Answer
Acid-Base Extraction and Functional Group Classification
Principle of Acid-Base Extraction
Acid-base extraction is used to separate compounds based on their acid-base properties by exploiting their differential solubility in aqueous and organic solvents.
Functional Group Behavior
- Carboxylic acids (–COOH): Strong acids, deprotonated by
NaHCO₃to form water-soluble carboxylate salts. - Phenols (–OH on aromatic ring): Weak acids, deprotonated by
NaOHto form water-soluble phenoxide ions. - Amines (–NH₂): Basic, protonated by
HClto form water-soluble ammonium salts. - Neutral compounds: Do not ionize, remain in the organic layer.
Molecule Classification
| Molecule | Functional Group | Classification |
|---|---|---|
| 1 | No acidic/basic groups | Neutral (N) |
| 2 | Amine (–NH₂) | Basic (B) |
| 3 | Carboxylic acid (–COOH) | Acidic (A) |
| 4 | Phenol (–OH) | Mildly Acidic (MA) |
Extraction Sequence
All compounds are initially dissolved in diethyl ether (organic layer).
- Step 1: Add HCl – Amines are protonated to ammonium salts and move to the aqueous layer.
- Step 2: Add NaHCO₃ – Carboxylic acids are deprotonated to carboxylate salts and move to the aqueous layer.
- Step 3: Add NaOH – Phenols are deprotonated to phenoxide ions and move to the aqueous layer.
- Remaining: Neutral compounds stay in the organic layer throughout.
Summary Table
| Step | Aqueous Layer Contains | Organic Layer Contains |
|---|---|---|
| Start | — | All molecules (1–4) |
| +HCl | Amines (Molecule 2) | 1, 3, 4 |
| +NaHCO₃ | Carboxylic acids (Molecule 3) | 1, 4 |
| +NaOH | Phenols (Molecule 4) | 1 (Neutral) |
Conclusion:
Acid-base extraction enables selective separation based on the functional groups’ ability to ionize. The order of addition (acid → weak base → strong base) allows for stepwise removal of basic, strong acidic, and mildly acidic compounds, leaving neutral ones in the organic layer.
Acid-base extraction enables selective separation based on the functional groups’ ability to ionize. The order of addition (acid → weak base → strong base) allows for stepwise removal of basic, strong acidic, and mildly acidic compounds, leaving neutral ones in the organic layer.