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urea

urea (yŏŏē´ə), organic compound that is the principal end product of nitrogen metabolism in most mammals. Urea was the first animal metabolite to be isolated in crystalline form; its crystallization was described in the early 18th cent., and in 1773 it was noted that urea gave off ammonia when heated. This discovery provided a clue to its structure. In 1828 urea also became the first organic compound to be synthesized from inorganic materials (lead or silver cyanate and ammonia); this work was done by German chemist Friedrich Wöhler in 1828. Years of investigation of the biosynthesis of urea culminated in the proposal of the ornithine cycle (sometimes known as the Krebs urea cycle, named for German-born chemist Hans Krebs) in 1932. The proposed cycle has since been amended only in detail. It involves the linking of one molecule of ammonia with one molecule of carbon dioxide to form carbamoyl phosphate which then is added to ornithine resulting in the formation of citrulline. Next the nitrogen-containing amino group from aspartic acid is combined with the citrulline, resulting in the formation of arginine. The addition of a water molecule, arginine is then split into one molecule of urea and one molecule of ornithine, which can now repeat the cycle. In metabolism of proteins and other materials, the ammonia molecule that enters the cycle originates from glutamic acid, but glutamic acid can acquire the group that generates this ammonia from many other amino acids; thus most of the nitrogen in protein can eventually be converted to nitrogen in urea. These reactions have been shown to occur in the liver. Urea is transported in the blood to the kidneys, where it is filtered out; its concentration in urine is about 60 to 70 times as great as that in blood.

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urea

urea (carbamide) A white crystalline water-soluble solid, CO(NH2)2. Urea is the major end product of nitrogen excretion in mammals and other ureotelic animals, being synthesized by the urea cycle. Urea is synthesized industrially from ammonia and carbon dioxide for use in urea–formaldehyde resins and pharmaceuticals, as a source of nonprotein nitrogen for ruminant livestock, and as a nitrogen fertilizer.

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urea

urea The end‐product of nitrogen metabolism, excreted in the urine. Chemically it is CO(NH2)2. Synthesized in the liver from ammonia and the amino acid aspartic acid; the major nitrogenous compound in urine, and the major component of the non‐protein nitrogen in blood plasma.

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urea

urea CO(NH2)2; the compound that is formed from carbon dioxide and ammonia via the urea cycle as a result of amino-acid catabolism in ureotelic animals. It is also the final product of purine catabolism in most fish, Amphibia, and freshwater bivalve molluscs (Bivalvia).

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urea

urea (CO(NH2)2) Organic compound, a white, crystalline solid excreted in urine. Most vertebrates excrete their nitrogen wastes as urea; human urine contains c.25 grams of urea to a litre. Because it is so high in nitrogen, urea is a good fertilizer.

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urea

u·re·a / yoŏˈrēə/ • n. Biochem. a colorless crystalline compound, CO(NH2)2, that is the main nitrogenous breakdown product of protein metabolism in mammals and is excreted in urine.

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urea

urea (yoor-ee-ă) n. the main breakdown product of protein metabolism. It is the chemical form in which unrequired nitrogen is excreted by the body in the urine. Urea is formed in the liver from ammonia and carbon dioxide.

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urea

urea constituent of urine. XIX. f. F. urée, f. Gr. oûron urine or oureîn urinate.

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urea

ureaAchaea, aliyah, Almería, Apia, Bahía, Caesarea, Cassiopeia, Chaldea, Cytherea, Euboea, foreseer, freer, galleria, gynaecea, Iphigenia, Kampuchea, kea, keyer, Latakia, Leah, Lucia, Nicaea, Nicosia, onomatopoeia, Oriya, Pangaea, Pantelleria, pharmacopoeia, pizzeria, ria, rupiah, sangría, seer, sharia, Shia, skier, spiraea (US spirea), Tanzania, taqueria, Tarpeia, Thea, trachea, trattoria, urea •sightseer

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Urea

Urea

Urea and metabolism

Urea and industry

Resources

Urea is a white, crystalline solid also known as carbamide. It is highly soluble in water and is the major molecule used by mammals and amphibians as a means of excreting nitrogenous waste (which generally comes from proteins). It is used in making fertilizers (where it serves as source of nitrogen) and in cattle feed, where it also raises the nitrogen levels. Urea is also used in the manufacturing of barbiturates and in manufacturing some plastics such as urethanes. Urea melts at 271° F (133° C). Solutions of urea in water are slightly basic. The formula of urea is shown in Figure 1.

The NH2 groups are derived from nitrogen containing portions of proteins. Urea was first isolated from urine in 1773 by Hillaire-Malin Rouelle. In 1828 urea became the first organic (carbon based) molecule to be synthesized from inorganic components. This was accomplished by Freidrich Wolher by heating ammonium cyanate, forming urea. This synthesis began the decline of a vital force theory which held that only living things could make organic compounds.

Urea and metabolism

Urea is the final product of the metabolism of amino acids (the building blocks of proteins) in mammals, amphibians, and turtles. In the liver, ammonia reacts with carbon dioxide and through a series of seven steps that are controlled by enzymes (protein catalysts that speed up specific reactions), urea is produced. Each molecule of urea is built from two ammonia molecules (NH3) and one carbon dioxide (CO2) molecule. Ammonia itself is toxic so many animals have developed metabolic steps that take the ammonia formed and convert it into less toxic and easily dealt with molecules. The extremely high solubility of urea in water (35 oz [1,000 g] of urea dissolve in a liter of water) make it ideal for eliminating nitrogen-based waste products. The concentration of urea rises in many kidney diseases, and blood urea concentration is often used to monitor kidney function. The urea produced by the body is excreted in urine. A healthy adult will excrete about 0.9 oz (25 g) of urea per day. Upon standing the urea in urine will decompose to carbon dioxide and ammonia, accounting for the ammonia smell of old urine. In many animals and in some vegetarians, cloudy urine is common. This is the result of a precipitate (insoluble compound) formed from urea and calcium or magnesium ions. Medically urea is used as a diuretic, or substance that promotes water loss through urination. Urea-containing creams are used on wounds.

Urea and industry

Industrially, urea is used in the manufacturing of fertilizers (as a source of nitrogen) and in the synthesis of some barbiturates and in the petroleum industry to help separate straight chain and branched hydrocarbons in petroleum. Urea is widely used in the production of many plastics and resins. One of the most common of these is a resin formed by the reaction of urea and formaldehyde. Urea-formaldehyde resins are used in the adhesives industry (urea-formaldehyde resins are used in making laminated woods), in textile

KEY TERMS

Barbiturates A group of drugs widely used as tranquilizers and anti-anxiety medications. One of the basic molecules of this class is barbituric acid, which is made directly from urea.

Diuretic A substance that increases water loss through urination.

Resin A type of organic polymer. A polymer is a large molecule made of repeating basic units known as monomers.

finishes, and surface coatings for plastics. These resins are widely used since they accept dyes easily. Over 300,000 kilograms of urea-formaldehyde resins are produced annually in the United States. Urea is also used as a stabilizer for many explosives, allowing greater control over the reactions. Urea is made commercially by reacting ammonia and carbon dioxide under high pressure.

See also Excretory system.

Resources

BOOKS

Atkins, Peter Atkins Molecules. Cambridge University Press, 2nd ed. 2003.

Louis Gotlib

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Urea

Urea

Urea is a white, crystalline solid also known as carbamide. It is highly soluble in water and is the major molecule used by mammals and amphibians as a means of excreting nitrogenous waste (which generally comes from proteins ). It is used in making fertilizers (where it serves as source of nitrogen ) and in cattle feed, where it also raises the nitrogen levels. Urea is also used in the manufacturing of barbiturates and in manufacturing some plastics such as urethanes. Urea melts at 271°F (133°C). Solutions of urea in water are slightly basic. The formula of urea is shown in Figure 1.

The NH2 groups are derived from nitrogen containing portions of proteins. Urea was first isolated from urine in 1773 by Hillaire-Malin Rouelle. In 1828 urea became the first organic (carbon based) molecule to be synthesized from inorganic components. This was accomplished by Freidrich Wolher by heating ammonium cyanate, forming urea. This synthesis began the decline of a "vital force" theory which held that only living things could make organic compounds.


Urea and metabolism

Urea is the final product of the metabolism of amino acids (the building blocks of proteins) in mammals, amphibians, and turtles . In the liver, ammonia reacts with carbon dioxide and through a series of seven steps that are controlled by enzymes (protein catalysts that speed up specific reactions), urea is produced. Each molecule of urea is "built" from two ammonia molecules (NH3) and one carbon dioxide (CO2) molecule. Ammonia itself is toxic so many animals have developed metabolic steps that take the ammonia formed and convert it into less toxic and easily dealt with molecules. The extremely high solubility of urea in water (35 oz [1,000 g] of urea dissolve in a gal [l] of water) make it ideal for eliminating nitrogen-based waste products. The concentration of urea rises in many kidney diseases, and blood urea concentration is often used to monitor kidney function. The urea produced by the body is excreted in urine. A healthy adult will excrete about 0.9 oz (25 g) of urea per day. Upon standing the urea in urine will decompose to carbon dioxide and ammonia, accounting for the "ammonia" smell of old urine. In many animals and in some vegetarians, cloudy urine is common. This is the result of a precipitate (insoluble compound) formed from urea and calcium or magnesium ions. Medically urea is used as a diuretic, or substance that promotes water loss through urination. Urea-containing creams are used on wounds.




Urea and industry

Industrially, urea is used in the manufacturing of fertilizers (as a source of nitrogen) and in the synthesis of some barbiturates and in the petroleum industry to help separate straight chain and branched hydrocarbons in petroleum. Urea is widely used in the production of many plastics and resins . One of the most common of these is a resin formed by the reaction of urea and formaldehyde. Urea-formaldehyde resins are used in the adhesives industry (urea-formaldehyde resins are used in making laminated woods), in textile finishes, and surface coatings for plastics. These resins are widely used since they accept dyes easily. Over 661,000 lb (300,000 kg) of urea-formaldehyde resins are produced annually in the United States. Urea is also used as a stabilizer for many explosives , allowing greater control over the reactions. Urea is made commercially by reacting ammonia and carbon dioxide under high pressure .

See also Excretory system.


Resources

books

Atkins, P.W. Molecules. W. H. Freeman, 1987.

Louis Gotlib

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Barbiturates

—A group of drugs widely used as tranquilizers and anti-anxiety medications. One of the basic molecules of this class is barbituric acid, which is made directly from urea.

Diuretic

—A substance that increases water loss through urination.

Resin

—A type of organic polymer. A polymer is a large molecule made of repeating basic units known as monomers.

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Urea

Urea

KEY FACTS

OTHER NAMES:

Carbamide; carbonyldiamide

FORMULA:

(NH2)2CO

ELEMENTS:

Carbon, nitrogen, hydrogen, oxygen

COMPOUND TYPE:

Organic

STATE:

Solid

MOLECULAR WEIGHT:

60.06 g/mol

MELTING POINT:

133.3°C (271.9°F)

BOILING POINT:

Not applicable; decomposes above its melting point

SOLUBILITY:

Soluble in water, ethyl alcohol, and benzene; slightly soluble in ether

OVERVIEW

Urea (yoo-REE-uh) is a white crystalline solid or powder with almost no odor and a salty taste. It is a product of the decomposition of proteins in the bodies of terrestrial animals. Urea is produced in the liver and transferred to the kidneys, from which it is excreted in urine. The compound was first identified as a component of urine by French chemist Hilaire Marin Rouelle (1718–1799) in 1773. It was first synthesized accidentally in 1828 by German chemist Friedrich Wöhler (1800–1882). The synthesis of urea was one of the most important historical events in the history of chemistry. It was the first time that a scientist had synthesized an organic compound. Prior to Wöhler's discovery, scientists believed that organic compounds could be made only by the intervention of some supernatural force. Wöhler's discovery showed that organic compounds were subject to the same set of natural laws as were inorganic compounds (compounds for non-living substances). For this reason, Wöhler is often called the Father of Organic Chemistry.

HOW IT IS MADE

The formation of urea is the evolutionary solution to the problem of what to do with poisonous nitrogen compounds that formed when proteins decompose in the body. Proteins are large, complex compounds that contain relatively large amounts of nitrogen. When they decompose, that nitrogen is converted to ammonia (NH3), a substance that is toxic to animals. If animals are to survive the decomposition of proteins (as happens whenever foods are metabolized), some method must be found to avoid the buildup of ammonia in the body.

That method involves a series of seven chemical reactions called the urea cycle by which nitrogen from proteins is converted into urea. Although high concentrations of urea do pose a risk to animal bodies, the urea formed in these reactions is normally excreted fast enough to avoid health problems for an animal.

Urea is produced commercially by the direct synthesis of liquid ammonia (NH3) and liquid carbon dioxide (CO2). The product of this reaction is ammonium carbamate (NH4CO2NH2):

2NH3 + CO2 → NH4CO2NH2

Interesting Facts

  • Different species of animals have evolved different methods of eliminating ammonia from their bodies. For example, fish excrete the ammonia produced by the decomposition of proteins directly into the watery environment in which they live. Birds, who consume less water by gram of weight than do most other animals, convert ammonia to uric acid (C5H4N4O3), a white crystalline solid that is even less toxic than urea.
  • Urea is transported from the liver to the kidneys in the bloodstream. By the time it leaves the body in urine, its concentration is sixty to seventy times its concentration in the bloodstream.

Ammonia and carbon dioxide do not react with each other under normal conditions of temperature and pressure. If the pressure is raised to 100 to 200 atmospheres (1750 to 3000 pounds per square inch) and the temperature is raised to about 200°C (400°C), however, the reaction proceeds efficiently with the formation of ammonium carbamate. When the pressure is then reduced to about 5 atmosphere (80 pounds per square inch), the ammonium carbamate decomposes to form urea and water:

NH4CO2NH2 → (NH2)2CO + H2O

COMMON USES AND POTENTIAL HAZARDS

Urea is the sixteenth most important chemical in the United States, based on the amount produced annually. In 2004, the chemical industry produced 5.755 million metric tons (6.344 million short tons) of urea. Almost 90 percent of that output was used in the manufacture of fertilizers. An additional 5 percent went to the production of animal feeds. In both fertilizers and animal feeds, urea and the compounds from which it is made provide the nitrogen needed by growing plants and animals for their good health and survival. The other major use of urea is in the manufacture of various types of plastics, especially urea-formaldehyde resins and melamine.

Words to Know

METABOLISM
All of the chemical reactions that occur in cells by which fats, carbohydrates, and other compounds are broken down to produce energy and the compounds needed to build new cells and tissues.
SYNTHESIS
A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.

Urea is also used:

  • In the production of personal care products, such as hair conditioners, body lotions, and dental products;
  • In certain pharmaceutical and medical products, such as creams to treat wounds and damaged skin;
  • As a stabilizer in explosives, a compound that places limits on the rate at which an explosion proceeds;
  • In the manufacture of adhesives;
  • For the flame-proofing of fabrics;
  • For the separation of products produced during the refining of petroleum;
  • In the production of sulfamic acid (HOSO2NH2), an important raw material in many chemical processes;
  • As a coating for paper products; and
  • In the production of deicing agents.

FOR FURTHER INFORMATION

National Urea Cycle Disorders Foundation. http://www.nucdf.org/ (accessed on November 19, 2005).

Ophardt, Charles E. "Urea Cycle." Virtual Chembook. http://www.elmhurst.edu/∼chm/vchembook/633ureacycle.html (accessed on November 19, 2005).

"Urea." International Programme on Chemical Safety. http://www.inchem.org/documents/icsc/icsc/eics0595.htm (accessed on November 19, 2005).

"Urea." Third Millennium Online. http://www.3rd1000.com/urea/urea.htm (accessed on November 19, 2005).

See AlsoAmmonia

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