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The invention discloses a method for preparing gluconic acid from glucose as a raw material with a catalytic oxidation means. Gluconic acid is prepared through oxidation of glucose by an aqueous phasewith air or oxygen as an oxidizing agent and a transition metal compound and nitrous acid or nitrite as a composite catalyst. The reaction is simple in operation and mild in condition, the glucose conversion rate is high, the selectivity of the gluconic acid product is good, and the method has important application prospects.

Aldonic acids are receiving increased interest due to their applications in nanotechnology, food, pharmaceutical and chemical industries. Microbes with aldose-oxidizing activity, rather than purified enzymes, are used for commercial production with limited success. Thus it is still very important to develop new processes using strains with more efficient and novel biocatalytic activities for the production of adonic acids. In the present study, Pseudomonas fragi TCCC11892 was found to be an efficient producer of aldonic acids, with the production of galactonic and l-rhamnonic acid by P. fragi reported for the first time. The semi-continuous production of maltobionic acid and lactobionic acid was developed for P. fragi TCCC11892, achieving a yield of over 90 g L?1 for the first 7 cycles. The excellent performance of P. fragi in the production of lactobionic acid (119 g L?1) was also observed when using waste cheese whey as an inexpensive fermentation medium. Scaling up of the above process for production of aldonic acids with P. fragi TCCC11892 cells should facilitate their commercial applications.

Hydrotalcite-supported gold nanoparticles show good activity as a heterogeneous catalyst for the oxidation of monosaccharides (xylose, ribose, galactose and mannose) and disaccharides (lactose and cellobiose) into the corresponding sugar acids under external base-free conditions in water solvent using atmospheric pressure of molecular oxygen. The produced sugar acids were thoroughly identified by 1H-, 13C-, and HMQC-NMR and ESI-FT-ICR MS spectroscopic techniques.

Herein, uronic acids available from hemicelluloses and pectin were used as raw material for the synthesis of aldaric acids. Au/Al2O3 catalyst oxidized glucuronic and galacturonic acids quantitatively to the corresponding glucaric and galactaric acids at pH 8-10 and 40-60 °C with oxygen as oxidant. The pH has a significant effect on the initial reaction rate as well as desorption of acid from the catalyst surface. At pH 10, a TOF value close to 8000 h-1 was measured for glucuronic acid oxidation. The apparent activation energy Ea for glucuronic acid oxidation is dependent on the pH which can be attributed to the higher energy barrier for desorption of acids at lower pH. This journal is

Electrochemistry (EC) combined with mass spectrometry (MS) is a powerful tool for elucidation of electrochemical reaction mechanisms. However, direct online analysis of electrochemical reaction in aqueous phase was rarely explored. This paper presents the online investigation of several electrochemical reactions with biological relevance in the aqueous phase, such as nitrosothiol reduction, carbohydrate oxidation, and carbamazepine oxidation using desorption electrospray ionization mass spectrometry (DESI-MS). It was found that electroreduction of nitrosothiols [e.g.; nitrosylated insulin B (13-23)] leads to free thiols by loss of NO, as confirmed by online MS analysis for the first time. The characteristic mass shift of 29 Da and the reduced intensity provide a quick way to identify nitrosylated species. Equally importantly, upon collision-induced dissociation (CID), the reduced peptide ion produces more fragment ions than its nitrosylated precursor ion (presumably the backbone fragmentation cannot compete with the facile NO loss for the precursor ion), thus facilitating peptide sequencing. In the case of saccharide oxidation, it was found that glucose undergoes electro-oxidation to produce gluconic acid at alkaline pH, but not at neutral and acidic pHs. Such a pH-dependent electrochemical behavior was also observed for disaccharides such as maltose and cellobiose. Upon electrochemical oxidation, carbamazepine was found to undergo ring contraction and amide bond cleavage, which parallels the oxidative metabolism observed for this drug in leucocytes. The mechanistic information of these redox reactions revealed by EC/DESI-MS would be of value in nitroso-proteome research and carbohydrate/drug metabolic studies.

Thiol-induced core etching of gold nanoparticles is a general method for the production of gold nanoclusters (AuNCs) of various sizes. This paper is the first report on the efficient reaction of glutathione-capped gold nanoparticles (GSH-AuNPs) with hydroxyl radicals to produce oligomeric AuI-thiolate complexes at ambient temperature. Also, hydroxyl radicals can etch commercially available gold nanoparticles (100 nm); this strategy can be applied for the removal of gold from scrap electronics. Additionally, proteins can trigger the aggregation of oligomeric AuI-thiolate complexes under neutral conditions resulting in the formation of fluorescent AuNCs. For example, the reaction of trypsin, lysozyme, and glucose oxidase with oligomeric AuI-thiolate complexes produces Au5, Au8, and Au13 clusters with emission maxima at 415, 460, and 535 nm, respectively. Interestingly, trypsin- and glucose oxidase-stabilized AuNCs could sense GSH and glucose via GSH-induced etching of AuNCs and H2O2-mediated oxidation of AuNCs, respectively. This journal is

An integrated experimental and computational investigation reveals that surface lattice oxygen of copper oxide (CuO) nanoleaves activates the formyl C-H bond in glucose and incorporates itself into the glucose molecule to oxidize it to gluconic acid. The reduced CuO catalyst regains its structure, morphology, and activity upon reoxidation. The activity of lattice oxygen is shown to be superior to that of the chemisorbed oxygen on the metal surface and the hydrogen abstraction ability of the catalyst is correlated with the adsorption energy. Based on the present investigation, it is suggested that surface lattice oxygen is critical for the oxidation of glucose to gluconic acid, without further breaking down the glucose molecule into smaller fragments, because of C-C cleavage. Using CuO nanoleaves as catalyst, an excellent yield of gluconic acid is also obtained for the direct oxidation of cellobiose and polymeric cellulose, as biomass substrates.

A previously unknown metabolic pathway for the utilization of l-galactose was discovered in a prevalent gut bacterium, Bacteroides vulgatus. The new pathway consists of three previously uncharacterized enzymes that were found to be responsible for the conversion of l-galactose to d-tagaturonate. Bvu0219 (l-galactose dehydrogenase) was determined to oxidize l-galactose to l-galactono-1,5-lactone with kcat and kcat/Km values of 21 s-1 and 2.0 × 105 M-1 s -1, respectively. The kinetic product of Bvu0219 is rapidly converted nonenzymatically to the thermodynamically more stable l-galactono-1,4-lactone. Bvu0220 (l-galactono-1,5-lactonase) hydrolyzes both the kinetic and thermodynamic products of Bvu0219 to l-galactonate. However, l-galactono-1,5-lactone is estimated to be hydrolyzed 300-fold faster than its thermodynamically more stable counterpart, l-galactono-1,4-lactone. In the final step of this pathway, Bvu0222 (l-galactonate dehydrogenase) oxidizes l-galactonate to d-tagaturonate with kcat and kcat/K m values of 0.6 s-1 and 1.7 × 104 M -1 s-1, respectively. In the reverse direction, d-tagaturonate is reduced to l-galactonate with values of kcat and kcat/Km of 90 s-1 and 1.6 × 10 5 M-1 s-1, respectively. d-Tagaturonate is subsequently converted to d-glyceraldehyde and pyruvate through enzymes encoded within the degradation pathway for d-glucuronate and d-galacturonate.

Kinetic investigation in Ru(III) catalyzed oxidation of D(+)-galactose and lactose in an alkaline solution of potassium bromate in the presence of mercuric acetate as a scavenger for Br - ion has been carried out in the temperature range 30-45°C. The rate shows first order dependence with respect to the bromate and zeroth order with respect to the substrate (sugars). The reaction exhibits first order dependence on the catalyst ruthenium(III) and there is inverse order on the rate of reaction. Potassium chloride and acetic acid have a positive effect on the rate. Negligible effect of change in Hg(OAc) 2, ionic strength of the medium and D2O. [RuCl 3(H2O)OH]-1 and BrO3- are the most reactive species Ru(III) chloride and bromated, respectively. Galactonic acid and lactobionic acid have been identified as the main oxidation products of the reaction. Various activation parameters have bee calculated and recorded. On the basis of experimental findings, a suitable mechanism consistent with the observed kinetics was proposed and the rate law has been derived on the basis of obtained data.

Nitric acid oxidation of D-mannose was carried out under an oxygen atmosphere using a computer controlled reactor. The process represents a catalytic oxidation of D-mannose with oxygen as the terminal oxidant. The crude oxidation product was esterified with methanolic HCl and the esterified product directly converted to crystalline N,N0-dimethyl-D-mannaramide with methylamine. Treatment of the diamide in aqueous sodium hydroxide gave solid disodium D-mannarate. The X-ray crystal structure of N,N0-dimethyl-D-mannaramide was determined as a model for the repeating D-mannaramide units of stereoregular poly(alkylene-D-mannaramides). Disodium D-mannarate was prepared as a precursor of esterified D-mannaric acid for use as a reactive diacid monomer to prepare poly-D-mannaramides.

Galactokinases (GalKs) have attracted significant research attention for their potential applications in the enzymatic synthesis of unique sugar phosphates. The galactokinase (GalKSpe4) cloned from Streptococcus pneumoniae TIGR4 presents a remarkably broad substrate range including 14 diverse natural and unnatural sugars. TLC and MS studies revealed that GalKSpe4 had relaxed activity towards galactose derivatives with modifications on the C-6, 4- or 2-positions. Additionally, GalKSpe4 can also tolerate glucose while glucose derivatives with modifications on the C-6, 4- or 2-positions were unacceptable. More interestingly, GalKSpe4 can phosphorylate l-mannose in moderate yield (43%), while other l-sugars such as l-Gal cannot be recognized by this enzyme. These results are very significant because there is rarely enzyme reported that can phosphorylate such uncommon substrates as l-mannose.

The hydroxyl radicals are widely implicated in oxidation of carbohydrates during biological and industrial processes being responsible for their structural modifications and causing functional damage. The identification of intermediate oxidation products is hampered by a lack of reliable sensible methods for their detection. In this study, the oxidation of two models of galactomannans (Man3 and GalMan2) has been studied in reaction with hydroxyl radical generated by Fenton reaction. The oxidation patterns were assessed using preparative ligand-exchange/size-exclusion chromatography (LEX/SEC) coupled with tandem electrospray mass spectrometry (ESI-MS/MS). This allowed the identification of derived oligosaccharides (OS) containing hexuronic, hexonic, pentonic and erythronic acid residues and neutral OS bearing hydroperoxy, hydrated carbonyl moieties and residues from pyranosyl ring cleavage. The depolymerization products have been also detected upon oxidation of oligomers. This study allowed developing a simple, effective 'fingerprinting' protocol for detecting the damage done to mannans by oxidative radicals.

In this communication, we demonstrate that certain kinds of Rh porphyrins on carbon black can electrochemically oxidize aldose at low potentials. The onset potential was much lower than those with the other complex-based catalysts. A product analysis suggested that this reaction involves 2-electron oxidation of the aldehyde group.

The kinetics of RuIII catalyzed oxidation of D(+)-galactose (galac) and cyclopentanol (cyclopen) by KBrO3 in alkaline medium using mercuric acetate as a scavenger for Br- ion (galac) as well as co-catalyst (cyclopen), have been studied in the temperature range 30-45°C. The reactions exhibit first-order kinetics with respect to oxidant and catalyst while zero-order kinetics with respect to substrate was observed in case of both galactose and cyclopentanol. For cyclopentanol, a positive effect on the rate of reaction were observed on successive addition of [Hg(OAc)2] and [Cl-] whereas [OH-] exhibited an inverse fractional order. In case of galactose, [OH-] and [Hg(OAc)2] have no effect on the reaction velocity. A positive fractional order in acetic acid concentration (AcOH) and negligible effect of ionic strength of the medium were observed. The reactive species of RuIII in alkaline medium is [RuCl2(H2O)3(OH)] (galac) and [RuCl 3(H2O)2OH]-1 (cyclopen) under the experimental pH range. A suitable mechanism in conformity with the kinetic observation has been proposed. The various activation parameters such as energy of activation (ΔE*), Arrhenius factor (A), entropy of activation (ΔS*) were calculated from the rate measurements at 30, 35, 40 and 45°C. A rate law has been derived on the basis of data obtained.

The invention relates to a process for the catalytic conversion of a carbohydrate, an alcohol, an aldehyde or a polyhydroxy compound in the presence of a catalyst containing gold in a solvent.

Kinetics of oxidation of some aldoses like glucose, galactose, xylose and ribose by hexacyanoferrate(III) ions in aqueous alkaline buttered medium has been investigated. The kinetic results indicate the zero-order kinetics in hexacyanoferrate(III) and first-order in aldoses and OH-. The ionic strength of the medium has no influence on oxidation rate. Various activation parameters were also calculated at four different temperatures : 30, 35, 40 and 45°C. The corresponding acids were identified as the main oxidation products of the reaction. A suitable mechanism consistent with experimental findings has been proposed.

D-Galacturonic acid reductase, a key enzyme in ascorbate biosynthesis, was purified to homogeneity from Euglena gracilis. The enzyme was a monomer with a molecular mass of 38-39 kDa, as judged by SDS-PAGE and gel filtration. Apparently it utilized NADPH with a Km value of 62:5 ± 4:5 μM and uronic acids, such as D-galacturonic acid (Km = 3:79 ± 0:5 mM) and D-glucuronic acid (Km = 4:67 ± 0:6 mM). It failed to catalyze the reverse reaction with L-galactonic acid and NADP+. The optimal pH for the reduction of D-galacturonic acid was 7.2. The enzyme was activated 45.6% by 0.1mM H2O2, suggesting that enzyme activity is regulated by cellular redox status. No feedback regulation of the enzyme activity by L-galactono-1,4-lactone or ascorbate was observed. N-terminal amino acid sequence analysis revealed that the enzyme is closely related to the malate dehydrogenase families.

Several aldonic acids (d-mannonic, d-galactonic, d-xylonic, 2-deoxy-d-arabinohexonic (2-deoxy-d-gluconic)) were prepared on a scale of several grams by a simple oxidation catalyzed by glucose oxidase in pure water.

The present invention relates to the production of xylitol. In particular, processes utilising L-xylose as an intermediate for xylitol production are described. The present invention also relates to process for the preparation or L-xylose, as an intermediate, by-product or end-product to be used per se.

A novel L-pantolactone hydrolase, Lph, from Agrobacterium tumefaciens Lu681 was characterized, which stereospecifically hydrolyses L-pantolactone to L-pantoic acid yielding D-pantolactone with > 95% enantiomeric excess. The enzyme was found to be a 30 kDa-Zn2+-hydrolase with a Km for L-pantolactone of 7 mM and a Vmax of 30 U/mg. The corresponding lph gene was identified as an 807 bp ORF and cloned into E. coli. It was overexpressed under control of Ptac and Prha yielding enzyme activities of up to 600 U/g dry weight. Resolution of D,L-pantolactone in repeated batches with isolated Lph and enzyme recovery by membrane filtration gave D-pantolactone with 50% yield and 90-95% ee over 6 days. Covalent immobilization to EupergitC led to a stable biocatalyst easy to handle in a repeated batch production of D-pantolactone. Further improvements in the activity of Lph were achieved by directed evolution of the enzyme. Activities of mutants F62S, K197D and F100L were increased 2.3, 1.7, and 1.5 fold, respectively.

An efficient and inexpensive method for large-scale preparation of α-D-(1→4)-oligogalacturonic acids (oligo-GalA), up to DP 5, from pectic acid is described. Pectic acid was digested with a commercially available pectinase to yield a mixture of oligo-GalA, which was effectively separated by a combination of low-pressure - size-exclusion chromatography based on ion-exchange chromatography to obtain pure oligo-GalA of DP 2-5.

Kinetic studies of the oxidation of D-galactose, L-sorbose and D-xylose by bromamine-T (sodium-N-bromo-p-toluenesulphonamide or BAT) and bromamine-B (sodium-N-bromobenzene sulphonamide or BAB) in alkaline medium has been investigated at 303 K. The rate of the reaction is first order both with respect to oxidant and 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 the decrease in dielectric constant of the medium and values of dAB, the size of activated complex are calculated. Proton inventory studies in H2O · D2O mixtures suggest a single transition state. Product analysis for D-galactose, L-sorbose and D-xylose reveal that hexoses give mainly mixture of lyxonic and threonic acids with minor proportions of hexonic, xylonic and glyceric acids, whereas xylose yields a mixture of lyxonic, threonic and glyceric acids with minor amounts of xylonic and hexonic acids. From the results of kinetic studies, reaction stoichiometry and product analysis, a possible mechanism for the oxidation of threose-series sugars is suggested.

The kinetics of oxidation of some aldoses and aminosugars by potassium bromate in hydrochloric acid medium have been studied. The reactions appear to proceed through the intermediate formation of bromate esters followed by the decomposition of the esters to give products. Hydrogen-ion accelerates tide rate of each reaction. The thermodynamic values associated with the equilibrium stage and the activation parameters associated with the rate- determining step have been computed.

Kinetics of the oxidation D-glucose, D-fructose, D-mannose and L-sorbose by manganese (III) have been studied in the presence of sulphate ions in acidic medium at 32 °C. The reaction has been followed spectrophotometrically at γ(max) = 500nm. A first order dependence of the rate on both Mn (III) and the hexose concentrations is observed. The rate is independent of the concentration of reduction product Mn (II) and hydrogen ions. Effects of varying dielectric constant of the medium and addition of anions such as sulphate, flouride, chloride and perchlorate have been investigated. Activation parameters have also been evaluated using Arrhenius and Eyring plots. A mechanism involving the formation of enediol from hexoses which reacts with Mn (III) in the rate limiting step is suggested.

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.

The kinetics of oxidation of some aldoses, amino sugars and methylated sugars by osmium (VIII) have been studied spectrophotometrically in alkaline medium. The reactions are first-order with respect to both [sugar]≤9.0×10-3 mol dm-3 and [OH-]≤10.0×10-2 mol dm-3 but tends toward zero order with respect to each at higher concentration. Activation parameters of the reactions have been calculated and plausible reaction mechanisms have been suggested.

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.

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.

The kinetic behaviour and relative reactivities of some carbohydrates (aldoses, amino sugars and methylated sugars) towards platinum(IV) in alkaline medium have been investigated. The reactions are first order with respect to [substrate] and PtIV. The rates increase with the increase in OH-. The reactions show pseudo-first-order dependence on OH-. The oxidation rates in alkaline medium follow the order triose>tetrose>pentose>hexose. Activation parameters of the reactions have been calculated. Mechanisms have been proposed for the reactions. Copyright (C) 1998 Elsevier Science Ltd.

The kinetics of Pd(II) catalysed oxidation of Ara, Xyl and Gal by N-bromosuccinimide (NBS) in acidic medium has been studied using Hg(OAc)2 as a scavenger for the Br- ion. The reaction data show that first-order kinetics in each pentose and hexose at low concentrations tend to zero-order at high concentrations. First-order kinetics with respect to NBS and Pd(II) and inverse fractional order, i.e., decreasing effect of [H+] and [Cl-], were observed, whereas ionic strength, Hg(OAc)2 and succinimide did not influence the oxidation rate. Various activation parameters have been calculated and recorded. The corresponding acids, arabonic, xylonic and galactonic, were identified as the main oxidation products of the reactions. On the basis of the experimental findings, a suitable mechanism has been proposed. Copyright (C) 1998 Elsevier Science Ltd.

The kinetics and mechanism of oxidation of threose-series hexoses and pentoses by chloramine-T in alkaline medium was investigated. Kinetic studies with D-galactose, D-sorbose, D-xylose, and D-lyxose showed that the rate of the reaction was first order with respect to sugar and chloramine-T, and second order with respect to hydroxide ion. p-Toluenesulfonamide and chloride ions, the reduced products of chloramine-T, have no effect on the reaction rate. The rate increases with increase in ionic strength of the medium, and the dielectric effect is negative. Proton inventory studies in H2O-D2O mixtures suggested a single transition state. Product analysis for D-gulose, Didose, L-sorbose, D-galactose, D-talose, D-tagatose, D-xylose, and D-lyxose revealed that all lyxoseseries hexoses gave mainly mixtures of lyxonic and threonic acids with minor proportions of hexonic, xylonic and glyceric acids, whereas all xylose-series hexoses gave mixtures of lyxonic, threonic and glyceric acids with minor amounts of xylonic and hexonic acids. Xylose and lyxose gave mixtures consisting mainly of lyxonic, threonic, and glyceric acids with minor proportions of xylonic acid. From the results of kinetic studies, reaction stoichiometry, and product analysis, a possible mechanism for the oxidation of threose-series sugars with chloramine-T is suggested.

An inhibition effect of PdCl2 on the rate of oxidation of sugars, by alkaline hexacyano-ferrate(III) has been observed. The order of reactions in hexacyanoferrate(III) and OH- is zero and unity, respectively, while that in sugars decreases from unity at higher sugar concentration. The kinetic data and spectrophotometric evidence support the formation of {PdII - (sugar)} and {PdII - sugar)2} complexes and their resistance to react with Fe(CN)63-.

Kinetics of oxidation of D-glucose, D-galactose, D-mannose and D-fructose by t-butyl hypochlorite have been investigated in alkaline medium at 298 K.The reactions follow both zero and first order pathways in and fractional order kinetics each in and .Variation in ionic strength of the medium and addition of reduced products, t-butyl alcohol (small amounts: 0.001-0.005 mol dm-3) and Cl- ions (0.01-0.25 mol dm-3), have negligible effects on the rate, while lowering of the dielectric constant of the medium by the addition of large amounts of t-BuOH (5-25percent v/v) increases the rate.The rates decrease in the order D-fructose > D-glucose ca.D-galactose > D-mannose.A two-pathway mechanism has been suggested to explain the observed results.Coefficients of the rate limiting steps as function of temperature have been evaluated and the related activation parameters computed.The validity of the isokinetic relationship has also been tested. - Keywords: Kinetics / Oxidation of hexoses / t-Butyl hypochlorite

A new approach towards simple aldonic acid derivatives starting from the corresponding aldoses via the 2-acetamido-2-deoxy formazans resulted in the synthesis of 2-acetamido-2-deoxy-D-galactono-1,4-lactone (8), and its 6-deoxy (11) and 6-azido-6-deoxy (14) analogues on treatment with trifluoroacetic acid.The five-membered ring structure of the lactones and that of the intermediate lactone phenylhydrazone (7) was proved by 1H and 13C NMR studies, including deuterium-induced differential isotope shift (DIS) measurements.With sodium borohydride, lactones 8 and 11 were converted into 2-acetamido-2-deoxy-D-galactitol (15) and its 6-deoxy analogue (17), respectively.

Reactions of D-glucose, D-galactose, and D-mannose with palladium(II) follow the general relations holding for two-electron oxidation of aldoses, the main reaction products being aldo acids.

The oxidation of D-glucose by Cu(II) has been studied in NaAcO buffers within the pH range 4-5 at 110 deg C.The observed pseudo-first-order rate constant is given by: a->+b/+> + c-> + d/+>2, where a = 5.3 +/- 0.4*10-4 s-1M-1, b = 1.30 +/- 0.07*10-8 s-1M, c = 6.16 +/- 0.04*10-3 s-1 M-2, and d = 3.2 +/- 0.2*10-13 s-1 M.This rate law corresponds to the formation of glutonic acid and Cu(I) when a ten-fold or higher excess of D-glucose over Cu(II) is employed.The results are discussed in terms of a possible mechanism of oxidation of D-glucose by CuOAc+, present in solution.

Kinetic studies of the oxidation of D-fructose, D-glucose, D-galactose, D-mannose, D-xylose, D-ribose, D-lyxose and D-arabinose by bromamine-B (sodium-N-bromobenzene sulphonamide, BAB) have been carried out in alkaline medium at 30 deg.The reaction shows a zero order dependence on 0 and fractional orders in 0 and ->0.The rates tend to level off at higher 0 and ->0.Variation in ionic strength of the medium, and the addition of benzene sulphonamide, Cl- and Br- ions do not alter the rate while lowering the dielectric constant of the medium increases the rate slightly.Solvent isotope and proton-inventory studies have been made.Enolization rate coefficients and activation parameters for the rate limiting step have been determined from Michaelis-Menten type of plots.A probable scheme for the oxidation of monosaccharides through a common intermediate, 1,2-enediol has been proposed.

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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.

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The oxidation of D-galactose, D-xylose and L-arabinose by chromium peroxydichromate has been studied in very dilute sulphuric acid (0.12-0.066 N).The reaction is of first order each in substrate, oxidant and sulphuric acid.HCrO4- ion appears to be the predominant oxidant.Neutral salts and Mn(II) have retarding effect on the reaction.A mechanism which is consistent with the observed rate laws and experimental facts has been proposed.

The oxidation of glucose to gluconic acid was carried out at 20 deg C in a membrane reactor in which a solution of glucose oxidase (EC 1.1.3.4) and catalase (EC. 1.11.1.6) was entrapped between two semipermeable membranes of regenerated cellulose.A buffered solution (pH 5.5) of glucose saturated with oxygen was fed continuously through one grooved compartment outside the membranes (liquid side), and oxygen gas was supplied at a pressure slightly higher than 1 atm to the opposite grooved compartment (gas side).First, by holding one sheet of membrane between the two sides, experiments were performed to determine the membrane permeation coefficient for oxygen in liquid (kM and the liquid-to-membrane mass transfer coefficient for oxygen in liquid (kL).The value of kM was proportional to the difference between the gas- and liquid-side pressures and the value of kL was proportional to the 0.56th power of the liquid flow rate.The reaction studies were done under conditions where the transfer of oxygen was a key process.From individual measurements of the absorption (permeation) rates of oxygen in the liquid through both membranes, it was found that, at low liquid flow rate, the transfer through the gas-side membrane contributed greatly to the global rate of absorption (reaction).For the mixing of enzyme solution, two models were considered; the stagnant and mixing models.At low liquid flow rate, the rate data were well explained by the stagnant model.At high liquid flow rate, in contrast, the mixing model was applicable.The oxygen pressure and the membrane permeation coefficient were the most important factors affecting the global rate of reaction.Keywords-- membrane reactor; oxidation; glucose; glucose oxidase; catalase; permeation coefficient; regenerated cellulose; mass transfer

Oxidation of glucose to gluconic acid using a catalyst consisting of glucose oxidase and catalase both immobilized on activated carbon was employed to study the liquid-solid contacting efficiency (f) in a trickle-bed reactor.The global rates of reaction were measured at 25 deg C and at atmospheric pressure, as a function of catalyst loading (1.0 to 9.0 g), catalyst particle size (0.055 and 0.110 cm), superficial liquid velocity (0.044 to 0.337 cm/s), and superficial gas velocity (1.63 to 7.35 cm/s).The measured rate was considered to be the sum of the rates at the liquid-covered and gas-covered outer surfaces of catalyst particles.The value of f was determined by integrating numerically the mass balance equations for oxygen and the equation for the intrinsic rate of reaction simultaneously.The estimated value of f did not vary with catalyst loading.While f was independent of gas flow rates, it was influenced by both liquid flow rates and particle sizes.The effects of these operating parameters on f are discussed on the basis of the static and/or dynamic holdup. Keywords - trickle-bed reactor; contacting efficiency; oxidation; glucose; immobilized enzyme catalyst; glucose oxidase; catalase; activated carbon; mass transfer; liquid-full reactor.

Aldoses in alkaline medium under the catalytic action of platinum of rhodium are converted into aldonic acids with high selectivity and with concomitant evolution of hydrogen gas.The dehydrogenation reaction has been studied for 25 different mono- and di-saccharides, and is generally applicable for reducing sugars.The influence of several reaction variables has been studied, leading to an adsorption model in which both the negatively charged O-1 and the close contact of H-1 with the catalyst surface are considered to be driving forces for the transfer of hydride from C-1 of the sugar to the catalyst.

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Kinetics of oxidation of dulcitol by chloramine-T in alkaline media has been investigated.A brief initial induction period has been observed after which the reaction shows a first order dependence each in , and ->.The effect of added neutral salts on the reaction rate is negligible.Energy of activation is observed to be 33.3 Kcal/mole for the reaction.A plausible mechanism consistent to the experimental data has been proposed.

The oxidation of glucose to gluconic acid in aqueous alkaline solution on a platinum-carbon catalyst was chosen as a model reaction to study the liquid-solid contacting efficiency in trickle-bed reactors.The global rates of dissipation of oxygen were measured for both liquid-full and trickle-bed reactors under conditions of neglible liquid-solid masss transfer effects.The liquid-solid contacting efficiency was evaluated from the rates for both reactors, which were measured under the same conditions of temperature, oxygen concentration and liquid flow rate using the same catalyst.Under the range of experimental conditions used (catalyst partcle sizes; 0.110 and 0.242 cm, superficial liquid velocity; 0.0236 to 0.337 cm/sec), the liquid-solid contacting efficiency was nearly constant.The average value was 0.91.Data were taken in a gas-continous flow regime and showed no significant change in the rate of reaction with change in superficial gas (oxygen) velocity.