Question 1

Compound X (benzoic acid) can be used to synthesise Compound Y (ethyl benzoate), a liquid ester used in flavorings and fragrances, as shown below.

$Reaction scheme showing the conversion of Compound X to Compound Y. Compound X is benzoic acid, represented by a benzene ring attached to a carboxylic acid group. An arrow labeled 'reflux with excess ethanol and a small amount of sulfuric acid catalyst' points to Compound Y. Compound Y is ethyl benzoate, represented by a benzene ring attached to an ethyl ester group. Physical properties of Compound Y are stated as: boiling point = 212 °C, density = 1.045 g cm^{-3}.$

A student prepares a sample of Compound Y by the following method:

Step 1: Reflux $g6.10\text{ g}$ of Compound X ( $mol−1M_r = 122.1\text{ g mol}^{-1}$ ) for 45 minutes with an excess of ethanol in the presence of a small amount of sulfuric acid as a catalyst.
Step 2: Add an excess of aqueous sodium carbonate, $Na2CO3(aq)\text{Na}_2\text{CO}_3\text{(aq)}$ . Two distinct layers are obtained.
Step 3: Purify the impure Compound Y ( $mol−1M_r = 150.2\text{ g mol}^{-1}$ ) that forms from the resulting mixture.

The student follows this method and obtains $g4.85\text{ g}$ of pure Compound Y.

Why does the student use reflux in Step 1?

In Step 2, $Na2CO3(aq)\text{Na}_2\text{CO}_3\text{(aq)}$ removes the sulfuric acid catalyst and any unreacted Compound X from the mixture. Write balanced chemical equations for these two removal reactions. (Use $C6H5COOH\text{C}_6\text{H}_5\text{COOH}$ to represent Compound X.)

Another student suggests that adding aqueous sodium hydroxide, $NaOH(aq)\text{NaOH(aq)}$ , would be more effective in removing the sulfuric acid catalyst than $Na2CO3(aq)\text{Na}_2\text{CO}_3\text{(aq)}$ . Comment on whether this suggestion is an improvement.

Calculate the percentage yield of Compound Y. Give your answer to three significant figures.

Describe how to purify the impure Compound Y from the two layers in Step 2.