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Thursday, January 24, 2013

Preparation of Benzil - Synthesis of Dilantin - Lu Le Laboratory

α-Diketones are very useful in the preparation of cyclic compounds of great value. Benzil, an α-diketone, is prepared by the oxidation of an α-hydroxyketone, benzoin. This oxidation can easily be done with mild oxidizing agent. In the experiment, the oxidation is performed with ironic chloride hexahydrate.

Reaction equation

Possible Mechanism

Step 1

Step 2


1.      Benzoin: 1.20g

2.      Ironic chloride hexahydrate: 5.10g

3.      Ethanol
4.      Acetic acid: ~6mL

1.      Place 6mL of glacial acetic acid, 3mL of water, 5.1g FeCl3˙6H2O and a stir bar in a 100mL round-bottom flask fitted with a reflux condenser.

 I used a air condenser because the boiling point of the distillate is high
and it also safe more energy
2.      Heat gently the mixture to boil and shake the mixture occasionally. Stop heating and cool the solution slightly.

3.      Add 1.20g benzoin to the flask and continue to heat. Reflux the mixture 1 hour.
4.      Then add 30mL of water to the flask and heat the mixture again. After boil, cool the solution, yellow solid separates. Collect the crude product by filtration, and wash it three times with a small amount of cold water. 

 After add water

 Boil the solution again

 Place in an ice bath
5.      Recrystallize the crude product from 75% aqueous ethanol (about 30mL).

6.      Air dry the product and weight it.

 Get 0.80g

Experimental Record

Weight of benzoin added
1.20 g
Weight of benzil after recrystallization
0.80 g
Theory weight of benzil
1.19 g
Yield Rate
67.2 %

1 comment:

  1. Hello, thanks for this idea, I'll try it out.
    It would be helpful to have a simple analytical method, such as TLC. When I tried this with Acetonitrile, I could not find a difference between Benzoin and Benzil, so another solvent for TLC would be useful.