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.
