INTRODUCTION
At the moment there is a shortage of Asian peppermint oils and of natural menthol. The prices of Mentha arvensis oil and of the important natural flavour material L-menthol have more than doubled during the last two years. BACIS questioned: what is the situation now ? What can be said about the near future ? And if there continues to be shortage, are there any alternatives ?
DISCUSSION
Peppermint oils
There are two important peppermint oils, namely derived from the plants Mentha arvensis and Mentha piperita. The world production of Mentha arvensis oil is about 7,000 tons, of which 3,000 tons are produced in China, 3,000 tons in India and circa 1,000 in the rest of the world (mainly in South America). About 4,000 tons of Mentha piperita oil is produced, mainly in the United States.
Mentha arvensis oil is the main source for natural L-menthol, whereas Mentha piperita oil is used as such in the food-, oral care- and tobacco-industry. The open world marketprice for Asian Mentha arvensis oil increased in two years time from about US$ 5.-- per kilogram to about $ 12.-- whereas the price of American Mentha piperita oil decreased. The price for Asian natural L-menthol, however, increased in the same time from about $ 14.--/Kg. to around $ 40.--/Kg.
The main reason for this lies in the production and consumption of Mentha arvensis oil in China. Although there are continuous reports from China about increasing cultivation of Mentha arvensis (and as a consequence the production of the oil), the prognosis of a growing consumption within China may be more important.
Price development during the last two years (in US Dollars per kilogram):
|
PRODUCT: |
1994 |
1995 |
1996 |
|
Mentha arvensis oil (Asia) |
5.-- |
8.50 |
12.-- |
|
Mentha piperita oil (USA) |
60.-- |
57.-- |
54.-- |
|
Menthol cryst. (China) |
14.50 |
20.-- |
42.-- |
|
Menthol cryst. (India) |
13.50 |
21.-- |
39.-- |
PRODUCTION OF L-MENTHOL
Isolation from Mentha arvensis oil:
L-Menthol is manufactured from Mentha arvensis oil by slow
crystallisation as described by us in detail (Perf. Flav., Vol. 18,
27-32, Sept/Oct 1993).
Totally synthetic menthol:
Synthetic L-menthol is produced on technical scale in Europe and the
USA from m-cresol by alkylation with propene to thymol and
hydrogenation to DL-menthol. The optical isomers are separated and
the D-isomer is recycled.
Conversion of citronellal ex citronella oil:
Java citronella oil contains 30-40% of D-citronellal, which can be
isolated from the oil. D-citronellal can be converted over an acidic
(active clay) catalyst into L-isopulegol, which then can be
hydrogenated to L-menthol. A disadvantage of this method is that with
every kilogram L-menthol one obtains about 2,5 Kg. citronellol and
geraniol.
Conversion of pulegone ex pennyroyal oil:
Pennyroyal oil contains 80-90% L-pulegone, which can be easily
hydrogenated to L-menthone. L-menthone can be reduced with sodium in
ethanol to L-menthol.
Reprinted by Leffingwell & Associates, 2006, with Permission