Encyclopedia
>| Urea |
|---|
| |
| General |
|---|
| Systematic name | Diaminomethanal |
| Other names | ? |
| Molecular formula | 2CO |
| SMILES | NCN |
| 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
167 g/100 ml
251 g/100 ml
400 g/100 ml
733 g/100 ml |
| Melting point | 132.7 °C
decomposes |
| Boiling point | n.a. |
| Acidity | 0.18 |
| Basicity | 13.82 |
| Chiral rotation [a]D | Not chiral |
| Viscosity | ? cP at ? °C |
| Critical relative humidity | 81%
73% |
| Heat of solution in water | -57,8 cal/g |
| Nitrogen content | 46,6 %N |
> Structure | | Molecular shape | ? |
| Coordination geometry | trigonal planar |
| Crystal structure | ? |
| Dipole moment | ? D |
> Hazards | | MSDS | |
| Main hazards | ? |
| Flash point | ? °C |
| R/S statement | R: ? S: ? |
| RTECS number | ? |
> Supplementary data page | | Structure & properties | n, er, 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
|
|
Urea is an
organic compound of
carbon,
nitrogen,
oxygen and
hydrogen, with the
formula CON2H4 or
2CO.
Urea is also known as
carbamide, especially in the recommended International Non-proprietary Names in use in Europe. For example, the medicinal compound
hydroxyurea is now
hydroxycarbamide. Other names include
carbamide resin,
isourea,
carbonyl diamide, and
carbonyldiamine.
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, by forming urea, he inadvertently disproved
vitalism, the theory that the chemicals of living organisms are fundamentally different from inanimate matter, thus starting the discipline of
organic chemistry.
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.
Most
organisms have to deal with the excretion of nitrogen waste originating from
protein and
amino acid catabolism. In aquatic organisms the
most common form of nitrogen waste is ammonia, while land-dwelling organisms developed ways to convert the toxic ammonia to either urea or
uric acid. Generally, birds and saurian
reptiles excrete uric acid, while the remaining species, including mammals, excrete urea. Remarkably,
tadpoles excrete ammonia, and shift to urea production during
metamorphosis.
The urea is formed in the livers of mammals in a cyclic pathway, from the break down of
ammonia, , which was initially named the Krebs-Henseleit cycle after its discoverers, and later became known simply as the
urea cycle. This cycle was partially deduced by Krebs & Henseleit in 1932 and was clarified in the 1940s as the roles of
citrulline and
argininosuccinate as intermediates were understood.
In this cycle, amino groups donated by
ammonia and L-
aspartate are converted to urea, while L-
ornithine, citrulline, L-arginino-succinate, and L-
arginine act as intermediates.
Despite the generalization above, the pathway has been documented not only in mammals and amphibians, but in many other organisms as well, including birds, invertebrates,
insects,
plants,
yeast,
fungi, and even microorganisms.
Humans produce a little uric acid as a result of
purine breakdown. 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 and excreted by the
kidney in the urine.
Many researchers used to believe that a small amount of urea was excreted in human sweat. However that was proved wrong when Dr. M. Falk determined at RC Institute that only
sodium chloride and water are excreted from sweat.
Commercial production
Urea is a nitrogen-containing chemical product which is produced on a scale of some 100,000,000 tonnes per year worldwide.
Urea is produced commercially from synthetic
ammonia and
carbon dioxide. Urea can be produced as prills, granules, flakes, pellets, crystals and solutions.
More than 90% of world production is destined for use as a
fertilizer. Urea has the highest
nitrogen content of all solid nitrogeneous fertilizers in common use. It therefore has the lowest transportation costs per unit of nitrogen
nutrient.
Urea is highly soluble in water and is therefore also very suitable for use in fertilizer solutions , e.g. in “foliar feed’ fertilizers.
Solid urea is marketed as prills or granules. The advantage of prills is that in general they can be produced more cheaply than granules which, because of their narrower particle size distribution have an advantage over prills if applied mechanically to the
soil. Properties such as impact strength, crushing strength and free-flowing behaviour are particularly important in product handling, storage and bulk transportation.
Production
Urea is produced commercially from two raw materials, ammonia and carbon dioxide. Large quantities of carbon dioxide are produced during the manufacture of ammonia from coal or from hydrocarbons such as natural gas and petroleum derived raw materials. This allows direct synthesis of urea from these raw materials.
The production of urea from ammonia and carbon dioxide takes place in an equilibrium reaction, with incomplete conversion of the reactants. The various urea processes are characterized by the conditions under which urea formation takes place and the way in which unconverted reactants are further processed.
Unconverted reactants can be used for the manufacture of other products, for example ammonium nitrate or sulphate, or they can be recycled for complete conversion to urea in a total-recycle process.
Two principal reactions take place in the formation of urea from ammonia and carbon dioxide.
The first reaction is exothermic and the second reaction is endothermic. Both reactions combined are exothermic.
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 . 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 and some other SCR systems.
- 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 was used in the past to separate paraffins.
- As a flame-proofing agent.
- As a clean burning fuel for motor vehicles and stationary engines.
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 10 M.
Urea is used to effectively disrupt the noncovalent bonds in proteins.
Urea is an ingredient in the synthesis of urea nitrate.
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 for a commonly performed urea test, and marker of renal function.;Other diagnostic use
Isotopically-labeled urea is used in the Urea breath test, which is used to detect the presence of
Helicobacter pylori is a bacterium [i] that infects the mucus [i] lining of the human stomach [i]. ...
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 of the stomach environment around the bacteria.
Similar bacteria species to
H. pylori can be identified by the same test in animals .
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.
External links
