585-08-0Relevant articles and documents
The catalytic function of a silica gel-immobilized Mn(II)-hydrazide complex for alkene epoxidation with H2O2
Ghorbanloo, Massomeh,Monfared, Hassan Hosseini,Janiak, Christoph
experimental part, p. 12 - 20 (2011/10/05)
An efficient and highly selective heterogeneous catalyst was developed by immobilization of a manganese complex on an inorganic support to yield (silica gel)-O2(EtO)Si-L1-Mn(HL2) [(L1) - modified salicylaldiminato and H2L2(E)- N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide]. Mn(II) has been anchored on the surface of functionalized silica by means of N,O-coordination to the covalently Si-O bound modified salicylaldiminato Schiff base ligand. The prepared material (silica gel)-O2(EtO)Si-L1-Mn(HL 2), was characterized by elemental and thermogravimetric analyses (TGA and DTA), UV-vis and FT-IR spectroscopy. This new material is demonstrated to be a very active catalyst in clean epoxidation reactions using a combined oxidant of aqueous hydrogen peroxide and actonitrile in the presence of aqueous sodium hydrogencarbonate. The effects of reaction parameters such as solvent, NaHCO3 and oxidant in the epoxidation of cis-cyclooctene were investigated. Cycloalkenes were oxidized efficiently to their corresponding epoxide with 87-100% selectivity in the presence of this catalyst. This catalytic system showed also good activities in the epoxidation of linear alkenes. The obtained results show that this catalyst is a robust and stable heterogeneous catalyst which can be recovered quantitatively by simple filtration and reused multiple times without loss of its activity.
Stabilities and partitioning of arenonium ions in aqueous media
Lawlor, D. A.,O'Ferrall, R. A. More,Rao, S. N.
experimental part, p. 17997 - 18007 (2009/06/25)
The phenathrenonium ion is formed as a reactive intermediate in the solvolysis of 9-dichloro-acetoxy-9,10-dihydrophenanthrene in aqueous acetonitrile and undergoes competing reactions with water acting as a base and nucleophile. Measurements of product ratios in the presence of azide ion as a trap and 'clock' yield rate constants kp ) 3.7 × 10 10 and kH2O ) 1.5 × 108 s-1, respectively. Combining these with rate constants for the reverse reactions (protonation of phenanthrene and acid-catalyzed aromatization of its water adduct) gives equilibrium constants pKa ) -20.9 and pKR ) -11.6. For a series of arenonium and benzylic cations, correlation of log kp with pK a, taking account of the limit to kp set by the relaxation of water (1011 s-1), leads to extrapolation of k p ) 9.0 × 1010 s-1 and pKa ) -24.5 for the benzenonium ion and kp ) 6.5 × 1010 s-1 and pKa ) -22.5 for the 1-naphthalenonium ion. Combining these pKa's with estimates of equilibrium constants pK H2O for the hydration of benzene and naphthalene, and the relationship pKR ) pKa + pKH2O based on Hess's law, gives pKR ) -2.3 and -8.0 respectively, and highlights the inherent stability of the benzenonium ion. A correlation exists between the partitioning ratio, kp/kH2O, for carbocations reacting in water and KH2O the equilibrium constant between the respective reaction products, i.e., log(kp/kH2O) ) 0.46pK H2O - 3.7. It implies that kp exceeds kH2O only when KH2O > 108. This is consistent with the proton transfer (a) possessing a lower intrinsic reactivity than reaction of the carbocation with water as a nucleophile and (b) being rate-determining in the hydration of alkenes (and dehydration of alcohols) except when the double bond of the alkene is unusually stabilized, as in the case of aromatic molecules.
Efficient electrophilic and nucleophilic epoxidations utilizing a sulfonylperoxy radical and peroxysulfate species
Park, Min Young,Yang, Seung Gak,Kim, Yong Hae
, p. 431 - 436 (2007/10/03)
Reaction of superoxide anion radical (O2-. with o-nitrobenzenesulfonyl chloride yields a o-nitrobenzenesulfonyl peroxy radical with strong oxidizing ability, which is capable of oxidizing aryl methylene moieties to aryl ketones and relatively electron-rich alkenes regioselectively to epoxides. The oxidizing species is tentatively attributed to the o-nitrobenzenesulfonyl peroxy radical of structure 1. Tetrabutylammonium peroxydisulfate (TBA)2S2O8, 2) was prepared by the reaction of tetrabutylammonium hydrogen sulfate with potassium peroxydisulfate. The epoxidation of enals and enones, such as α,β-unsaturated aldehydes or ketones, was efficiently achieved with 2 in the presence of hydrogen peroxide and base in acetonitrile or in methanol at 25°C. A base-sensitive substrate, such as cinnamaldehyde, could be successfully epoxidized under mild reaction conditions and in short reaction time.
