- The catalytic function of a silica gel-immobilized Mn(II)-hydrazide complex for alkene epoxidation with H2O2
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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.
- Ghorbanloo, Massomeh,Monfared, Hassan Hosseini,Janiak, Christoph
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experimental part
p. 12 - 20
(2011/10/05)
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- Manganese catalysts for C-H activation: An experimental/theoretical study identifies the stereoelectronic factor that controls the switch between hydroxylation and desaturation pathways
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We describe competitive C-H bond activation chemistry of two types, desaturation and hydroxylation, using synthetic manganese catalysts with several substrates. 9,10-Dihydrophenanthrene (DHP) gives the highest desaturation activity, the final products being phenanthrene (P1) and phenanthrene 9,10-oxide (P3), the latter being thought to arise from epoxidation of some of the phenanthrene. The hydroxylase pathway also occurs as suggested by the presence of the dione product, phenanthrene-9,10-dione (P2), thought to arise from further oxidation of hydroxylation intermediate 9-hydroxy-9,10- dihydrophenanthrene. The experimental work together with the density functional theory (DFT) calculations shows that the postulated Mn oxo active species, [Mn(O)(tpp)(Cl)] (tpp = tetraphenylporphyrin), can promote the oxidation of dihydrophenanthrene by either desaturation or hydroxylation pathways. The calculations show that these two competing reactions have a common initial step, radical H abstraction from one of the DHP sp3 C-H bonds. The resulting Mn hydroxo intermediate is capable of promoting not only OH rebound (hydroxylation) but also a second H abstraction adjacent to the first (desaturation). Like the active MnV=O species, this Mn IV-OH species also has radical character on oxygen and can thus give H abstraction. Both steps have very low and therefore very similar energy barriers, leading to a product mixture. Since the radical character of the catalyst is located on the oxygen p orbital perpendicular to the Mn IV-OH plane, the orientation of the organic radical with respect to this plane determines which reaction, desaturation or hydroxylation, will occur. Stereoelectronic factors such as the rotational orientation of the OH group in the enzyme active site are thus likely to constitute the switch between hydroxylase and desaturase behavior.
- Hull, Jonathan F.,Balcells, David,Sauer, Effiette L.O.,Raynaud, Christophe,Brudvig, Gary W.,Crabtree, Robert H.,Eisenstein, Odile
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experimental part
p. 7605 - 7616
(2010/07/08)
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- Stabilities and partitioning of arenonium ions in aqueous media
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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.
- Lawlor, D. A.,O'Ferrall, R. A. More,Rao, S. N.
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experimental part
p. 17997 - 18007
(2009/06/25)
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- An efficient approach for aromatic epoxidation using hydrogen peroxide and Mn(III) porphyrins
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Efficient epoxidation, in very high conversions and selectivities, of aromatic hydrocarbons with hydrogen peroxide, in the presence of Mn III porphyrins [Mn(TDCPP)Cl, Mn(βNO2TDCPP)Cl, Mn(TPFPP)Cl] as catalysts is described; naphthalene and anthracene afford the anti-1,2:3,4-arene dioxides whereas with phenanthrene the 9,10-oxide is obtained.
- Rebelo, Susana L. H.,Simoes, Mario M. Q.,Neves, M. Graca P. M. S.,Silva, Artur M. S.,Cavaleiro, Jose A. S.
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p. 608 - 609
(2007/10/03)
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- Efficient electrophilic and nucleophilic epoxidations utilizing a sulfonylperoxy radical and peroxysulfate species
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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.
- Park, Min Young,Yang, Seung Gak,Kim, Yong Hae
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p. 431 - 436
(2007/10/03)
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- Epoxidation of polyaromatics using HOF·CH3CN
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The reaction of the HOF·CH3CN complex, made directly by passing fluorine through aqueous acetonitrile, with some phenanthrene and pyrene derivatives results in fast epoxidation.
- Rozen, Shlomo,Bareket, Yifat,Blum, Jochanan
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p. 2333 - 2334
(2007/10/03)
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- Novel (α,β-Epoxyalkyl)lithium Reagents via the Lithiation of Organyl-Substituted Epoxides
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A series of epoxides bearing unsaturated organyl groups attached directly to the epoxy group was found to have sufficient kinetic acidity to undergo clean lithiation at low temperatures.Epoxides of the type is aryl, vinylic, acetylenic, alkoxycarbonyl, or cyano, were smoothly converted into by either t-BuLi or LDA in the temperature range of -80 to -115 deg C.The resulting (α,β-epoxyalkyl)lithium reagents could be transformed into a variety of substituted epoxides, such as R2C-CE(Un)-O, where E = D, R3Si, R3Sn, R, RCO, CO2H, or COH(R)2.In cases where Un is acyl, addition to the carbonyl, rather than lithiation, occurred preferentially.Attempted lithiations of aziridines and thiiranes led to extrusion of nitrogen and sulfur, respectively.Even the relatively stable intermediates generated at -90 deg C underwent carbenoid-like decomposition at higher temperatures to yield isomerization and intermolecular-insertion products.Observation of these processes gives direct corroboration of reaction mechanisms proposed for the base-promoted isomerizations of epoxides.
- Eisch, John J.,Galle, James E.
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p. 4835 - 4840
(2007/10/02)
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- BIOMIMETIC HYDROXYLATION OF AROMATIC COMPOUNDS: HYDROGEN PEROXIDE AND MANGANESE-POLYHALOGENATED PORPHYRINS AS A PARTICULARLY GOOD SYSTEM.
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Various iron- and manganese-porphyrins were compared as catalysts for the hydroxylation of anisole by H2O2 or PhIO.Whereas all the iron-porphyrins tested gave low hydroxylation yields, Mn(III)-meso-tetraarylporphyrins bearing halogen substituents on their meso-aryl and pyrrole groups gave good yields (up to 70percent based on the oxidant) for the para-hydroxylation of anisole, especially with H2O2 as oxidant in the presence of imidazole.Under these conditions, phenanthrene was quantitatively oxidized into its 9,10-epoxide and naphthalene was mainly oxidized into 1-naphthol (40percent yield).Hydroxylation yields appeared dependent upon the reactivity of the oxidizing system not only toward the starting aromatic compound but also toward the phenol products.
- Carrier, Marie-Noelle,Scheer, Corinne,Gouvine, Pascal,Bartoli, Jean-Francois,Battioni, Pierrette,Mansuy, Daniel
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p. 6645 - 6648
(2007/10/02)
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- Oxidations by methyl(trifluoromethyl)dioxirane. 4.1 Oxyfunctionalization of aromatic hydrocarbons
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By using the title dioxirane (1a), naphthalene (2), phenanthrene (3), and anthracene (4) have been converted into anti-naphthalene-1,2;3,4-dioxide (2′), phenonthrene-9,10-oxide (3′), and anthraquinone (4′), respectively, in high yield and under mild conditions. However, the transformation of pyrene (5) - an higher homologue of the polycyclic aromatic hydrocarbon series - into the corresponding arene oxide was found to proceed much less effectively.
- Mello, Rossella,Ciminale, Francesco,Fiorentino, Michele,Fusco, Caterina,Prencipe, Teresa,Curci, Ruggero
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p. 6097 - 6100
(2007/10/02)
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- Direct Oxidation of Arenes to Arene Oxides by 2-Nitrobenzene Peroxysulfur Intermediate Generated from 2-Nitrobenzenesulfonyl Chloride and Superoxide
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Acenaphthylene, phenanthrene, and pyrene, which are inert with superoxide itself, were readily oxidized to the corresponding arene oxides by a 2-nitrobenzene sulfonyl-peroxyl radical intermediate (A) generated from 2-nitrobenzenesulfonyl chloride and potassium superoxide in polar aprotic solvents such as acetonitrile, nitromethane, and dimethylformamide under mild conditions.
- LEE, Hyeon Kye,KIM, Kyoung Soo,KIM, Jack C.,KIM, Yong Hae
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p. 561 - 564
(2007/10/02)
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- THE SYNTHETIC UTILITY OF DIOXYPHOSPHORANES IN ORGANIC SYNTHESIS
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Diethoxytriphenylphosphorane, DTPP, prepared by reaction of triphenylphosphine and diethyl peroxide, is a "hydrolytically active" dioxyphosphorane which promotes mild and efficient cyclodehydration of diols to cyclic ethers in neutral media.Simple 1,2-, 1,4-, and 1,5-diols afford good yields of the cyclic ethers but 1,3-propanediol and 1,6-hexanediol give mainly 3-ethoxy-1-propanol and 6-ethoxy-1-hexanol, respectively, with DTPP.Tri- and tetra-substituted 1,2-diols afford the relatively stable 1,3,2-dioxaphospholanes in the presence of DTPP and the reaction conditions dictate whether epoxides, ketones, or allylic alcohols are obtained.
- Robinson, Philip L.,Kelly, Jeffery W.,Evans, Slayton A.
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- Diethoxytriphenylphosphorane: A Mild, Regioselective Cyclodehydrating Reagent for Conversion of Diols to Cyclic Ethers. Stereochemistry, Synthetic Utility, and Scope
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Diethoxytriphenylphosphorane, Ph3P(OEt)2, prepared by reaction of triphenylphosphine and diethyl peroxide, is a "hydrolytically active" dioxyphosphorane which promotes mild cyclodehydration (40-110 deg C) of diols to cyclic ethers in neutral media.The regioselectivity in the closure of (S)-(+)-propane-1,2-diol and (R)-(-)-pentane-1,4-diol with Ph3P(OEt)2 is high (81-82 percent) while the cyclodehydration of (S)-(+)-phenylethane-1,2-diol gives racemized (+/-)-styrene oxide.Simple 1,2-, 1,4-, and 1,5-diols afford good yields of the cyclic ethers but 1,3-propanediol and 1,6-hexanediol give mainly 3-ethoxy-1-propanol and 6-ethoxy-1-hexanol, respectively with Ph3P(OEt)2.Tri- and tetra-substituted 1,2-diols afford the relatively stable 1,3,2-dioxaphospholanes (or ?-dioxyphosphoranes) in the presence of Ph3P(OEt)2, and, depending on conditions, the 1,3,2-dioxaphospholanes are selectively converted to epoxides, ketones or allylic alcohols.The carbonyl compounds arise from 1,2-hydride and 1,2-methyl migrations; the allylic alcohols are derived from thermolytic eliminations. trans-1,2-Cyclohexanediols afford essentially quantitative yields (>95 percent) of the cyclohexene oxides while cis-1,2-cyclohexanediol gives the stable 1,3,2-dioxaphospholane with Ph3P(OEt)2 which decomposes under thermal conditions to cyclohexanone (90 percent).Ph3P(OEt)2 is extremely useful for conversion of "sensitive" 1,2-diols to acidic and /or thermally labile epoxides as demonstrated by the quantitative conversion of 9,10-dihydro-trans-9,10-phenanthrenediol to 9,10-dihydrophenanthrene oxide and 2α,10-pinanediol to 2α,10-epoxypinane.
- Robinson, Philip L.,Barry, Carey N.,Kelly, Jeffery W.,Evans, Slayton A.
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p. 5210 - 5219
(2007/10/02)
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- Dioxiranes: Synthesis and Reactions of Methyldioxiranes
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The peroxymonosulfate-acetone system produces dimethyldioxirane under conditions permitting distillation of the dioxirane from the synthesis vessel.The same conditions were used to prepare other methyldioxiranes.Solutions of dimethyldioxirane prepared in this manner were used to study its chemical and spectroscopic properties.The caroate-acetone system was also used to study the chemistry of in situ generated dimethyldioxirane.
- Murray, Robert W.,Jeyaraman, Ramasubbu
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p. 2847 - 2853
(2007/10/02)
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- FACILE SYNTHESIS OF K-REGION ARENE OXIDES
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Polycyclic aromatic hydrocarbons reacts at the K-region with N-bromoacetamide in acetic acid to provide trans-bromohydrin acetates which are readly cyclized to arene oxides.The simplicity of the approach makes radioactive and optically active K-region arene oxides easily available.
- Bladeren, P. J. van,Jerina, D. M.
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p. 4903 - 4906
(2007/10/02)
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- DIRECT EPOXIDATION OF POLYCYCLIC AROMATIC COMPOUNDS BY SUPEROXIDE IN THE PRESENCE OF PHOSGENE DIMER
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Olefins and polycyclic aromatic compounds were oxidized to their epoxides by superoxide (O2-.) in the presence of phosgene dimer.The reaction mechanisms are discussed.
- Nagano, Tetsuo,Yokoohji, Kiyomi,Hirobe, Masaaki
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p. 3481 - 3484
(2007/10/02)
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- Reactions of the K-Region Epoxides of Polycyclic Aromatic Hydrocarbons with Phosphodiesters. A Potential Detoxification Reaction
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Phenanthrene 9,10-oxide reacts with diethyl hydrogen phosphate to give 9-phenanthrol.The reaction was first order in both epoxide and phosphate concentrations, with a pseudo-first-order rate constant kφ = 6.2e-1 mol-1Ls-1.Similarly, chrysene 5,6-oxide on reaction with phosphate opened regiospecifically to give 6-chrysenol.Several anilinium phosphate salts were prepared and reacted with phenanthrene 9,10-oxide.The extent of reaction was markedly influenced by the pKa of the anilinium salt.The biological implications of this study in understanding the relative noncarcinogenicity of K-region arene oxides are discussed.
- Raddo, P. Di,Chan, T.H.
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p. 1427 - 1431
(2007/10/02)
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- Model Systems for Cytochrome P450 Dependent Mono-oxygenases. Part 1. Oxidation of Alkenes and Aromatic Compounds by Tetraphenylporphinatoiron(III) Chloride and Iodosylbenzene
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A selection of aliphatic alkenes, substituted styrenes, and cis- and trans-stilbene have been epoxidised with tetraphenylporphinatoiron(III) chloride and iodosylbenzene, a model system for the cytochrome P450 dependent mono-oxygenases.The epoxidations are stereospecifically syn and the reactivities of the alkenes show that cis-alkenes are more reactive than their trans-isomers and that electron-releasing substituents favour the reaction.A Hammett ρ value of -0.93 is obtained from the epoxidation of the substituted styrenes.Three polycyclic hydrocarbons, phenanthrene, acenaphthylene, and pyrene, are epoxidised in low yield.The model system hydroxylates anisole and naphthalene but is insufficiently reactive to oxidise benzene; with toluene, side-chain oxidation but no ring hydroxylation occurs.The mechanisms of these oxidations and the nature of the reactive species are discussed.
- Smith, John R. Lindsay,Sleath, Paul R.
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p. 1009 - 1016
(2007/10/02)
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- Stereochemical and Mechanistic Aspects of Sulphoxide, Epoxide, Arene Oxide, and Phenol Formation by Photochemical Oxygen Atom Transfer from Aza-aromatic N-Oxides
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Stereoselectivity and relative yields are determined for the sulphoxide formation resulting from the u.v. irradiation of a range of aza-aromatic N-oxides in the presence of cyclic thioethers.A comparison is made with the results of oxidation by oxaziridines and by mono-oxygenase enzymes present in the fungus Aspergillus niger.The photochemical oxidation results are consistent with a transition state involving an oxaziridine intermediate where partial bonding of the oxygen atom to the ring nitrogen atom is maintained during the oxygen transfer process.Photolysis of aza-aromatic N-oxides in the presence of cis- and trans-olefins yields epoxides. cis-4-Methylpent-2-ene yielded both cis and trans-epoxides in almost equal proportions indicating that the oxygen atom addition to a carbon-carbon bond in this system is non-concerted.The photochemically induced oxygenation of perdeuteriated aromatic substrates provides no evidence for direct insertion of an oxygen atom into an aromatic carbon-hydrogen bond.Addition of an oxygen atom to form an epoxide (arene oxide) intermediate in this system is evidenced by the NIH shift in a wide range of aromatic substrates, and by the detection of arene oxide intermediates (and their isomeric phenols) from naphthalene and phenanthrene.
- Akhtar, M. Naseem,Boyd, Derek R.,Neill, John D.,Jerina, Donald M.
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p. 1693 - 1699
(2007/10/02)
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