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Osmium(VIII) catalyzed oxidation of a sulfur containing amino acid - A kinetics and mechanistic approach
Abstract
The kinetics of osmium (VIII) catalyzed oxidation of DL-methionine by hexacyanoferrate(III) (HCF) in aqueous alkaline medium at a constant ionic strength of 0.50 mol dm−3 was studied spectrophoto-metrically. The reaction between hexacyanoferrate(III) and DL-methionine in alkaline medium exhibits 2:1 stoichiometry (2HCF:DL-methionine). The reaction is of first order each in [HCF] and [Os(VIII)], less than unit order in [alkali] and zero order for [DL-methionine]. The decrease in dielectric constant of the medium increases the rate of the reaction. The added products have no effect on the rate of reaction. The main products were identified by spot test. A free radical mechanism has been proposed. In a prior equilibrium step Os(VIII) binds to OH− species to form a hydroxide species and reacts with [Fe(CN)6]3− in slow step to form an intermediate species(C1). This reacts with a molecule of DL-methionine in a fast step to give the sulfur radical cation of methionine and yields the sulfoxide product by reacting with another molecule of [Fe(CN)6]3−. The rate constant of the slow step of the mechanism is calculated. The activation parameters with respect to slow step of the mechanism are evaluated and discussed.
... Oxidation of organic compounds by hexacyanoferrate(III) as an efficient one-electron oxidant has been a subject of much interest especially in alkaline media [6][7][8][9][10][11][12][13][14][15][16][17]. The usefulness of HCF may be due to its high stability, water solubility and its moderate reduction potential of 0.45 V, leading to its reduction to HCF(II), a stable product [18]. ...
... On the other hand, complexes of metal ions with organic ligands containing N, S or O are well known [13][14][15][16][17]. The presence of heteroatom in such ligands plays a key role when coordinated with transition metal ions. ...
... Moreover, fluorene is considered as effective and pronounced precursor for synthesis of photochromic di and tetrahydroindolizines [11][12][13][14]. On the other hand, oxidation of organic compounds by hexacyanoferrate (III) has been a subject of much interest especially in alkaline media [15][16][17][18][19][20][21][22][23][24][25][26] because hexacyanoferrate (III) has a high stability, water solubility and moderate reduction potential [27]. A literature survey revealed no work has been reported about the kinetics of oxidation of fluorene by any oxidant. ...
... The oxidative cleavage of formamidines is quite important, since the N,N-dialkyl formamidine group is one of the most versatile protecting groups, especially in biosynthetic applications. Furthermore, complexes of metal ions with organic ligands containing N, S or O are well known [5][6][7][8][9]. The presence of heteroatom in such ligands plays a key role when coordinated with transition metal ions. ...
Oxidation of methylaminopyrazole formamidine (MAPF) by permanganate ion was studied spectrophotometrically in neutral medium in the presence of phosphate buffer solution. The stoichiometry of the reaction was found to be 3: 2 (MAPF: MnO 4 - ). The oxidation reaction showed a first order kinetics with respect to [MnO 4 - ] and a fractional-first order dependence with respect to [MAPF]. Addition of small amounts of some metal ions increased the oxidation rate and the order of catalytic efficiency was: Ag(I) > Cu(II) > Al(III). The suggested oxidation mechanism involves formation of a 1:1 intermediate complex between permanganate ion and MAPF. The formed complex decomposes in the rate-determining step to yield a free radical derived from MAPF and an intermediate Mn(VI). The free radical is attacked by Mn(VI) species to give rise to the final oxidation products which were identified by both spectroscopic and chemical tools as methylaminopyrazole, dimethylamine and carbon dioxide. The rate-law expression was deduced and the reaction constants involved in the different steps of the suggested mechanism were evaluated. The activation parameters of the rate constant of the slow step along with the thermodynamic quantities of the formation constant of the intermediate complex were evaluated and discussed.
... Hexacyanoferrate(III) is an efficient one-electron oxidant for oxidation of various organic compounds especially in alkaline media [7,8,[15][16][17][18][19][20][21][22][23][24][25][26]. The usefulness of HCF may be due to its high stability, water solubility and its moderate reduction potential of 0.45 V, leading to its reduction to HCF(II), a stable product [27]. ...
... The ion paired species like Na[Fe(CN) 6 ] 2may be formed in situ, by interacting [Fe(CN) 6 ] 3with Na + of aqueous solutions of NaNO 3 and NaOH. Similar type of ion pairing between K + and [Fe(CN) 6 ] 3was observed [26]. ...
Kinetics of ruthenium(III) catalyzed oxidation of L-proline by hexacyanoferrate(III)(HCF) in alkali was studied spectrophotometrically at 30 0 C. A reaction was found to be independent upon [L-proline]. The reaction was occurred without intervening free radical. Since unit order each in [Ru(III)] and [HCF], the oxidation follows an outer-sphere mechanism. A suitable mechanism was proposed and rate law was derived as k obs = k K 1 [Ru(III) [OH ] 1+ K 1 [OH ] The rate constant, 'k' and equilibrium constant 'K 1 ' of the prior equilibrium step of reaction, [Ru(H 2 O) 6 ] 3+ + OH [Ru(H 2 O) 5 (OH)] 2+ were calculated. The oxidative product of L-proline was analyzed quantitatively as L-glutamic acid. Activation parameters were evaluated.
The kinetic investigation of Os(VIII) accelerated oxidation of L-phenylalanine (L-Pheala) by hexacyanoferrate(III) (HCF(III)) in CTAB micellar medium was carried out by measuring the decrease in absorbance at 420 nm, which corresponds to HCF(III). By adjusting one variable at a time, the progression of the reaction has been inspected as a function of [OH−], ionic strength, [CTAB], [Os(VIII)], [L-Pheala], [HCF(III)], and temperature using the pseudo-first-order condition. The results show that [OH−], [CTAB], and [L-Pheala] are the critical parameters with a discernible influence on reaction rate. The reaction exhibits first-order kinetics in the examined concentration range of Os(VIII), HCF(III), as well as at lower [L-Pheala] and [OH−], but follows less than unit order at higher concentrations of L-Pheala and alkali. The incremental trend in reaction rate with electrolyte concentration demonstrates a positive salt effect. CTAB significantly catalyzes the process, and once at a maximum, the rate remains almost constant as [CTAB] increases. The observed decrease in CTAB CMC could be attributed to reduced repulsion between the positively charged heads of surfactant molecules caused by the negatively charged HCF(III) and OH−. The activation values also support our proposed outer-sphere electron transport mechanism.
The kinetics and mechanistic aspects of the oxidation of two beta-lactam antibiotics (A), ampicillin and flucloxacillin, by alkaline hexacyanoferrate(III) (HCF(III)) were examined using spectrophotometry at fixed temperature. The oxidation reactions showed a 1:4 (A: HCF(III)) stoichiometry. The reaction kinetics were found to follow first order dependence for the oxidant and fractional-first order dependence for [A] and [OH-]. The enhancement of the ionic strength and dielectric constant was found to increase the oxidation rates. Free radical tests of the reactions showed positive results. The addition of HCF(II) as a predicted oxidation product did not considerably change the oxidation rates. Under the same experimental conditions, the oxidation rate of ampicillin was found to be slightly lower than that the rate of flucloxacillin oxidation. The acquired oxidation products were recognized using spot testing and FT-IR spectra. A conceivable oxidation mechanism was suggested. A derived rate-law expression was found to be consistent with the experimental results. The activation parameters were assessed and discussed.
The catalytic effect of ruthenium(III) on the oxidation of N, N-dimethyl- N
′-(4H-1,2,4-triazol- 3-yl) formamidine (ATF) by hexacyanoferrate(III) (HCF) was studied spectrophotometrically in aqueous alkaline medium. Both uncatalyzed and catalyzed reactions showed first order kinetics with respect to [HCF], whereas the reaction orders with respect to [ATF] and [OH −] were apparently less than unity over the concentration range studied. A first order dependence with respect to [RuIII] was obtained. Increasing ionic strength increased the rate of uncatalyzed reaction and decreased the rate of the catalyzed one Plausible mechanistic schemes of oxidation reactions have been proposed. In both cases, the final oxidation products are identified as aminotriazole, dimethyl amine and carbon dioxide. The rate laws associated with the reaction mechanisms are derived. The reaction constants involved in the different steps of the mechanisms were calculated. The activation and thermodynamic parameters have been computed and discussed.
Graphical Abstract
The catalytic effect of ruthenium(III) on the oxidation of N,N-dimethyl-N’-(4H-1,2,4-triazol-3-yl) formamidine by alkaline hexacyanoferrate(III) has been studied. The final oxidation products are identified as aminotriazole, dimethyl amine and carbon dioxide.
Kinetics of oxidation of alanine by osmium(VIII) was studied in alkaline medium at 25°C. The reaction was found to have first order dependence each in [OsVIII] and [alanine] and second order in [OH-], which changed to zero order at higher concentration of [OH-]. The main product of the oxidation is the corresponding aldehyde. Temperature variation has also been studied for calculating different activation parameters. Spectroscopic evidence for the complex formation between OsVIII and substrate was obtained from a UV-Visible spectra of OsVIII, alanine and mixture of both. A plausible mechanism has been proposed to account for the experimental results.
The iridium(III) catalyzed hexacyanoferrate(III) (abbreviated HCF(III)) oxidation of cystine in aqueous alkaline medium has been investigated spectrophotometrically. The reaction is found first order in oxidant, catalyst and alkali concentration while with substrate concentration reaction follows Michaelis-Menten type kinetics. Positive salt effect was observed by using the potassium chloride solution. Different activation parameters were also evaluated by studying the reaction at four different temperatures. The stoichiometry of the reaction was found 1:8 of reductant and oxidant. A suitable mechanism has been proposed to explain all the experimental results. It is assumed that reaction proceeds through complex formation between substrate (abbreviated S) and iridium trichloride. A rate law has been derived which verifies the results.
The kinetics of oxidation of methionine, an important, sulphur-containing essential amino acid, by N-chloronicotinamide (NCN) in the presence of 0.8 mol dm-3 HCl in aqueous acetic acid medium at constant ionic strength has been studied. The reaction shows fractional order with respect to substrate, inverse first order to oxidant and first order to hydrochloric acid. Addition of the reaction product, nicotinamide (NA), retarded the reaction. The rate increases with the increase in acetic acid proportion. Increase in temperature increases the rate. The activation parameters have been evaluated by studying the reaction at temperatures 300-325 K. The stoichiometry of the reaction was found to be 1:2. Molecular chlorine has been postulated as the reactive oxidising species. Methionine sulphoxide was the product. The product obtained was isolated and identified.
The kinetics of oxidation of methionine, an important sulphur-containing essential amino acid, by N-bromonicotinamide (NBN) in the presence of 0.8 mol dm-3 HCl in aqueous acetic acid medium at constant ionic strength has been studied. The reaction shows fractional order with respect to substrate, inverse first order about oxidant and hydrochloric acid. Addition of the reaction product, nicotinamide (NA), retarded the reaction. The rate increases with the increase in acetic acid proportion. Increase in temperature increases the rate. The activation parameters have been evaluated by studying the reaction at different temperatures. The stoichiometry of the reaction was found to be 1:1. HOBr has been postulated as the reactive oxidising species. Methionine sulphoxide was the product. The product obtained was isolated and identified.
The kinetics of the silver(I)-catalysed oxidation of valine with cerium(IV) has been studied in perchloric acid medium. An usual decrease in rate with increasing concentration of cerium(IV) is observed and the detailed quantitative analysis of this behaviour is presented on the basis of dimerisation of cerium(IV). The reaction exhibits fractional dependence on valine and that has been accounted for the formation of an adduct with silver(I). A plausible reaction mechanism is given and the rate law is derived: (equation) where the observed k is second order rate constant.
pH metric equilibrium measurements have been performed at a temperature of 303 K and an ionic strength of 0.16 mol L-1 NaCl for the interaction of calcium(II), magnesium(II), and zinc(II) with L-Histidine in (0-60 % v/v) DMSO-water mixtures. The complexation models for systems of histidine with calcium(II), magnesium(II), and zinc(II) have been established from modeling studies using the computer program MINIQUAD75 from the pH metric data. The best fit chemical models were selected based on the statistical parameters like crystallographic R factor and sum of the squares of residuals in mass-balance equations. The models for binary species contain ML2H, ML2H2, ML2H3, and ML2H4 for Ca(II), and ML2 , ML2H, ML2H2, ML2H3, and ML2H4 for Mg(II) and Zn(II) in DMSO-water mixtures. The variation of stability constants with change in the dielectric constant of the medium was explained based on electrostatic and non-electrostatic forces. Distribution diagrams of various species of the complexes in relation to pH are presented at different compositions of DMSO-water mixtures.
Keywords: complex equilibria, stability constants, metal, histidine, DMSO, pH-metry.
Kinetics of oxidation of glycine (gly) and valine (val) by N-bromosuccinimide (NBS) using chloro complex of Rh(III) in its nano-concentration range as homogeneous catalyst have been investigated at 35 °C . The reaction shows first order kinetics with respect to NBS and Rh(III) in the oxidation of both the amino acids. The first order kinetics with respect to amino acid obtained at its lower concentration changes to zero order at its higher concentration. Inverse fractional order with respect to [H+] was obtained in Rh(III)-catalysed oxidation of gly and val. Variation in [Hg(II)], [NHS], [Cl?], ionic strength and dielectric constant of the medium has no effect on the rate of oxidation of both the amino acids. NBS itself and [RhCl 5(H 2O)] 2- have been postulated as the reactive species of NBS and Rh(III) chloride in acidic medium, respectively. Various activation parameters have been calculated with the pseudo-first-order rate constant values observed at four different temperatures. The main oxidation products of the reactions have been identified as formaldehyde and ammonia in the case of gly and isobutaldehyde and ammonia in the case of val. The proposed reaction mechanism is well supported by kinetic data, spectrophotometric evidence and positive entropy of activation.
The title reaction was studied spectrophotometrically. The reaction was found to be first order in [HCF] and fractional order each in [dl-methionine] and [OH-]. Initially added products did not alter the rate of reaction. The variation of ionic strength had unaltered the rate of reaction whereas dielectric constant of the medium had an influence on kobs values. A suitable mechanism was proposed in which oxidant was involved in the formation of adduct (K2) which is formed by reacting with dl-methionine in a prior equilibrium step. It decomposes in a slow step (k) to form a free radical generated on dl-methionine. This free radical leads to methionine sulfoxide in the fast step by reacting with another molecule of hexacyanoferrate(III). The effect of temperature on rate of reaction was also studied. Activation parameters were evaluated. The rate law was derived as: [image omitted] The reaction constants are calculated.
A catalytic effect of non-ionic (tween-80) micelles on the rate of oxidation of thiaminehydrochloride (vitamin B 1) and pyridoxine hydrochloride (vitamin B 6) by sodium salt of p-toluene sulphonamide (chloramine-T) in acidic medium has been observed and rate has been found to be proportional to { k' + k" (Tween-80)}, where k' and k" are the rate constants in absence and in presence of surfactant, respectively. The rate showed a first order, a fractional order and a zero order dependence on (Chloramine-T) 0, (Vitamin) 0 and (H + )0, respectively. The association/binding between the oxidant and the surfactant micelle is supported by the spectrophotometric evidence. A mechanism has been proposed and binding parameters have been evaluated.
The kinetics of the title reaction showed first-order behaviour both in hexacyanoferrate(III) and osmium(VIII) and fractional order each in fursemide and alkali concentrations. The added product, [Fe(CN) 6 ] ⁴⁻ , retarded the rate of reaction. The active species of osmium(VIII) in alkali appears to be [OsO 5 (OH)] ³⁻ . A mechanism involving a complex formed between osmium(VIII) and fursemide, followed by its oxidation with hexacyanoferrate(III) in a rate-determining step is proposed. A rate law for the mechanism was derived and verified. The formation constant, K 2 for [OsO 5 (OH)] ³⁻ , K 3 for the complex, and the rate constant of the slow step, k, were evaluated. The activation parameters E a , Δ H # , Δ S # , Δ G # and log A were calculated as 55.2 ± 2kJ mol ⁻¹ , 52.7 ± 2 kJ mol ⁻¹ , - 52.0 ± 2 JK ⁻¹ mol ⁻¹ , 69.8 ± 2.5 kJ mol ⁻¹ and 6.5 ± 0.1 respectively.
Fursemide is used in the pharmacotherapy for various diseases and it is also considered as a doping agent in sports. A simple and specific procedure for its analysis was developed being based on its oxidation by alkaline hexacyanoferrate(III) in the presence of trace amount of osmium(VIII) catalyst. Three different methods have been recommended, namely, the rate constant method, fixed time method and fixed change in optical density method. of these, the latter two were found to be fast, simple, and accurate. from these methods, fursemide could be analysed from a few micrograms to milligrams per cm ³ . The interference by binders of tablets, and other possible substances like proteins and amino acids, have also been studied.
Kinetics of oxidation of L-proline by hexacyanoferrate(III) catalyzed by osmium(VIII) in alkaline medium was studied at 30 °C. A mechanism involving free radical path was proposed. Rate law of the reaction was derived as The rate constant k and equilibrium constants K 1 and K 2 were evaluated as 3.79 × 10 3 dm 3 mol -1 s -1 , 0.52 dm 3 mol -1 , and 3.78 × 10 3 dm 3 mol -1 , respectively. The main reactive species of the catalyst appears to be OsO 5 (OH) 3-. The oxidative product of L-proline was identified as L-glutamic acid which is different from the earlier reports. The literature reveals that 4-amino butyric acid, 4-amino butaraldehyde and keto acids were the oxidative products. Activation parameters were evaluated as E a) 33.5 (2 kJ mol -1 , ∆H q) 31.0 (0.2 kJ mol -1 , ∆S q) -24 (1.5 J K -1 mol -1 , ∆G q) 38.0 (2 kJ mol -1 .
The kinetics of oxidation of DL-methionine by cerium(IV) in aqueous perchloric acid solution have been studied spectrophotometrically. The reaction shows first order kinetics in [CeIV] and an apparent less than unit order dependence each in [DL-methionine] and [acid]. The data suggest that the oxidation proceeds via the formation of a complex between methionine and cerium(IV) which decomposes in a slow step to give a free radical which on reacting with one more molecule of cerium(IV) in a fast step gives the products. The reaction constants involved in the mechanism are evaluated.
The kinetics of ruthenium(III) catalyzed oxidation of L-valine by permanganate in alkaline medium at a con-stant ionic strength has been studied spectrophotometrically. The reaction between permanganate and L-valine in alka-line medium exhibits 2:1 stoichiometry (KMnO 4 :L-valine). The reaction shows first-order dependence on the concentration of permanganate and ruthenium(III) and less than unit-order dependence on the concentrations of L-valine and alkali. The reaction rate increases both with an increase in ionic strength and a decrease in solvent polarity of the medium. Initial addition of reaction products did not significantly affect the rate. A mechanism involving the formation of a complex between catalyst and substrate has been proposed. The activation parameters were computed with respect to the slowest step of the mechanism. Résumé : Faisant appel à des méthodes spectrophotométriques, on a étudié la cinétique de l'oxydation de la L-valine par le permanganate, catalysée par le ruthénium(III), en milieu alcalin et à force ionique constante. En milieu alcalin, la réaction entre le permanganate et la L-valine présente une stoechiométrie de 2:1 (KMnO 4 :L-valine). La réaction pré-sente une dépendance du premier ordre avec les concentrations de permanganate et de ruthénium(III) et cette dépen-dance est inférieure à l'unité pour les concentrations de L-valine et de base. La vitesse de réaction augmente avec une augmentation de la force ionique et avec une diminution dans la polarité du solvant. L'addition initiale de produits réactionnels n'affecte pas la vitesse de façon significative. On propose un mécanisme impliquant la formation initiale d'un complexe entre le catalyseur et le substrat. On a calculé les paramètres d'activation par rapport à l'étape la plus lente du mécanisme. Mots clés : oxydation, L-valine, catalyse, ruthénium(III), cinétique. [Traduit par la Rédaction] Bilehal et al. 1933
The rate constants of oxidation of vitamin B1 and its O-acyl derivatives with ferricyanide in phosphate buffer at pH 7.2-7.8 were determined. The kinetics of the oxidation of thiamine, O-(2-norbornylcarbonyl)thiamine, O-(1-adamantylcarbonyl)thiamine, O-(5-methyl-1-adamantylcarbonyl)thiamine, O-(2-adamantylcarbonyl)thiamine, O-(2-adamantyl)acetylthiamine, and O-(1-adamantyl)acetylthiamine, followed by spectrophotometry by the formation of the corresponding thiochrome, fits first order both in substrate and in oxidant. With excess ferricyanide, the reciprocal of the apparent preudo-first-order rate constant increases with increasing ferrocyanide concentration. The intramolecular assistance by the hydrocarbon fragment of O-acyl-substituted thiamine is explained by the formation of an intermediate neutral tricyclic form of the substrate in a stage preceding electron transfer on ferricyanide. The reaction is assumed to mimic the effect of the hydrophobic environment during the transformation of vitamin B1 into the neutral tricyclic form on the surface of thiamin-binding protein.
Outer-sphere redox reactions between [CoIII(NH3)5(HxPyOz)](m– 3)–(HxPyOzm–= H2PO2–, H2PO3–, HPO32–, HP2O73–, P2O74–, γ-H2P3O103–, -HP3O104–, -P3O105–, β-H3P3O102–, -H2P3O103–, -HP3O104– or -P3O105–) and [Fe(CN)6]4– have been studied as a function of pH, HxPyOzm– oxoanion, temperature and pressure. The effect of the oxidation state, size, geometry and extent of protonation of the HxPyOzm– oxoanions on the precursor-complex formation constant, electron-transfer rate constant, and thermal and pressure activation parameters has been investigated. The values obtained indicate that all the precursor-complex formation equilibrium constants, KOS, are the same except for the non-linear β-H3P3O102–, -H2P3O103–, -HP3O104– and -P3O105– oxoanions, where the values are consistently larger, indicating that hydrogen bonding plays a very important role. The electron-transfer rate constant for a series of [Co(NH3)5(HxPyOz)](m– 3)–, with linear oxoanions, increases on decreasing the negative charge on the complex {k308= 0.73 × 10–3 and (8.5–11)× 10–3 s–1 for the γ-[Co(NH3)5(P3O10)]2– and γ-[Co(NH3)5(H2P3O10)], respectively}. For the non-linear β-P3O105– oxoanions a threshold is observed when the external oxo groups are protonated {k308= 20 × 10–3 for β-[Co(NH3)5(H3P3O10)]+ species and 0.84 × 10–3 s–1 for β-[Co(NH3)5(H2P3O10)], -[Co(NH3)5(HP3O10)]– or -[Co(NH3)5(P3O10)]2–}. The ΔH‡ values are within the range expected, while those of ΔS‡ and ΔV‡ vary considerably with the extent of protonation of the phosphorus oxoanionic ligands, being 13 J K–1 mol–1 and + 36 cm3 mol–1 and 69 J K–1 mol–1 and + 13 cm3 mol–1, respectively for the [Co(NH3)5(HP2O7)]–[Co(NH3)5(P2O7)]– couple. The ΔV‡ values depend strongly on the oxo group distribution of the oxophosphorus ligand {+ 13 and + 32 cm3 mol–1 for β- and γ-[Co(NH3)5(P3O10)]2–, respectively}. Hydrogen bonding and solvent reorganization play a key role in the interpretation of the activation parameters.
The ferricyanide–sulphite reaction has been shown to proceed via the intermediates [Fe(CN)5(CNSO3)]5– and [Fe(CN)5(CNSO3)]4–, followed by hydrolysis of the latter to ferrocyanide and sulphate. In the presence of catalysts such as animal charcoal and Cu++aq ions, there is a reduction in the amount of intermediate formed, and radioactive tracer experiments indicate the formation of appreciable quantities of dithionate ion.
The rate of disappearance of potassium persulfate has been determined in aqueous solutions containing methanol, ethanol or allyl alcohol in the absence and presence of allyl acetate. Allyl acetate does not affect the initial rate of disappearance of persulfate. Methanol and ethanol cause pronounced increases in the rate, but in the presence of allyl acetate and methanol or ethanol the rate is about the same as in the presence of allyl acetate alone. The results are interpreted on the assumption that persulfate does not react directly with any of the above organic substances but that sulfate free radicals are produced only by thermal dissociation of persulfate. In the absence of allyl acetate the sulfate radical reacts with methanol or ethanol forming a free radical derived from the alcohol. This in turn reacts with persulfate forming another sulfate radical thus leading to chain decomposition of persulfate. In the presence of both allyl acetate and alcohol essentially all the sulfate radicals are captured by allyl acetate and the chain decomposition is prevented.
HAuCl4 oxidiert Methionin in wäßriger Lösung stereospezifisch zum Sulfoxid.
The complex (Trpy)RuCl3 (Trpy = 2,2′:6′,2″-terpyridine) reacts with alkaline hexacyanoferrate(III) to form a terpyridyl ruthenium(IV)-oxo complex that catalyzes the oxidation of 2-propanol and benzyl alcohol by alkaline hexacyanoferrate(III). The reaction kinetics of this catalytic oxidation have been studied photometrically. The reaction rate shows a first-order dependence on [RU(IV)], a zero-order dependence on [hexacyanoferrate(III)], a fractional order in [substrate], and a fractional inverse order in [HO−]. The kinetic data suggest a reaction mechanism in which the catalytic species and its protonated form oxidize the uncoordinated alcohol in parallel slow steps. Isotope effects, substituent effects, and product studies suggest that both species oxidize alcohol through similar pericyclic processes. The reduced catalytic intermediates react rapidly with hexacyanoferrate(III) and hydroxide to reform the unprotonated catalytic species. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 760–770, 2000
Alkaline hexacyanoferrate(III) oxidation of freshly prepared solutions of CrIII (pH>12) at 27C follows the rate law, Equation 1:
(1 + K_OH [OH^ - ]_T )Rate = \frac{{kK_{OH} [Fe(CN)_6 ]^{3 - } [Cr^{III} ]_T [OH^ - ]_T }}{{(1 + K_{OH} [OH^ - ]_T )}}
(1) [Fe(CN)6]3– and [Cr(OH)4]– are the active species. The values of KOH(1.620.02 dm3 mol–1) and k (2.50.2 dm3 mol–1s–1), the formation constant of [Cr(OH)4]– from soluble Cr(OH)3 and the rate constant respectively, were determined at 27.0C. The solubility of CrIII at pH>12 decreases with time, presumably due to slow formation of polynuclear CrIII species.
The osmium(VIII) catalysed IO4
− oxidation of DMF in aqueous alkaline medium follows the rate law:
- \textd[ \textIO4- ]/\textdt = \frackK2 K3 [\textDMF][\textOH- ][\textOs\textVIII ]T 1 + K2 K3 [\textDMF][\textOH- ] + K2 [\textOH- ] - {\text{d}}\left[ {{\text{IO}}_4^ - } \right]/{\text{d}}t = \frac{{kK_2 K_3 [{\text{DMF}}][{\text{OH}}^ - ][{\text{Os}}^{{\text{VIII}}} ]_T }}{{1 + K_2 K_3 [{\text{DMF}}][{\text{OH}}^ - ] + K_2 [{\text{OH}}^ - ]}}
where K
2 is the equilibrium constant of the reaction [OsO4(OH)2]2− + OH− ⇌ [OsO5(OH)]3− + H2O K
3 is the formation constant for the complex between DMF and [OsO5(OH)]3− and k is the decomposition rate constant. The data suggest that the oxidation of DMF proceeds via the formation of a complex between
DMF and osmium(VIII) which decomposes slowly, followed by a fast reaction between the reduced osmium(VI) species and IO4
−. The reaction constants involved in the mechanism are derived.
Oxidation of D-mannosamine (1), D-glucosamine (2), and D-galctosamine (3) by sodium N-chlorobenzenesulfonamide or chloramine-B (CAB) at 313 K is followed by a shortening of carbon chain and obeys the rate law, rate = k[CAB][sugar][HO(-)](x)(), where x is less than unity. The products are arabinonic acid, ribonic acid, and erythronic acid for 1 and 2 with smaller amounts of glyceric and hexonic acids, while lyxonic and threonic acids are predominant in the oxidation of 3 with smaller amounts of glyceric and hexonic acids. Proton inventory studies made in a H(2)O-D(2)O mixture point toward a single transition state. In the proposed mechanism the alkoxy anion (S(-)) of the hexosamine formed in a base-catalyzed reaction at C-1 carbon is subjected to an electrophilic rate-limiting attack by Cl(+) of the oxidant. The hexonic acid formed is decarboxylated with loss of ammonia to form the respective pentose, which is further converted into the corresponding pentonic acid. The breaking of the bond between C-1 and C-2 carbons in pentose yields tetronic acids. The thermodynamic parameters for sugar alkoxy anion formation and activation parameters for the rate-limiting step have been evaluated.