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I'm not an expert teacher or lecturer of chemistry. I was only a student from SMA NEGERI 15 SURABAYA who had been one of the Bronze Medalist Participants of Olimpiade Sains Nasional X (2011) of Chemistry In Manado, North Sulawesi, 11 - 16 September 2011 and graduated in 2012. Now, I'm studying at Universitas Airlangga in Surabaya, Indonesia. I do love chemistry and I would like to help them who had difficulties in studying chemistry. That's why, please understand me if you found some misconcepts in my entries. Suggestions are always necessary in order to develop this blog. And I'm sorry because my English isn't so well.

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Sunday, January 01, 2012

Menthol

(Source: http://upload.wikimedia.org/wikipedia/commons/2/29/Menthol.jpg)

Menthol is an organic compound made synthetically or obtained from peppermint or other mint oils. It is a waxy, crystalline substance, clear or white in color, which is solid at room temperature and melts slightly above. The main form of menthol occurring in nature is (−)-menthol, which is assigned the (1R,2S,5R) configuration. Menthol has local anesthetic and counterirritant qualities, and it is widely used to relieve minor throat irritation.

Menthol has 3 steric carbons. That mean Menthol has 23 stereoisomer. The picutre below shows 8 isomers of Menthol.



Menthol's ability to chemically trigger the cold-sensitive TRPM8 receptors in the skin is responsible for the well-known cooling sensation it provokes when inhaled, eaten, or applied to the skin. In this sense, it is similar to capsaicin, the chemical responsible for the spiciness of hot peppers (which stimulates heat sensors, also without causing an actual change in temperature). Menthol's analgesic properties are mediated through a selective activation of κ-opioid receptors. Menthol also blocks voltage-sensitive sodium channels, reducing neural activity that may stimulate muscles. Menthol also enhances the efficacy of ibuprofen in topical applications via vasodilation, which reduces skin barrier function.

As with many widely used natural products, the demand for menthol greatly exceeds the supply from natural sources. Menthol is manufactured as a single enantiomer (94% ee) on the scale of 3,000 tons per year by Takasago International Corporation. The process involves an asymmetric synthesis developed by a team led by Ryōji Noyori:



The process begins by forming an allylic amine from myrcene, which undergoes asymmetric isomerisation in the presence of a BINAP rhodium complex to give (after hydrolysis) enantiomerically pure R-citronellal. This is cyclised by a carbonyl-ene-reaction initiated by zinc bromide to isopulegol which is then hydrogenated to give pure (1R,2S,5R)-menthol.

Source and Further Reading. . .
Wikipedia


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