How is urea described in chemistry?
Product of protein metabolism in the urine
|molar mass 60.055 g / mol |
AGW10 mg / m3 E.
(inhalable fraction for dusts in general)
density 1.3230 g / cm3
Melting point +132.4 ° C
decomposes on further heating
Conc. At 20 ° C 1000 g / l
|-||-||disposal Household waste, sewage|
|print a label||German designation |
|English designation |
|CAS 57-13-6||urea |
Carbonic acid diamide
Urea forms colorless and odorless crystals. It crystallizes out of an aqueous solution in long, prismatic needles according to the tetragonal crystal system. Urea is not soluble in chloroform and ether. It dissolves well in methanol, ethanol and glycerine, and when heated in an acidic or alkaline solution, urea is broken down into carbon dioxide and ammonia:
H2N-CO-NH2 + H2O CO2 + 2 NH3
The amino group NH2 in the urea reacts with the aldehydes with the addition of concentrated hydrochloric acid in a polycondensation. In this way, the heat-resistant aminoplasts such as urea-formaldehyde (UF resin) can be produced.
Urea is an important end product of the human and animal metabolism of nitrogen compounds. Humans excrete around 20 to 30 grams of urea daily in the urine. Urea is produced in the liver in the urea cycle. Ammonia reacts with carbon dioxide in a relatively complicated reaction to form urea. The process serves to break down ammonia in the metabolism and at the same time enables the production of the vital protein building blocks L-arginine and L-ornithine.
Friedrich Wöhler (1800-1882)
Urea was discovered in urine as early as 1729 by the Dutch professor of medicine and chemistry Hermann Boerhaave (1668-1738). He produced crystalline urea from urine for the first time. The Paris chemist Guillaume-Francois Rouelle (1703-1770) carried out this experiment again in 1773. The first synthesis, and thus also the clarification of the atomic composition, was only achieved by the German chemist Friedrich Wöhler. Wöhler obtained urea in 1828 by evaporating an aqueous solution of ammonium cyanate. With this synthesis - and also with his previous synthesis of oxalic acid in 1824 - Wöhler refuted the opinion that was widespread at the time that organic substances can basically only be produced by living things.
The industrial production of urea takes place today mainly from ammonia and carbon dioxide. This creates ammonium carbamate as an intermediate product, which converts to urea at high pressure of up to 40 bar and a three-fold excess of ammonia:
Urea is an important fertilizer and animal feed due to its high nitrogen content. In the chemical industry it is used for the production of aminoplasts and melamine, in medicine for the synthesis of the sleeping pill Carbromal. The urea crystals form cage-like lattice structures in which other substances can be enclosed, so urea is suitable for separating paraffins from a hydrocarbon mixture, since the paraffins are enclosed in the urea crystals.
Modern diesel vehicles contain a small additional tank that contains a clear liquid that is available under the trade name AdBlue. A 32.5% solution of urea in distilled water is used. In the SCR catalytic converter, the urea is converted into ammonia, which converts the nitrogen oxides into nitrogen and water vapor.
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