2. Aim:
• To prepare and submit Benzimidazole from o-
phenylenediamine/
• To perform synthesis of Benzimidazole.
What is Benzimidazole?
• Benzimidazole is a heterocyclic aromatic organic
compound. This bicyclic compound consists of the fusion
of benzene and imidazole.
• It is a colorless solid.
Synthesis of Benzimidazole from
o- Phynylenediamine
-Pratik Terse 2
3. Synthesis of Benzimidazole from
o- Phynylenediamine
-Pratik Terse 3
Properties of Benzimidazole:
• Solubility: It is soluble in alcohol, very slightly soluble in water,
insoluble in benzene
• Melting point: 171-172℃
• Molecular formula: C7H6N2
• Molecular Weight: 118 g/mol
Uses of Benzimidazole:
• Antiviral, Antifungal, anthelmintic, antihistaminic drug
• Also used in cardiovascular diseases, neurology,
endocrinology & ophthalmology.
4. Synthesis of Benzimidazole from
o- Phynylenediamine
• Apparatus:
Round bottom flask, beaker,
condenser assembly, Water
bath/ heating mantle, Porcelain
pieces.
• Chemicals:
o-phenylenediamine, formic
acid, 10% NaOH, Distilled water
REQUIREMENTS:
-Pratik Terse 4
5. Synthesis of Benzimidazole from
o- Phynylenediamine
-Pratik Terse 5
Round bottom flask:
• Allows uniform heating
• Especially for reflux setups & laboratory
scale synthesis
Heating mantle:
• Heat is distributed very evenly
• Heating mantles are suitable for organic
liquids which can sometimes inflame
when using other equipment's (Bunsen
burner, water bath, hot plates)
7. Synthesis of Benzimidazole from
o- Phynylenediamine
Precursor for the practical:
O- Phenylenediamine
• Its is an organic aromatic diamine
• Mol. Formula: C6H8N2
• Mol. Weight: 108 g/mol
Formic Acid:
Sodium Hydroxide (NaOH):
-Pratik Terse 7
8. Synthesis of Benzimidazole from
o- Phynylenediamine
-Pratik Terse 8
Theory:
• o-Phenylenediamine on reaction with formic acid
gives benimidazole with the liberation of two
moles of water.
Principal:
• It is a cyclization reaction. o-Phenylenediamine
on reaction with formic acid gives benimidazole.
• o-Phenylenediamine having N atom contains a
lone pair of electrons i.e. negative charge. The
formic acid contains carboxylic group: it will
attack the nitrogen atom of o-Phenylenediamine
eliminating a water molecule.
• Further carboxylic acid attack another nitrogen
atom and the elimination of water molecule will
lead to formation of benzimidazole as the final
product by electron rearrangement.
10. Synthesis of Benzimidazole from
o- Phynylenediamine
-Pratik Terse 10
Procedun:
• Place 27 g (0.25 mol) of o-phenylenediamine in in a 250 ml round
bottom flask and add 17.5 g (16 ml, 0.34 mol) of 90 percent formic acid
• Heat the mixture on a water bath at 100℃ for 2 hours.
• Cool and add 10 percent sodium hydroxide solution slowly with constant
shaking until the mixture is just alkaline to litmus.
• Filter off the crude benimidazole at the pump, wash with ice-cold water,
drain well and wash again with 25 ml of cold water. '
• Dissolve the crude product in 400 ml of boiling water, add 2 g of
decolourising carbon and digest for 15 minutes.
• Filter rapidly at the pump through a preheated Buchner funnel and flask.
• Cool the filtrate to about 10℃, filter off the benzimidazole, wash with 25
ml of cold water and dry at 100℃.
11. Synthesis of Benzimidazole from
o- Phynylenediamine
-Pratik Terse 11
Calculations:
• Mol. wt. of o- Phenylenediamine=
• Mol. wt. of Benzimidazole=
• Theoretical yield:
108g of o- Phenylenediamine gives 118 g of Benzimidazole
Therefore:
12. Synthesis of Benzimidazole from
o- Phynylenediamine
-Pratik Terse 12
• Practical yield: Suppose you get 25g
• % Practical yield:
𝑃𝑟𝑎𝑐𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑
× 100
• % Practical yield:
• Result: The practical of benzimidazole was found to
be ____g and the % practical was _____% and the
melting point was found to be____℃
13. Synthesis of Benzimidazole from
o- Phynylenediamine
-Pratik Terse 13
Synthesis of Benzimidazole
• Molecular formula: C7H6N2
• Molecular weight: 118 g/mol
• Theoretical yield: 29.5 g
• Practical yield: 25g
• % Practical yield: 85%
• Melting point: 171
