Question

You wish to use your skills to prepare another ester, ethyl isobutyrate (butterscotch flavoring). Provide the following for the reaction to prepare ethyl isobutyrate.

(2 points) Using ChemDraw, provide a balanced reaction for the ester you chose above.

(2 points) Provide three specific ways whereby Le Châtélier’s principle may be applied to this equilibrium to drive the reaction completely to the desired ester.

(1 point)   Explain which reagent you would choose to use in excess and provide a rationale.

(2 points) Using ChemDraw, provide a step‐by‐step mechanism for the ester you chose above.

(4 points) If you started with 7.50 g of your chosen carboxylic acid for the ester you chose to prepare, then how much of the other reagent is needed to bring the reaction about?

Answer 1

Part (i)

Part (ii)

a) Increasing the concentration of isobutyric acid

b) Increasing the concentration of ethanol

c) Increasing the concentration of H₂SO₄

Part (iii)

The increase in the concentration of isobutyric acid increases stress on the reactant side of the equilibrium system, according to Le-Chatelier's principle, the system tries to nullify the stress by shifting towards the right side of the equilibrium, i.e. towards the product (ethyl isobutyrate).

The above explanation applies to the increase in the concentration of ethanol, as well as H₂SO₄. Hence, the equilibrium shifts toward the product (ethyl isobutyrate).

Part (iv)

Part (v)

The no. of moles of isobutyric acid = 7.5 g/88 g.mol^-1 = 0.085 mol

i.e. The no. of moles of ethanol = 0.085 mol * 46 g/mol = 3.92 g

The density of ethanol = 0.789 g/mL

i.e. The volume of ethanol = 3.92 g/(0.789 g/mL) = 4.97 mL