- C2 molecule: formation from bromoacetylene and reactions with cyclohexene or 2,3-dimethyl-2-butene
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The C2 molecule (1,2-ethynediyl) has been prepared by dehydrohalogenation of 1,2-dibromoethylene with an excess of potassium tert-butoxide in 2,3-dimethyl-2-butene as the solvent and the reagent. The major products of this reaction were 2,3-dim
- Galy, Nicolas,Doucet, Henri,Santelli, Maurice
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- Reaction of 4,7-dimethylbenzofurazan with singlet oxygen
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4,7-Dimethylbenzofurazan (1) was transformed by 1O2 produced by irradiation of C60 into 4,7-dimethylbenzofurazan 4,7-endoperoxide (2) in CDCl3 or CD2Cl2 at 0°C in excellent yields. The endo
- Takabatake, Tohru,Miyazawa, Tomoyuki,Hasegawa, Minoru,Foote, Christopher S.
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- Selective photooxidation of small alkenes by O2 with red light in zeolite Y
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Upon loading of 2,3-dimethyl-2-butene (DMB) and O2 into zeolite NaY, photochemistry was observed at wavelengths as long as 760 nm. Similarly, photoexcitation of trans- or cis-2-butene and O2 in this zeolite resulted in chemical reaction at a threshold wavelength of 600 nm. Reactions were initiated either with filtered tungsten-source light or the emission of a CW dye laser and typically conducted at -50°C. Products identified by FT-infrared spectroscopy were 2,3-dimethyl-3-hydroperoxy-l-butene (>90%) and acetone in the case of DMB + O2. trans- or cis-2-butene + O2 gave exclusively 3-hydroperoxy-1-butene. The constitutes the first synthesis of this hydroperoxide by direct photolysis of 2-butene-O2 pairs. Laser reaction excitation spectra in the 500-700-nm region revealed a continuous absorption for both the DMB-O2 and the 2-butene-O2 systems. It is attributed to a charge-transfer transition. Comparison with corresponding absorption spectra in conventional media shows that the excited alkene-O2 charge-transfer states are stabilized by electrostatic interactions with the zeolite NaY environment by 12 000cm-1. Substantially stabilization was observed in high-silica faujasite. Thermal decomposition of the hydroperoxide photoproducts upon warm-up from -50 °C to room temperature was monitored by infrared spectroscopy. It was found that 3-hydroperoxy-1-butene thermally epoxidizes the excess cis-or trans-2-butene in room temperature NaY under complete stereochemical retention.
- Blatter,Frei
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- Photooxygenation of oxygen-substituted naphthalenes
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The reaction of oxygen-substituted naphthalenes with singlet oxygen (1O2) has been investigated, and labile endoperoxides have been isolated and characterized at –78°C for the first time. Low-temperature kinetics by UV spectroscopy revealed that alkoxy and silyloxy substituents remarkably increase the rate of photooxygenations compared to 1,4-dimethylnaphthalene, whereas acyloxy-substituted acenes are inert towards 1O2. The reactivities nicely correlate with HOMO energies and free activation energies, which we determined by density functional theory calculations. The lability of the isolated endoperoxides is due to their very fast back reaction to the corresponding naphthalenes even at –20°C under release of 1O2, making them to superior sources of this reactive species under very mild conditions. Finally, a carbohydrate-substituted naphthalene has been synthesized, which reacts reversibly with 1O2 and might be applied for enantioselective oxidations in future work.
- Bauch, Marcel,Krtitschka, Angela,Linker, Torsten
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supporting information
(2017/08/23)
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- Singlet oxygen generation from poly[4-diacetoxyiodo]styrene and hydrogen peroxide
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Treatment of hydrogen peroxide with a polymer-supported hypervalent iodine compound, poly[4-diacetoxyiodo] styrene (PDAIS), generates singlet molecular oxygen (1O2). Singlet oxygen generation was proved by trapping with typical organic compounds such as conjugated dienes, aromatic dienes, and electron-rich alkene. When compared to monomer analogue, the use of PDAIS in peroxidation of substrates gave slightly better yields (45%–96%). Regeneration and reuse of PDAIS showed similar activity. The mechanism underlying generation of singlet oxygen and reaction scope was examined.
- ?atir, Mustafa
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p. 467 - 475
(2017/09/15)
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- Photoreduction of Pt(IV) halo-hydroxo complexes: Possible hypohalous acid elimination
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Concentrated hydrogen peroxide addition to trans-Pt(PEt3) 2Cl(R) [1 (R = 9-phenanthryl), 2 (R = 4-trifluoromethylphenyl)] yields hydroxo-hydroperoxo complexes trans-Pt(PEt3) 2(Cl)(OOH)(OH)(R) [5 (R = 9-phenanthryl), 4 (R = 4- trifluoromethylphenyl)], where the hydroperoxo ligand is trans to R. Complex 5 is unstable and reacts with solvent CH2Cl2 to give trans,cis-Pt(PEt3)2(Cl)2(OH)(9-phenanthryl) (3). Treatment of 4 with HCl yields analogous trans,cis-Pt(PEt3) 2(Cl)2(OH)(4-trifluoromethylphenyl) (6) and HBr gives trans-Pt(PEt3)2(Br)(Cl)(OH)(4-trifluoromethylphenyl) (7), where the Br and 4-trifluoromethylphenyl ligands are trans. Photolysis of 3 or 6 at 313 or 380 nm causes reduction to trans-Pt(PEt3)2Cl(R) (1 or 2, respectively). Expected coproduct HOCl is not detected, but authentic solutions of HOCl are shown to decompose under the reaction conditions. Chlorobenzene and other unidentified products that oxidize PPh3 to OPPh3 are detected in photolyzed benzene solutions. Photolysis of 3 or 6 in the presence of 2,3-dimethyl-2-butene (TME) yields the chlorohydrin (2-chloro-2,3-dimethyl-3-butanol), 3-chloro-2,3-dimethyl-1-butene, and acetone, all expected products from HOCl trapping, but additional oxidation products are also observed. Photolysis of mixed chloro-bromo complex 7 with TME yields the bromohydrin (2-bromo-2,3-dimethyl-3-butanol) and 2, consistent with cis-elimination of HOBr. Computational results (TDDFT and DFT) and photochemistry of related complexes suggest a dissociative triplet excited state reaction pathway and that HOCl elimination may occur by an incipient hydroxo radical abstraction of an adjacent halogen atom, but a pathway involving hydroxo radical reaction with solvent or TME to generate a carbon-based radical followed by halogen abstraction from Pt cannot be eliminated.
- Wickramasinghe, Lasantha A.,Sharp, Paul R.
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p. 1430 - 1442
(2014/03/21)
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- Dihydrogen trioxide (HOOOH) photoelimination from a platinum(IV) hydroperoxo-hydroxo complex
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Photolysis (380 nm) of trans-Pt(PEt3)2(Cl)(OH)(OOH)(4-trifluoromethylphenyl) (1) at -78 °C in acetone-d6 or toluene-d8 yields HOOOH (16-20%) and trans-Pt(PEt3)2(Cl)(4-trifluoromethylphenyl) (2). Also observed in acetone-d6 are H2O2, (CD3)2C(OH)(OOH), and (CD3)2C(OOH)2. Thermal decomposition or room-temperature photolysis of 1 gives O2, water, and 2. Computational modeling (DFT) suggests two intramolecular hydrogen-bonding-dependent triplet pathways for the photolysis and two possible pathways for the thermolysis, one involving proton transfer from the OOH to the OH ligand and the other homolysis of the Pt-OOH bond, abstraction of the OH ligand, and decomposition of the resulting H2O3. Trapping studies suggest the latter pathway.
- Wickramasinghe, Lasantha A.,Sharp, Paul R.
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supporting information
p. 13979 - 13982
(2015/01/08)
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- Reaction of tri- and tetrasubstituted alkenes with the low-temperature oxidizing system aluminum terf-butylate-terf-butyl hydroperoxide
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The system consisting of aluminum tert-butylate and tert-butyl hydroperoxide under mild conditions (20°C) oxidizes tri- and tetrasubstituted ethylenes containing at least one α-methyl group. The reaction proceeds via formation of tertiary allylic hydroperoxides and their subsequent transformations into unsaturated alcohols and epoxy alcohols, and also into carbonyl compounds. The presence of the latter products suggests degradation of the carbon skeleton of alkenes.
- Martynova,Stepovik,Dodonov
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p. 736 - 741
(2007/10/03)
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- Heterogeneous molybdate catalysts for the generation of singlet molecular oxygen (1Δg) from H2O2
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The immobilisation of molybdate on Mg,Al-LDH leads to an active, heterogeneous catalyst that generates singlet molecular oxygen from hydrogen peroxide in the absence of soluble base.
- Laar, F. van,Vos, D. De,Vanoppen, D.,Sels, B.,Jacobs, P. A.,et al.
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p. 267 - 268
(2007/10/03)
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- The Ozonolysis of Tetramethylethylene. Concentration and Temperature Effects
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The products of the ozonolysis of tetramethylethylene in hexane or methylene chloride are remarkably dependent on the concentration of tetramethylethylene.Ozonolysis in neat tetramethylethylene gives mostly tetramethylene epoxide as product.As the concentration of tetramethylethylene is reduced, more acetone diperoxide is formed until it becomes the major product.The reaction also produces 3-hydroperoxy-2,3-dimethyl-1-butene.The product distribution is also quite dependent on reaction temperature.At a given concentration of the alkene the epoxide yield decreases as the temperature is lowered.Simultaneously the acetone diperoxide yield increases with lower temperature.The results are explained by postulating that energy-rich acetone oxide can be partially converted to dimethyldioxirane which is primarily responsible for the epoxidation.The proposed reaction scheme also has acetone oxide dimerize in a stepwise manner to give an intermediate which can either close to give diperoxide or lose singlet oxygen.The singlet oxygen would then react with tetramethylethylene to give the hydroperoxide.
- Murray, Robert W.,Kong, Wei,Rajadhyaksha, Shirish N.
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p. 315 - 321
(2007/10/02)
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- Monooxygen Donation Potential of 4a-Hydroperoxyflavins As Compared with Those of a Percarboxylic Acid and Other Hydroperoxides. Monooxygen Donation to Olefin, Tertiary Amine, Alkyl Sulfide, and Iodide Ion
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The reaction of the hydroxyperoxides diphenylhydroperoxyacetonitrile (4), methyl diphenylhydroperoxyacetate (5), and 5',6',7',8'-tetrahydro-4a'-hydroperoxy-3'-methylspiro-4'(3'H)-one (6) with I-, thioxane, and N,N-dimethylbenzylamine (DMBA) are first order in both hydroperoxide and substrate.For both 5 and 6, I3- is produced in 100percent yield.Product analysis for the reaction of 4, 5, and 6 with thioxane and DMBA established that the hydroxyperoxides are converted to the corresponding alcohols and that thioxane sulfoxide and N,N-dimethylbenzylamine N-oxide are formed.The reactions are quantitative.The reaction of 4 with I- proved to be complicated.The alcohol generated from 4 is the cyanohydrin of benzophenone.The dissociation of the benzophenone cyanohydrin product is competitive with I3- formation so that CN- produced in the dissociation reacts with I3- to yield ICN.Kinetic and thermodynamic analyses have provided the pertinent rate and equilibrium constants associated with the overall time course for reaction of 4 with I-.The second-order rate constant for the reaction of m-chloroperbenzoic acid (1) with I- has been determined and the second-order rate constant for reaction of 1 with thioxane was obtained from experiments in which thioxane and I- were employed as competitive substrates.The second-order rate constants for reaction of 1, 4, 5, and 6 with I-, thioxane, and DMBA were compared with like constants for the reactions of 4a-hydroperoxy-5-ethyl-3-methyllumiflavin (2), 1-carba-1-deaza-4a-hydroperoxy-5-ethyl-3-methyllumiflavin (3), t-BuOOH (7), and H2O2 (8).A log - log plot of the rate constants for monooxygen transfer from hydroperoxides to thioxane (kS) and to DMBA (kN) was found to be linear and of slope 1.0.The best line for the plot of log kS vs. the log of the rate constants for reactions with I- (kI) was of slope 1.1.The points for m-chloroperbenzoic acid were found to fit the log kS vs. log KI plot.These results show that the second-order rate constants for reactions of I-, thioxane, and DMBA are of like dependence on the electronic and steric characteristics of the hydroperoxides and percarboxylic acid 1.A linear free energy plot correlates the log of the second-order rate constants vs. pKa of YOH for oxygen transfer from YOOH = 1, 2, 4, 5, 7, and 8 (βlg = -0.6).In these reactions the 4a-hydroperoxyflavin 2 is the most efficient monooxygen donor of the hydroperoxides investigated, being 103 - 106 more reactive than t-BuOOH and ca. 103 less reactive than the peracid 1.The kinetics of epoxidation of 2,3-dimethyl-2-butene by the hydroperoxides 2 - 6 were invesigated by following both hydroperoxide disappearance and product formation.The results of these investigations, which include further reaction of epoxide with hydroperoxide to provide pinacol and 2,3-dimethyl-1-buten-3-ol, are discussed.Evidence for epoxidation of 2,3-dimethyl-2-butene ...
- Bruice, Thomas C.,Noar, J. Barry,Ball, Sheldon S.,Venkataram, U. V.
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p. 2452 - 2463
(2007/10/02)
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