Medicinal preparations, thymol

Monoterpenes, 10-carbon-containing terpenoids, are composed of two isoprene units, and found abundantly in plants, e.g. (+)-limonene from lemon oil, and (—)-linalool from rose oil. Many monoterpenes are the constituents of plant volatile oils or essential oils. These compounds are particularly important as flavouring agents in pharmaceutical, confectionery and perfume products. However, a number of monoterpenes show various types of bioactivity and are used in medicinal preparations. For example, camphor is used in liniments against rheumatic pain, menthol is used in ointments and liniments as a remedy against itching, bitter-orange peel is used as an aromatic bitter tonic and as a remedy for poor appetite and thymol and carvacrol are used in bactericidal preparations. 

The characteristic odour of ajowan oil is due to the high content of thymol (61%). Thymol easily crystallizes out from the oil and is sold in Indian markets as ajowan ka-phool, or sat-ajowan, and is much valued in medicines. Thymol is used as an ingredient of deodorants, mouthwashes, toothpastes and many pharmaceutical preparations. The leftover residue after distillation contains 15-17% protein and 20-25% fat and is valued as cattle feed. The major processed products are ajowan oil, oleoresin, thymol, thymol crystals, dethymolized oil (thymene) and fatty oils (Malhotra and Vijay, 2004). 

C10H14O, Mr 150.22, pioi.3kPa 232.5 °C, df 0.9756, n53° 1.5227, is the main constituent of thyme and some origanum oils it also occurs in many other essential oils. It forms colorless crystals (mp 51.5 °C) with a spicy-herbal, slightly medicinal odor reminiscent of thyme. Thymol is prepared on a technical scale in a continuous high-temperature, high-pressure, liquid-phase, ort/io-alkylation process, from m-cresol and propylene, in the presence of activated aluminum oxide hydrate [163a],... 

The characteristic odour of the oil is due to the presence of thymol. In addition, cymene, a-pinene, dipentene, and -y-terpinene are present. The oil itself is used to a certain extent in India for medicinal purposes, but its principal use is for the preparation of thymol. According to Stohmann, carvacrol is also present, but this statement requires con> firmation. 

Thymol (169) is found in a number of species, mostly from the Thymus, Ocimum, and Monarda families. It takes its name from thyme (T. vulgaris) of which it is an organoleptically important component. The levels present vary widely not only from species to species, but also from plant to plant within a species. As it is a phenol, it can be extracted from herb oils using aqueous sodium hydroxide and subsequent acidification. Such techniques were used to produce thymol in the past, particularly from thyme, oregano, and basil. Material isolated in this way tended to contain some carvacrol (213). This is a disadvantage as the medicinal, phenolic, and tarry odor of carvacrol spoils the sweeter, herbal, and medicinal odor of thymol. Since thymol is easily prepared, as described above under menthol, the modem supply is entirely synthetic, mostly from Symrise. The major use for thymol is as an intermediate for menthol production. 

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