Why is uric acid converted to urea

Structural formula
Surname urea
other names
  • Carbonic acid diamide
  • Carbamide
  • Carbonyl diamide
  • Carbonic acid diamide
  • Urea (lat.)
  • Piagran (granulated urea)
Molecular formula CH4N2O
CAS number 57-13-6
Brief description colorless, crystalline solid with an ammonia-like odor[1]
Molar mass 60.06 g mol−1
Physical state firmly
density 1.3230 g cm−3 [1]
Melting point 132.5-134.5 ° C[1]
boiling point Decomposition from 130 ° C[1]
Vapor pressure

0.2 Pa (75 ° C)[1]


Easily soluble in water: approx. 1000 g · l−1 (20 ° C)[1], soluble in ethanol: 50 g · l−1 (20 ° C), sparingly soluble in ether and chloroform

safety instructions
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions.

  urea (Latin urea), also carbonic acid diamide, - not to be confused with uric acid - is an organic compound that is produced by many animals 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 smells slightly of ammonia.


Urea was the first synthetic organic compound. It was discovered as a substance by Hilaire Rouelle in 1773 and was first artificially synthesized in 1828 by Friedrich Wöhler by reacting potassium cyanate and ammonium sulfate. This contradicted the idea that was widespread at that time that organic substances were basically only obtained from living beings by the so-called "Vis vitalis" (Life force) could be produced, and paved the way for organic chemistry.

Physiological importance

Urea comes from the protein and amino acid metabolism and is one of the substances that require urine. In order to prevent the formation of ammonia (NH3) from the amino groups, these are transferred in the liver to the non-toxic urea molecule in the course of the urea cycle. This is excreted as a metabolic end product through the kidneys.

Diseases such as acute or chronic kidney failure as well as diabetic impaired kidney function can lead to increased urea values ​​in the serum / plasma.

Faults and special features: A high protein intake leads to increased urea levels even with normal kidney function, which makes it a poor kidney parameter.


Due to its high nitrogen content of 46%, 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 antimycotic (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. For example, supposedly light cigarettes with a low nicotine value on the packaging turn into strong cigarettes.

Urea can also be used as a substitute for road salt; however, this is not profitable for reasons of cost.

In diesel engine technology, urea is injected into the hot exhaust gas flow behind a soot filter to reduce nitrogen oxides in the exhaust gas. Consumption is around 2 to 8% in relation to fuel.

It 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.


When it melts, urea breaks down with the elimination of ammonia (NH3) to biuret:

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. In countries with large natural gas reserves, which in the past were often simply flared, natural gas is now converted into urea. Large plants are used for this purpose, which finally produce urea from natural gas, air and water in the process steps hydrogen production → ammonia production → urea synthesis. The CO produced during the production of hydrogen is removed2 bound as urea and not released into the atmosphere. 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:

Ammonia and carbon dioxide react to form ammonium carbamate.
Ammonium carbamate reacts to form urea and water.

Another industrial use of urea is the production of melamine, which z. 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.


  1. abcdefGHi BGIA GESTIS substance database: http://www.hvbg.de/d/bia/gestis/stoffdb/index.html. Jul 23, 2007

See also

Categories: Amide | Fertilizer | Metabolic intermediate