Urea

Urea wiki link: [] Urea serves an important role in the [|metabolism] of nitrogen-containing compounds by animals and is the main nitrogen-containing substance in the [|urine] of [|mammals]. It is solid, colourless, and odorless (although the [|ammonia] that it gives off in the presence of water, including water vapor in the air, has a strong odor). It is highly soluble in water and practically non-toxic (LD50 is 15 g/kg for rat). Dissolved in water, it is neither [|acidic] nor [|alkaline]. The body uses it in many processes, the most notable one being nitrogen excretion. Urea is widely used in [|fertilizers] as a convenient source of nitrogen. Urea is also an important [|raw material] for the [|chemical industry]. The synthesis of this organic compound by [|Friedrich Wöhler] in 1828 from an inorganic precursor was an important milestone in the development of organic chemistry, as it showed for the first time that a molecule found in living organisms could be synthesized in the lab without biological starting materials (thus contradicting a theory widely prevalent at one time, called [|vitalism] ). The terms **urea** and **carbamide** are also used for a class of [|chemical compounds] sharing the same [|functional group] RR'N—CO—NRR', namely a carbonyl group attached to two organic amine residues. Examples include [|carbamide peroxide], [|allantoin] , and [|hydantoin]. Ureas are closely related to [|biurets] and related in structure to [|amides], [|carbamates] , [|carbodiimides] , and [|thiocarbamides].
 * Urea** or **carbamide** is an [|organic compound] with the [|chemical formula] [|C][|O] ( [|N][|H] 2)2. The molecule has two —NH2 groups joined by a [|carbonyl] (C=O) [|functional group].

History
Urea was first discovered in urine in 1727 by the Dutch scientist [|Herman Boerhaave], though this discovery is often attributed to the [|French] chemist [|Hilaire Rouelle]. [|[3]] In 1828, the [|German] chemist [|Friedrich Wöhler] obtained urea by treating silver [|isocyanate] with [|ammonium chloride]. [|[4]][|[5]] AgNCO + NH4Cl → (NH2)2CO + AgCl This was the first time an organic compound was artificially synthesized from inorganic starting materials, without the involvement of living organisms. The results of this experiment implicitly discredited [|vitalism] : the theory that the chemicals of living organisms are fundamentally different from inanimate matter. This insight was important for the development of [|organic chemistry]. His discovery prompted Wöhler to write triumphantly to [|Berzelius] : "I must tell you that I can make urea without the use of kidneys, either man or dog. Ammonium cyanate is urea." For this discovery, Wöhler is considered by many[// [|who?] //] the father of organic chemistry.

Physiology
Urea is synthesized in the body of many organisms as part of the [|urea cycle], either from the oxidation of [|amino acids] or from [|ammonia]. In this cycle, [|amino] groups donated by ammonia and L- [|aspartate] are converted to urea, while L- [|ornithine], [|citrulline] , L- [|argininosuccinate] , and L- [|arginine] act as intermediates. Urea production occurs in the [|liver] and is regulated by [|N-acetylglutamate]. Urea is found dissolved in blood (in the [|reference range] of 2.5 to 6.7 mmol/liter) and is excreted by the kidney as a component of [|urine]. In addition, a small amount of urea is excreted (along with [|sodium chloride] and water) in [|sweat]. Amino acids from ingested food that are not used for the synthesis of proteins and other biological substances are oxidized by the body, yielding urea and carbon dioxide, as an alternative source of energy. [|[6]] The oxidation pathway starts with the removal of the amino group by a [|transaminase], the amino group is then fed into the urea cycle. Ammonia (NH3) is another common byproduct of the metabolism of nitrogenous compounds. Ammonia is smaller, more volatile and more mobile than urea. If allowed to accumulate, ammonia would raise the pH in cells to toxic levels. Therefore many organisms convert ammonia to urea, even though this synthesis has a net energy cost. Being practically neutral and highly soluble in water, urea is a safe vehicle for the body to transport and excrete excess nitrogen. In water, the amine groups undergo slow displacement by water molecules, producing ammonia and carbonate anion. For this reason, old, stale urine has a stronger odor than fresh urine. [|[show]] || [|[show]] || 167 g/100ml (40 °C) 251 g/100 ml (60 °C) 400 g/100 ml (80 °C) || [|Hydroxycarbamide] || [|Urea phosphate] ||
 * ~ Urea ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/3/3d/Harnstoff.svg/150px-Harnstoff.svg.png width="150" height="89" link="http://en.wikipedia.org/wiki/File:Harnstoff.svg"]] ||
 * [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Urea-3D-balls.png/120px-Urea-3D-balls.png width="120" height="95" link="http://en.wikipedia.org/wiki/File:Urea-3D-balls.png"]] || [[image:http://upload.wikimedia.org/wikipedia/commons/thumb/2/29/Urea-3D-vdW.png/100px-Urea-3D-vdW.png width="100" height="97" link="http://en.wikipedia.org/wiki/File:Urea-3D-vdW.png"]] ||
 * her names [|[hide]] Carbamide, carbonyl diamide, carbonyldiamine, diaminomethanal, diaminomethanone ||
 * ~ Identifiers ||
 * [|CAS number] || [|57-13-6]  [[image:http://upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png width="7" height="7" caption="Yes"]] ||
 * [|PubChem] || [|1176]  ||
 * [|ChemSpider] || [|1143]  [[image:http://upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png width="7" height="7" caption="Yes"]] ||
 * [|UNII] || [|8W8T17847W]  [[image:http://upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png width="7" height="7" caption="Yes"]] ||
 * [|DrugBank] || [|DB03904]  ||
 * [|KEGG] || [|D00023]  [[image:http://upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png width="7" height="7" caption="Yes"]] ||
 * [|ChEBI] || [|CHEBI:16199]  [[image:http://upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png width="7" height="7" caption="Yes"]] ||
 * [|ChEMBL] || [|CHEMBL985]  [[image:http://upload.wikimedia.org/wikipedia/en/thumb/f/fb/Yes_check.svg/7px-Yes_check.svg.png width="7" height="7" caption="Yes"]] ||
 * [|RTECS number] || YR6250000 ||
 * [|ATC code] || [|B05] [|BC02] , [|D02]  [|AE01]  ||
 * [|Jmol] -3D images || [|Image 1] ||
 * [|SMILES]
 * [|SMILES]
 * [|InChI]
 * ~ Properties ||
 * [|Molecular formula] || CH4N2O ||
 * [|Molar mass] || 60.06 g mol−1 ||
 * Appearance || White solid ||
 * [|Density] || 1.32 g/cm3 ||
 * [|Melting point] || 133–135 °C ||
 * [|Solubility] in [|water] || 107.9 g/100 ml (20 °C)
 * [|Solubility] || 50g/L ethanol, 500g/L glycerol [|[1]] ||
 * [|Basicity] (p//K//b) || p//K//BH+ = 0.18 [|[2]] ||
 * ~ Structure ||
 * [|Dipole moment] || 4.56 [|D] ||
 * ~ Hazards ||
 * [|MSDS] || [|JT Baker] ||
 * EU Index || Not listed ||
 * [|Flash point] || Non-flammable ||
 * [|LD50] || 8500 mg/kg (oral, rat) ||
 * ~ Related compounds ||
 * Related ureas || [|Thiourea]
 * Related compounds || [|Carbamide peroxide]

[ [|edit] ] Agriculture
More than 90% of world production of urea is destined for use as a nitrogen-release fertilizer. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in common use. Therefore, it has the lowest transportation costs per unit of nitrogen [|nutrient]. The standard crop-nutrient rating of urea is 46-0-0. [|[9]] Many soil bacteria possess the enzyme [|urease], which catalyzes the conversion of the urea molecule to two [|ammonia] molecules and one [|carbon dioxide] molecule, thus urea fertilizers are very rapidly transformed to the ammonium form in soils. Among soil bacteria known to carry urease, some ammonia-oxidizing bacteria (AOB) such as species of [|Nitrosomonas] are also able to assimilate the carbon dioxide released by the reaction to make biomass via the [|Calvin Cycle], and harvest energy by oxidizing ammonia (the other product of urease) to nitrite, a process termed [|nitrification]. [|[10]] Nitrite-oxidizing bacteria, especially [|Nitrobacter], oxidize nitrite to nitrate, which is extremely mobile in soils and is a major cause of water pollution from agriculture. Ammonia and nitrate are readily absorbed by plants, and are the dominant sources of nitrogen for plant growth. Urea is also used in many multi-component solid fertilizer formulations. 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. For fertilizer use, granules are preferred over prills because of their narrower particle size distribution, which is an advantage for mechanical application. The most common impurity of synthetic urea is [|biuret], which impairs plant growth. Urea is usually spread at rates of between 40 and 300 kg/ha but rates vary. Smaller applications incur lower losses due to leaching. During summer, urea is often spread just before or during rain to minimize losses from [|volatilization] (process wherein nitrogen is lost to the atmosphere as ammonia gas). Urea is not compatible with other fertilizers. Because of the high nitrogen concentration in urea, it is very important to achieve an even spread. The application equipment must be correctly calibrated and properly used. Drilling must not occur on contact with or close to seed, due to the risk of germination damage. Urea dissolves in water for application as a spray or through irrigation systems. In grain and cotton crops, urea is often applied at the time of the last cultivation before planting. In high rainfall areas and on sandy soils (where nitrogen can be lost through leaching) and where good in-season rainfall is expected, urea can be side- or top-dressed during the growing season. Top-dressing is also popular on pasture and forage crops. In cultivating sugarcane, urea is side-dressed after planting, and applied to each [|ratoon] crop. In irrigated crops, urea can be applied dry to the soil, or dissolved and applied through the irrigation water. Urea will dissolve in its own weight in water, but it becomes increasingly difficult to dissolve as the concentration increases. Dissolving urea in water is endothermic, causing the temperature of the solution to fall when urea dissolves. As a practical guide, when preparing urea solutions for [|fertigation] (injection into irrigation lines), dissolve no more than 30 kg urea per 100 L water. In foliar sprays, urea concentrations of 0.5% – 2.0% are often used in horticultural crops. Low- [|biuret] grades of urea are often indicated. Urea absorbs moisture from the atmosphere and therefore is typically stored either in closed/sealed bags on pallets or, if stored in bulk, under cover with a tarpaulin. As with most solid fertilizers, storage in a cool, dry, well-ventilated area is recommended.

[ [|edit] ] Chemical industry
Urea is a raw material for the manufacture of many important chemical compounds, such as
 * Various [|plastics], especially the [|urea-formaldehyde resins].
 * Various [|adhesives], such as urea-formaldehyde or the [|urea-melamine-formaldehyde] used in marine [|plywood].
 * [|Potassium cyanate], another industrial feedstock.

[ [|edit] ] Explosive
Urea can be used to make [|urea nitrate], a [|high explosive] that is used industrially and as part of some [|improvised explosive devices].

[ [|edit] ] Automobile systems
Urea is used in [|SNCR] and [|SCR] reactions to reduce the [|NOx] [|pollutants] in [|exhaust gases] from [|combustion] from [|diesel], dual fuel, and lean-burn [|natural gas] engines. The [|BlueTec] system, for example, injects water-based urea solution into the exhaust system. The ammonia produced by the [|hydrolysis] of the urea reacts with the nitrogen oxide emissions and is converted into nitrogen and water within the catalytic converter.