Urea

Urea
Urea 3D representation
General
Systematic name	Diaminomethanal
Other names	?
Molecular formula	(NH2)2CO
SMILES	NC(=O)N
Molar mass	60.07 g/mol
Appearance	white odourless solid
CAS number	[57-13-6]
Properties
Density and phase	750 kg/m3
Solubility in water	108 g/100 ml (20 °C)
Melting point	133 °C (406 K) decomposes
Boiling point	n.a.
Acidity (pKa)	0.1
Basicity (pKb)	low
Chiral rotation [α]D	Not chiral
Viscosity	? cP at ? °C
Structure
Molecular shape	?
Coordination geometry	trigonal planar
Crystal structure	?
Dipole moment	? D
Hazards
MSDS	J.T. Baker
Main hazards	?
Flash point	? °C
R/S statement	R: ? S: ?
RTECS number	?
Supplementary data page
Structure & properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Other anions	?
Other cations	?
Related ?	?
Related compounds	?
Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references

Urea is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula CON₂H₄ or (NH₂)₂CO.

Urea is also known as carbamide, especially in the recommended International Non-proprietary Names (rINN) in use in Europe. For example, the medicinal compound hydroxyurea (old British Approved Name) is now hydroxycarbamide. Other names include carbamide resin, isourea, carbonyl diamide, and carbonyldiamine.

Physiology

The individual atoms of urea come from carbon dioxide, water, aspartate and ammonia in a metabolic pathway known as the urea cycle, an anabolic process. This expenditure of energy is necessary because ammonia, a common metabolic waste product, is toxic and must be neutralized. Urea production occurs in the liver and is under the regulatory control of N-acetylglutamate.

Aquatic animals do not produce urea; living in an abundant supply of water, they can simply excrete ammonia immediately as it is produced. Birds, with more severe restrictions on water consumption than most other animals, produce uric acid, a compound even less toxic than urea. Humans produce a little uric acid as a result of purine breakdown. Indeed, excess uric acid production can lead to a type of arthritis known as gout.

Urea is essentially a waste product: it has no physiological function. It is dissolved in blood (in humans in a concentration of 2.5 - 7.5 mmol/liter) and excreted by the kidney.

Discovery

Urea was discovered by Hilaire Rouelle in 1773. It was the first organic compound to be artificially synthesized from inorganic starting materials, in 1828 by Friedrich Woehler, who prepared it by the reaction of potassium cyanate with ammonium sulfate. Although Woehler was attempting to prepare ammonium cyanate, he inadvertently disproved the theory that the chemicals of living organisms are fundamentally different from inanimate matter by forming urea, thus starting the discipline of organic chemistry.

Commercial Production

Urea is produced commercially from synthetic ammonia and carbon dioxide.

Industrial use

Urea's commercial uses include:

• As a raw material for the manufacture of plastics specifically, urea-formaldehyde resin.
• As a raw material for the manufacture of various glues (urea-formaldehyde or urea-melamine-formaldehyde). The latter is waterproof and is used for marine plywood.
• As a component of fertilizer and animal feed, providing a relatively cheap source of fixed nitrogen to promote growth.
• As an alternative to rock salt in the deicing of roadways and runways. It does not promote metal corrosion to the extent that salt does.
• As an additive ingredient in cigarettes, designed to enhance flavour.
• Sometimes used as a browning agent in factory-produced pretzels.
• As an ingredient in some hair conditioners, facial cleansers, bath oils and lotions.
• It is also used as a reactant in some ready-to-use cold compresses for first-aid use, due to the endothermic reaction it creates when mixed with water.
• Active ingredient for diesel engine exhaust treatment AdBlue.
• Used, along with salts, as a cloud seeding agent to expedite the condensation of water in clouds, producing precipitation.
• The ability of urea to form clathrates (also called host-guest complexes, inclusion compounds, and adducts) was used in the past to separate paraffins.

Laboratory use

Urea is a powerful protein denaturant. This property can be exploited to increase the solubility of some proteins. For this application it is used in concentrations up to 10M.

Medical use

Drug use

Urea is used in topical dermatological products to promote rehydration of the skin. If covered by an occlusive dressing, 40% urea preparations may also be used for nonsurgical debridement of nails.

Urea is used as a diuretic to reduce the symptoms of Meniere's disease by reducing the levels of excess endolymphatic fluid in the inner ear.

Physiological diagnosis

See also blood urea nitrogen for a commonly performed urea test, a marker of renal function

Because urea is produced and excreted at a roughly constant rate, high levels of urea in the blood indicate a problem with the removal or, more rarely, the over-production of urea in the body.

The most common cause of uremia is renal problems. It is measured along with creatinine to indicate direct problems with the kidneys (e.g., chronic renal failure) or secondary problems such as hypothyroidism.

Urea levels can be increased also in some malignant blood disorders (e.g., leukaemia and multiple myeloma).

Markedly high levels of urea (uremia) can cause neurological disturbances (encephalopathy). Prolonged periods of uremia may result in the skin taking on a grey discolouration or even forming frank urea crystals ("uremic frost").

Other diagnostic use

Isotopically-labeled urea (carbon 14 - radioactive, or carbon 13 - stable isotope) is used in the Urea breath test, which is used to detect the presence of Helicobacter pylori (H. pylori, a bacterium) in the stomach and duodenum of humans. The test detects the characteristic enzyme urease, produced by H. pylori, by a reaction that produces ammonia from urea. This increases the pH (reduces acidity) of the stomach environment around the bacteria.

Similar bacteria species to H. pylori can be identified by the same test in animals (apes, dogs, cats - including big cats).

External links

• MSDS sheet on urea