Controlled Release of Volatile Enones from Monomeric and Dimeric Thioether, Sulfoxide and Sulfone Profragrances

Thioether (sulfide) profragrances are readily prepared by 1,4-addition of alkanethiols to enones (thia-Michael reaction). Under ambient conditions, they slowly release the parent enones, thus generating a long-lasting perfumery effect. The fragrance release of profragrances obtained by 1,4-addition of S, O and N nucleophiles to enones was compared on cotton and on a hard surface for monomeric and dimeric structures. To avoid the uncontrolled generation of volatile sulfur compounds from thioethers, we investigated the extent to which different side reactions occurred next to the expected formation of enones and alkanethiols. Headspace analyses on cotton showed that enones and aldehydes were the major reaction products, whereas none or only traces of β-mercaptoketones, diketones or alkanethiols were detected. The absence of alkanethiols indicated that 1,4-elimination of thioethers was not a major pathway for fragrance release. Extraction of the cotton sheets after analysis showed that thioethers were oxidised to sulfoxides, which then can generate enones by 1,4-elimination. Thioethers, sulfoxides and sulfones were shown to efficiently release enones in practical applications.