|Molar mass||60.07 g/mol|
|Appearance||white odourless solid|
|Density and phase||1.33•103 kg/m3, solid|
|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||132.7 °C (406 K)
|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|
|Coordination geometry||trigonal planar|
|Dipole moment||4.56 p/D|
|Flash point||? °C|
|R/S statement||R: ? S: ?|
|Supplementary data page|
|Structure & properties||n, εr, etc.|
|Thermodynamic data||Phase behaviour
Solid, liquid, gas
|Spectral data||UV, IR, NMR, MS|
|Except where noted otherwise, data are given for
materials in their standard state (at 26°C, 100 kPa)
Urea is an organic compound of carbon, nitrogen, oxygen, and hydrogen. Its chemical formula may be written as CO(NH2)2, CON2H4, or CN2H4O. It is also known as carbamide, carbamide resin, isourea, carbonyl diamide, and carbonyldiamine.
Urea is found in mammalian and amphibian urine as well as in some fishes. It was the first organic compound to be artificially synthesized from inorganic starting materials, thereby dealing a serious blow to the theory of vitalism.
Besides its physiological role, urea has many practical applications. For instance, it is a component of fertilizers and animal feed; a raw material for the production of certain plastics and adhesives; a flame-proofing agent; an ingredient in some hair conditioners, facial cleansers, and bath oils; an ingredient in various tooth whitening products; a substance that reduces nitrogen oxides in diesel-engine exhausts; an agent used in the dyeing and printing of textiles; a chemical for denaturing proteins in the laboratory; an agent used in the dyeing and printing of textiles; and an ingredient in products that promote rehydration of the skin. Commercial production of urea is on the order of 100,000,000 tons per year worldwide.
Urea was discovered by Hilaire Rouelle in 1773. In 1828, in attempting to prepare ammonium cyanate, Friedrich Wöhler reacted potassium cyanate with ammonium sulfate. He inadvertently obtained urea, which thus became the first organic compound to be artificially synthesized from inorganic starting materials. This result dealt a severe blow to the concept of vitalism—the belief that chemicals that originated in living organisms could only be produced with the assistance of a "vital force" (present in living tissue) and could not be artificially synthesized.
The individual atoms that make up a urea molecule 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. In veterinary medicine, dalmatian breeds of dogs are different in that they excrete urea in the form of uric acid in the urine rather than in the urea form. This is due to a defect in one of the genes controlling expression of the conversion enzymes in the urea cycle.
The urea is formed in the livers of mammals in a cyclic pathway, from the break down of ammonia, (a metabolic waste), 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 Hans Adolf Krebs and Kurt Henseleit in 1932 and was clarified in the 1940s as the roles of citrulline and argininosuccinate as intermediates were understood.
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.
Urea is essentially a waste product, although it is used by the body during times of volume reduction. It is dissolved in blood (in humans at 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.
More than 90 percent of world production is destined for use as a fertilizer. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in common use (46.4 percent) 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 (in combination with ammonium nitrate: UAN), 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 behavior are particularly important in product handling, storage, and bulk transportation.
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.
The second reaction is endothermic (it absorbs heat):
The combination of the two reactions is exothermic.
Isotopically labeled urea (carbon 14-radioactive, or carbon 13-stable isotope) is used in the Urea breath test, which helps detect the presence of certain bacteria (Helicobacter pylori) 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.
Bacterial species similar to H. pylori can be identified by the same test in various animals, such as apes, dogs, and cats (including big cats).
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.
All links retrieved June 15, 2007.
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