alkaloids

Physical Properties:
I- CondMost alkaloids are crystalline solids.
Few alkaloids are amorphous solids e.g. emetine.
Some are liquids that are either:
Volatile e.g. nicotine and coniine, or
Non-volatile e.g. pilocarpine and hyoscine.
II- Color:
The majority of alkaloids are colorless but some are colored e.g.:
Nitrogen:
Primary amines R-NH2 e.g. Norephedrine
Secondary amines R2-NH e.g. Ephedrine
Tertiary amines R3-N e.g. Atropine
Quaternary ammonium salts R4-N e.g d-Tubocurarine

II- Basicity:
R2-NH > R-NH2 > R3-N
Most alkaloids contain Oxygen and are solid in nature e.g. Atropine.

Some alkaloids are free from Oxygen and are mostly liquids e.g. Nicotine, Coniine.
Precipitation Reagents:Froehd’s Reagent: Phosphomolybdic acid
2- Marqui’s Reagent: Formaldehyde/ Conc. H2SO4
3- Mandalin’s Reagent: Sulphovanidic acid
4- Erdmann’s Reagent: Conc. HNO3/Conc. H2SO4
5- Mecke s Reagent: Selenious acid / conc. H2SO4
6- Shaer s Reagent: Hydrogen peroxide / conc. H2SO4
7- Rosenthaler s Reagent: Potassium arsenate / conc. H2SO4
8- Conc. HNO3

They are used to:
1- Indicate the absence or presence of Alkaloids
2- Test for complete of extraction