- A new binuclear oxovanadium(v) complex as a catalyst in combination with pyrazinecarboxylic acid (PCA) for efficient alkane oxygenation by H 2O2
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A new binuclear oxovanadium(v) complex [{VO(OEt)(EtOH)}2L] (1) where H4L is bis(2-hydroxybenzylidene)terephthalohydrazide has been synthesized and fully characterized. The combination of 1 with pyrazine-2-carboxylic acid (PCA; a cocatalyst) affords a catalytic system for the efficient oxidation of saturated hydrocarbons, RH, with hydrogen peroxide and air in acetonitrile solution at 50°C to produce alkyl hydroperoxides, ROOH, as the main primary products. Very high turnover numbers (TONs) have been attained in this reaction: for example, after 2220 min, TON = 44 000 and initial TOF (turnover frequency) = 3300 h-1 per molecule of complex 1. The estimated activation energy of the cyclohexane oxygenation in the presence of 1/PCA is Ea = 16 ± 2 kcal mol-1. This value is identical to that obtained for the cyclohexane oxidation with H 2O2 catalyzed by the (n-Bu4N)[VO 3]/PCA combination (17 ± 2 kcal mol-1). The dependences of initial oxidation rates W0 on the initial concentrations of all components of the reaction mixture have been determined. Based on these kinetic data and on the regio- and bond-selectivity parameters measured in the oxidation of linear and branched alkanes a mechanism of the oxidation has been proposed which includes the generation of hydroxyl radicals in the crucial stage. The Royal Society of Chemistry.
- Sutradhar, Manas,Shvydkiy, Nikita V.,Guedes Da Silva, M. Fátima C.,Kirillova, Marina V.,Kozlov, Yuriy N.,Pombeiro, Armando J. L.,Shul'Pin, Georgiy B.
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supporting information
p. 11791 - 11803
(2013/09/02)
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- Hydrogen peroxide oxygenation of alkanes including methane and ethane catalyzed by iron complexes in acetonitrile
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This paper describes an investigation of the alkane oxidation with hydrogen peroxide in acetonitrile catalyzed by iron(III) perchlorate (1), iron(III) chloride (2), iron(III) acetate (3) and a binuclear iron(III) complex with 1,4,7-triazacyclononane (4). The corresponding alkyl hydroperoxides are the main products. Nevertheless in the kinetic study of cyclohexane oxidation, the concentrations of oxygenates (cyclohexanone and cyclohexanol) were measured after reduction of the reaction solution with triphenylphosphine (which converts the cyclohexyl hydroperoxide to the cyclohexanol). Methane and ethane can be also oxidized with TONs up to 30 and 70, respectively. Chloride anions added to the oxidation solution with 1 activate the perchlorate iron derivative in acetonitrile, whereas the water as additive inactivates 2 in the H 2O2 decomposition process. Pyrazine-2-carboxylic acid (PCA) added to the reaction mixture decreases the oxidation rate if 1 or 2 are used as catalysts, whereas compounds 3 and 4 are active as catalysts only in the presence of small amount of PCA. The investigation of kinetics and selectivities of the oxidations demonstrated that the mechanisms of the reactions are different. Thus, in the oxidations catalyzed by the 1, 3+PCA and 4+ PCA systems the main oxidizing species is hydroxyl radical, and the oxidation in the presence of 2 as a catalyst has been assumed to proceed (partially) with the formation of ferryl ion, (FeIV=O)2+. In the oxidation catalyzed by the 4+PCA system (TONs attain 240) hydroxyl radicals were generated in the rate-determining step of monomolecular decomposition of the iron diperoxo adduct containing one PCA molecule. A kinetic model of the process which satisfactorily describes the whole set of experimental data was suggested. The constants of supposed equilibriums and the rate constant for the decomposition of the iron diperoxo adduct with PCA were estimated.
- Shul'pin, Georgiy B.,Nizova, Galina V.,Kozlov, Yuriy N.,Cuervo, Laura Gonzalez,Su?ss-Fink, Georg
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p. 317 - 332
(2007/10/03)
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- Unusual chemoselective addition of diisopropylzinc to 2,2′-bipyridine-5,5′-dicarbonyl compounds in the 2-position and autoxidative reconversion with carbon-carbon bond cleavage
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The chemoselective addition of diisopropylzinc to 2,2′-bipyridine-5,5′-dicarbonyl compounds in the 2-position and autoxidative reconversion with carbon-carbon bond cleavage was presented. It was shown that i-Pr2Zn do not add to the aldehyde moiety but to the 2-position of the bipyridine to afford possessing a quaternary carbon atom in a yield of 69%. It was found that the i-Pr2Zn does not add to the aldehyde but to the 2-position of the bipyridine ring by destroying the aromaticity of the pyridine ring.
- Tanji, Shigehisa,Shibata, Takanori,Sato, Itaru,Soai, Kenso
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p. 217 - 218
(2007/10/03)
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- Oxidations by the system 'hydrogen peroxide-manganese(IV) complex- acetic acid' - Part II: Hydroperoxidation and hydroxylation of alkanes in acetonitrile
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Higher alkanes (cyclohexane, n-pentane, n-heptane, methylbutane, 2- and 3-methylpentanes, 3-methylhexane, cis- and trans-decalins) are oxidized at 20 °C by H2O2 in air in acetonitrile (or nitromethane) solution in the presence of the manganese(IV) salt [L2Mn2O3](PF6)2 (L = 1,4,7-trimethyl- 1,4-7-triazacyclononane) as the catalyst. An obligatory component of the reaction mixture is acetic acid. Turnover numbers attain 3300 after 2 h, the yield of oxygenated products is 46% based on the alkane. The oxidation affords initially the corresponding alkyl hydroperoxide as the predominant product, however later these compounds decompose to produce the corresponding ketones and alcohols. Regio- and bond selectivities of the reaction are high: C(1): C(2): C(3): C(4) ? 1: 40: 35: 35 and 1°: 2°: 3°is 1: (15-40): (180-300). The reaction with both isomers of decalin gives (after treatment with PPh3) alcohols hydroxylated in the tertiary positions with the cis/trans ratio of ~2 in the case of cis-decalin, and of ~30 in the case of trans-decalin (i.e. in the latter case the reaction is stereospecific). Light alkanes (methane, ethane, propane, normal butane and isobutane) can be also easily oxidized by the same reagent in acetonitrile solution, the conditions being very mild: low pressure (1-7 bar of the alkane) and low temperature (- 22 to +27°C). Catalyst turnover numbers attain 3100, the yield of oxygenated products is 22% based on the alkane. The yields of oxygenates are higher at low temperatures. The ratio of products formed (hydroperoxide: ketone: alcohol) depends very strongly on the conditions of the reaction and especially on the catalyst concentration (at higher catalyst concentration the ketone is predominantly produced).
- Shul'pin, Georgiy B.,Suess-Fink, Georg,Lindsay Smith, John R.
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p. 5345 - 5358
(2007/10/03)
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- Oxidations by the reagent 'O2-H2O2-vanadium complex-pyrazine-2-carboxylic acid' - VIII. Efficient oxygenation of methane and other lower alkanes in acetonitrile
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Methane, ethane, propane, n-butane and isobutane can be readily oxidized in acetonitrile solution by air and H2O2 at 20-75°C using the catalytic system [n-Bu4N]VO3/pyrazine-2-carboxylic acid, Apart from alkyl hydroperoxides which are the primary oxidation products, more stable derivatives (alcohols, aldehydes or ketones and carboxylic acids) are obtained with high total turnover numbers (e.g., at 75°C after 4 h: 420 for methane and 2130 for ethane). It was shown in the case of ethane and cyclohexane that alkanes do not yield oxygenated products in the absence of air. The cyclohexane oxidation under an 18O2 atmosphere showed a high degree of 18O incorporation into the oxygenated products. Thus in the oxidation reaction described here H2O2 is only the promoter while O2 is the 'true' oxidant.
- Nizova, Galina V.,Suess-Fink, Georg,Shul'pin, Georgiy B.
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p. 3603 - 3614
(2007/10/03)
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- A kinetic study of the reactions of 2-propyl radicals in the liquid phase in the presence and absence of oxygen
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2-Propyl radicals have been generated from the photolysis of solutions of 2,2-azopropane and 2,4-dimethyl-3-pentanone in decane in a glass and a metal cell. The time course of their reactions in the presence and absence of oxygen has been monitored between 323 and 373 K. The primary process involves the formation of solvent-caged radical pairs, two 2-propyl radicals and a 2-propyl and a 2-methylpropanoyl radical from the azo and ketone precursors, respectively. Subsequently these radicals are partitioned between cage escape and dimerization and disproportionation within the cage. In oxygenated solution the free 2-propyl radicals are effectively trapped as 2-propylperoxyl radicals. However, oxygen does not react with the solvent-caged radicals. This leads to a major difference in the hydrocarbon products from the two precursors. 2,2′-Azopropane gives propane, propene, and 2,3-dimethylbutane from the start of the reaction whereas the ketone only gives propene. Following the depletion of oxygen, or in the absence of oxygen, both precursors behave analogously and give all three hydrocarbons. The 2-propylperoxyl radicals undergo self-reaction and hydrogen abstraction from the solvent to give 2-propanol, propanone, and 2-propyl hydroperoxide and, under conditions of low oxygen concentration, by reaction with 2-propyl radicals they give 2,2′-dipropylperoxide. Although the two cells lead to different overall rates of reaction, the relative rates and product distributions are unaffected by the cell design. A unified mechanism is described and the known and best estimates of rate constants for the individual steps are used to simulate the time dependence of the product yields from the photolysis of both precursors.
- Costello, Andrew R.,Lindsay Smith, John R.,Waddington, David J.
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p. 201 - 215
(2007/10/03)
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- Rate Constants for Reduction of substituted Methylperoxyl Radicals by Ascorbate Ions and N,N,N',N'-tetramethyl-p-phenylenediamine
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Absolute rate constants (k) for reduction of substituted methylperoxyl radicals by ascorbate ions and by TMPD (N,N,N',N'-tetramethyl-p-phenylenediamine) in aqueous solutions have been determined by pulse radiolysis.The rate constants vary from 1E6 to 1E9 M-1 s-1, increasing as the electron-withdraving capacity of the substituent on the peroxyl group increases.Linear correlations are observed between log k and the Taft substituents ?* for a wide variety of substituents, but not all substituents fit the same line.In the case of ascorbate as reductant, the points for peroxyl radicals that contain halogens on the α-carbon lie on a different line (ρ*=0.41) than that for the other substituents (ρ*=1.25).In the case of TMPD there are alsotwo families of peroxyl radicals: Those comprimising the electron-donating groups Me through t-Bu (ρ=5.6) and those containing electron-withdrawing substituents (ρ*=0.64).
- Neta, P.,Huie, R. E.,Mosseri, S.,Shastri, L. V.,Mittal, J. P.,et al.
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p. 4099 - 4104
(2007/10/02)
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- Reactions of Alkylperoxyl Radicals in Solution. Part 1. A Kinetic and Product Study of Self-reactions of 2-Propylperoxyl Radicals between 253 and 323 K
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The self-reactions of 2-propylperoxyl radicals have been studied between 253 and 323 K in decane solution.The ratio of the major products, propanone and propan-2-ol, as a function of temperature is in good agreement with the behaviour of other secondary peroxyl radicals in solution.The roles played by the solvent are considered by comparison with pervious studies of this radical in the gas phase.It is concluded that the increase in ketone production relative to the alcohol as the temperature is lowered is best explained by the inclusion of the bimolecular reaction of the peroxyl radical producing propanone and hydrogen peroxide.It is suggested that this reaction has Arrhenius parameters of A ca.E+6 dm3 mol-1 s-1 and Ea ca. 5 kJ mol-1.
- Bennett, John E.,Brunton, George,Schmith, Lindsay John R.,Salmon, Tom M. F.,Waddington, David J.
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p. 2433 - 2448
(2007/10/02)
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- REACTIONS OF OXYGENATED RADICALS IN THE GAS PHASE. PART 16. DECOMPOSITION OF ISOPROPOXYL RADICALS
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The photo-oxidation of trans-2,2'-azopropane has been studied between 333 and 434 K.The main products are propan-2-ol, isopropyl hydroperoxide, and acetone.Acetaldehyde becomes an increasingly important product as the temperature and pressure are increased.By altering the total pressure of the system, using nitrogen as diluent, quantitative data for the rate of decomposition of isopropoxyl radicals may be obtained. k11 varies markedly with pressure between 20 and 760 Torr in this temperature regime. .
- Akeel, Najah Y. Al,Waddington, David J.
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p. 1575 - 1580
(2007/10/02)
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- Reactions of Oxygenated Radicals in the Gas Phase. Part 12. The Reactions of Isopropylperoxyl Radicals and Alkenes
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The co-oxidation of trans-2,2'-azopropane and some aliphatic alkenes has been studied between 303 and 408 K.From the yields of molecular products, rate data have been obtained for the reaction of isopropylperoxyl radicals and the following alkenes, 2-methylbut-2-ene, 2-methylbut-1-ene, 2-methyl-propene, propene, and 3-fluoropropene (reaction (22)).It is shown that the isopropylperoxyl radical is less reactive than methylperoxyl but still shows distinct electrophilic character in these reactions.
- Sway, Mohammed I.,Waddington, David J.
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p. 139 - 144
(2007/10/02)
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- Reactions of Oxygenated Radicals in the Gas Phase. Part 11. Reaction of Isopropylperoxyl Radicals with 2,3-Dimethylbut-2-ene
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The reaction of isopropylperoxyl radicals with 2,3-dimethylbut-2-ene has been studied between 303 and 363 K, using the photo-oxidation of trans-2,2'-azopropane as a source of the radicals.The only product formed from the alkene is 2,3-dimethyl-2,3-epoxybutane.From a detailed study of the products, Arrhenius parameters for reaction (22) of log (A/dm3 mol-1s-1) = 7.96 +/- 0.50 and E/kJ mol-1 = 40.87 +/- 1.78 have been obtained.
- Sway, Mohammed I.,Waddington, David J.
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p. 999 - 1004
(2007/10/02)
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- Reactions of Oxigenated Radicals in the Gas Phase
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The principal product of the photo-oxidation of trans-2,2'-azopropane between 333 and 373 K are acetone, isopropyl alcohol, isopropyl hydroperoxide, acetaldehyde, formaldehyde, methyl alcohol and cis-2,2'-azopropane.The reaction mechanism has been simulated in detail, and, in conjunction with results obtained earlier for the overall self-reaction of isopropylperoxy radicals, the following rate data have been obtained for the reactions 2(CH3)2CHO2. --> (CH3)2CHOH + (CH3)2CO + O2 (3a) 2(CH3)2CHO2. --> 2(CH3)2CHO. + O2 (3b) k3b/k3a increases with temperature, from 1.39 +/-0.04 at 302 K and 2.80 +/- 0.08 at 373 K.Values of A3a and A3b of 2.44 +/- 0.31E7 and 1.38 +/-0.26E9 dm3 mol-1 s-1 and E3a and E3b of 12.0 +/- 1.0 and 21.3 +/- 1.5 kJ mol-1 were determined.
- Cowley, Leslie T.,Waddington, David J.,Woolley, Allan
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p. 2535 - 2546
(2007/10/02)
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