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 -methylstyrene (2) by dimethyldioxirane (DDO, 1a) generate “in situ” and of laurolactam (3) by isolated methyl(trifluorometyl)dioxirane (TFDO, 1b) 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 1a) 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 (3) to 12-nitro-lauric acid (3a) by TFDO (1b). This opens the way to an easy and green procedure (performed in water under mild conditions) to synthetize omega-nitroacids.

Oxidation-proof microemulsions: microstructure and reactivity in the presence of dioxiranes

D'ACCOLTI, Lucia;COLAFEMMINA, Giuseppe;PALAZZO, Gerardo
2013-01-01

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 -methylstyrene (2) by dimethyldioxirane (DDO, 1a) generate “in situ” and of laurolactam (3) by isolated methyl(trifluorometyl)dioxirane (TFDO, 1b) 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 1a) 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 (3) to 12-nitro-lauric acid (3a) by TFDO (1b). This opens the way to an easy and green procedure (performed in water under mild conditions) to synthetize omega-nitroacids.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11586/132269
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