The thermal decomposition of (—)∼menthyl esters

It has been reported in the literature by various investigators that the pyrolysis of (—)‐menthyl acetate (in the gas phase) results in the formation of (+)‐ p ‐menthene‐3 only. We investigated the thermal decomposition of (—)‐menthyl acetate in the gas phase and of (—)‐menthyl stearate in the liquid state. It was found that the two methods give about the same yield of terpene. This terpene is a mixture essentially consisting of (+)‐trans‐ p ‐menthene‐2 (33—36%) and of (+)‐ p ‐menthene‐3 (67—64%) The infrared spectra of these mixtures agree with the spectrum given in the literature for “(+)‐ p ‐menthene‐3”. A statement in the literature with regard to characteristic infrared absorption of unsaturated hydrocarbons seems to have no application to this case