Alkaloids
Introduction
General Characteristics
General Methods of determination of structure
Introduction: definition of alkaloid have with as study in alkaloids
have progressed
Alkaloids means alkali like, basic in nature
Originally the name alkaloid was given to all organic bases isolated
from plants
Konig (1880) suggested alkaloids should be defined as naturally
occurring organic bases which contain pyridine ring
As per Ladenburg, Alkaloids are natural plant product having basic
character and containing at least one nitrogen in heterocyclic ring
Considering all the previous definitions
Alkaloids may be defined as Organic bases of plant origin, containing a
nitrogen heterocycle with strong physiological activity. Most of them are
chiral (laevorotatory)
Alkaloids are generally solids
-Colourless (few are coloured e.g. berberine is yellow)
-Crystalline (Some alkaloids e.g. nicotine, coniine liquids soluble in water)
-Non Volatile
-insoluble in water
-Soluble in organic solvents e.g. ethanol, chloroform, ether
-Bitter in taste
General Methods for determining structure
Ziesel Method: It is used to determine the presence and number of methoxyl
groups. The alkaloid is heated with conc. Hydriodic acid at its boiling point
(126o C). The methoxyl groups are therby converted into methyl iodide,
which is then absorbed by ethanolic silver nitrate and silver iodide is weighed
Herzig-Meyer Method: It is used to determine the presence and number of
N-Methyl group. The alkaloid is heated with conc. Hydriodic acid under
pressure ( at 150 to 300o C). The N-Me are therby converted into methyl
iodide, which is then absorbed by ethanolic silver nitrate and silver iodide is
weighed.
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