- Highly Selective Direct Oxidation of Thioethers to Sulfoxides Using Molecular Oxygen
-
Dialkyl sulfides are converted to sulfoxides in high yield by use of molecular oxygen, ca. 40-atm pressure, and polar solvents.
- Correa, Paul E.,Riley, Dennis P.
-
-
Read Online
- Mechanistic Studies of the Selective Oxygen Oxidation of Sulfides to Sulfoxides Catalyzed by Dihaloruthenium(II) Complexes
-
The selective and facile molecular oxygen oxidation of dialkyl sulfides to their sulfoxides can be effectively catalyzed by neutral ruthenium(II) complexes of the type cis- or trans-RuX2(Me2SO)4.The results of kinetic studies for two of these catalysts, cis-RuCl2(Me2SO)4 and trans-RuBr2(Me2SO)4, show that these catalytic oxidations are first order with respect to total catalyst concentration, less than first order in oxygen concentration, zero order in the sulfide substrate, and approximately first order in alcohol.These and other observations plus 18O-labeling studies support a mechanism involving oxidation of a "Ru(II)" species to give an oxidized metal species, probably "Ru(IV)" and peroxide.The active sulfide oxidant is peroxide, whose concentration is approximated by the steady-state assumption.The reductant of the oxidized metal is the solvent alcohol, thus completing the catalytic cycle.
- Riley, Dennis P.,Shumate, Robert E.
-
-
Read Online
- The Novel Cerium(IV)-catalysed Molecular Oxygen Oxidation of Thioethers to Sulphoxides
-
Thioethers can be oxidized with catalytic amounts of Ce(IV) salts rapidly and selectively to sulphoxides using molecular oxygen (PO2 = 5-15 bar) as the oxidant.
- Riley, Dennis P.,Correa, Paul E.
-
-
Read Online
- SELECTIVE MOLECULAR OXYGEN OXIDATION OF THIOETHERS TO SULFOXIDES CATALYZED BY Ce(IV).
-
The selective molecular oxygen conversion of thioethers to sulfoxides is catalyzed by ceric ammonium nitrate (CAN) with rate enhancements that are at least three orders of magnitude greater than the uncatalyzed autoxidation of thioethers. Mechanistic studies (including spectroscopic, labeling, uptake, mixed reactant, and autocatalysis studies) of this novel reaction reveal that both atoms of dioxygen are incorporated into product sulfoxide, that a novel oxygen-driven Ce(IV)/Ce(III) redox cycle gives rise to the catalysis, and that molecular oxygen efficiently traps a sulfur-centered radial cation of the thioether (produced by Ce(IV) oxidation of thioether) to yield the oxygenated radical cation R//2S** plus OO multiplied by (times) , which, it is proposed, reoxidizes Ce(III) to Ce(IV).
- Riley,Smith,Correa
-
-
Read Online
- Metal- and additive-free oxygen-atom transfer reaction: an efficient and chemoselective oxidation of sulfides to sulfoxides with cyclic diacyl peroxides
-
Metal- and additive-free oxidation of a series of sulfides/thioketones has been achieved using cyclic diacyl peroxides as mild oxygen sources. This protocol features simple manipulation, high chemo- and diastereoselectivity, and a broad substrate scope (up to 42 examples), tolerates many common functional groups, and is scalable and applicable to the late-stage sulfoxidation strategy. A preliminary mechanistic study by quantum mechanical calculations suggests that a single two-electron transfer process is energetically more favorable, and indicates the reactivity of cyclic diacyl peroxides distinct from conventional acyclic acyl peroxides.
- Gan, Shaoyan,Yin, Junjie,Yao, Yuan,Liu, Yang,Chang, Denghu,Zhu, Dan,Shi, Lei
-
supporting information
p. 2647 - 2654
(2017/04/03)
-
- Efficient and selective oxidation of sulfides in batch and continuous flow using styrene-based polymer immobilised ionic liquid phase supported peroxotungstates
-
Styrene-based peroxotungstate-modified polymer immobilized ionic liquid phase catalysts [PO4{WO(O2)2}4]@ImPIILP (Im = imidazolium) are remarkably efficient systems for the selective oxidation of sulfides under mild conditions both in batch and as a segmented or continuous flow process using ethanol as the solvent and mobile phase, respectively. The performance of these styrene-based systems has been compared against their ring opening metathesis polymerisation derived counterparts to assess their relative merits. A comparative survey revealed the catalyst supported on N-benzyl imidazolium decorated polymer immobilised ionic liquid to be the most efficient and a cartridge packed with a mixture of [PO4{WO(O2)2}4]@ImPIILP and silica operated as a segmented or continuous flow system giving good conversions and high selectivity for sulfoxide. The immobilised catalyst remained highly active for the sulfoxidation of thioanisole in ethanol with a stable conversion-selectivity profile for up to 8 h under continuous flow operation; for comparison conversions with a mixture of [NBu4]3[PO4{WO(O2)2}4] and silica dropped dramatically after only 15 min as a result of rapid leaching while [PO4{WO(O2)2}4]@ImPIILP prepared from commercially available Merrifield resin also gave consistently lower conversions; these benchmark comparisons serve to underpin the potential benefits of preparing the polymer immobilized ionic liquid supports.
- Doherty,Knight,Carroll,Clemmet,Ellison,Backhouse,Holmes,Thompson,Bourne
-
p. 73118 - 73131
(2016/08/18)
-
- Selective Synthesis of Sulfoxides through Oxidation of Sulfides with Sodium Hypochlorite Pentahydrate Crystals
-
Oxidation of sulfides with sodium hypochlorite pentahydrate crystals (1.1 equiv) in an aqueous acetonitrile solution selectively produces the corresponding sulfoxides in high yields. This procedure is catalyst-free and environmentally benign.
- Okada, Tomohide,Matsumuro, Hiroaki,Kitagawa, Saori,Iwai, Toshiaki,Yamazaki, Kento,Kinoshita, Yukari,Kimura, Yoshikazu,Kirihara, Masayuki
-
p. 2547 - 2552
(2015/11/16)
-
- Flavin-cyclodextrin conjugates: Effect of the structure on the catalytic activity in enantioselective sulfoxidations
-
A series of flavin-cyclodextrin conjugates has been prepared and tested in the enantioselective oxidations of prochiral aromatic and aliphatic sulfides with hydrogen peroxide. The newly prepared conjugates contain isoalloxazinium or alloxazinium moieties attached to the primary rim of α- and β-cyclodextrins at the C-6 positions. In addition, flavinium units were attached to the secondary rim of the β-cyclodextrin macrocycle. The relationship between the structural features and the catalytic performance of the conjugates, including those recently reported by us, was analyzed. The rate and enantioselectivity of the sulfoxidations catalyzed by flavin-cyclodextrin conjugates are influenced mainly by the size of the cyclodextrin cavity, the type of flavin unit (alloxazine or isoalloxazine), and by the relative orientation of the flavin and cyclodextrin moieties.
- Hartman, Tomas,Herzig, Vladimir,Budesinsky, Milos,Jindrich, Jindrich,Cibulka, Radek,Kraus, Tomas
-
p. 1571 - 1583
(2013/02/23)
-
- Alloxazine-cyclodextrin conjugates for organocatalytic enantioselective sulfoxidations
-
Four structurally different alloxazine-cyclodextrin conjugates were prepared and tested as catalysts for the enantioselective oxidation of prochiral sulfides to sulfoxides by hydrogen peroxide in aqueous solutions. The alloxazinium unit was appended to the primary face of α- and β-cyclodextrins via a linker with variable length. A series of sulfides was used as substrates: n-alkyl methyl sulfides (n-alkyl = hexyl, octyl, decyl, dodecyl), cyclohexyl methyl sulfide, tert-butyl methyl sulfide, benzyl methyl sulfide and thioanisol. α-Cyclodextrin conjugate having alloxazinium unit attached via a short linker proved to be a suitable catalyst for oxidations of n-alkyl methyl sulfides, displaying conversions up to 98% and enantioselectivities up to 77% ee. β-Cyclodextrin conjugates were optimal catalysts for the oxidation of sulfides carrying bulkier substituents; e.g. tert-butyl methyl sulfide was oxidized with quantitative conversion and 91% ee. Low loadings (0.3-5 mol%) of the catalysts were used. No overoxidation to sulfones was observed in this study.
- Mojr, Viktor,Budesinsky, Milos,Cibulka, Radek,Kraus, Tomas
-
experimental part
p. 7318 - 7326
(2011/12/03)
-
- Selective Autoxidation of Electron-Rich Substrates under Elevated Oxygen Pressures
-
We report here the observation of a novel autoxidation pathway which occurs with electron-rich substrates.Tertiary amines, dialkyl thioethers, olefins, and alkynes under high oxygen pressures (>20 bars of O2), in polar solvents, and at elevated temperatures (>90 deg C) yield in good to excellent selectivity amine oxides, sulfoxides, and site-specific olefin and alkyne cleavage products, respectively.The results of mechanistic studies, including high oxygen pressure electrochemical studies, are discussed.A mechanism for this novel oxygenation reaction pathway that is consistent with the observed results is proposed.It involves an initial unfavorable electron transfer from the electron-rich substrate to oxygen to yield superoxide and the radical cation, which reacts with triplet oxygen to yield the oxygenated radical cation intermediate, a suspected potent oxidant.Electron transfer to the oxygenated radical cation from additional substrate (chain reaction) or superoxide yields a zwitterionic intermediate.This intermediate either reacts with additional substrate (O-atom transfer) to yield product (sulfoxide and N-oxide, in the case of thioethers and tertiary amines) or is converted with unimolecular reactivity to dioxetane-like (in the case of alkenes) or dioxetene-like (in the case alkynes) derived products.
- Correa, Paul E.,Hardy, Gordon,Riley, Dennis P.
-
p. 1695 - 1702
(2007/10/02)
-
