To prepare and submit Benzimidazole from o-phenylenediamine.

 Experiment

Aim: 

To prepare and submit Benzimidazole from o-phenylenediamine.

Requirements: 

0-Phenylenediamine, formic acid, sodium hydroxide, round bottom flask,

water bath, reflux condenser.

Theory: 

0-Phenylenediamine on reaction with formic acid gives benzimidazole with the

liberation of two moles of water.

Reaction involved:

Procedure:

1. Place 27 g (0.25 mol) of o-phenylenediamine in a 250 ml round bottom flask and add 17.5 g (16 ml, 0.34 mol) of 90 percent formic acid.
2. Heat the mixture on a water bath at 100°C for 2 hours.
3. Cool and add 10 percent sodium hydroxide solution slowly with constant shaking until the mixture is just alkaline to litmus.
4. Filter off the crude benzimidazole at the pump, wash with ice-cold water, drain well and wash again with 25 ml of cold water.
5. Dissolve the crude product in 400 ml of boiling water, add 2 g of decolourising
6. carbon and digest for 15 minutes.
7. Filter rapidly at the pump through a preheated Buchner funnel and flask.
8. Cool the filtrate to about 10°C, filter off the benzimidazole, wash with 25 ml of cold water and dry at 100°C.
9. The yield of pure benzimidazole with M.P. 171-172°C is 25 g (85%).

Results:

 The yield of obtained product was found to be ....... gm and percentage yield

was.......% and melting point was found to be.........°C.

Observation/ Calculation:

Theoretical yield =

Practical yield =

Percentage of yield =Practical yield / Theoretical yield×100

Uses: 

•Benzimidazole is an example of intermediate used in bulk drug industry.

 •It is the basic nucleus present in drugs like Mebendazole and Thiobendazole.

Caution: 

Glass ware should be clean and dry before being used.