True alkaloids: contain heterocyclic Nitrogen which is derived from amino acid and always basic in nature due to presence of lone pair of electrons on nitrogen.
Proto alkaloids: are simple amines in which Nitrogen is not heterocyclic. E.g. ephedrine, Colchicine, mescaline
Pseudo alkaloids: they are not derived from amino acids but they show positive test for alkaloids. E.g. purines(caffeine), steroidal and terpenoidal alkaloids Conessine, solanidine, protoveratrine, aconine.
Volatile alkaloids: coniine, nicotine, sparteine
Colored alkaloids: Berberine (yellow), Betanidin (Red)
• Some of proto and pseudo alkaloids show higher solubility in water e.g. Colchicine, caffeine, quinine HCl are freely soluble in water. So solubility of alkaloid is also employed for extraction procedures.
Alkaloids with Primary amine Nitrogen: Mescaline
Alkaloids with Secondary amine Nitrogen: Ephedrine
Alkaloids with Tertiary amine Nitrogen: Atropine
Alkaloids with Quaternary Nitrogen: Tubocurarine
Chemical test:
1. Mayer’s reagent test (K+ mercuric iodide solution)=> Cream colored ppt
2. Dragendroff’s reagent (K+ bismuth iodide solution)=> Red brown ppt
3. Wagner’s reagent (iodine K+ iodide solution )=> Red brown ppt
4. Hager’s reagent (Picric acid) => Yellow colored ppt
5. Picrolonic acid => Yellow colored ppt
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