned to the reactor, whereby economical stripping processes are used for this today.

In countries with large natural gas reserves, which in the past were often simply flared, natural gas is now converted into urea. This is done by large plants that use natural gas, air and water in the process steps of hydrogen production → ammonia production → urea synthesis, and finally urea. (Strictly speaking, the starting materials mentioned are converted into a process gas consisting of H.2, N2 and Co2 implemented, from which the CO2 Will get removed. Hydrogen and nitrogen are then converted into ammonia. Pure hydrogen does not appear in this chain). The CO separated off for the production of ammonia2 only 2/3 is bound by urea. The urea, which is initially obtained in solution, is converted into granules and sold in bags or loose. The largest plants in the world produce around 4,000 tons of urea per day.

Reaction equations:

$ \ mathrm {2 \ NH_3 + CO_2 \ longrightarrow \ lbrack H_2N {-} CO {-} O \ rbrack NH_4} $
Ammonia and carbon dioxide react exothermically to form ammonium carbamate.
$ \ mathrm {\ lbrack H_2N {-} CO {-} O \ rbrack NH_4 \ longrightarrow H_2N {-} CO {-} NH_2 + H_2O} $
Ammonium carbamate reacts endothermically to form urea and water.

An industrial use of urea is the production of melamine, which is e.g. B. is processed with formaldehyde to synthetic resins, and urea-formaldehyde resins (urea resin, so-called UF resins), the z. B. be used for the production of chipboard.

Urea as a mineral

Urea was found in 1973 as a natural secondary mineral at Toppin Hill on Lake Rason (Western Australia). It has been recognized as a separate mineral by the International Mineralogical Association (IMA). According to the systematics of minerals according to Strunz (9th edition), these are listed as "Various organic compounds" under system no. "10.CA.35". The systematics of minerals according to Dana, which is also common in English-speaking countries, lists the mineral under system no. "50.4.6.1".[10][11][12] Urea crystallizes in the tetragonal crystal system. It develops colorless to pale yellow or pale brown, needle-shaped crystals.[13]

Urea is a component of the urine or excrement of birds and bats and is therefore a component of guano and bat guano (Chiropterite)[14]. As a mineral, urea is not stable and can only be formed under arid conditions.

See also

literature

Web links

Individual evidence

Urea molecule and formula of urea synthesis on the special postage stamp of the Deutsche Bundespost from 1982 on the 100th anniversary of Friedrich Wöhler's death
  1. ^ Römpp CD 2006, Georg Thieme Verlag 2006.
  2. 2,02,12,22,32,4Entry to urea in the GESTIS substance database of the IFA, accessed on July 23, 2007 (JavaScript required).
  3. ^ Bordwell pKa-Table.
  4. ↑ pKa Data Compiled by R. Williams.
  5. 5,05,1David R. Lide (Ed.): CRC Handbook of Chemistry and Physics, 90th Ed., 2009, Taylor & Francis, pp. 8-120, ISBN 978-1-4200-9084-0.
  6. urea at ChemIDplus.
  7. ↑ Burckhard Frank: 250 years of chemistry in Göttingen. In: Hans-Heinrich Voigt (Ed.): Natural sciences in Göttingen. A series of lectures. Vandenhoeck + Ruprecht Gm, Göttingen 1988, ISBN 3-525-35843-1 (Göttingen university publications. Volume 13), p. 72 (on books.google.de).
  8. ↑ http: //www.wien.gv.at/umweltschutz/auftaumittel.html
  9. ↑: M. Wood, M. Mayele Influence of Additives on Hydrophobic Association in Polynary Aqueous Mixtures In: DFG Research Report. Thermodynamic Properties of Complex Fluid Mixtures Wiley-VCH 2004, pp. 150-183, ISBN 3-527-27770-6.
  10. ^ Bridge, P.J. (1973): Urea, a new mineral, and neotype phosphammite from Western Australia. Mineral. Mag., 39, 346-348.
  11. ^ American Mineralogist (1974): 59: 874.
  12. ^ Acta Crystallographica (1999).
  13. ↑ http: //www.mindat.org/min-4117.html.
  14. ^ Thieme Chemistry (Ed.): Entry on guano in the Römpp Online. Version 3.29. Georg Thieme Verlag, Stuttgart 2012, accessed on May 22, 2012.