AVCN3_EXTRACTION

​We have a mixture in dichloromethane consists of:

• 4-chloroaniline

• Naphthalene

Separation of the two components will be achieved, if one component is converted into a water soluble salt which is then extracted into the aqueous layer. The other component will then remain in the organic layer.

Multiple Choice

Which compound can be removed from the organic solution by changing it to a water soluble salt?

• 4-Chloroaniline

• Naphthalene

Multiple Choice

Which aqueous solution will you add?

• dilute aqueous HCl (a strong inorganic acid)

• dilute aqueous NaOH (a strong inorganic base)

You  will see two layers in the separatory funnel because water and dichloromethane are immiscible.​

The aqueous phase is the top layer because water is less dense than dichloromethane.

Multiple Choice

After adding HCl, what is the next step?

• Separate the layers

• Shake the separatory funnel

• Now 4-chloroaniline is present as its salt (4-chloroanilinium chloride) in the aqueous layer and naphthalene remains in the organic layer.

• ​After shaking the separatory funnel, we see a reaction.

• Separate the lower organic phases (layer) containing the naphthalene.

• ​Let's isolate 4-chloroaniline from the solution which contains it.

• An acidic aqueous solution contains the salt of 4-chloroaniline, (p-chloroanilinium hydrochloride.)

Multiple Choice

You want to change 4-chloroaniline hydrochloride to the water-insoluble 4-chloroaniline (organic base) by converting the salt to a non-protonated form.

Which solution will you add?

• 5% HCl

• 5% NaOH

• conc. HCl

• conc. NaOH

• You need to add concentrated NaOH until the solution becomes basic.

• In a basic solution, 4-chloroaniline is no longer protonated and no longer very soluble in aqueous solution.

• Note that sodium chloride (NaCl), a byproduct of the reaction, is dissolved in the aqueous solution while the 4-chloroaniline has oiled out of the solution.

Multiple Choice

Now you need to collect the 4-chloroaniline, that has not crystallized, but oiled out. What technique will you use?

• Back extraction

• Filtration

• Use a separatory funnel

• If the compound oiled out, back extraction is the best method to isolate the crude organic compound from the aqueous solution.

• The organic compound will be extracted from the aqueous phase back into the organic phase.

• ​You have placed the aqueous solution of 4-chloroanilinium chloride in the separatory funnel, and added about 1/2 volume of dichloromethane. Two layers are formed.

Multiple Choice

Which is the aqueous layer?

• Top layer

• Bottom layer

• The top layer is the aqueous layer! (cause the density of dichloromethane is 1,325 g/cm³)

• Shaking will allow the organic compound to move to the dichloromethane layer.

• Now the basic compound has been back-extracted into the dichloromethane layer.

• Drain the bottom (dichloromethane) layer into a clean flask to separate from the aqueous layer.

Multiple Choice

Your compound is dissolved in the dichloromethane phase. 

How will you isolate your compound from the solution?

• Filtration

• Distillation

• Recrystallization

• But before doing distillation, we must remove inorganic impurities (in this case NaOH and NaCl) then water from the organic phase.

• First, let's wash the organic solution to remove inorganic impurities.

Multiple Choice

Which liquid will you use to remove inorganic impurities?

• Methanol

• Brine (saturated NaCl)

• Water

To wash the organic solution in a separatory funnel

1. Let's place the organic solution in a separatory funnel.

2. Add water (about half volume)

3. Shake!

4. Drain the bottom (organic) layer into an Erlenmeyer flask.

• Now let's remove the small amount of water dissolved in the organic solution.

Multiple Choice

How to remove the small amount of water dissolved in the organic solution?

• First, add anhydrous sodium sulfate (drying agent) to solution then shake it with brine (saturated sodium chloride)

• First, shake the solution with brine (saturated sodium chloride) then add anhydrous sodium sulfate (drying agent)

• Brine (sat. aqueous solution of sodium chloride) is a very ionic medium. Water, a polar substance, is more soluble in an ionic solution than in most organic solvents.

• Therefore, if you shake a wet organic solution with brine, most of the water molecules move to the brine layer.

• This pre-drying process should be done before you use a drying agent.

• ​Return the organic solution to the separatory funnel, brine (half a volume), then shake

• Now the bulk of water has been removed from the organic layer.

• Drain the bottom layer (organic) layer into a dry, clean flask, and discard the top layer.

• ​Return the organic solution to the separatory funnel, brine (half a volume), then shake

• Now the bulk of water has been removed from the organic layer.

• Drain the bottom layer (organic) layer into a dry, clean flask, and discard the top layer.

• Anhydrous sodium sulfate is a drying agent, which absorbs water to form hydrates.

Multiple Choice

What will you do to remove the drying agent from the organic solution?

• Vacuum filtration

• Gravity filtration

• Now your organic solution, free of inorganic impurities and water, is ready for distillation.

• If you are to start distillation right away, you can filter the solution into a round bottom flask.

• After distillation, you will have the distillate and the residue.

Multiple Choice

Where is your p-chloroaniline?

• The distillate

• The residue