Structure-Odor Correlations in Homologous Series of Mercaptoalkanols

To study the influence of molecular structure on the sensory properties of mercaptoalkanols, homologous series of 1-mercaptoalkan-3-ols, 3-mercaptoalkan-1-ols, 2-mercaptoalkan-1-ols, 4-mercaptoalkan-2-ols, 3-mercapto-3-methylalkan-1-ols, 1-mercapto-2-methylalkan-3-ols, 3-mercapto-2-methylalkan-1-ols, and 2-ethyl-3-mercaptoalkan-1-ols were synthesized. Odor thresholds in air and odor qualities were determined, and the results obtained were correlated to the chemical structures. Sensory properties were strongly influenced by steric effects: All homologous series revealed a minimum in odor thresholds between five and seven carbon atoms, and increasing the length of the carbon chain led to an exponential increase in odor thresholds. The olfactory power of the thiols was considerably improved by methyl or ethyl substitution in the α-position to the thiol group as well as by an additional methyl or ethyl group at the mercapto-containing carbon atom. By using comparative molecular similarity indices analysis, a 3D-quantitative structure-activity relationship model could be created, which was able to predict the odor thresholds of mercaptoalkanols in good agreement with the experimental results. Retention indices, NMR data, and mass spectra for 49 mercaptoalkanols, most of them synthetically prepared for the first time, are supplied.