title: Oxidation-proof microemulsions: Microstructure and reactivity in the presence of dioxiranes.
abstract: Dioxiranes are used as reagents in a myriad of synthetically useful oxidations performed in aqueous medium. To extend such an approach also to substrates that are highly hydrophobic, we propose here the use of microemulsions based on the surfactant hexadecyltrimethylammonium hydrogen sulphate (CTAHS) because of its high stability against peroxide species. In this paper, we examine the dioxirane (isolated or generated in situ) reactivity in different CTAHS microemulsions. Yield and selectivity of the oxidation of β-methylstyrene by dimethyldioxirane (DDO) generate "in situ" and of laurolactam by isolated methyl(trifluorometyl)dioxirane (TFDO) were studied. For each microemulsion, the aggregate size and the localization of the components were determined by a combination of NMR and light scattering techniques. The hydrodynamic radius of the micelles is close to the length of the surfactant and this suggests they are spherical in shape. When acetone (the precursor of DDO) is present in the formulation, it partitions itself between the aqueous bulk and the micellar palisade so that the dioxirane eventually formed is readily available to oxidize substrates secluded in the micelle. Apolar substrates, confined within the micelles, are protected from uncontrolled oxidations, leading to an astonishing high selectivity of oxidation of laurolactam to 12-nitro-lauric acid by TFDO. This opens the way to an easy procedure (performed in water under mild conditions) to synthetize ω-nitroacids.
authors: Department of Chemistry, University of Bari Aldo Moro, via Orabona 4, 70126 Bari, Italy.
authors: Cosimo
authors: C
authors: Annese
authors: Lucia
authors: L
authors: D'Accolti
authors: Caterina
authors: C
authors: Fusco
authors: Giuseppe
authors: G
authors: Mele
authors: Gianfranco
authors: G
authors: Giorgio
authors: Giuseppe
authors: G
authors: Colafemmina
authors: Sergio
authors: S
authors: Murgia
authors: Gerardo
authors: G
authors: Palazzo
keywords: Cetyltrimethylammonium hydrogen sulphate; DLS; Dioxiranes; Micelles; Oxidation; PFGSE-NMR