Urea is a nitrogenous compound that is present in a major quantity in the dissolved state in the urine of mammals and is formed by the protein breakdown in the liver. The chemical \({\rm{C}}{{\rm{H}}_{\rm{4}}}{{\rm{N}}_{\rm{2}}}{\rm{O}}\) Urea is also known as ‘Carbamide’ as it has an amide group \(\left( {{\rm{ – C = O}}} \right)\) attached to two \(\left( {{\rm{ – N}}{{\rm{H}}_{\rm{2}}}} \right)\) groups.

In all mammals and some fishes, urea is the primary nitrogenous end product of protein metabolism. It can be found not just in mammals’ urine, but also in their blood, bile, milk, and perspiration. Urea is used as a fertilizer and feed supplement, as well as a starting material for the manufacture of plastics and drugs.

In this article, we will discuss in detail about Urea, its definition, Chemical Formula, Structure, Properties, Uses, etc. Continue reading to know more.

Introduction

Urea is named after the Greek word “oura” which means urine. In \(1773\), urea was first isolated by a French chemist Hilaire-Marin Rouelle from urine. Later, urea was the first organic compound that was synthesized artificially from inorganic compounds (ammonium cyanate). This laboratory preparation of urea was discovered by German chemist Friedrich Wohler in \(1828\) which was a milestone in the field of organic chemistry!  On treating silver cyanate with ammonium chloride solution Wohler obtained a white crystalline material that was identical to urea that was obtained from the urine.

Urea is soluble in water. It is a non-toxic chemical substance and is widely used as fertiliser.

What is Urea?

The world’s most commonly used nitrogenous compound is ‘UREA’ and its production is among the highest manufactured organic compound by mass! Urea is the main nitrogenous end product produced by the metabolic breakdown of proteins in all mammals as well as some fishes. Along with the urine of mammals urea also occurs in their blood, bile, milk, and sweat. 

Definition of Urea

Urea is defined as an organic compound that is soluble in water, has the chemical formula \({\rm{CO(N}}{{\rm{H}}_{\rm{2}}}{{\rm{)}}_{\rm{2}}}.\) They are formed by protein metabolism and excreted in the urine of mammals.

Urea Structure

The chemical name of urea is Carbamide or Carbonyl-diamide. It has an amide group that has a carbonyl group \(\left( {{\rm{ – C = O}}} \right)\) attached to two \(\left( {{\rm{ – N}}{{\rm{H}}_{\rm{2}}}} \right)\) The structure of urea is given below:

Physical Properties of Urea

Chemical Formula	\({\rm{C}}{{\rm{H}}_{\rm{4}}}{{\rm{N}}_{\rm{2}}}{\rm{O}}\)
IUPAC name	Urea
Systematic IUPAC name	Carbonyl diamide
Molar mass / Molecular Weight	\(60.06\,{\rm{g/mol}}\)
Density	\({\rm{1}}{\rm{.32 g/c}}{{\rm{m}}^3}\)

Melting Point	\({\rm{133\;^\circ C}}\)
Solubility	Water Soluble
Appearance	White crystalline solid
Odor	Odorless compound
Toxicity	Non – toxic

Study About Excretion in Animals

Manufacture or Production of Urea

Urea is manufactured from ammonia and carbon dioxide. At high pressure and temperature, ammonia and carbon dioxide are fed into the reactor, and urea is formed in a \(2\) steps reaction given below:

At the initial stage, urea contains unreacted ammonia and carbon dioxide, and ammonium carbamate. When gradually the pressure is reduced and heat is supplied, this \({\rm{N}}{{\rm{H}}_{\rm{2}}}{\rm{COON}}{{\rm{H}}_{\rm{4}}}\;.\) decomposes to \({\rm{N}}{{\rm{H}}_3}\) and \({\rm{C}}{{\rm{O}}_2}\) In the end, ammonia and carbon dioxide are recycled. The urea solution is then concentrated to \(99\%\) pure molten urea, and granulated for use as fertilizers and chemical purposes. A complete flowchart of Urea production is given below:

Uses of Urea

1. Urea is widely used in the field of agriculture as fertilizers. Urea fertilizer is used to provide nitrogen to the plants that help to promote their green leafy growth and make the plants look lush and fresh.
2. Various adhesives made from urea, such as Urea-formaldehyde or urea-melamine-formaldehyde is used in making marine plywood.
3. Urea-formaldehyde resins are also used in the manufacture of plastics.
4. Nowadays DEF (Diesel Exhaust Fluid) which is \(32.5\%\) urea and \(67.5\%\) de-ionized water is sprayed into the exhaust stream of diesel vehicles that helps in the breakdown of dangerous \({\rm{N}}{{\rm{O}}_{\rm{x}}}\) emissions into harmless nitrogen and water. Thus, it reduces air pollution from diesel vehicles.
5. Urea is also used as a stabilizer in nitrocellulose explosives.
6. Urea is very useful in detecting particular bacteria in our stomach that causes ulcers in the stomach and intestine by Urea Breath Test.
7. Urea is also widely used in cosmetic products. It is used in creams and lotions that act as moisturizers for dry or flaking skin or as a chemical exfoliator. 
8. Urea is present as a component of aqueous compositions such as liquid detergents.
9. Urea – potassium bicarbonate mixture is also used in dry chemical fire extinguishers.
10. Urea is used as a food supplement in the diet of cattle and other ruminants. Feed-grade urea can prove to be an effective source of protein in beef cattle diets.

Urea Cycle

The urea cycle is also known as the ornithine cycle. It is a biochemical cycle that produces urea from ammonia in humans and mammals. In our body, almost \(80\%\) of the nitrogen excreted is in the form of urea, which is produced through a series of reactions occurring in liver cells. Ammonia is a toxic product produced on nitrogen metabolism which should be necessarily from our body. This urea cycle helps in the removal of urea. The urea formed, then enters the bloodstream, which is filtered by the kidneys and is finally excreted in the urine.

The overall reaction for urea formation from ammonia is as follows:

\({\rm{2}}\,{\rm{Ammonia + C}}{{\rm{O}}_{\rm{2}}}{\rm{ + 3ATP}} \to {\rm{Urea + water + 3}}\,{\rm{ADP}}\)

Steps of Urea Cycle

1. Formation of Carbamoyl Phosphate:

Formation of carbamoyl phosphate by the condensation of ammonium ion with bicarbonate ion with the help of the enzyme carbamoyl phosphate synthase-I present in the mitochondria of the liver. It requires \({\rm{M}}{{\rm{g}}^{{\rm{2 + }}}}\) and a dicarboxylic acid i.e. N-acetyl glutamate. This step requires \(2\) ATP.

2. Synthesis of Citrulline:

Carbamoyl phosphate formed in the first step combines with ornithine that results in the synthesis of citrulline with the help of the enzyme citrulline synthase or ornithine transcarbamoylase. Citrulline diffuses into the cytosol as it is easily permeable to the mitochondrial membrane.

3. Synthesis of Argininosuccinate:

Inside cytosol, citrulline combines with the amino acid ‘aspartate’ forming argininosuccinate catalyzed by the enzyme arginine-succinate synthase. This step requires ATP which is hydrolyzed to AMP which requires the utilization of two high-energy bonds.

4. Cleavage of Argininosuccinate:

The enzyme argininosuccinase acts reversibly to break argininosuccinate into Arginine and fumarate. Fumarate enters the TCA cycle.

5. Cleavage of Arginine:

Arginine is cleaved into ornithine and urea under the influence of the enzyme ‘arginase’. Hence, arginine is also well known as a semi-essential amino acid. Ornithine is regenerated or reoccurs in this step and the urea cycle completes with the formation of urea.

Summary

Frequently Asked Questions

We have provided some frequently asked question about Urea here:

Q.1. What chemicals are in urea?
Ans. The chemical formula of urea is \({\rm{C}}{{\rm{H}}_{\rm{4}}}{{\rm{N}}_{\rm{2}}}{\rm{O}}\) It is also known as ‘Carbamide’ as it has an amide group that has carbonyl group \(\left( {{\rm{ – C = O}}} \right)\) attached to two \(\left( {{\rm{ – N}}{{\rm{H}}_{\rm{2}}}} \right)\) groups. Urea is formed from ammonia and carbon dioxide.

Q.2. Is urea toxic to the body?
Ans. Normally urea is a non-toxic compound but in some cases, it may irritate the skin, eyes, and respiratory tract. Prolonged exposure to urea in the form of fertilizer may cause dermatitis. High concentrations of urea in the blood can be damaging to our bodies. 

Q.3. Is urea good for the skin?
Ans. Urea is good for the skin as it is used to treat dry/rough skin conditions and some nail problems. It can also be used to help remove dead tissue in wounds to help them heal faster. Urea is known as a keratolytic i.e. a type of medical treatment to remove, calluses, warts, and other lesions in the skin.

Q.4. What is urea and how is it made?
Ans. Urea is an organic compound that is soluble in water, has the chemical formula\({\rm{CO(N}}{{\rm{H}}_{\rm{2}}}{{\rm{)}}_{\rm{2}}}{\rm{.}}\) They are formed by protein metabolism and are excreted in the urine of mammals.
Synthetically urea is made from ammonia and carbon dioxide. At high pressure and temperature, both ammonia and carbon dioxide are fed into the reactor, and urea is formed which is obtained as crystals after evaporation.

Q.5. Is urea made from urine?
Ans. Urea is not made from urine rather it is a waste product of many living organisms, and is one of the major organic components of human urine. This is because it is the end product of a chain of reactions that occur to break down the amino acids that form proteins.

Q.6.How is urea formed?
Ans. Urea is formed in our body by the breakdown of protein. In industries, urea is prepared from ammonia and carbon dioxide

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