Page 12 - Phytochemistry 2 (06-PG 605)

The choice of alkali depends on :

• The degree of basicity of alkaloids.
• The chemical nature of alkaloidal bases.
• The nature of the acid in combination with alkaloids.

The alkali used for liberation of free bases usually
• Sodium hydroxide.
• Calcium hydroxide.
• Magnesium hydroxide.
• Sodium Carbonate.
• Sodium bicarbonate.
• and in most cases Ammonia.

NH4OH

The alkali of choice in alkalinization, and liberation of free bases, and it is
the most widely used because:
1. It is volatile and easily removed on evaporate
2. It is suitable for alkalinization of phenolic & ester alkaloids (where we cannot
use NaOH).
3. It is also suitable for alkalinization of powder that contain traces of fatty
matter (NaOH cause saponification).

NaOH

Disadvantages:.
1. Non volatile.
2. Unsuitable for ester alkaloids, phenolic alk., also in presence of fatty matters.

2- Extraction with water miscible organic solvent (alcohol)

Alk. salts, alk. bases as well as alk. N-oxides and quaternary alkaloids can be
extracted with Ethanol & Methanol.

3- Extraction with dilute aquous acid (acidulated H2O)
• In this method the powdered drug is heated with dilute acid (1-2%) then cool,

filter → crude alk. extract.

11