Synthesis and thermal release of menthyl carbonates as flavor precursors derived from hydroxy acids

Menthyl carbonates based on malic acid and tartaric acid were designed and synthesized to reduce menthol volatilization at room temperature while enabling controlled release through thermo pyrolysis. The synthesis involves two key steps: reaction of dimethyl malate or dibenzyl tartrate with menthyl chloroformate, followed by enzymatic hydrolysis or hydrogenolysis to deprotect the carboxyl moieties, yielding the target menthyl carbonates. Thermogravimetry analysis (TG-DTG) demonstrated that menthyl carbonate exhibits significant weight loss starting at around 150 °C within a narrow temperature range. Online pyrolysis gas chromatography mass spectroscopy (Py-GC-MS) confirmed efficient menthol release at 150–300 °C, with menthol as the dominant product. The proposed pyrolysis mechanism involves preferential elimination of the hydroxy acid moiety, triggering rapid monocarbonate decomposition into menthol due to its inherent instability. Compared to free menthol, these carbonates demonstrated superior storage stability for heat-not-burn (HNB) products applications while maintaining controlled menthol release at typical HNB operating temperatures. Parallel studies with phenylethanol, benzyl alcohol, and leaf alcohol carbonates revealed similar thermal behavior, with corresponding flavor compounds as primary pyrolysis products. This collective evidence suggests that hydroxy acid based carbonates constitute promising precursor structures for fragrance delivery systems.