New method for menthol synthesis

We know it from toothpaste, it is found in medicines for colds and we can taste it in our chewing gum: menthol is a component of various mint spices, which humans have recognised as helpful and made use of for many years. However, because the demand for menthol is so great worldwide and because industrial extraction from the mint plant itself is very costly, menthol is also produced synthetically. Thousands of tonnes are produced in chemical plants every year.

A team led by Mülheim researcher Benjamin List has now succeeded in simplifying the synthetic production of menthol, making it more cost-effective and sustainable. The same method can also be used to produce cannabinoids, which are also sought-after active ingredients due to their medical applications. The Mülheim scientists have now published their results in the journal Nature.

Special catalyst enables „desired reaction“

In chemistry, there has long been a kind of „desired reaction“, which would mean a significant reduction in the synthesis of menthol or cannabinoids because some synthesis steps could be saved. Specifically, it involves the direct, selective conversion of neral into a specific molecule called isopiperitenol. „For a long time, however, this particular reaction was considered impossible because the product reacted even more to the catalyst than the starting materials“, explains Joyce Grimm. She is a doctoral student at Benjamin List and is mainly responsible for the project. More than 100 years ago, the chemists Albert Verley and Friedrich Wilhelm Semmler tried their hand at it - to no avail. However, Ben List, Joyce Grimm and their colleagues have now succeeded.

The special thing: For their method, the Mülheim researchers use a special „umzäunte“ acid as a catalyser, i.e. as a „molecular tool“. This asymmetric, strong acid catalyses the desired product with high efficiency and selectivity. This is achieved by the catalyst binding the product in a „trägen“ form so that no further, unwanted side reactions can take place.

Using the same method, the researchers have also succeeded in demonstrating how isopiperitenol can be converted into cannabinoids or menthol in the shortest and most efficient way currently available. This in turn is of great interest to the chemical industry because processes can be shortened and chemical waste avoided.

Article from the "Max-Planck-Institut für Kohlenforschung" from 7 March 2023