Urea

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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.