experiments practical exam b. sc part 3 preparation of benzoic acid from benzaldehyde
Answers
Explanation:
20 g of benzaldehyde are treated in a stoppered cylinder or a thick-walled vessel with a cold solution of 18 g of potassium hydroxide in 12 g of water, and mixed until a permanent emulsion is formed. The mixture is then allowed to stand over night. The vessel is closed by a cork, and not a glass stopper, since at times a glass stopper becomes so firmly fastened that it can be removed only with great difficulty. To the crystalline paste (potassium benzoate) separating out, water is added until a clear solution is obtained from which the benzyl alcohol is extracted by repeatedly shaking with ether. After the evaporation of the ether the residue is subjected to distillation; benzyl alcohol passes over at 206° C. Yield, about-8 g. The benzoic acid is precipitated from the alkaline solution on acidifying with hydrochloric acid and purified from hot water yielding final product with melting point 121°C