Answer to Question #165351 in Organic Chemistry for Darren Agbor

Question

Question:

Benzyl alcohol (C₆H₅CH₂OH) and benzoic acid may be obtained from benzaldehyde by the reaction with potassium hydroxide, using the method described below.

Benzaldehyde (26.5g) was added to a concentrated solution of potassium hydroxide in a corked bottle. The mixture was shaken and allowed to stand for several hours. Water was added and the mixture extracted with two separate portions of ether. The ether extracts were combined, dried, and distilled to give a liquid product A. The aqueous layer was acidified with concentrated hydrochloric acid and the white precipitate B filtered off by suction and purified. 10g of product A and 12g of product B were formed.

(a) Why were 2 separate portions of ether used rather than one large one?

(b) How would you have dried the ether solution?

(c) How would you purify B and how would you confirm its purity?

Answer 1

a) For extraction it is better to use few small portions than one large. It is encreases the efficency of extraction

b) Standart dryer for ether solution is Na₂SO₄. If you need it to be even more dry, you can add molcular sieves 3A.

c) Benzoic acid can be purified by recrystallisation from water. The purity can be confirmed by measuring it's melting point.