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- Aldol Reaction (1)
- Asymmetric Catalysis (1)
- Basic Ion Exchange Resin (1)
- Chemical Sciences (1)
- Diacetone Alcohol (1)
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- Menthol (1)
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Abstract
(−)‐Menthol is one of the most popular aroma compounds worldwide. While in the past mostly extracted from mint plants, today (−)‐menthol synthesis from other raw materials is becoming more relevant. Common starting materials for menthol synthesis are m‐cresol, citral and myrcene, but also substrates like menthone, mono‐ and bicyclic terpenes and terpenoids have been used for this purpose in the past. As for many applications (−)‐menthol of high purity is required, asymmetric syntheses and enantiomeric resolution of obtained raw products are applied for menthol production. This review gives an overview on the most important synthetic menthol production processes of the companies Symrise, Takasago and BASF and relevant literature in the field of menthol synthesis with a focus on the last 20 years.
The aldol reaction of bio acetone in presence of a strongly basic ion exchange resin was carried out with and without the addition of water in a temperature range between − 30 °C and 45 °C. The conversion, selectivity and service time of the ion exchange resins were investigated in a stirred batch reactor and a continuous fixed bed reactor. For the batch experiments, both conversion and selectivity increased with decreasing temperature. Furthermore, the addition of water to the reaction medium has a positive effect on selectivity and catalyst service time of the resins. For the continuous flow experiments carried out in a fixed bed reactor, the selectivity towards diacetone alcohol is higher than in a batch reactor. This high selectivity is favored by a short contact time which inhibits as expected most of the consecutive reactions.