Page 66 - phytochemistry general program

The alkaloid is treated with fuming nitric acid. The mixture is evaporated to
dryness on a water bath. The yellow residue is cooled then treated with few drops

of 3 % alcoholic KOH solution, it gives a bright purple or violet color.

It is the most useful, although it is non-specific test. This test is sensitive and
can be used for colorimetric estimation of tropane alkaloids.

2- Gerrard's reaction

When few mg of the alkaloids are treated with 2% HgCl2 in 50% ethanol, a
red color is formed in case of hyoscyamine and a white precipitate in case of

hyoscine.

3- Test with p-dimethylaminobenzaldehyde reagent (PDMAB).

The alkaloid is treated with PDMAB /H2SO4. On warming in a water bath a
red color is produced that turns to cherry red color on cooling.

Natural tropane N-oxides

Me O
ON Me N

H H

OR OR
Hyoscyamine N-oxides

R = tropoyl

Two isomers of hyoscyamine N-oxide were isolated from the roots, stems,
leaves, flowers, pericarp and seeds of Atropa belladonna, Hyoscyamus niger and

Datura stramonium.

The equatorial N-oxide of hyoscine was isolated from all parts of the latter
two species and from the leaves of belladonna. The proportion of N-oxides to
tertiary base varied among the organs and with different stages of plant

development.

Separation of a mixture of atropine, hyoscyamine and hyoscine

64