2.1.4 Thymol
Synonyms Thyme camphor;
m-Thymol; 3-p-Cymenol; 3-Hydroxy-p-cymene;
Biological Sources It is
obtained from the essential oil of Thymus vulgaris L., (Thyme oil); Monarda
punctata L., (Horsemint oil), and Monarda didyma L., (Oswego
tea oil), belonging to family Lbiatae. It may also be derived from Carum
capticum Bentham er Hooker, (Ajowan oil), belonging to family Umbelliferae,
and several species of Ocimum, for instance: Ocimum gratissimum L.
(Tulsi oil), belonging to family Labiatae.
Geographical Source T.
vulgaris is grown and cultivated abundantly in many parts of Europe, Australia
and North Asia.
Preparation Thymol may
be extracted from thyme oil by agitation with dilute aqueous alkali solution
(= 5% w/v in water). The aqueous layer is first separated and subsequently made
acidic with dilute acid, when thymol gets separated as an oily layer
floating on the surface that may be recovered either by extraction with ether
or by steam distillation.
Another means of obtaining thymol
from thyme oil is to subject the latter to very low temperature (–25oC)
when thymol separates as crystals.
Synthetic Thymol The thymol
of commerce may be prepared synthetically by anyone of the following
routes, namely:
(a) From Menthone:
Menthone is first treated with bromine. and then quinoline to produce thymol:
(b) From m-Cresol: m-Cresol
on being treated with isopropanol in the presence of a suitable catalyst
yields thymol.
(c) From
Piperitone: When pipertone, usually obtained from the Australian Eucalyptus
oils, is treated with ferric chloride it gives rise to thymol.
Description
Colour : Transparent,
colourless
Odour : Aromatic
thyme—like odour
Taste : Pungent taste
Solubility : In water
(1: 1200); in alcohol (1:1), in glycerol (1: 1000); Freely soluble in ether, chloroform,
carbon disulphide, benzene and glacial acetic acid; soluble in fixed oil and volatile
oil.
Chemical Structure The
phenolic OH moiety present in thymol enables it to form salts of acetate
and carbonate easily which are used as antiseptic and anthelmintic
respectively.
Thymol when disolved in
NaOH solution and treated with an I2-KI solution it forms thymol iodide
that finds its use as an anti-infective and antifungal agent.
Chemical Tests
1. Thymol when fused
with phthalic anhydride develops bright violet red to intense red colouration, and
on adding dilute alkali it gives an intense blue coluration due to the
formation of thymolphthalein.
2. Thymol on being
dissolved in concentrated sulphuric acid yields the corresponding
thymesulphuric acid [C6H2(SO3H) (CH3).
(C3H7).OH], which produces a distinct violet colour with ferric
chloride solution.
3. An alcoholic solution of thymol
on being treated with FeCl3 solution does not produce any colouration.
Note: Carvacrol on identical
treatment gives a green colouration.
4. A small crystal of thymol
is dissolved in 1 ml of glacial acetic acid and to this is added one drop of
HNO3 and six drops of sulphuric acid, when it exhibits a deep bluish
green colour.
5. Dissolve 0.1 g of thymol in
2 ml of NaOH solution (10% w/v) and heat in a water bath to produce either a
clear colourless solution or a pale red solution, that ultimately turns darker
in shade on keeping without the separation of oily drops. If the resulting
solution is shaken with a few drops of chloroform it gives a violet
colouration.
6. Thymol forms definite
derivatives with various reagents e.g., napthylurethane derivative
(m.p.160oC); phenylurethane derivative (106-107oC).
Uses
1. It is invariably employed as
an antifungal and antibacterial agent.
2. It is a vital component in
several analgesic and topical antiseptic formulatios in low concentrations ranging
between 0.1 to 1% in personal health care products.
3. It is widely employed in
preparation exclusively intended for mouthwashes, gargles, oral preparations
and as a local anaesthetic in toothache.
Source:Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar
Source:Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar
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