Influence of the chain length on the aroma properties of homologous epoxy-aldehydes, ketones, and alcohols

Homologous series of epoxyalkanals, epoxyalkenals, alka-1,5-dien-3-ones, alka-1,5-dien-3-ols, alk-1-en-3-ones and alk-1-en-3-ols were synthesized and their aroma properties (odor quality; odor threshold) were determined by means of GC/Olfactometry. The results showed odor thresholds in the same order of magnitude (2.6-15.4 ng/L in air) for the 2,3-epoxyalkanals from C-5 to C-12. Contrary, in the series of 4,5-epoxy-(E)-2-alkenals a clear minimum was found for the C-10 homologue (0.001 ng/L in air). 1-Nonen-3-one, exhibiting a mushroom-like aroma, was found to be the most potent among the series of 1-alken-3-ones (C-5 to C-13), whereas the geranium-like smelling 1,(Z)-5-heptadien-3-one showed the lowest threshold (0.0006 ng/L) among the 1,(Z)-5-alkadien-3-ones. Reduction of the ketones into the respective alcohols increased the odor thresholds significantly.