Answer to Question #165302 in Organic Chemistry for Gartiffer

Question

The following is a description of an experiment in which ethyl benzoate is hydrolyzed. 5cm (0.03 moles) of ethyl benzoate   are mixed with 30cm³  of 2M NaOH solution and heated under reflux for about 15minutes until all the oily drops have disappeared.  The flask is then filled for fractional distillation and the mixture distilled until the boiling point reaches 75⁰ to give a distillate "A".     

 The content of the flask is allowed to cool and then slowly acidified with concentrated hydrochloric acid when a precipitate "B" separates. This precipitate is purified by recrystallization from water.

a. White is the white precipitate B?

b. Write the equation for its formation

Answer 1

This process as mentioned in this experiment is called base hydrolysis (or saponification) of an ester. When the fractional distillation is done and the mixture is distilled until the boiling point reaches 75^0, then the obtained distillate A was ethanol.

a) When the content of the flask is allowed to cool and slowly acidified with concentrated hydrochloric acid then a precipitate "B" separates. This white precipitate B is the Benzoic acid (as shown in the below scheme)

b) The equation for its formation is shown below