It is monocyclic monoterpene secondary alcohol, having the structure:
Menthol occurs in peppermint oil and Japanese mint oil.
Preparation of menthol.
(1) From peppermint or mint oil. The oil is chilled when crystals of menthol separate. These are purified by recrystallization.
(2) From Thymol. Menthol is also obtained by catalytic hydrogenation of thymol.
Physical Properties Of Menthol.
Menthol is a white crystalline solid with a strong minty odor and cooling taste. It melts at 42°C and boils at 216°C. Natural menthol is optically active, the (-)-form. It has an anaesthetic and antiseptic action.
Chemical Properties Of Menthol.
It gives the reactions of alicyclic secondary alcohol.
(1) Oxidation. Upon oxidation with chromic acid, it gives the corresponding ketone, menthone.
(2) Dehydration. When heated with potassium hydrogen sulfate, it gives menthene.
Uses Of Menthol.
Menthol, on account of its anesthetic and antiseptic action, pleasant odor and cooling taste, is used : (1) In pharmaceuticals as local anesthetic and for relief of headache ; (2) In mouth washed, nasal sprays and inhalers (Vick’s Inhaler), cough drops, chewing-gums, and mentholated cigarettes ; (3) In cosmetics – toothpaste, shaving creams, shaving lotions, face creams and powders.
Menthol Formula. C10H20O
Menthol Boiling Point. 212 °C
Molar Mass of Menthol. 156.27 g/mol
Menthol Melting Point. 31 °C