- A hydrogen-atom transfer mechanism in the oxidation of alcohols by [FeO4]2- in aqueous solution
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The ferrate(vi) ion, [FeO4]2-, has attracted much interest in recent years because of its potential use as a green oxidant in organic synthesis and water treatment. Although there have been several reports on the use of ferrate(vi) for the oxidation of alcohols to the corresponding carbonyl compounds, the mechanism remains unclear. In this work, the kinetics of the oxidation of a series of alcohols with α-C-H bond dissociation energies ranging from 81 to 95 kcal mol-1 have been studied by UV/Vis spectrophotometry. The reactions are first-order in both [FeO4]2- and [alcohol]. The deuterium isotope effects for the oxidation of methanol/d4-methanol, ethanol/d6-ethanol and benzyl alcohol/d7-benzyl alcohol are 18.0 ± 0.1, 4.1 ± 0.1 and 11.2 ± 0.1, respectively. A linear correlation is found between the second-order rate constants and the α-C-H bond dissociation energies (BDEs) of the alcohols, consistent with a hydrogen atom transfer (HAT) mechanism. The proposed HAT mechanism is supported by DFT calculations.
- Xie, Jianhui,Lo, Po-Kam,Lam, Chow-Shing,Lau, Kai-Chung,Lau, Tai-Chu
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- Reactions of OH Radicals with Methanethiol, Dimethyl Sulfide, and Dimethyl Disulfide in Air
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Photooxidations of CH3SH, CH3SSCH3 (DMDS), and CH3SCH3 (DMS) in air were performed with alkyl nitrites as sources of OH radicals.Sulfur-containing final products are SO2, CH3SO3H (methanesulfonic acid), and a little H2SO4 in all cases.CH3SH reacts with OH to form an adduct, which further reacts with alkyl nitrites to give CH3SNO (methyl thionitrite) and the corresponding alcohols.CH3S radical produced by photolysis of CH3SNO gives final products.DMDS also reacts with OH via addition followed by rapid cleavage of the S-S bond, resulting in CH3S and CH3SOH.Reaction of DMS with OH can be explained by both addition and abstraction.In both cases the CH3S radical is the main intermediate which produces final products.The reaction of the CH3S radical with O2 proceeds via addition and gives HCHO + SO2 or CH3SO3H as final products.The rate constant ratios of CH3S with NO and O2 were obtained to be ca. 2 x 1E3, which is about one-tenth of that for CH3O.
- Hatakeyama, Shiro,Akimoto, Hajime
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- Photoinduced Oxygen Transfer from NO2 to Ethylene in the Vicinity of the NO2 Dissociation Threshold. A Laser Photochemical Study on Reactant Pairs Isolated in Solid Argon
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The wavelength dependence of the photochemistry of C2H4*NO2 and C2D4*NO2 pairs, isolated in solid Ar, in the range 555-355 nm is reported.Continuos-wave pulsed dye lasers were used to excite the reactants, and the products were monitored by FT infrared sp
- Fitzmaurice, Donald J.,Frei, Heinz
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- Nazarov Reaction of Trisubstituted Dienones: Mechanism Involving Wagner-Meerwein Shift
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The Nazarov reactions of trisubstituted α,α'-dienones were studied.Whereas α,β-dimethyl-β'-alkyl α,α'-dienones gave 2,3-dimethyl-4-alkyl-2-cyclopentenones when heated in concentrated sulfuric acid, the reaction of β,β-dimethyl-β'-alkyl α,α'-dienones afforded 3,4-dimethyl-4-alkyl-2-cyclopentenones as the rearranged products.A mechanistic investigation using two deuterated dienones suggests that the Nazarov reactions of the latter dienones are accompanied by Wagner-Meerwein shifts to form the most stable carbocations.
- Motoyoshiya, Jiro,Yazaki, Toshikazu,Hayashi, Sadao
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- Photochemical reactions of alkyl phenylglyoxylates
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Three new photoproducts, ethyl O-benzoyl mandelate (5a), ethyl O-acetylmandelate (6a), and biphenyl triketone (7a) are isolated and identified in the reactions of ethyl phenylglyoxylate (1a) in benzene. Quantum yields and initial rate constants of product formation are shown to be concentration dependent. For the formation of carbonyl product 3 at lower starting material concentrations (N) and intermolecular H abstraction (k1) of methyl phenylglyoxylate (1d) are measured.
- Hu, Shengkui,Neckers, Douglas C.
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p. 6407 - 6415
(2007/10/03)
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- Biosynthesis of the benz[a]anthraquinone antibiotic PD 116198
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The labelling pattern obtained from incorporation of a mixture of sodium [1-13C]- and [2-13C]acetates has confirmed the irregular derivation of the benz[a]anthraquinone skeleton of the angucycline antibiotic PD 116198. Subsequent incorporations of sodium [1-13C, 18O2]-, and [1-13C, 2-2H3]acetates and of 18O2 have revealed the origins of the hydrogen and oxygen atoms of the antibiotic. The possibility of a 'two-chain' biosynthesis was tested by feeding 2H-labeled orsellinates; however, no incorporation was detected. PD 116198 seems most plausibly derived by rearrangement of an initially-formed linear tetracyclic intermediate.
- Gould,Cheng
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p. 11135 - 11144
(2007/10/02)
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- Oxidation of alcohols, aldehydes, and carboxylates by the aquachromium(IV) ion
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Four methods have been developed to prepare aquachromium(IV), which we believe to be an oxo ion, CrO2+. It readily converts Ph3P to Ph3PO (k = 2.1 × 103 L mol-1 s-1) at 25 °C in 85% CH3CN/H2O (0.10 M HClO4). The reactions used to form CrO2+ are those between Cr2+ and (a) O2 (b) anaerobic CrO22+, (c) anaerobic CrOOCr4+, and (d) anaerobic Tl(III). The CrO2+ has a half-life of 30 s in acidic solution at room temperature and will oxidize alcohols, aldehydes, and certain carboxylates as well as diethyl ether. The second-order rate constants (L mol-1 s-1) in acidic solution (μ = 1.0 M HClO4/LiClO4, 25 °C) are as follows: CH3OH, 52; CD3OH, 15; C2H5OH, 88; C2D5OH, 41; (CH3)2CHOH, 12.0; (CD3)2CDOH, 4.6; CH2=CHCH2OH, 101; CH3(CH2)2CH2OH, 44; (C2H5)(CH3)CHOH, 41; (CH3)3CCH2OH, 39; C6H5CH2OH, 56; (C6H5)(CH3)CHOH, 30; (C6H5)2CHOH, 10.5;p-CH3OC6H4CH2OH, 71;p-CH3C6H4CH2OH, 66; p-CF3C6H4CH2OH, 60; c-C4H7OH, 44; c-C5H9OH, 31; HCHO·H2O, 92; (CH3)3CCHO, 37; HCO2H, 11.6; HCO2-, 6.9 × 103; HC2O4-, 2.2 × 103; (C2H5)2O, 4.5. Activation parameters were also determined for selected reactions. In all but two of these reactions (cyclobutanol and pivaldehyde), Cr2+ is the immediate product as shown by trapping with O2. On the basis of the kinetic and product data, the mechanism of oxidation by CrO2+ is proposed to be hydride transfer. The reactivity order for alcohols (1° > CH3 > 2°), the small substituent effect for the benzyl alcohols, and the similarity of all the rate constants regardless of the organic substrate are inconsistent with the formation of carbon-centered radicals. The reaction of HCrO4- with (CH3)2CHOH is also shown to involve CrO2+ and Cr2+ as intermediates. The latter reacts with HCrO4- with a rate constant of 2 × 109 L mol-1 s-1 in 2.0 M HClO4.
- Scott, Susannah L.,Bakac, Andreja,Espenson, James H.
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p. 4205 - 4213
(2007/10/02)
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- Characterization of transition states by isotopic mapping and structure-reactivity coefficients: Solvent and secondary deuterium isotope effects for the base-catalyzed breakdown of acetaldehyde hemiacetals
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Rate constants and structure-reactivity coefficients for the breakdown of acetaldehyde and acetaldehyde-d4 hemiacetals were determined in water and deuterium oxide by trapping the acetaldehyde formed with α-effect nucleophiles. General-base catalysis by substituted acetate and cacodylate ion catalysts represents equilibrium ionization of the hemiacetal CL3CL(OL)OR (L = H or D) to form the hemiacetal anion, CL3CL(O-)OR followed by rate-determining general-acid catalysis of the cleavage of the hemiacetal anion to form acetaldehyde and ROL. Solvent isotope effects for the catalytically active proton kpBH/kpBD = 0.9-2.5 do not change significantly with changes in the pK of the catalyst or the leaving group alcohol. The increase in the secondary αβ-deuterium isotope effects kαβH/kαβD = 1.21-1.30 with decreases in the pK of the leaving group alcohol can be described by the interaction coefficient pyy′ = ?ρn/-?pK1g = -0.069. The increase in Br?nsted β = 0.48-0.72 with decreases in the pK of the leaving group alcohol in water can be described by the interaction coefficient pxy′, = ?β/-?pK1g = 0.090 and in D2O by pxy′ = 0.078. The interaction coefficients and the observation of both solvent and secondary deuterium isotope effects are consistent with a coupling between proton transfer to the leaving group oxygen and changes in hybridization about the central carbon in the transition state for cleavage of the hemiacetal anion. The results are discussed in the context of proposals for stable hydrogen-bonded protons in concerted acid- and base-catalyzed reactions in water.
- Coleman, Charolotte A.,Murray, Christopher J.
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p. 1677 - 1684
(2007/10/02)
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- Deuterium Isotope Effects on Nuclear Shielding. Directional Effects and Nonadditivity in Acyl Derivatives
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Deuterium isotope effects on the 19F and 13C nuclear shieldings have been investigated in acyl derivatives.A nonadditivity of the 3ΔF(D) of acetyl fluoride has been experimentally established and related primarily to nonuniform rotamer distributions of the mono- and dideuteriated isotopomers.The 3ΔF(D)'s show furthermore a distinct orientational dependence.The isotope effects for the configurations where the nuclei in question are in a trans position are positive and those in which they are gauche are negative.The 2ΔCO(D)'s are negative and additive in all the investigated cases.The observed isotope effects are discussed in general in terms of substituent and vibrational effects.
- Hansen, Poul Erik,Nicolaisen, Flemming M.,Schaumburg, Kjeld
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p. 625 - 629
(2007/10/02)
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