Kinetics and mechanism of OsO4 catalyzed oxidation of chalcones by Ce4 in aqueous acetic sulfuric acid media

Kinetics of OsO₄ catalyzed oxidation of chalcones by Ce⁴⁺ has been studied in aqueous acetic-sulfuric acid medium in the temperature range 313 to 338 K. The order in [oxidant] is zero while the order with respect to [substrate] and [catalyst] are each fractional. The rate of the reaction decreased with increase in percentage of acetic acid while [H⁺] had practically no effect on the rate The rates of various substituted chalcones (with substituents in the phenyl. ring attached to the moiety) are in the orderp-CH₃>m-CH₃>H>p-Cl>m-Cl>m-NO₂>p-NO₂. A mechanism in which formation of a cyclic ester between chalcone and OsO₄ in a fast step followed by its decomposition in a rate-determining step is envisaged.

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Ce⁴⁺, OsO₄, - 313–338 . —, —. , [H⁺] . ( , : -CH₃>-CH₃>H>-Cl>-NO₂>-NO₂. , OsO₄ , , .

     

Kinetics and mechanism of oxidation of methanol by acid bromate

The kinetics of oxidation of methanol by bromate ion in hydrochloric acid medium has been investigated. A mechanism consistent with the experimental observations is suggested.

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. , .

     

Kinetics and mechanism of oxidation of benzoic acid hydrazide by bromate catalyzed by octamolybdomanganate(II)

Oxidation of benzoic acid hydrazide by bromate in the presence of octamolybdomanganate(II), [Mn^IIMo₈O₂₇]⁴⁻, was studied in hydrochloric acid medium. The mechanism of the reaction involves oxidation of the catalyst to [Mn^IVMo₈O₂₇]²⁻ by bromate which then forms a complex with the unoxidized catalyst. Both the complex and [Mn^IVMo₈O₂₇]²⁻ react with the substrate in rate-determining steps to generate an intermediate acyl diimide, RCONNH. The reaction of water with the diimide then leads to the formation of benzoic acid and nitrogen as products through an NH–NH intermediate. There was no formation of free radical, indicating the involvement of only two-electron transfer steps in the mechanism. The order of more than unity in catalyst concentration is due to the formation of complex between the catalyst and the oxidized form of the catalyst. A rate law explaining all the kinetic results has been derived and verified. The effects of ionic strength and solvent polarity have also been studied, and the thermodynamic parameters were determined. A less solvated transition state as a result of interaction between the complex and oxidized form of the catalyst satisfactorily explains all the effects observed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Kinetics and mechanism of oxidation of N, N'-dimethylaminoiminomethanesulfinic acid by acidic bromate

The major metabolites of the physiologically active compound dimethylthiourea (DMTU), dimethylaminoiminomethansesulfinic acid (DMAIMSA), and dimethylaminoiminomethanesulfonic acid (DMAIMSOA) were synthesized, and their kinetics and mechanisms of oxidation by acidic bromate and aqueous bromine was determined. The oxidation of DMAIMSA is much more facile and rapid as compared to a comparable oxidation by the same reagents of the parent compound, DMTU. The stoichiometry of the bromate-DMAIMSA reaction was determined to be 2BrO 3 (-) + 3NHCH 3(NCH 3)CSO 2H + 3H 2O --> 3SO 4 (2) (-) + 2Br (-) + 3CO(NHCH 3) 2 + 6H (+), with quantitative formation of sulfate. In excess bromate conditions, the stoichiometry was 4BrO 3 (-) + 5NHCH 3(NCH 3)CSO 2H + 3H 2O --> 5SO 4 (2) (-) + 2Br 2 + 5CO(NHCH 3) 2 + 6H (+). The direct bromine-DMAIMSA reaction gave an expected stoichiometric ratio of 2:1 with no further oxidation of product dimethylurea (DMU) by aqueous bromine. The bromine-DMAIMSA reaction was so fast that it was close to diffusion-controlled. Excess bromate conditions delivered a clock reaction behavior with the formation of bromine after an initial quiescent period. DMAIMSOA, on the other hand, was extremely inert to further oxidation in the acidic conditions used for this study. Rate of consumption of DMAIMSA showed a sigmoidal autocatalytic decay. The postulated mechanism involves an initial autocatalytic build-up of bromide that fuels the formation of the reactive oxidizing species HBrO 2 and HOBr through standard oxybromine reactions. The long and weak C-S bond in DMAIMSA ensures that its oxidation goes directly to DMU and sulfate, bypassing inert DMAIMSOA.     

Kinetics and mechanism of oxidation of some aryl alcohols by acid bromate

The kinetics of oxidation of some substituted benzyl alcohols as well as the unsubstituted one by bromate ion in hydrochloric acid medium has been suggested. The results indicate that the reaction takes place by way of intermediate ester formation. Methoxy compounds react at much faster rates than the corresponding nitro substituted derivatives. The thermodynamic values associated with the equilibrium step and also for the slow step have been evaluated. A mechanism consistent with the experimental observations has been suggested.     

Kinetics of oxidation of ethanol by acid bromate

The kinetics of oxidation of ethanol by bromate ion in hydrochloric acid medium has been investigated. The reaction involves the formation of the intermediate bromate ester which is facilitated by the methyl group in ethanol but the electron attracting character (F>Cl>Br) of the halogens attached to the -carbon of the alcohol makes the esterification more difficult.

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. , , , (F>Cl>Br), - , .

     

Kinetics of vanadium (V) catalyzed oxidation of gallic acid by potassium bromate in acid medium

The kinetics of oxidation of gallic acid with potassium bromate in the presence of vanadium(V) catalyst in aqueous acid medium has been studied under varying conditions. The active species of catalyst and oxidant in the reaction were understood to be HBrO₃ and VO₂⁺. The autocatalysis exhibited by one of the products, i.e. Br⁻, was attributed to complex formation between bromide and vanadium(V). A composite scheme and rate law were possible, some reaction constants involved in the mechanism have been evaluated. © 1996 John Wiley & Sons, Inc.     

The He(I) photoelectron spectra of OsO4, and RuO4

The photoelectron spectra of ruthenium tetroxide and osmium tetroxide excited by He(I) radiation are reported. From their interpretation it follows that the first two strong low energy transitions in the electronic absorption spectra of OsO₄, RuO₄, TcO^?₄, ReO^?₄, MoO^2?₄ and WO^2?₄ can be assigned to t₁ → 2e and 3t₂ → 2e respectively.     

Kinetics and mechanism of hydrazine oxidation by oxygenated Co2(L-his)4O2 complex

The kinetics of Co₂ (L-his)₄O₂ reduction by hydrazine in aqueous solution has been studied and the rate constants, the energy and entropy of activation have been determined.

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, , Co₂ (L-)₄O₂ .

     

Kinetics and mechanism of oxidation of secondary alcohols by potassium bromate

The oxidation by Br(V) of propan-2-ol follows the rate law (?d[Br(V)]/dt) = k₄ [alcohol][Br(V)][H⁺]². The initial reaction is complicated by the presence of the product bromide ion. The reaction is composed of two second order reactions—the first, a comparatively slow one and the second stage, a faster reaction which is mainly bromine oxidation. The pure bromate oxidation can be followed by the initial addition of mercuric acetate which prevents the accumulation of bromine in the system under these conditions. The reaction rate does not depend on the nature and structure of the alcohol. A mechanism involving a slow rate-determining formation of an alkyl-bromate ester followed by a fast decomposition to the products is in accord with the observed results.     

Kinetics and mechanism of oxidation of benzohydrazide by bromate catalyzed by vanadium(IV) in aqueous acidic medium

The reaction between benzohydrazide and potassium bromate catalyzed by vanadium(IV) was studied under pseudo‐first‐order condition keeping large excess of hydrazide concentration over that of the oxidant. The initiation of the reaction occurs through oxidation of the catalyst vanadium(IV), VO²⁺, to vanadium(V), VO, which then reacts with hydrazide to give N,N′‐diacylhydrazine and benzoic acid as the products. The order in [H⁺] is found to be two, and its effect is due to protonation and hydrolysis of oxidized form of the catalyst to form HVO₃. The oxidized form of the catalyst, VO, forms a complex with the protonated hydrazide as evidenced by the occurrence of absorption maxima at 390 nm. The rate of the reaction remains unaffected by the increase in the ionic strength. The activation parameters were determined, and data support the mechanism. The detailed mechanism and the rate equation are proposed for the reaction. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 151–159, 2008     

Kinetics of oxidation of isopropanol by IO4? catalyzed by metal ions

The kinetics of oxidation of isopropanol (IPA) by IO ₄ ^– in the presence of Os(VIII), Ru(III) and mixture of Os(VIII) and Ru(III) has been studied. The catalytic effect was found to be in the order Os(VIII)

IO ₄ ^– Os(VIII), Ru(III) Os(VIII) Ru(III), . : Os(VIII)     

Kinetics and mechanism of rhodium(III)-catalysed oxidation of 1,2-glycols by acid bromate

Summary Rh^III-catalysed oxidation of 1,2-glycols by acid bromate was studied in the presence of Hg(OAc)₂ at 40°C. The order is zero with respect to [BrO ₃ ^– ] and unity in [Rh^III] and in [glycol]. The oxidation rate is unaffected by variation in [H⁺] and added salts. Stoichiometric studies indicate that one mole of bromate consumes three moles of glycol giving the corresponding carbonyl compounds. A suitable mechanism involving direct reaction between Rh^III and glycol to give product,via hydride ion abstraction by Rh^III, is proposed.     

Kinetics and mechanism of the oxidation of acrylic acid and methyl methacrylate

The kinetics of the initiated oxidation of acrylic acid and methyl methacrylate in the liquid phase were studied volumetrically by measuring oxygen uptake during the reaction. Both processes proceed via the chain mechanism with quadratic-law chain termination. The oxidation rate is described by the equation w = k ₂/(2k ₆)^1/2[monomer]w _i ^1/2 , where w _i is the initiation rate and k ₂ and k ₆ are the rate constants of chain propagation and termination. The parameter k ₂/(2k ₆)^1/2 is 7.58 × 10^?4 (l mol^?1 s^?1)^1/2 for acrylic acid oxidation and 2.09 × 10^?3 (l mol^?1 s^?1)^1/2 for the oxidation of methyl methacrylate (T = 333 K). For the oxidation of acrylic acid, k ₂ = 2.84 l mol^?1 s^?1 (T = 333 K) and the activation energy is E ₂ = 54.5 kJ/mol; for methyl methacrylate oxidation, k ₂ = 2.96 l mol^?1 s^?1 (T = 333 K) and E ₂ = 54.4 kJ/mol. The enthalpies of the reactions of RO ₂ ^? with acrylic acid and methyl methacrylate were calculated, and their activation energies were determined by the intersecting parabolas method. The contribution from the polar interaction to the activation energy was determined by comparing experimental and calculated E ₂ values: ΔE _μ = 5.7 kJ/mol for the reaction of RO ₂ ^? with acrylic acid and ΔE _μ = 0.9 kJ/mol for the reaction of RO ₂ ^? with methyl methacrylate. Experiments on the spontaneous oxidation of acrylic acid provided an estimate of the rate of chain initiation via the reaction of oxygen with the monomer: w _i,0 = (3.51 ± 0.85) × 10^?11 mol l^?1 s^?1 (T = 333 K).     

The OsO4-mediated oxidative cleavage of olefins catalyzed by alternative osmium sources

The OsO₄-mediated oxidative cleavage of olefins is compatible with alternative, easier-to-handle osmium sources. Four different osmium sources were employed with favorable results.     

Kinetics and mechanism of Ru(III)-catalyzed oxidation of aliphatic alcohols by trichloroisocyanuric acid in HClO4 medium

The kinetics and mechanism of Ru(III)-catalyzed oxidation of some aliphatic alcohols by trichloroisocyanuric acid (TCICA) has been studied in aqueous HOAc-HClO₄ medium. The reaction is zero order in [TCICA], fractional order in [alcohol] and first order in [Ru(III)]. The reaction is insensitive towards changes in acid concentration. The rate is not affected by an increase in [Cl⁻]. The polar reaction constant (ρ*) was found to be −1.27 at 308 K. A mechanism involving complex formation between the substrate and catalyst in the fast equilibrium step followed by its decomposition in a slow step is proposed.     

Kinetics and mechanism of oxidation of anisole and substituted anisoles by acid bromate in acetic acid-water mixture

Oxidation of anisoles by acid bromate has been studied in acetic acid-water system in the presence of sulphuric acid. The reaction is first order each in [anisole] and [Br(V)]. The rate of reaction increased with increase in [H⁺] and percentage of acetic acid. The products of oxidation have been identified as ortho and para hydroxyanisoles. From the effect of [H⁺] and [acetic acid] on rate, H ₂ ⁺ BrO₃ has been established as the reactive species. Anisoles having electron-donating substituents in the benzene ring accelerate the rates and vice versa with a Hammett ρ value of −0.6. A mechanism involving the attack of H ₂ ⁺ BrO₃ on ortho/para position of the anisole in the rate-determining step has been proposed.     

Kinetics and mechanism of the oxidation of substituted mandelic acids by acid permanganate

The oxidation of mandelic acid and nine monosubstituted mandelic acids by acid permanganate, in the presence of fluoride ions, have been studied. The reaction is of first order with respect to each the oxidant, the substrate and hydrogen ions. The kinetic isotope effect, k_H/k_D = 3·76 at 25°. The oxidation exhibits a reaction constant ?+= ?2·23 ± 0·07 at 25°. The oxidation does not induce polymerisation of acrylonitrile and does not show any solvent isotope effect. The activation enthalpies entropies are linearly related (r = 0·979). A mechanism involving transfer of a hydride ion to the oxidant is proposed.     

Kinetics and mechanism of acid catalyzed oxidation of phenol and substituted phenols by isoquinolinium bromochromate

Oxidation of phenols by isoquinolinium bromochromate (IQBC) in aqueous acetic acid leads to the formation of corresponding quinones. The reaction is first order with respect to both phenol and IQBC and catalysed by hydrogen ion. The rate of oxidation decreases with increase in dielectric constant of solvent indicating ion-dipole interaction. The rate of oxidation decreases with increase in concentration of KCl, this may be due to the formation of less reactive species by interaction of Cl⁻ and protonated IQBC. The specific rates of oxidizing phenol reaction correlate with substituents constants affording negative reaction constants. Hammett plot is found to be valid and the correlation between enthalpies and free energies of activation is reasonably linear with an isokinetic temperature of 320 K.     

Ruthenium catalysed oxidation without CCl4 of oleic acid, other monoenic fatty acids and alkenes

Ruthenium catalysed oxidation of alkenes and monoenic fatty acids is reported. The study of the influence of cosolvents (H₂O/MeCN/X) shows that toxic CCl₄ initially used in the Sharpless system (H₂O/MeCN/CCl₄) can be avoided and demonstrates that the oxidative cleavage of CC bond could be accomplished in good yields with H₂O/MeCN/AcOEt solvent system in a ratio 3/2/2, respectively.