Question

Acid/Base Extraction

1. Provide a flow chart detailing the acid/base extraction/separation of the compounds shown below. Your answer must employ the following reagents: methylene chloride, hydrochloric acid (1M & 6M), sodium hydroxide (1M & 6M), 10% sodium bicarbonate (aq). Clearly indicate the product(s) and layers formed following each step of your separation scheme. IMPORTANT: p-cresol is soluble in sodium hydroxide solution but insoluble in neutral water or sodium bicarbonate solution. 2- ethylbenzoic acid is soluble in both sodium hydroxide and sodium bicarbonate solutions. Use skeletal structures only in your answer:

2. Why must you remove the separatory funnel stopper prior to opening the stopcock and draining out the lower layer?

3. During your extraction, you become confused as to which layer is the organic and which is the aqueous. How would you identify them experimentally?

4. Why is the solubility of a neutral organic compound unaltered by exposure to aqueous acid or base?

5. Identify which of the following solvents in each pair would constitute the upper layer in a liquid/liquid extraction solution. If layer separation would not be observed, indicate this by stating miscible. HINT knowing the physical properties of each solvent/solvent system are essential to answering this question correctly.

a) Ethyl acetate and 6M sodium hydroxide solution (aq):

b) Diethyl ether and water:

6. Acetone is an organic solvent in which all three components of the 3-component mixture are soluble. Why would it not be a good substitute for dichloromethane in this experiment?

Answer 1

Concepts and reason

This problem is based on the concept of an acid-base solvent extraction.

Acid-base extraction is typically used to separate organic compounds from each other based on their acid-base properties. The solvent extraction is done by adding acid and base to the mixture and unaltered the neutrality of organic compound.

Fundamentals

Acid-base extraction method based on the assumption that most organic compounds are more soluble in organic solvents than that the water.  However, if the organic compound is ionic, it becomes more soluble in water than in the organic solvent. 

Part 1

The flow chart for the separation of compounds of a mixture is as follows:

Part 2

The stopper of separatory funnel must be removed to allow sufficient amount of air to enter the funnel and release the internal pressure that has been building in the funnel. After this only, we will allow the lower layer to be drained.

Part 3

The experimental method is the taking a small sample from the bottom of separatory funnel and mixing with water helps to identify the two layers.

[Part 3]

Ans: Part 1

The flow chart for the separation of compounds of a mixture is as follows:

Part 2

The stopper of separatory funnel must be removed to release the internal pressure.

Part 3

By treatment of small sample from the bottom of separatory funnel with water.