Influence of the chemical structure on the odor characters of beta-citronellol and its oxygenated derivatives

beta-Citronellol, 1, and citronellyl acetate, 2, are renowned fragrant constituents in perfumes and flavoring agents in foods and beverages. Both substances smell citrussy, fresh and floral. To elucidate the structural features required for these sensory effects, six C-8 oxygenated derivatives of 1 and 2 were synthesized and analytically characterized. All compounds were tested for their odor qualities and odor thresholds in air, revealing that there were no significant differences in odor impressions from the parent monoterpenes and their derivatives in most cases; however, substantial differences in their odor threshold values were observed, with beta-citronellol as the most potent (10 ng/L-air) and 8-hydroxycitronellyl acetate as the least potent odorant (1261 ng/L-air). 8-Oxocitronellyl acetate was the only compound that was described with divergent odor attributes, namely musty, rotten and coconut-like. 8-Carboxycitronellol and 8-carboxycitronellyl acetate were found to be odorless.