Preparation of Benzonitrile

Preparation of Benzonitrile

Benzonitrile: A solution of benzenediazonium chloride is prepared by dissolving 20 ml (or 20.5 g) aniline in a mixture of 50 ml of concentrated hydrochloric acid and 50 ml of water. The obtained aniline hydrochloride solution is cooled to 5° C, and then cautiously a solution of 17 g of sodium nitrite dissolved in 40 ml of water is added dropwise. During the diazotization the temperature is maintained between 5° C and 10° C.

Then, while the benzene-diazonium chloride solution is standing in ice-water, 55 g of powdered copper sulfate are dissolved in 200 ml of water and placed in 2000 ml distillation flask, for which a steam-distillation fitting is available for subsequent use. The copper solution is gently warmed to 60-65° C and cautiously a solution of 60 g of powdered potassium cyanide dissolved in 100 ml of water is added. The mixture is stirred or shaken during the addition to facilitate the evolution of the cyanogen until a clear pale-brown solution of potassium cupro-cyanide is obtained.

To this solution in small quantities and with vigorously stirring, benzenediazonium chloride is added by maintaining the temperature of the mixture between 60° C and 70° C. When all benzenediazonium chloride have been added the reaction solution is heated under reflux for 15 minutes and when reaction is complete the mixture is steam distilled until no more oily benzonitrile passes over. From the distillate benzonitrile is extracted with ether by repeating extraction process few times.

Combined ethereal solution is washed with 10 % sodium hydroxide solution in order to eliminate phenol. Traces of phenyl isocyanide are removed by washing with equal volume of dilute sulfuric acid and inorganic acid is removed by washing with water. Finally the ethereal solution is dried over granular calcium chloride, filtered and ether evaporated in vacuo. The crude benzonitrile is purified by distillation, collecting fraction boiling between 187° C and 191° C. The final yield of benzonitrile is 16.5 g. (16 ml.). Benzonitrile is a colorless liquid, which boils at 190° C, d=1.02 g/ml, it is almost insoluble in water.

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