Fischer Esterification - Lu Lu Laboratory

A Fischer esterification is the reverse reaction of the acid-catalyzed hydrolysis of an ester. The mechanism of the Fischer esterification reaction is a series of protonations and deprotonations., along with an addition step and an elimination step. First, the carbonyl group of the carboxylic acid is protonated bt the acidic catalyst. Next, the weakly nucleophilic alcohol attacks the carbonyl carbon. In the final steps, an OH group is protonated and then elimination as water. A final deprotonation yields the ester.

Mechanism:

Step 1, protonation :

Step 2, addition of alcohol and loss of H⁺ :

Step 3, protonation, elimination, and deprotonation :

    Because the reaction mixture is an equilibrium mixture, the concentration of reactants and products may be used to determine an equilibrium constant, K:

    The equilibrium constants for Fischer esterifications are generally less than 4. From a synthetic standpoint, this means that when a 1:1 molar ration of reactants is used, the equilibrium mixture contains a substantial amount of the starting carboxylic acid. For example, if K = 4 and a 1:1 molar ration of alcohol to carboxylic acid is used, the highest possible yield of an ester can be 67%.

Chemicals:

1.      1-hexanol: 0.25 moles, 12.771g

2.      Acetic acid: 0.25 moles, 15.013g

3.      Concentrated sulfuric acid: 0.5mL

Procedure:

1.      Heat a mixture of 0.25 mol of glacial acetic acid, 0.25 mol of a primary alcohol, and 0.5 mL of concentrated sulfuric acid under reflux for 1.5 hours.

2.      Cool the reaction mixture.

 Concentrated sulfuric acid is the lower layer

3.      Dilute the mixture with an amount of water 3~4 times its volume.

4.      Wash the organic layer with water, with 10~15 mL of saturated sodium bicarbonate solution.

5.      And again wash with water.

6.      Dry the ester with anhydrous Na₂SO₄.

 

7.      Typical yield is about 80%.

 Other classmates' work. Different kinds

 of alcohols make different esters

Experimental Record

Theoretical Weight of 1-Hexyl Acetate	18.026g
Weight of 1-Hexyl Acetate	14.790g
Yield	82.0%
Theoretical nd20℃	1.4092
nd20℃ of the final product	1.4005