50727-95-2Relevant articles and documents
Olefin epoxidation with hydrogen peroxide catalyzed by lacunary polyoxometalate [γ-SiW10O34(H2O) 2]4-
Kamata, Keigo,Kotani, Miyuki,Yamaguchi, Kazuya,Hikichi, Shiro,Mizuno, Noritaka
, p. 639 - 648 (2007/10/03)
The tetra-n-butylammonium (TBA) salt of the divacant Keggin-type polyoxometalate [TBA]4[γ-SiW10O34-(H 2O)2] (I) catalyzes the oxygen-transfer reactions of olefins, allylic alcohols, and sulfides with 30% aqueous hydrogen peroxide. The negative Hammett ρ+ (-0.99) for the competitive oxidation of p-substituted styrenes and the low value of (nucleophilic oxidation)/(total oxidation), Xso = 0.04, for I-catalyzed oxidation of thianthrene 5-oxide (SSO) reveals that a strongly electrophilic oxidant species is formed on I. The preferential formation of trans-spoxide during epoxidation of 3-methyl-1-cyclohexene demonstrates the steric constraints of the active site of I. The I-catalyzed epoxidation proceeds with an induction period that disappears upon treatment of I with hydrogen peroxide. 29Si and 183W NMR spectroscopy and CSI mass spectrometry show that reaction of I with excess hydrogen peroxide leads to fast formation of a diperoxo species, [TBA]4[γ-SiW10O32(O2) 2] (II), with retention of a γ-Keggin type structure. Whereas the isolated compound II is inactive for stoichiometric epoxidation of cyclooctene, epoxidation with II does proceed in the presence of hydrogen peroxide. The reaction of II with hydrogen peroxide would form a reactive species (III), and this step corresponds to the induction period observed in the catalytic epoxidation. The steric and electronic characters of III are the same as those for the catalytic epoxidation by I. Kinetic, spectroscopic, and mechanistic investigations show that the present epoxidation proceeds via III.
Epoxidation of alkenes with H2O2 generated in situ from alcohols and molecular oxygen using N-hydroxyphthalimide and hexafluoroacetone as catalysts
Iwahama, Takahiro,Sakaguchi, Satoshi,Ishii, Yasutaka
, p. 693 - 705 (2007/10/03)
A new epoxidation method of olefins with hydrogen peroxide and/or α- hydroxy hydroperoxide which are generated in situ from an alcohol and molecular oxygen was developed. A variety of alkenes were smoothly epoxidized with molecular oxygen in the presence of an alcohol under the influence of hexafluoroacetone (HFA) and N-hydroxyphthalimide (NHPI) as catalysts. The reaction involves the formation of α-hydroxy hydroperoxide and/or hydrogen peroxide derived from 1-phenylethanol and dioxygen by the action of NHPI and the active oxygen transfer from these hydroperoxides to HFA, giving 2- hydroperoxyhexafluoro-2-propanol which serves as the actual epoxidizing agent.
Regio-, diastereo-, and chemoselectivities in the dioxirane oxidation of acyclic and cyclic allylic alcohols by methyl(trifluoromethyl)dioxirane (TFD): A comparison with dimethyldioxirane
Adam, Waldemar,Paredes, Rodrigo,Smerz, Alexander K.,Veloza, L. Angela
, p. 349 - 354 (2007/10/03)
The solvent-dependent shift in the regioselectivity of the geraniol epoxidation by methyl(trifluoromethyl)dioxirane (TFD) reveals that as for the less reactive dimethyldioxirane (DMD). hydrogen bonding stabilizes the transition state of the epoxidation. In protic media, the hydrogen bonding is exerted intermolecularly by the solvent, whereas in unpolar, non-hydrogen-bonding solvents intramolecular assistance through the adjacent hydroxy functionality comes into the play and the attack on the allylic alcohol moiety is favored. For chiral allylic alcohols, additional steric interactions control the π-facial selectivity in the conformationally fixed transition state. Analogous to DMD, the preferred dihedral angle in the hydrogen-bonded transition state of the TFD epoxidation constitutes approximately 130°, but contrary to DMD and for synthetic purposes important, the allylic alcohols and derivatives 1 and 3-5 investigated here are chemoselectively epoxidized by TFD without formation of the corresponding enones.
