Question

Experiment:

A mixture of equal proportions of benzoic acid, ethyl 4-aminobenzoate, and 1,4-dimethoxybenzene are to be separated by extraction using the solvent diethyl ether.

Day 1:

Part A. Isolation of the basic component: In a small beaker, dissolve 3 g of the mixture (benzoic acid, ethyl 4-aminobenzoate, and 1,4-dimethoxybenzene) in 30 mL of diethyl ether and transfer the mixture to a 125- mL separatory funnel (see Fig. 1) using a little diethyl ether to complete the transfer. Add 10 mL of an aqueous solution of 1.5 M HCl to the funnel. Swirl the mixture. Stopper the funnel and cautiously mix the contents. Your instructor will demonstrate the proper technique. Vent the funnel then shake the mixture thoroughly with frequent venting of the funnel. Allow the layers to separate completely and then draw off the lower layer into a 50-mL Erlenmeyer flask (labeled ethyl 4-aminobenzoate). Repeat the process with another 10 mL of 1.5 M HCl.

While swirling, add 6 M NaOH dropwise to the ethyl 4-aminobenzoate flask until the solution is cloudy and the contents are acidic to litmus (red litmus paper turns blue). Cool the flask in ice for 10-15 minutes. Isolate the ethyl 4-aminobenzoate by employing vacuum filtration on a Büchner funnel, and wash it on the filter with a small quantity of ice-cold water. Once dry, obtain final mass and melting point of ethyl 4-aminobenzoate.

Drain the rest of the solution in the separatory funnel into a small Erlenmeyer flask. Cover with parafilm and label with your full name and “mixture B and C”. Save the mixture to work on the next lab period.

Day 2:

Determine whether your “mixture B and C” still has about 30 mL of diethyl ether solvent. If it has evaporated (partially or completely) add some diethyl ether to make up for the loss.

Part B. Isolation of the acidic component: Transfer the mixture to a separatory funnel. Add 10 mL of a 3.0 M aqueous NaOH solution to the separatory funnel, shake the mixture thoroughly, and vent. Repeat the shaking and venting several times. Allow the layers to separate and draw off the lower layer into a 50-mL Erlenmeyer flask (labeled benzoic acid). Repeat the process with another 10 mL of 3.0 M NaOH, adding the lower layer to the benzoic acid flask. Acidify the contents of the benzoic acid flask by dropwise addition of 6.0 M HCl. The reaction will be complete when the solution is cloudy and blue litmus paper turns pink. Cool in an ice bath. You may start working on part C while the benzoic acid cools (10-15 mins). Collect the acid by vacuum filtration. Obtain mass and melting point.

Part C. Isolation of the neutral component: Add 15 mL of a saturated aqueous solution of sodium chloride to the separatory funnel, shake the mixture thoroughly, allow the layers to separate, and draw off the lower layer, which can be discarded. Carefully pour the ether layer into a 50-mL Erlenmeyer flask. Add just enough anhydrous calcium chloride to dry the ether extract (consult your instructor). Label a 125 mL Erlenmeyer flask “1,4-dimethoxybenzene” and obtain its mass (tare). Using gravity filtration, Fig. 2, filter the ether into the tared flask, making sure to leave all the drying agent behind. Wash the drying agent with additional ether to ensure complete transfer of the product. Add a boiling stick (or Pasteur pipet) in the flask and evaporate with gentle heating the ether in the hood. Determine the weight and melting point of the recovered 1,4-dimethoxybenzene.

In this experiment you separated a mixture of benzoic acid, 4-t-butylphenol, and 1,4-dimethoxybenzene. Which component was isolated in flask1? Explain your reasoning. Which component was isolated in flask 2? Explain your reasoning. Which component was isolated in flask 3? Explain your reasoning.

In Flask 1, we had 4-t-butylphenol. This is he first substance separated from the mixture in the experiment by adding HCl and draining the bottom layer from a separatory funnel into flask 1.

In Flask 2, we had benzoic acid. This is he second substance separated from the mixture in the experiment by adding NaOH and draining the bottom layer from a separatory funnel into flask 2.

In Flask 3, we had 1,4-dimethoxybenzene. I'm pretty sure the reasoning on this one is because the substance is neutral, it does not react, therefor it the only substance left in the last flask (3). Its the reasoning for the first 2 flasks I'm questioning.

Answer 1