Carvone is a cyclic monoterpene ketone that exists in two enantiomeric forms; R- and S-carvone. It looks like a colourless to pale yellowish oily liquid at room temperature. Due to its pleasant smell and aroma, it is used as a fragrance in cosmetic products, aromatherapy and the food industry. It also has many proven pharmacological effects, including antimicrobial, anti-inflammatory and antioxidant, which is why it also plays an important role in the pharmaceutical and agricultural industries. S-carvone is the main component of the essential oils of caraway (Carum carvi) and dill (Anethum graveolens) and has a characteristic caraway smell, while R-carvone is found mainly in the essential oil of spearmint (Mentha spicata) and gives the plant its characteristic sweet-menthol smell. They can be obtained by extraction from plant materials or by chemical synthesis from limonene.
The aim of the thesis was the synthesis and olfactory evaluation of esters, ethers and acetals obtained from R- and S-carvone. We strived to obtain as many volatile low-molecular lipophilic derivates with a pleasant smell as possible, which could be used as fragrances in cosmetic products. The esterification and etherification reactions occurred on the free hydroxyl group of the compounds, which were prepared by the stereoselective reduction of R- and S-carvone. The acetal was prepared on the carbonyl group of R-carvone. We managed to synthesize six esters, two ethers and one acetal. The progress and success of the reactions were monitored by thin-layer chromatography, and the crude products were purified by column adsorption chromatography. The final products were analysed using two spectroscopic methods, nuclear magnetic resonance and infrared spectroscopy, which confirmed the identity of the compounds.
The final products were evaluated with an olfactory test, where volunteers rated the pleasantness and strength of the smells and indicated what the smell reminded them of. Most of the samples were attributed with a pleasant smell and a medium to strong strength. Stereoselectively reduced R-carvone was chosen as the sample with the most pleasant smell, which most people associated with the smell of toothpaste, fresh herbs and refreshing mints. We observed that volatile derivatives of R-carvone possess a more pleasant aroma than their S-carvone counterparts, despite also being stronger in scent.
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