CHEMICAL TESTS FOR ALKALOIDS

CHEMICAL
TEST
S FOR ALKALOIDS

 

The chemical tests used for detection of alkaloids depend on their character to precipitate
with  organic
 acids
 in
 the
 form
 of
 their
 salts.  


These
 are
 also  precipitated
 by  the  reaction  of
compounds of   heavy metals like mercury, gold, platinum etc. 


Caffeine
and some other alkaloids which are highly
water soluble, do not give the tests with usual reagents. 

 

 Reagents used for the detection
of alkaloids

S.No

Name of reagent

Chemical composition

Colour obtained

Example

1

Mayer’s reagent

Potassium
mercuric iodide

 

solution

Cream

Common

2

Wagners reagent

Solution of iodine in potassium

 

iodide

Reddishbrown

Common

3

Dragendorffs

 

reagent

Potassium
bismuth iodide

 

solution

Reddishbrown

Common

4

Hagers
reagent

Saturated solution of picric acid

Yellow

Common

5

Picrolonic acid

Solution of picrolonic acid

Yellow

Common

6

Tannic acid

Solution of tannic
ac
id

 

Common

7

Murexide test

*Potassium chlorate+HCl+NH3

Purple

Caffeine

8

Mineral
acids

Phosphotungstic acid,

 

phosphomolybdic acid

Yellow

Colchicine

9

Acidic pmethyl-

 

aminobenzaldehyde

pMethyl-aminobenzaldehyde

 

and sulphuric
ac
id

Bluishviolet to

 

red

Indole

10

Nitric acid

Dilute nitric acid

Orange-red

Morphine

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