1. CH3204 Organic Chemistry Laboratory
PROJECT
By -
Soumav Nath
Shouryya Mitra
Swarnadip Saha
Saif Ali

2. Microwave-Assisted synthesis of 2-Methyl Benzimidazole
TITLE –
Microwave-Assisted synthesis of 2-Methyl Benzimidazole
GUIDE -
Dr. Debasish Haldar
Associate Professor
DCS, IISER Kolkata

3. Importance of 2-Methyl Benzimidazole –
Derivative of Benzimidazole class of heterocyclic compounds with fused rings.
They exhibit a wide range of biological activities like anti-microbial, anti-fungal properties etc.
These are mainly used in pharmaceutical industries
Benzimidazole ring displays an important heterocyclic pharmacophore in drug discovery.

4. Importance of Microwave-Assisted synthesis –
Microwaves are forms of electromagnetic energy; corresponds to the frequency of 30 GHz to 300 MHz
Principles of Microwave Synthesis –
Dipole Interaction
Ionic Conduction
Advantages of Microwave Synthesis over conventional heating –
Uniform heating occurs throughout the material
Process speed is increased
Reduction in unwanted side reaction
Purity in final product
Improve reproducibility
Environmental heat loss can be avoided
**Gangrade, et al., Int J Res Pharm Sci 2015, 5(2); 37 – 42

5. Reaction Scheme – 1. 2. Acetone 2-Nitroaniline o-phenylenediamine
M.W. , 200W, 1 Min
2-methyl Benzimidazole
o-phenylenediamine
**Journal of Che. Edu., 83, 4 (2006)

6. Proposed Mechanism –
o-phenylenediamine
2-methyl Benzimidazole

7. Experimental Section –
Reduction of 2-nitroaniline to o-phenylenediamine.
1.2 g of 2-nitroaniline, 0.8 g of Fe salt and 1.2 mL of acetic acid are added in 10 mL of acetone (solvent) and refluxed for 5 hrs.
Acetone was separated using rotavap and in the remaining solution Na2CO3 was added until the efferevesence was completed.
Then Ethyl Acetoacetate was added to the solution and the organic part was collected using separating funnel
Finally Na2SO4 was added to it to ensure no water was present and Ethyl acetoacetate was removed using rotavap and the product was dried.
2. Synthesis of 2-methyl benzimidazole.
0.7 g of o-phenelyenediamine, 0.5 mL of acetic acid and 0.2 g of Al2O3 was added together in a round bottom flask.
Then microwave was irradiated at 200 W for 1 min.
Then the product was filtered by Buchner funnel and finally the product was recrystallized from ethanol.
And it was characterized by TLC, UV-Vis, FTIR and 1H NMR Spectra.

8. OBSERVATION – Yield Percentage –
M.W. of o-phenylenediamine = g/mol
M.W. of 2-methyl benzimidazole = g/mol
108.1 g o-phenylnediamine produces = g of 2-methyl benzimidazole
0.7 g of o-phenlyenediamine produces = 0.85 g of 2-methyl benzimidazole
Theoretical yield = 0.85 g of o-phenylenediamine
Experimental Yield = 0.73 g of 2-methyl benzimidazole
% Yield = (0.73/0.85)*100 = 86%

9. TLC of the Product – Mobile Phase – 3:2 Hexane : Ethyl Acetate
Distance of the solvent head = 4.5 cm
Distance of the reactant = 3.8
Distance of the product= 3.2
R.F. (Reactant) = 0.84
R.F. (Product) = 0.71
The product, i.e. 2-methyl benzimidazole is more polar may be due to the imidazole ring, so its R.F. value is less.
The product is more polar may be due to the imidazole ring, so its R.F. value is less. R P

10. UV-Vis Spectra of the as-prepared product –
Analysis :
214 nm – may be due to pi-pi* transition of extended conjugation of the Benzene ring.
237 nm – may be due to pi-pi* transition of the Imidazole ring.
Shoulder peaks may be due to difference in electron distribution among the rings.

11. FTIR Spectra of the as-prepared product –
Analysis :
cm-1 : Aromatic C-H stretching
cm-1 : C-H stretching
cm-1 : N-H stretching
cm-1 : C=N stretching
cm-1 : Aromatic C-C stretching
cm-1 : CH3 deformation
cm-1 : Aromatic C-H deformation

12. 1H NMR Spectra of the as-prepared product –
Expected chemical shifts around for aromatic H, 3.0 – 5.0 for N-H, 2.21 for CH3. But NMR don’t show this.

13. CONCLUSION –
From our FTIR and UV-Vis spectra, we got very nice confirmations of the structure/bonds that are present in our experimentally prepared product. But the observations from the 1H NMR of the product ,where we didn’t got the discreet peaks as we expected, so we can’t conclude about the successful preparations of the product. This may be due to the low concentration of the sample used during NMR Analysis.