Page 117 - Medicinal Plants_PharmD general
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Properties:
1-Most alkaloids are well-defined crystalline substances which unite with
acids to form salts. In plant they may exist in the free state or as salt
Alkaloidal base + Acid → Alkaloidal salt
Insoluble in water Soluble in water
Soluble in chloroform Insoluble in chloroform
2-Alkaloids contain the elements C, H , N & O; few alkaloids are oxygen
free e.g. nicotine from tobacco and coniine from hemlock.
3-Very few alkaloids are coloured e.g. berberine which is yellow in colour.
Chemical Tests for Alkaloids:
(Precipitating reagents)
The alkaloids are extracted from powdered plant by dilute mineral,
acid and the following reagents are used for testing alkaloids by formation
of precipitates.
1- Mayer’s reagent (K2HgI4 )
Mercuric chloride.
Potassium iodide.
Water.
It gives a creamy precipitate.
2- Wagner’s reagent (I2 /K1) :
Iodine
Potassium iodide.
Water.
It gives reddish brown precipitate.
3- Dragendorff’s reagent ( Potassium bismuth iodide)
Potassium iodide
Bismuth subnitrate
Glacial acetic acid
It gives a reddish-brown precipitate.
4 -Tannic acid solution: It gives a white precipitate.
5- Picric acid solution: It gives yellow precipitates.
Caffeine and some other alkaloids do not give these precipitates.
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