Question

The Question: Why was the reaction mixture from this experiment extracted with sodium carbonate? What gas is evolved during the addition? Write out the reaction(s) and explain why it is necessary to do this extraction.

The only part of this question I know is that CO2 is the gas formed because we saw it in lab but I need help answering this question for my lab workup. Here is the lab information:

The lab: was the synthesis of an ester via Fischer esterification. The reaction: 3.0mL unknown alcohol, ~5mL glacial acetic acid, 3-4 drops concentrated sulfuric acid refluxed for 45 min. Once cooled added the 5mL 10% sodium carbonate, stir, extract organic layer and repeat extraction twice more.

Thank you in advance for your help.

Answer 1

Dear friend

We are using concentrated sulfuric acid as a catalyst for esterification of alcohol with carboxylic acid. Any unreacted sulfuric acid should be removed from product ester. otherwise ester hydrolyses back to alcohol and carboxylic acid. For this purpose we will add a weak base like Na₂CO₃ or NaHCO₃ to the reaction mixture during product extraction (workup). Traces of sulfuric acid reacts with soduim carbonate as follows

H₂SO₄ + Na₂CO₃ --> Na₂SO₄ + H₂O + CO₂

Na₂SO₄ + H₂SO₄ ⇌ 2 NaHSO₄

In the laboratory, anhydrous sodium sulfate is widely used as an inert drying agent, for removing traces of water from organic solutions. It is more efficient, but slower-acting, than the similar agent magnesium sulfate.