Synthesis of (−)‐menthol: Industrial synthesis routes and recent development

Abstract

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.

Facile immobilization of PNNNP-Pd pincer complexes in MFU-4l-OH and the effects of guest loading on Lewis acid catalytic activity

“…39 Citronellal cyclization reactions typically produce a mixture of diastereomeric products among which isopulegol is the major component and most desirable product as a precursor to menthol. 40 All of the PdBF 4 -x catalysts yield a consistent isopulegol selectivity of 65%, which is comparable to most reported Lewis acid catalysts and indicates that the MOF microenvironment does not prove any beneficial influence on product selectivity. 41,42 Substrate conversion was also monitored as function of time to gain further insight into the differences in catalytic activity among the PdBF 4 -x series (Fig.…”

Catalytic asymmetric synthesis of cannabinoids and menthol from neral

“…Indeed, exhaustive hydrogenation of (1 R ,6 S )- trans -isopiperitenol ( 2 ) using 10 mol% of Lindlar’s catalyst provides 88% yield of a mixture of enantioenriched menthol isomers, in which (–)-menthol ( 7 ) (68%) and (–)-isomenthol ( 8 ) (26%) are the main products. Although separation of the isomeric menthol mixtures on a laboratory scale is tedious, purification on an industrial scale routinely involves distillation and subsequent crystallization 26 , 27 . It should be noted that despite the long history of technical menthol syntheses, which has provided several highly efficient routes to the stereochemically pure product 26 , our two-step synthesis starting from easily accessible neral ( 1 ) is perfectly atom-economic and presents the shortest route reported so far.…”

Transcriptome analysis of transcription factors and enzymes involved in monoterpenoid biosynthesis in different chemotypes of Mentha haplocalyx Briq

“…Global menthol production is approximately 34,000 metric tons per year, with the share of synthetic menthol being approximately 60% of this. However, natural menthol is generally preferred because the scent of synthetic l -menthol is influenced by contaminants that arise during the crystallization process ( Dylong et al, 2022 ; Lange et al, 2011 ). In addition, improving the composition of the oil has focused on reducing the accumulation of (+)-menthofuran and its intermediate product (+)-pulegone (the main component of pulegone chemotype mint) ( Grulova et al, 2015 ).…”