Detailed study of Resins including its Definition, properties, types, classification, isolation/extraction

1. TANNINS: INTRODUCTION,
PROPERTIES,CLASSIFICATION,CHEMICAL
TESTS AND ISOLATION

3. • Tannins are naturally occurring complex organic
compounds possessing nitrogen free
polyphenols of high molecular weight.
• They form colloidal solution with water giving
acid reactions.
• They also precipitate proteins and alkaloids.

4. • The astringent in nature of tannins is due to the
fact that they can precipitate proteins and
render them resistant to enzymatic attack.
When applied on a wound or injury, tannins
form a protective coating so as to prevent
external irritation and thus promote healing.

5. Properties of tannins:
• Tannins are freely soluble in water, alcohol,
glycerol, and acetone and dilute alkalies.
• They are sparingly soluble in chloroform, ethyl
acetate and other organic solvents.
• They have an astringent taste.
• They combine with alkaloids to form tannates,
most of which are insoluble in water.

6. Classification of tannins:
1. Hydrolysable tannins
2. Condensed tannins
3. Pseudotannins.

7. 1. Hydrolysable tannins:
• These tannins are hydrolyzed by acids, or enzyme
and produce gallic acid and ellagic acid.
• Chemically, these are esters of phenolic acid like
gallic acid and ellagic acid. The tannins derived
from gallic acid are known as gallitannins and from
that of ellagic acid are known as ellagitannins.
• The gallic acid is found in rhubarb, clove and ellagic
acid is found in eucalyptus leave and myrobalans
and pomegranate bark.
• These tannins treated with ferric chloride to
produced blue or black colour.

9. 2. Condensed tannins:
• These tannins are resistant to hydrolysis and they
derived from the flavonols, catechins and flavan-3,
4-diols.
• On treatment with acids or enzymes they are
decomposed into phlobaphenes(give characteristic
red color to many drugs).
• On dry distillation condensed tannin produce
catechol. These tannins are called as catechol
tannins.
• These tannins are found in cinchona bark, male
fern, areca seeds, tea leaves and wild cherry bark,
bahera fruits, Amla, etc. they produce green colour
with ferric chlorides.

11. 3. Pseudotannins:
• They are phenolic compounds of lower
molecular weight and do not show the
goldbeater’s test. They are found in catechu
and nux- vomica, etc.
(i) Catechins: Catechu, cocoa, etc (especially in
dead tissues and dying cells)
(ii) Ipecacuanhic acid: Ipecacuanha
(iii) Chlorogenic acid: Coffee and nux-vomica

12. CHEMICAL TESTS
1. Goldbeater’s skin test: (main test)
• Goldbeater’s skin is a membrane produced from the intestine of Ox. It
behaves just like untanned animal hide.
• A piece of goldbeaters skin previously soaked in 2% hydrochloric acid
• washed with distilled water is placed in a solution of tannin for 5
minutes.
• then washed with distilled water and transferred to 1% ferrous
sulphate solution.
• change of the colour of the goldbeater’s skin to brown or black
indicates the presence of tannin.

14. • Hydrolysable and condensed tannins both give
the positive goldbeater’s test, whereas
pseudotannins show very little colour or
negative test.

15. Test for Catechin (Matchstick Test): Catechin test
is the modification of the well-known
phloroglucinol test for lignin. Matchstick contains
lignin.
Dip a matchstick in the dilute extract of the drug,
dry, moisten it with concentrated hydrochloric
acid, and warm it near a flame. Catechin in the
presence of acid produces phloroglucinol which
stains the lignified wood pink or red.

16. ISOLATION
1. Both hydrolysable and condensed tannins are
highly soluble in water and alcohol but insoluble
in organic solvents such as ether, chloroform, and
benzene.
2. Tannin compounds can be easily extracted by
water or alcohol. The general method for the
extraction of tannic acid from various galls is
either with water-saturated ether, or with mixture
of water, alcohol, and ether.

17. 3. In such cases, free acids such as Gallic and
ellagic acid go along with ether, whereas true
tannin gets extracted in water. If the drug consists
of chlorophyll or pigment, it may be removed by
ether.
After extraction, the Aqueous and ethereal layers
are separately concentrated, dried, and subjected
to further isolation and purification using various
separation techniques of chromatography.

18. MEDICINAL PROPERTIES AND USES
1. Tannins are medicinally significant due to their
astringent properties.
2. Tannins are used in the treatment of
haemorrhoids, minor burns, frostbite, as well as
inflammation of gums.
3. Internally tannins are administered in cases of
diarrhoea, intestinal catarrh, and in cases of heavy
metal poisoning as an antidote.

19. MEDICINAL PROPERTIES AND USES
4. They are widely used in the leather industry for
conversion of hide into leather, the process being
known as tanning.
5. Tannins are also used for clarifying beer or
wine, in photography or as a coagulant in rubber
manufacture.
6. Tannins are used for the manufacture of gallic
acid and pyrogallol, and sometimes as a reagent in
analytical chemistry.