Urea (NH2CONH2)
It is an amide derivative of carbamic acid (NH2.COOH). Hence it is also called Carbamide. Its IUPAC name is Amino Methanamide. It is an important compound. Urea is formed due to the decomposition of proteins in the body.
About 30 grams of urea is excreted through urine daily in a healthy human body. It is the first organic compound made in the laboratory. Roulle first obtained it from Urine in 1773. Hence it is named simple urea.
Preparation
From Urine
After evaporating the urine, the concentrated nitric acid is added to it, causing the nitrate to separate into crystals. On filtering it, urine is produced by reaction with barium carbonate. It is separated by crystallization.
2NH2CONH2.HNO3 + BaCO3 → 2NH2CONH2 + Ba(NO3)2 + H2O + CO2
Laboratory
In the laboratory urea is produced by the action of ammonia on carbonyl chloride or ethyl carbonate.
Wöhler Synthesis
Ammonium Cyanate
Urea is the first organic compound made in the laboratory. It was first created in the laboratory by Friedrich Wöhler in 1828 by heating a mixture of Potassium cyanate and ammonium sulfate. Ammonium cyanate is formed due to the ionic reaction of potassium cyanate and ammonium sulfate. In which urea is formed by reorganization of atoms.
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2KCNO + (NH4)2SO4 → 2NH4CNO + K2SO4
NH4CNO → NH2CONH2
Industrial Manufacture
From Ammonia
Ammonium carbamate is formed by heating a mixture of liquid ammonia and liquid carbon dioxide in autoclave at high temperature. Which is obtained by heating to 150°C at 50 atmospheric pressure.
2NH3 + CO2 → NH2COONH4
NH2COONH4 → NH2CONH2 + H2O
From Cyanide
In this method, firstly, the mixture of calcium carbide and nitrogen to calcium cyanamide and carbon is obtained according to the following reaction. This mixture is called nitrolime and is used as fertilizer.
CaC2 + N2 → CaCN2 + C
This mixture is reacted with dilute sulfuric acid. Dilute sulfuric acid converts calcium cyanamide into cyanamide. This is followed by urea from partial water decomposition of Cyanamide.
CaCN2 + H2SO4 → H2N-C≡N + CaSO4
H2N-C≡N + H2O → H2N-CO-NH2
Urea Properties
Physical Properties
Urea is a white crystal substance. Its melting point is 132°C. It is more fusion between alcohol and water but is insoluble in ether.
Chemical Properties
Water Decomposition: Water decomposition of urea occurs when heated with water at high pressure or boiled with alkali or acid. Which gives carbon dioxide and ammonia gas.
Water decomposition of urea occurs quickly when urea is heated with an aqueous solution of NaOH or KOH. Ammonia gas is obtained in this reaction. This reaction can be used to test urea.
NH2CONH2 + 2NaOH → Na2CO3 + 2NH3
Reaction with Acids: Aqueous solution of urea is a weak alkali-like behavior.
Example: It reacts with concentrated nitric acid and concentrated oxalic acid to make urea nitrate and urea oxylate respectively.
Urea Nitrate: NH2CONH2.HNO3
Urea Oxalate: [(NH2CONH2)2.H2C2O4]
Action with nitrous acid: Urea is decomposed by nitrous acid to release nitrogen and carbon dioxide.
NH2CONH2 + 2HNO2 → CO2 + 3H2O + 2N2
Heating: By slowly heating the urea to 150°C, the ammonia gas comes out and a white solid substance Biuret is formed.
NH2CONH2 + NH2CONH2 → NH2CONHCONH2 + NH3
Purple solution is obtained by the addition of dilute sodium hydroxide and diluted copper sulphate solutions in aqueous solution of Biuret. This reaction is used in the testing of urea. This test is called biuret testing.
On heating the urea intensely, one molecule of ammonia is liberated from it and cyanic acid is formed which is multiply converted to Cyanic acid.
NH2CONH2 → HOCN + NH3
3HOCN → (HOCN)3
Hydrazine: It reacts with Hydrazine to form Semicarbengidae.
NH2CONH2 + HNHNH2 → NH2CONHNH2 + NH3
Reaction with Ethyl Alcohol: Ethyl alcohol and urea react together to form Ethyl carbamate(NH2COOC2H5), which is also known as Urethane.
NH2CONH2 + HOC2H5 → NH2COOC2H5 + NH3
Acetylation: It reacts with acetic anhydride or acetyl chloride to form acetyl urea.
CH3COCl + HNHCONH2 → CH3CONHCONH2 + HCl
Oxidation: Oxidized by sodium or potassium hypobromite, it forms nitrogen gas.
NH2CONH2 + 3NaOBr + 2NaOH → N2 + Na2CO3 + 3NaBr + 3H2O
It is oxidized by sodium or potassium hypochlorite to form hydrazine.
NH2CONH2 + NaOCl + 2NaOH → NH2NH2 + NaCl + Na2CO3 + H2O
Oxalic acid action: In the presence of Phosphoryl chloride (POCl3), the action of urea and oxalic acid produces oxalyl urea, also known as Parabanic acid.
Malonic Ester: The action of urea with malonic ester is as follows.
Reaction with Formaldehyde: This is the action of urea from formaldehyde.
Urea Uses
The major use of urea is as a fertilizer.
Urea is also used in the manufacture of many medicines, such as baronals. Many derivatives of Barbituric acid are used in sleepy medicines.
It is also used in the manufacture of hydrozine and other compounds.
Formaldehyde urea resins are used as plastics.
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Urea Tests
Biuret Test: By slowly heating the urea, ammonia gas comes out and a white solid material is obtained. Which is called Biuret. Ammonia can be identified by its pungent and distinct smell. Purple solution is obtained by adding a few drops of solutions of dilute sodium hydroxide and dilute copper sulphate in aqueous solution of a white solid.
Ammonia is formed by heating urea with a solution of caustic soda, which can be readily identified by its odor.
A white precipitate of urea nitrate or urea oxalate is obtained by adding concentrated nitric acid or concentrated oxalic acid solution to the concentrated solution of urea.
Nitrogen gas is released rapidly by adding sodium nitrite solution by adding dilute hydrochloric acid to the urea solution.
Nitrogen gas is released when alkaline Hypobromite is added to an alkaline solution of urea.
