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
Wo¨hler (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 Wo¨hler’s discovery, scientists
believed that organic compounds could be made only by the
intervention of some supernatural force. Wo¨hler’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, Wo¨hler is often
called the Father of Organic Chemistry.
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
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 200C (400C), 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
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.
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.
