Extraction (ch6)

What is extraction?

A separation technique where a desired compound is selectively dissolved in an appropriate solvent.

How does extraction differ from distillation?

Distillation separates liquids only; extraction separates mixtures of solids AND liquids.

What often accompanies extraction to fully purify a product?

Recrystallization or other purification steps.

What are the three types of extraction?

1. Solid-liquid extraction

2. Liquid-liquid extraction

3. Acid/base extraction

What is solid-liquid extraction?

A technique where a solvent selectively dissolves compounds from a solid mixture.

What happens after dissolving the desired compound?

Insoluble residue is filtered out and solvent is evaporated to yield product.

What is liquid-liquid extraction?

Separation based on solubility differences between two immiscible solvents, usually water + organic solvent.

Which glassware is essential for liquid-liquid extraction?

A separatory funnel.

Why must solvents be immiscible?

To form two distinct layers (organic and aqueous).

Properties of a good organic extraction solvent?

Dissolves compound at room temperature

Low boiling point

Does not react with solute or water

Nonflammable or nontoxic

Inexpensive

Immiscible with water

What is the partition coefficient?

The ratio of solubilities of a solute in the organic layer vs. aqueous layer at equilibrium.

Partition coefficient formula (concentration)?

k=concentration in organic layer/concentration in aqueaous layer

Partition coefficient formula (solubility)?

k=solubility in organic solvent/ solubility in water

What is acid/base extraction?

Technique that separates compounds by converting them into ionic salts that move into the aqueous layer.

Why are ionic salts soluble in water?

They are charged and form strong interactions with water molecules.

How are organic acids extracted?

Treat with NaHCO₃ or NaOH → forms water-soluble carboxylate salts.

How are organic bases extracted?

Treat with HCl → forms water-soluble ammonium salts.

What happens to neutral compounds in acid/base extraction?

They remain in the organic layer (do not form ionic salts).

Example: Benzoic acid + NaHCO₃ → ?

Sodium benzoate (water-soluble salt) + carbonic acid (H₂CO₃).

Why must extraction solvent be immiscible with water?

To create two layers for separation.

Key requirements for a good extraction solvent?

Immiscible with water

Completely dissolves compound

Does not react

Volatile

Different density than water