Object: Preparation of Benzilic acid in Benzil.

Object: Preparation of benzilic acid in benzil.

(I) Preparation of Benzil step I

Chemical Required:

Benzoin      -        10 gm

Acetic acid  -        50ml

Conc. HNO₃         -        25ml

Procedure:

A mixture of benzoin (10gm, 0.047 mole), acetic acid (50 ml) and concentrated HNO₃ (25ml) is heated in a round bottom flask boiling water bath for 2hrs. The flask is connected to a trap containing NaOH solution to absorb oxides of nitrogen. Alternatively, the reaction is carried out in a fume cupboard. The reaction mixture is cooled, poured with stirring into an ice cold water. The mixture is stirred well and the separated product filtered and wash with water. It is crystallized  from rectified spirit as yellow prisms.

yield – 8.7

          mpt  - 95°C

          

Second step-

Preparation of benzilic acid from benzil

Chemical Required-

Benzil                                      –        8 gm

Potassium Hydroxide pellets   –        10 gm (in 20ml H₂O)

Rectified spirit                          –        25 ml

Conc. HCl                                –         35 ml

A mixture of benzil (8 gm 0.038 mole), KOH solution (10 gm dissolved is 20ml water) and rectified spirit (25ml) is refluxed in water bath for 12 minutes. The hot reaction mixture is poured into water (150 ml) contained in a beaker. In case the reaction does not go to completion a colloidal solution is obtained due to separation of unreacted benzil.