Question

​This experiment involved the use of Fischer Esterification to create isopentyl acetate from reacting isopentyl alcohol with acetic acid and sufluric acid.

1. Provide a balanced equation to explain the evolution of gas during the sodium bicarbonate washing step.

2. The microscale synthesis of esters often uses a Dean-Stark trap. A Dean-Stark trap separates and collects water during a reaction. How would using a Dean-Stark trap during a Fisher-Esterification affect the synthesis?

3. Esters are often used in artificial flavorings. Provide a pathway for preparing esters that smell like pineapples and pears, respectively.

a. CH3CH2CH2CHO-OCH2CH3

b. CH2CHO-OCH2CH2CH3

Answer 1

1) Sodium bicarbonate quenches excess acid to liberate CO₂ gas. This reaction can be given as follows:

H⁺ + NaHCO₃ --------> Na⁺ + CO_{2 (g)} + H₂O

Note the acids used in this reaction are acetic acid and H₂SO₄ and the corresponding salts formed will be sodium acetate and sodium sulfate, respectively.

2) ROH + R'COOH <-----> R'COOR + H₂O

In the esterification reaction, if the water of the reaction is not removed then the equilibrium will shift to left and the reaction will not proceed to completion. That is more of alcohol and acid will remain unreacted. Hence Dean-Stark apparatus is used to remove excess of water and produce ester in higher yields. Acids such as H₂SO₄ are added to facilitate the equilibrium shift to right and yield more ester.

3) Ethyl butyrate and n-propyl acetate smell like pineapple and pear, respectively. Ethyl butyrate can be prepared by reacting butyric acid and ethanol in presence of catalytic amounts of H₂SO₄.

CH₃CH₂CH₂COOH + CH₃CH₂OH --------> CH₃CH₂CH₂COOCH₂CH₃ + H₂O

n-propyl acetate can be prepared by reacting acetic acid and n-propanol in presence of catalytic amounts of H₂SO₄.

CH₃COOH + CH₃CH₂ CH₂OH --------> CH₃COOCH₂CH₂CH₃ + H₂O