- Kinetics and mechanism of Ru(III) and Hg(II) co-catalyzed oxidation of D-galactose and D-ribose by N-bromoacetamide in perchloric acid
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Kinetics of oxidation of reducing sugars D-galactose (Gal) and D-ribose (Rib) by N-bromoacetamide (NBA) in the presence of ruthenium(III) chloride as a homogeneous catalyst and in perchloric acid medium, using mercuric acetate as a scavenger for Br-
- Singh, Ashok Kumar,Singh, Vineeta,Singh, Ajaya Kumar,Gupta, Neena,Singh, Bharat
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- Reaction pathways of glucose oxidation by ozone under acidic conditions
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The ozonation of d-glucose-1-13C, 2-13C, and 6-13C was carried out at pH 2.5 in a semi-batch reactor at room temperature. The products present in the liquid phase were analyzed by GC-MS, HPAEC-PAD, and 13C NMR s
- Marcq, Olivier,Barbe, Jean-Michel,Trichet, Alain,Guilard, Roger
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experimental part
p. 1303 - 1310
(2009/12/01)
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- Kinetic study of iridium(III) catalyzed oxidation of D-mannitol and erythritol by N-bromosuccinimide in acidic medium
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Kinetic investigations on iridium trichloride catalyzed oxidation of D-mannitol and erythritol by acidic solution of N-bromosuccinimide (NBS) in the presence of mercuric acetate as a scavenger for Br- have been carried out in the temperature range 30-45 °C. The reactions follow identical kinetics. The rate shows a first-order dependence on [NBS] in lower concentration range which tends to zero-order at its higher concentrations. A first-order dependence on [IrIII] is also observed. Negligible effect of [substrate], [Hg(OAc)2] and ionic strength have been observed. Addition of [H+], [Cl-] and succinimide shows a negative effect. Activation parameters have been computed and a suitable mechanism conforming to above results has been proposed.
- Srivastava, Sheila,Gupta, Vandana
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p. 1103 - 1106
(2008/02/04)
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- Kinetics and mechanism of oxidation of D-fructose and D-glucose by sodium salts of N-(chloro)-mono/di-substituted benzenesulfonamides in aqueous alkaline medium
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In an effort to introduce N-chloroarylsulfonamides of different oxidizing strengths, nine sodium salts of mono- and di-substituted N- chloroarylsulfonamides are employed as oxidants for studying the kinetics of oxidation of D-fructose and D-glucose in aqueous alkaline medium. The results are analyzed along with those by the sodium salts of N-chlorobenzenesulfonamide and N-chloro-4-methylbenzenesulfonamide. The reactions show first-order kinetics each in [oxidant], [Fru/Glu], and [OH-]. The rates slightly increase with increase in ionic strength of the medium. Further, the rate of oxidation of fructose is higher by 4 to 5 times than that of the glucose oxidation, by the same oxidant. Similarly, Ea values for glucose oxidations are higher by about 1.5 times the Ea values for fructose oxidations. The results have been explained by a plausible mechanism, and the related rate law deduced. The significant changes in the kinetics and thermodynamic data are observed with change of substituent in the benzene ring. It is because Cl + is the effective oxidizing species in the reactions of N-chloroarylsulfonamides. The oxidative strengths of the latter therefore depend on the ease with which Cl+ is released from them. The ease with which Cl+ is released from N-chloroarylsulfonamides depends on the electron density of the nitrogen atom of the sulfonamide group, which in turn depends on the nature of the substituent in the benzene ring. The following Hammett equations are valid for the oxidation of fructose and glucose, log kobs = -3.13 + 0.54 σ ρ and log kobs = -3.81 + 0.28 σ ρ, respectively. The enthalpies and entropies of activations for oxidations by all the N-chloroarylsulfonamides correlate well with isokinetic temperatures of 301 K and 299 K, for fructose and glucose oxidations, respectively. The effect of substitution in the oxidants on the Ea and log A for the oxidations is also considered.
- Gowda, B. Thimme,Damodara,Jyothi
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p. 572 - 582
(2007/10/03)
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- Ruthenium (III) catalysis of periodate oxidation of reducing sugars in aqueous alkaline medium
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The ruthenium (III) catalysis of periodate oxidation of D-ribose, D-sorbose and maltose in aqueous alkaline medium has been investigated. The reactions have been found to be zero order with respect to each reducing sugar and first order with respect to ruthenium (III). The linear dependence of the reaction rate at lower concentrations of periodate ion and hydroxide ion tends towards zero order at their higher concentrations. Positive effect of [Cl -] on the rate of reaction has also been observed. The observed kinetics with periodate ion, under the conditions [IO4 -]〉〉[Ru(III)]T suggests the formation of a 1:1 complex between Ru(III) and periodate in the rate controlling step, which subsequently interacts with reactive species of reducing sugar to give the final products, through a series of fast steps. The rate law is derived.
- Singh, Ashok Kumar,Gupta, Neena,Rahmani, Shahla,Singh, Vinod Kumar,Singh, Bharat
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p. 1871 - 1875
(2007/10/03)
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- A novel mechanism for the oxidation of erythro-series pentoses and hexoses by N-arylbromosulphonamides in alkaline medium
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Kinetic studies of the oxidation of D-mannose, D-glucose, D-fructose, L-arabinose and D-ribose by bromamine-T (sodium N-bromo-p-toluenesulphonamide or BAT) and bromamine-B (sodium N-bromobenzenesulphonamide or BAB) in alkaline medium were investigated at 30°C. The rate of the reaction was first order both with respect to the oxidant and the sugar and second order with respect to [HO-]. The addition of the reaction product, p-toluenesulphonamide (PTS) or benzenesulphonamide (BSA), and the variation of ionic strength of the medium have no effect on the rate. The rate decreases with decrease in dielectric constant of the medium and values of dAB, the size of activated complex, were calculated. Proton inventory studies were made in H2O-D2O mixtures. The activation parameters of the reaction were computed from Arrhenius plots. HPLC and GLC-MS analysis of the products indicated that the sugars were oxidized to a mixture of aldonic acids consisting of arabinonic, ribonic, erythronic and glyceric acids. A general mechanism consistent with the observed results has been proposed.
- Shashikala,Rangappa
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p. 219 - 234
(2007/10/03)
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- Kinetics and mechanism of oxidation of hexoses by bromamine-T in alkaline medium
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The kinetics and mechanism of oxidation of D-glucose and D-mannose with bromamine-T in alkaline medium have been studied and the rate = κ[BAT][sugar][OH-]2, is observed. The rate of the reaction is influenced by a change in ionic strength of the medium and the dielectric effect is found to be positive. The latter enables the computation of dAB, the size of the activated complex. Proton inventory studies are made for the reactions in H2O-D2O mixtures. Activation parameters are calculated from the Arrhenius plots. The product analyses indicates that the sugars are oxidized to a mixture of aldonic acids, consisting of arabinonic, ribonic, erythronic and glyceric acids. A mechanism consistent with the observed kinetics has been proposed.
- Prashanth,Mantelingu,Murthy, A. S. Ananda,Anitha,Rangaswamy,Rangappa
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p. 241 - 245
(2007/10/03)
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- The reaction of hyaluronic acid and its monomers, glucuronic acid and N- acetylglucosamine, with reactive oxygen species
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Synovial fluid is a ~0.15% (w/v) aqueous solution of hyaluronic acid (HA), a polysaccharide consisting of alternating units of GlcA and GlcNAc. In synovial fluid of patients suffering from rheumatoid arthritis, HA is thought to be degraded either by radicals generated by Fenton chemistry (Fe2+/H2O2) or by NaOCl generated by myeloperoxidase. We investigated the course of model reactions of these two reactants in physiological buffer with HA, and with the corresponding monomers GlcA and GlcNAc. meso-Tartaric acid, arabinuronic acid, arabinaric acid and glucaric acid were identified by GC-MS as oxidation products of glucuronic acid. When GlcNAc was oxidised, erythronic acid, arabinonic acid, 2-acetamido-2-deoxy-gluconic acid, glyceric acid, erythrose and arabinose were formed. NaOCl oxidation of HA yielded meso-tartaric acid; in addition, arabinaric acid and glucaric acid were obtained by oxidation with Fe2+/H2O2. These results indicate that oxidative degradation of HA proceeds primarily at glucuronic acid residues. meso-Tartaric acid may be a useful biomarker of hyaluronate oxidation since it is produced by both NaOCl and Fenton chemistry.
- Jahn, Michael,Baynes, John W.,Spiteller, Gerhard
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p. 228 - 234
(2007/10/03)
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- Kinetics and mechanism of the oxidation of some aldoses, amino sugars and methylated sugars by tris(pyridine-2-carboxylato)manganese(III) in weakly acidic medium
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The kinetics of oxidation of some aldoses, amino sugars and methylated sugars by tris(pyridine-2-carboxylato)manganese(III) have been studied spectrophotometrically in sodium picolinate -picolinic acid buffer medium. The reactions are first order with respect to both manganese(III) and sugar concentrations, but independent with respect to sodium picolinate - picolinic acid buffer medium. The mechanism for the reactions is discussed.
- Gupta, Kalyan Kali Sen,Begum, Bilkis Ara
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- Electrooxidation of mesoerythritol on platinum, modified or not by adatoms, in acid medium
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The electrocatalytic oxidation of meso-erythritol has been studied in 0.1 M HClO4 on platinum and on adatoms modified platinum. Preliminary investigations by cyclic voltammetry showed that erythritol was not reactive on a Pt electrode. Underpotential deposition of lead or thallium adatoms at platinum allowed to increase significantly the current densities. Long-time electrolyses were carded out using a three potential plateau program with different values of the oxidation potentials. Chromatographic analyses showed that the oxidation of erythritol led mainly to erythrose, erythrulose and to erythronic acid. Otherwise, electrolysis of erythritol on a Pt-Tl modified electrode orientated selectively the distribution of the reaction products towards the formation of erythrulose.
- Cherqaoui,Chbihi,Takky,Kokoh,Leger,Lamy
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p. 510 - 521
(2007/10/03)
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- Kinetics and mechanism of oxidation of erythro-series pentoses and hexoses by N-chloro-p-toluenesulfonamide
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The kinetics and mechanism of oxidation of D-glucose, D-mannose, D- fructose, D-arabinose, and D-ribose with chloramine-T in alkaline medium were studied. The rate law, rate = k [Chloramine-T] [Sugar] [HO-]2, was observed. The rate of the reaction was influenced by a change in ionic strength of the medium, and the dielectric effect was found to be negative. The latter enabled the computation of d(AB), the size of the activated complex. The reaction rate was almost doubled in deuterium oxide. Activation energies were calculated from the Arrhenius plots. HPLC and GLC-MS analyses of the products indicated that the sugars were oxidized to a mixture of aldonic acids, consisting of arabinonic, ribonic, erythronic, and glyceric acids. Based on these data, a plausible mechanism involving the aldo-enolic anions of pentoses and keto-enolic anions of hexoses is suggested.
- Rangappa, Kanchugarakoppal S.,Raghavendra, Manikanahally P.,Mahadevappa, Dandinasivara S.,Gowda, D. Channe
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- Oxidation of erythrose series sugars by sodium N-chlorobenzenesulphonamide in alkaline medium : A kinetic study
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The kinetics of oxidation of D-glucose, D-mannose, D-fructose, D-arabinose, and D-ribose, with sodium N-chlorobenzenesulphonamide (chloramine-B or CAB) in alkaline medium have been studied at 35°C and the rate law, rate = κ′ [CAB] [Sugar] [OH-]2 is observed. The rate of reaction is influenced by a change in ionic strength of the medium, and the dielectric effect is negative. The solvent isotope studies in D2O show that the rate is almost doubled in heavy water. HPLC and GLC-MS analyses of the products indicated that the erythrose-series sugars are oxidized to a mixture of aldonic acids consisting of arabinonic, ribonic, erythronic, and glyceric acids in varying proportions. Based on these data, a mechanism involving the aldoenolic anions of pentoses and keto-enolic anions of hexoses is suggested.
- Raghavendra,Rangappa,Mahadevappa,Channe Gowda
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p. 783 - 792
(2007/10/03)
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- Sodium N-Chlorobenzenesulfonamide as a Selective Oxidant for Hexosamines in Alkaline Medium: A Kinetic and Mechanistic Study
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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 H2)O-D2)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.
- Rangappa, Kanchugarakoppal S.,Raghavendra, Manikanahally P.,Mahadevappa, Dandinasivara S.,Channegowda, Doddegowda
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p. 531 - 536
(2007/10/03)
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- Kinetics and mechanism of oxidation of D-mannosamine by sodium N-chloro-p-toluenesulphonamide in alkaline medium
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The kinetics of oxidation of D-mannosamine (S) to the aldonic acids by sodium N-chloro-p-toluenesulphonamide or chloramine-T (CAT) in the presence of alkali at 40°C follows the rate law d[CAT]/dt=k[CAT] [S] [HO-]x, where x2O)/k(H2O) was found to be 1.62. The mechanism assumes stepwise, the formation of sugar alkoxy anion, followed by a rate limiting complexation with oxidant resulting in the formation of the respective pentose through decarboxylation and deammation. The latter is oxidised to arabonic, ribonic, erythronic and glyceric acids. A mechanism involving the reaction of enolanion of sugar with the oxidant in the rate limiting step is proposed.
- Rangappa,Mahadevappa,Raghavendra
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p. 890 - 896
(2007/10/03)
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- Oxidation of methyl and n-octyl α-D-glucopyranoside over graphite-supported platinum catalysts: Effect of the alkyl substituent on activity and selectivity
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The oxidation of methyl and n-octyl α-D-glucopyranoside to methyl and n-octyl α-D-glucopyranosiduronate with molecular oxygen over a graphite-supported platinum catalyst was investigated. An increase of the length of the n-alkyl substituent from methyl to n-octyl resulted in a ten-fold decrease of the catalyst activity and an increase of the selectivity at pH 8.0 and 323 K. The selectivity decreased with increasing pH. The lower activity for a longer n-alkyl substituent is attributed to steric effects upon adsorption on the platinum surface and not to internal diffusion limitations. A tentative reaction scheme is presented, which describes the formation of side products through oxidation of secondary hydroxyl groups, ring cleavage and hydrolysis. Major side products are mono- and di-carboxylates with 2, 4, and 6 carbon atoms and mono-carboxylates, resulting from the oxidation of the alkyl substituent. C-C-Bond cleavage mainly occurs between C-2 and C-3 or C-4 and C-5, the former being less important for a longer alkyl substituent. The higher selectivity for a longer alkyl substituent is attributed to its protecting ability against hydrolysis and the exposition of neighboring hydroxyl groups to the platinum surface.
- Vleeming, Johannes H.,Kuster, Ben F.M.,Marin, Guy B.
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p. 175 - 183
(2007/10/03)
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- OXIDATION OF MONOSACCHARIDES WITH OXYGEN IN ALKALINE SOLUTION. SEPARATION, IDENTIFICATION AND ESTIMATION OF THE ALDONIC ACIDS PRODUCED BY LIQUID CHROMATOGRAPHY
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A reliable liquid chromatographic method has been developed for the separation, identification and estimation of the products formed when saccharides are oxidized in alkaline solution with oxygen.The technique was then used to quantitate the acids produced when glucose is subjected to such an oxidation.The Bio-Rad cation exchange column HPX-87H(1+), when eluted with 0.01 N H2SO4 and attached to a UV detector, was found to be satisfactory.Quantitative estimation of the products formed during the oxidation of glucose was achieved by withdrawing aliquots from the reaction mixture and injecting them directly into the chromatographic system.It was found that about 90percent of the oxidation products formed were produced via a 1,2-enediol and less than 10percent via a 2,3-enediol.The results confirmed the mechanism proposed by Isbell to account for the acids produced.
- Shalaby, M. Ashraf,Isbell, Horace S.,Khadem, Hassan S. El
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p. 429 - 438
(2007/10/02)
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- Conversion of D-ribo-3-hexosulose into D-ribulose and D-erythronic acid in aqueous medium
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The decomposition of D-ribo-3-hexosulose in water, studied by HPLC, gave D-ribulose (60-65percent) and D-erythronic acid (20percent), both isolated by column chromatography.D-Ribulose was characterized using LC-MS and NMR.From the latter technique, the ratio of three isomeric structures was determined.D-Erythronic acid was characterized by NMR.
- Wit, D. de,Rantwijk, F. van,Maat, L.,Kieboom, A. P. G.
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p. 271 - 274
(2007/10/02)
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- KINETICS AND MECHANISM OF Ru(III) CATALYSED OXYDATION OF SOME POLYHYDRIC ALCOHOLS BY N-BROMOSUCCINIMIDE IN ACIDIC MEDIA
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Kinetics of oxydation of ethylene glycol, glycerol, erythritol and dulcitol by acidic solution of N-bromosuccinimide (NBS) in presence of ruthenium(III) chloride as a homogeneous catalyst and mercuric acetate as scavenger in the temperature range of 30-50 deg C have been reported.The reactions follow identical kinetics, being first order in each NBS, substrate and Ru(III).Zero effect of , and ionic strength has been observed.A negative effect of succinimide and acetic acid is observed while shows the positive effect on reaction velocity.Various activation parameters have been computed.The products of the reaction were identified as the corresponding acids.A suitable mechanism consistent with the experimental results has been proposed.
- Sharma, J. P.,Singh, R. N. P.,Singh, A. K.,Singh, Bharat
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p. 2739 - 2748
(2007/10/02)
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