Page 10 - phytochemistry II -pharmD general
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2-The substituents and functional groups adjacent to the N. atoms.
➢ The presence of electron withdrawing groups adjacent to N-atom will
decrease basicity of alkaloids e.g. (Cl, I, Br, O, C=O)
Weakly basic alkaloids form salts only with strong acids and easily hydrolysed
with water, e.g. purine bases
Neutral alkaloids, e.g. ricinine and colchicine cannot form salts with acids.
On the other hand,
➢ The presence of electron donating grps (alkyl groups) adjacent to N-
atom this will increase basicity of alkaloids e.g. coniine.
• Alkaloidal bases acid Alkaloidal salts
• Alkaloidal salts alkali Alkaloidal bases
➢ The majority of alkaloids (pH 4.5 - 8) are alkaline to litmus paper and
methyl red (pH 4-6) but neutral to Ph. Ph. (pH 8.3-10).
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