Principle: Here alcohol group of benzoin is oxidized to ketone group forming benzil in the presence of concentrated nitric acid. Nitration of aromatic ring is not occurring as sulphuric acid is totally absent in the whole process.
Aim: To prepare benzil from benzoin.
Use: It is used in the manufacture of glycollate pharmaceuticals including benzillic acid, clidinium, dilantin, and flutropium.
Chemicals: Benzoin, conc. HNO3, Ethanol etc.
Apparatus: Round bottom flask, Beaker, Pipette, Glass rod, Buchner funnel etc.
20 g of benzoin and 100 ml of concentrated nitric acid are taken in a round bottomed flask and heated on a boiling water bath for about 1.5 hour with occasional shaking until the evolution of oxides of nitrogen ceases. The content is poured into 300 – 400 ml ice cold water with shaking.
Then the product is filtered with suction and washed with cold water. It is recrystallized from ethanol, taking 2.5 ml per gram; m.p. 94-96 oC.
Here limiting reagent is benzion; hence yield should be calculated from its amount.
C14H12O2 = Molecular formula of benzion
C14H10O2 = Molecular formula of benzil
Molecular weight of benzion = 212 g/mole
Molecular weight of benzilic acid = 210 g/mole
212 g benzion forms 210 g benzil
Therefore, 20 g benzion will form …….? (X) g benzil
Hence, Theoretical yield = 19.8 g
Benzil was synthesized and the percentage yield was found to be 95.9%
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- Vogel’s Textbook of Practical Organic Chemistry by Brian S. Furniss, Antony J. Hannaford, Peter W. G. Smith & Austin R. Tatchell; Fifth Edition; Page No.- 1045.
- Practical in organic chemistry, by Hitesh G. Raval, Sunil L. Baldania and Dimal A. Shah, Nirav Prakashan, Page no: 273.