Urea
| Urea | |
|---|---|
 Urea 3D structure of urea
| |
| 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) 167 g/100 ml (40 °C) 251 g/100 ml (60 °C) 400 g/100 ml (80 °C) 733 g/100 ml (100 °C) |
| Melting point | 133 °C (406 K) decomposes |
| Boiling point | n.a. |
| Acidity (pKa) | 0.18 |
| Basicity (pKb) | 13.82 |
| Chiral rotation [α]D | Not chiral |
| Viscosity | ? cP at ? °C |
| Critical relative humidity | 81% (20°C) 73% (30°C) |
| Heat of solution in water | -57,8 cal/g (endothermic) |
| Nitrogen content | 46,6 %N |
| 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 ? | biuret triuret thiourea |
| Related compounds | ? |
| Except where noted otherwise, data are given for materials in their standard state (at 26°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 in the urine.
In addition, a small amount of urea is excreted (along with sodium chloride and water) in human sweat.
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. Urea can be produced as prills, granules, flakes, crystals and solutions.
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.
- As a flame-proofing agent.
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. Urea is used to effectively disrupt the noncovalent bonds in proteins.
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.
Clinical diagnosis
See blood urea nitrogen ("BUN") for a commonly performed urea test, and marker of renal function.
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).
Ureas
Ureas or carbamides are a class of chemical compounds sharing the same functional group RR'N-CO-NRR' based on a carbonyl group flanked by two organic amine residues. They can be accessed in the laboratory by reaction of phosgene with primary or secondary amines. Example of ureas are the compounds carbamide peroxide, allantoin and Hydantoin. Ureas are closely related to biurets and structurally related to amides, carbamates, diimides, carbodiimides and thiocarbamides.