Question

3) A solution of ethyl acetate contains the following three organic acids: phenol (pKa = 10.0), benzoic acid (pKa = 4.2), and 4-aminophenol (pKa = 10.3). In the laboratory, you are provided with aqueous solutions of 1.0 M hydrochloric acid (HCl), 1.0 M sodium hydroxide (NaOH), 1.0 M sodium bicarbonate (NaHCO₃), 1.0 M ammonia (NH₃), and 1.0 M sodium chloride (NaCl).

     Present a strategy for separating the three compounds using extractions. (To help you think about this problem, you might want to create a flow chart like was shown in the pre-lab lecture.)

Question 3 Answer. Use only the number of extractions you need to separate out the organic compounds. See the example on Collab for an example of how to correctly fill out the sections below. Make sure your descriptions of the solutions and contents of each layer are clear.

Extraction #1

Solutions used:
Aqueous Layer contains:
Organic Layer contains:

Extraction #2

Solutions used:
Aqueous Layer contains:
Organic Layer contains:

Extraction #3

Solutions used:
Aqueous Layer contains:
Organic Layer contains:

Extraction #4

Solutions used:
Aqueous Layer contains:
Organic Layer contains:

Extraction #5

Solutions used:
Aqueous Layer contains:
Organic Layer contains:

Extraction #6

Solutions used:
Aqueous Layer contains:
Organic Layer contains:

Extraction #7

Solutions used:
Aqueous Layer contains:
Organic Layer contains:

EXAMPLE

An ethyl acetate solution contains anthracene (a neutral organic) and aspirin (an acidic organic). Present a strategy for separating these two compounds using extractions.

Extraction #1 Solutions used: Initial ethyl acetate solution 1.0 M NaOH solution Aqueous Layer contains: Salt of the conjugate base of aspirin (sodium acetylsalicylate) Organic Layer contains: Anthracene

Extraction #2 Solutions used: Aqueous Layer from Extraction 1 1.0 M HCl solution Ethyl Acetate Aqueous Layer contains: Sodium Chloride (NaCl) Organic Layer contains: Aspirin (acetylsalicylic acid)

Answer 1

In first step, 1.0 M HCl solution was added. -NH₂ group of 4-aminophenol gets protonated and form quarternary ammonium salt which is soluble in aqueous layer instead of ethyl acetate (organic layer).

The two layer are separated and to organic layer 1.0 M of NaHCO₃ is added.

Phenol is very weakly acidic, therefore it don't react with NaHCO3 which is a weak base. But benzoic acid being strong base reacts with NaHCO₃ and produce sodium benzoate salt. Salt formed is soluble in water layer.

Ethyl acetate layer only contains phenol which can be collected by evaporating solvent.