Page 16 - phytochemistry II -pharmD general
P. 16
Isolation & Separation of individual alkaloids:
1. Fractional crystallization: It is usually preferred after converting alkaloidal
bases to salts as oxalates, tartrates, HCl, picrates,..etc.
2. PH gradient method: This method is suitable for separating alkaloids of
different pKa values.
3. Sulphonylation: Separation according to the type of amine group (1ry, 2 ry,
3 ry alkaloids)
4. Separation according to the functional group present in alkaloid, e.g.
phenolic, acidic gro...etc.
➢ PH gradient method for separation of Alkaloids with different degree
of basicity
• The principle of this method of separation depends mainly upon the
difference of basicity of diff. alkaloids
• Weak bases require a stronger acids to form salt than the strongly basic
alks are required
➢ Separation of mixture of 1ry, 2ry and 3ry alkaloids
Separation by sulphonylation:
The principle of this method depends on the fact that:
▪ 1ry (RNH2) and 2ry (R2NH) alkaloids contain replaceable protons on
nitrogen which react with p-toluene sulphonyl chloride to form the
corresponding sulphonamide derivatives as precipitate.
▪ 3ry alkaloids (R3N) (with no replaceable proton on nitrogen) do not react
with p-toluene sulphonyl chloride.
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