- Selective alkene oxidation with H2O2 and a heterogenized Mn catalyst: Epoxidation and a new entry to vicinal cis-diols
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Covalent anchoring of 1,4-dimethyl-1,4,7-triazacyclononane on silica gel is the first step in the preparation of a heterogenized Mn catalyst. When H2O2 is used as the oxidant, this material can catalyze the vicinal cis- dihydroxylation of disubstituted olefins, as shown schematically here. Both enantiomers of the product are obtained.
- De Vos, Dirk E.,De Wildeman, Stefaan,Sels, Bert F.,Grobet, Piet J.,Jacobs, Pierre A.
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p. 980 - 983
(2007/10/03)
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- Structure-reactivity dependence in the rearrangements of a family of alkylacetoxycarbenes
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Absolute rate constants and activation parameters are presented for the 1,2-H and 1,2-acetyl migrations of a family of alkylacetoxycarbenes.
- Moss, Robert A.,Merrer, Dina C.
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p. 8067 - 8070
(2007/10/03)
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- Competitive rearrangements of alkylacetoxycarbenes
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Absolute rate constants are determined for (1,2) acetyl, carbon, andhydride shifts in cyclobutylacetoxycarbene and isopropylacetoxycarbene; comparative reactivities are examined.
- Moss, Robert A.,Xue, Song,Ma, Wei,Ma, Huarong
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p. 4379 - 4382
(2007/10/03)
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- Ruthenium(VIII) mediated oxidation of some aliphatic and alicyclic ketones by periodate-ruthenium(III) system in aqueous HClO4 medium
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The kinetics of Ruthenium(III) chloride mediated oxidation of acetone, 2-butanone, 4-methyl-2-pentanone, 2-pentanone, 2-pentanone, cyclopentanone, and cyclohexanone by sodium periodate in aqueous HClO4 media was zero-order in [IO4-] and first-order dependence on [H+] for all the ketones independent of added [Ru(III)] and showed first-order dependence on [H+] for all the ketones studied, except acetone. In the case of acetone at [H+] +], the order in [Ru(III)] being unity; but at [H+] > 0.05 M the reaction showed unit dependence on [H+] and the order in [Ru(III)] was zero. Ruthenium(VIII) generated in situ is postulated as the hydride abstracting species. A mechanism involving enolization as the rate determining step is proposed. Acetone at lower acidity of the medium is shown to react directly with Ru(VIII). In the absence of ruthenium(III) chloride, the kinetics were first-order in [IO4-], [ketone], and [H+]. Structure-reactivity relationship is discussed and thermodynamic parameters are reported.
- Panda,Pati
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p. 453 - 460
(2007/10/03)
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- Cobalt(II)-Catalyzed Reaction of Aldehydes with Acetic Anhydride under an Oxygen Atmosphere: Scope and Mechanism
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The reaction of aldehydes with acetic anhydride in the presence of catalytic cobalt(II) chloride under an oxygen atmosphere at ambient temperature is dependent upon the reaction medium.Aliphatic aldehydes react in acetonitrile to give 1,2-diones whereas the aromatic aldehydes are acylated to yield the corresponding acylals.On the other hand, carboxylic acids are obtained from aliphatic and aromatic aldehydes by conducting the reaction in dichloroethane or benzene.Cobalt(II) chloride in acetonitrile catalyzes the conversion of aliphatic aldehydes to the correspondinganhydrides in the absence of acetic anhydride whereas aromatic aldehydes remain largely unaffected under these conditions.A preliminary mechanistic study in three different solvents (i.e. acetonitrile, dichloroethane, and DMF) has revealed that in acetonitrile and in the presence of acetic anhydride, aliphatic aldehydes behave differently than aromatic aldehydes.Some trapping experiments using methyl acrylate and stilbene have been conducted to demonstrate the occurence of an acyl cobalt and peroxyacyl cobalt intermediate during these reactions.
- Bhatia, Beena,Punniyamurthy, T.,Iqbal, Javed
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p. 5518 - 5523
(2007/10/02)
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- Kinetics and Mechanism of Oxidation of Aliphatic Ketones by Bromamine-B in Alkaline Buffer Medium
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The title reaction in buffer medium (pH 9-11) at 303.15 K shows first order dependence in 0 but variable dependence (one to zero) in 0.The rate increases with increase in pH.The reaction product, benzenesulphonamide retards the rate.Variation of ionic strength of medium or the addition of halide ions has no effect on the rate.Kinetic and thermodynamic parameters have been calculated and the isokinetic temperature, 350 K is much above the temperature employed (303.15 K).The rate increases in the order: pentan-3-one A suitable mechanism is proposed.
- Mohan, K.,Mahadevappa, D. S.
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p. 702 - 705
(2007/10/02)
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- Kinetics of Oxidaton of Aliphatic Ketones with Bromamine-T in Acid Medium
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The kinetics of oxidation of 2-propanone, 2-butanone, 2-pentanone, 3-pentanone, and 4-methyl-2-pentanone by sodium salt of N-bromo-p-toluenesulfonamide or bromamine-T (BAT) in presence of HClO4 was studied at 30 degC.The rate law is: .Variation of ionic strength of medium or addition of reaction product p-toluenesulfonamide have no effect on the rate.The dielectric effect is positive.The acid-catalyzed enolization of ketone is assumed to be the rate-limiting step and enolization rate coefficients have been calculated.Proton inventory studies made in H2O-D2O mixtures have been employed to calculate the isotropic fractionation factors.Isokinetic temperature is 320 K indicating enthalpy as a controlling factor.
- Mahadevappa, Dandinasivara S.,Swamy, Putta
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p. 543 - 548
(2007/10/02)
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- Kinetic Evidence for the Enol Intermediate in Oxidation of Isopropyl Methyl Ketone and Isobutyl Methyl Ketone by Bromamine-T in Perchloric Acid Media
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The oxidation kinetics of isopropyl methyl ketone (IPMK) and isobutyl methyl ketone (IBMK) by acidic solution of bromamine-T (BAT) show zero order dependence on BAT and first order on both ketones and H+.No effect of p-toluenesulphonamide (TSA) was evident.The observed stoichiometry, zero effect of ionic strength and a solvent isotope effect (koD2O/koH2O=2.04 -2.32 at 35 deg, 2.16 -2.42 at 40 deg for IPMK, and 1.80 - 2.18 at 35 deg, 1.89 -2.24 at 40 deg for IBMK oxidations) point to a mechanism involving catalysed enolisation of ketones in the slow and rate determining step, followed by its subsequent fast interaction with BAT giving final products.Activation parameters and isolation of products are in agreement with the proposed mechanism.
- Singh, Bharat,Singh, Deepika,Chand, Rajendra,Singh, A. K.
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p. 741 - 744
(2007/10/02)
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- KINETICS AND MECHANISM OF OXIDATION OF SOME KETONES BY N-BROMOACETAMIDE
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The kinetics of oxidation of n-butyl methyl ketone (n-BMK) and i-butyl methyl ketone (i-BMK) by N-bromoacetamide (NBA) is studied in perchloric acid media in the presence of mercuric acetate.The main product of the oxidation is the corresponding 1,2-dicarbonyl compound.The reaction order with respect to NBA is zero while with respect to ketone and H+ it is unity.Mercuric acetate, acetamide and sodium perchlorate have negligible effect on the reaction rate, while the dielectric effect is negative.A solvent isotope effect (k0(D2O)/k0(H2O) = 1.80-2.05 and 1.70-2.06 for n-BMK and i-BMK, respectively ) at 35 deg C is observed.On the basis of the available evidence a suitable mechanism consistent with the experimental results is proposed in which it is suggested that the mechanistic route for NBA oxidation is through the enol form of the ketone in an acidic medium.
- Singh, Bharat,Shrivastav, Rohit
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p. 2749 - 2756
(2007/10/02)
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- OXIDATION OF ALIPHATIC KETONES BY BROMAMINE-B: A KINETIC STUDY
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The kinetics of oxidation of propan-2-one, butan-2-one, pentan-2-one, pentan-3-one and 4-methyl pentan-2-one by sodium N-bromobenzenesulphonamide or bromamine-B (BAB) in perchloric acid medium was studied at 30 deg C.The rate shows a first order dependence each on and +> and is independent of .Variation of ionic strength of medium and addition of the reaction product benzenesulphonamide have no effect on the rate and the dielectric effect is positive.The proposed mechanism involves acid catalysed enolisation of ketone in the rate limiting step followed by a fast interaction with the oxidant.This is supported by the magnitude of inverse solvent isotope effect of 1.62 +/- 0.01 observed in D2O medium.Activation parameters Ea, ΔH*, ΔS*, ΔG* and log A have been calculated by studying the reaction at different temperatures (293-309 K).
- Mahadevappa, D.S.,Mohan, K.,Ananda, S.
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p. 4857 - 4866
(2007/10/02)
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- MECHANISM OF OXIDATION OF SOME ALIPHATIC KETONES BY N-BROMOSUCCINIMIDE IN ACIDIC MEDIA
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Kinetics of the oxidation of methyl n-propyl ketone and methyl isobutyl ketone by N-bromosuccinimide (NBS) have been studied in perchloric acid media in presence of mercuric acetate.A zero order dependence to N-bromosuccinimide and a first order dependence to both ketones and hydrogen ion concentrations have been observed.Sodium perchlorate, mercuric acetate and succinimide additions have negligible effect while methanol addition has a positive effect on the reaction rate.A solvent isotope effect (k0D2O/K0H2O=2.3-2.7 and 2.4-2.8 for MeCOn.pr and MeCOi-Bu, respectively) has been observed at 35 deg.Kinetic investigations have revealedthat the order of reactivity is methyl n-propyl ketone>methyl isobutyl ketone.Various thermodinamic parameters have been computed and corresponding 1,2-diketones were found to be the products.A suitable mechanism in conformity with the above observations has been proposed.
- Singh, Bharat,Pandey, Lalji,Sharma, J.,Pandey, S. M.
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p. 169 - 172
(2007/10/02)
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