Benzoic acid and benzyl alcohol from benzaldehyde

CANNIZZARO S REACTION. BENZOIC ACID AND BENZYL ALCOHOL FROM BENZALDEHYDE 1 

Freshly distilled benzaldehyde (20 g.) is shaken in a stoppered cylinder or in a thick-walled flask with a cold aqueous solution of potassium hydroxide (18 g. in 12 g. of water) until a permanent emulsion is formed. The container is corked and left over night. To the crystalline paste (potassium benzoate) which separates, just sufficient water2 is added to enable the benzyl alcohol to be ex- 

2 If too much is added it is difficult to extract the (water-soluble) benzyl alcohol completely. 

The aqueous alkaline liquid (from which the benzyl alcohol was removed with ether) is acidified with hydrochloric acid. Benzoic acid is precipitated and, when cold, is filtered off with suction. It is recrystallised from boiling water without previous washing. Melting point 121°. Yield 9-10 g. 

Cannizzaro s reaction probably proceeds in such a way that two molecules of aldehyde condense to form an ester which is then hydrolysed to alcohol and acid  

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