Showing papers on "Oxalic acid published in 1996"

Surface-Catalyzed Chromium(VI) Reduction: Reactivity Comparisons of Different Organic Reductants and Different Oxide Surfaces

Abstract: CrVI reduction by low molecular weight organic compounds with various functional groups was examined in the presence and absence of oxide surfaces. Surface-catalyzed CrVI reduction has been demonstrated with α-hydroxyl carboxylic acids (glycolic acid, lactic acid, mandelic acid, and tartaric acid) and their esters (methyl glycolate, methyl lactate, and methyl mandelate), with α-carbonyl carboxylic acids (glyoxylic acid and pyruvic acid), with oxalic acid, and with substituted phenols (salicylic acid, 4-methoxyphenol, and resorcinol). Both goethite (α-FeOOH) and aluminum oxide (γ-Al2O3) exert an appreciable catalytic effect, although somewhat less than that observed with titanium dioxide. This study indicates that surface-catalyzed CrVI reduction may occur in soils, sediments, aquifers, and other aquatic environments rich in mineral surfaces.

The use of manganese dioxide as a heterogeneous catalyst for oxalic acid ozonation in aqueous solution

Abstract: Heterogeneous catalysis by MnO2 of oxalic acid ozonation in aqueous solution has been investigated in the pH range 3.2–7.0. The influence of catalyst load and reaction temperature upon rate development of the ozonation process has also been examined. The observed dependence of system reactivity on pH and the results obtained by ozonation experiments with MnO2 catalysts of different pHzpc values agree with a reaction mechanism involving the formation of a surface Mn - oxalic acid complex.

Synthesis, characterization and photocatalytic properties of iron-doped titania semiconductors prepared from TiO2 and iron(III) acetylacetonate

Abstract: Specimens of iron-doped titania containing different amounts of Fe (0.5–5%) were prepared from TiO2 (Degussa P-25) and Fe(III) acetylacetonate by the wet impregnation method. Samples were characterized by X-ray diffraction analysis, specific surface area (BET) measurements, SEM-EDX, atomic absorption and IR and diffuse reflectance spectra. From the structural point of view, the samples were similar to those obtained with Fe(NO3)3 · 9H2O as the precursor, but with a more homogeneous distribution of iron for each mixed oxide sample on the particle surfaces but not between particles. The photocatalytic activity of these samples under near-UV irradiation was better for oxalic acid degradation than for EDTA, and similar for both types of mixed oxide samples. Mixed oxides showed however lower activity than TiO2. Some photodegradation under visible irradiation, not occurring with TiO2, could be observed for oxalic acid when using 5% Fe-containing samples.

Dealumination of zeolite {beta} via dicarboxylic acid treatment

Abstract: It is demonstrated that zeolite {beta} and zeolite {beta} containing catalysts can be dealuminated to very low acidity levels using a novel oxalic acid treatment without reducing zeolite integrity. The effect of the oxalic acid treatment has been studied over a wide range of treatment conditions for both silica-bound and unbound zeolite {beta} catalysts. Greater than 90% dealumination is observed with a concomitant reduction in n-hexane-cracking activity as measured by the alpha ({alpha}) test. Removal of framework aluminum occurs via a two-step hyrolysis/chelation mechanism, with the oxalic acid acting both as an acid and as a chelating agent. Framework aluminum removal is accompanied by the formation of internal silanol groups. Water soluble aluminum oxalates are present in the extracted solutions. Silanol groups are annealed with extended oxalic acid treatment. Oxalic acid treatment results in a unique contraction of the zeolite {beta} lattice structure not observed for mineral acid treated or steamed zeolite {beta} catalysts. 15 refs., 11 figs., 5 tabs.

In vitro weathering of phlogopite by ectomycorrhizal fungi. II. Effect of K+ and Mg2+ deficiency and N sources on accumulation of oxalate and H+

Abstract: Oxalate accumulation in external medium under hyphal mats of two ectomycorrhizal species is strongly stimulated (1.7 to 35 fold) by a simultaneous depletion of available K + and Mg 2+ . Pisolithus tinctorius strain 441 accumulates oxalate both on NH 4 -N and on NO 3 -N whereas Paxillus involutus strain COU only accumulates oxalate on NO 3 -N. On NO 3 -N, under a simultaneous K + and Mg 2+ deficiency, P. involutus COU is a very active oxalate producer compared to P. tinctorius 441. The present results could explain the various mineralogical evolutions of a phlogopite mica previously recorded under P. involutus COU or P. tinctorius 441 and suggest a key role for fungal oxalic acid during mineral weathering in response to nutrient deficiency.

Electrochemical and Infrared Spectroscopic Quantitative Determination of the Platinum-Catalyzed Ethylene Glycol Oxidation Mechanism at CO Adsorption Potentials

Abstract: The electrochemical mechanism for ethylene glycol oxidation by polycrystalline platinum at 030 V/SCE in 010 M HClO4 is investigated by reflection infrared spectroscopic, coulometric, and voltammetric measurements of 010 M ethylene glycol, glycolaldehyde, glyoxal, glycolic acid, glyoxylic acid, and oxalic acid CO2, glycolic acid, and adsorbed CO are identified as reaction products for ethylene glycol and glycolaldehyde oxidation A two-path mechanism is proposed for 030 V oxidation of ethylene glycol and glycolaldehyde: either the reacting molecule undergoes direct oxidation to desorbing glycolic acid or it undergoes direct dissociation of the carbon−carbon bond to form various amounts of aqueous CO2 and adsorbed CO Calculations are performed, assuming the quantities of CO and CO2 depend statistically upon the identities of the two functional groups comprising the two-carbon reactant molecule and upon oxidation conditions Calculation results for dissociation at 030 V show that nearly 100% of the c

Oxalic acid and calcium determination in wild edible plants.

Abstract: The contents of oxalic acid and calcium in several wild edible plants were analyzed. Oxalic acid was determined by an espectrophotometric method based on the decrease of absorbance at 335 nm due to the dissociation of the zirconium(IV)−chloranilate complex, consecutive to the addition of oxalic acid. Calcium was determined by atomic absorption spectroscopy. The results show the absence of this acid in two of the studied plants: hoary cress (Cardaria draba (L.) Desv.) and vervain (Verbena officinalis L.). Also noticeable is the high content of oxalic acid in goosefoot (Chenopodium album L.), with a range of values from 360 to 2000 mg/100 g of fresh weight, and the high ratio (oxalic acid/calcium) in curly dock (Rumex crispus L.), with a mean value of 32. Keywords: Oxalic acid; calcium; antinutritive substance; wild edible plants

Ion-chromatographic analysis of low molecular weight organic acids in spodosol forest floor solutions

Abstract: Low molecular weight organic acids (LMWOA) from root exudates, decomposing organic matter, and other sources are important ligands involved in solution complexation reactions as well as ligand exchange reactions at mineral surfaces. The purpose of this study was to (i) develop an ion chromatography method that could be used to determine LMWOA in soil solutions from Spodosols, (ii) assess methods for preserving LMWOA in soil solutions, and (iii) evaluate LMWOA concentrations in forest floor solutions during a growing season. Solutions were collected weekly from zero-tension lysimeters installed within the forest floor (forest floor leachate collectors). Limits of quantitation for acetic, formic, malonic, oxalic, phthalic, and citric acids were 0.35, 0.14, 0.43, 0.41, 0.07, and 0.04 μM, respectively, which in some cases are an order of magnitude lower than reported in previous studies. Freezing soil solutions after filtering resulted in the best recoveries (between 90 and 100% for all LMWOA); other methods of preservation, such as filtering alone and filtering and storing at 4°C, resulted in lower recoveries. The average concentrations of LMWOA in the forest floor solutions were 10 μM acetic acid, 0.7 μM formic acid, and 3.3 μM oxalic acid. Dissolved organic C from the forest floor contained a maximum concentration of 2.0% acetic acid, 0.01% formic acid, and 0.15% oxalic acid. There were no apparent temporal patterns in LMWOA concentrations, except for a decrease in LMWOA concentrations from late September to a minimum in October.

Distribution of Oxalic Acid between Water and Organic Solutions of Tri-n-octylamine

Abstract: The extraction of oxalic acid from an aqueous solution into solutions of tri-n-octylamine in single solvents toluene, chloroform, and methyl isobutyl ketone was investigated. In addition to batch extraction experiments and isopiestic measurements in the binary system oxalic acid/water, infrared spectroscopic measurements were performed. These spectroscopic investigations yield information about the stoichiometry of complex formation. All measurements were carried out at 298.15 K. A model for the liquid−liquid equilibrium is presented which was used to correlate the experimental data. The model takes into account chemical reactions as well as physical interactions in both phases. Many of the model parameters could be deduced from information about subsystems using also the new isopiestic measurements. However, as several complexes of oxalic acid and tri-n-octylamine with as well as without water have to be considered, some model parameters had to be adjusted using experimental data from batch extraction ex...

Sensitization of tio2 with phthalocyanines. part 1 : photo-oxidations using hydroxoaluminium tricarboxymonoamidephthalocyanine adsorbed on tio2

Abstract: Hydroxoaluminium tricarboxymonoamidephthalocyanine has been adsorbed on TiO2(Degussa P-25) particles. Water suspensions and solid samples were analysed by SEM and by IR, visible extinction, diffuse reflectance and fluorescence spectroscopy. Visible spectra showed that the dye is not highly aggregated on the surface. Fluorescence was completely quenched by the semiconductor. The sample is stable toward visible irradiation. The photocatalytic activity of the modified semiconductor for transformation of different substrates under visible irradiation in the phthalocyanine Q-band has been tested. While EDTA, oxalic acid and benzoquinone did not show any changes after irradiation, photooxidation of KI, phenol, thiophenol, 4-chlorophenol, hydroquinone and salicylic acid was observed. The analysis of the results as a function of the substrate redox potential suggests that the radical cation of the phthalocyanine, produced by electron injection of the dye into the TiO2 conduction band, is the species responsible for the oxidation of the substrates. No reaction was found, at least for phenol, when TiO2 free of AlTCPc was irradiated under the same conditions.

Synthesis and properties of oxalic acid‐doped polyaniline

Abstract: Conductive polyaniline was synthesized in aqueous 1.0M oxalic acid containing 0.1 M aniline by electrochemical and chemical oxidation and characterized by conductivity, solubility, ultraviolet and infrared spectroscopy, and cyclic voltammetry. The solubility experiments showed that the solubility of oxalic acid-doped polyaniline in dimethylsulfoxide and dimethylformamide increased to a certain extent. The soluble part of the polyaniline was free from impurities such as quinones. Cyclic voltammetric studies in oxalic acid medium revealed that aniline exhibited a similar behaviour to that in H 2 SO 4 and the polymerization rate was much slower than that in H 2 SO 4 .

Vacuum-UV photolysis of aqueous solutions of nitrate: effect of organic matter I. Phenol

Abstract: Water homolyses on vacuum-UV excitation (λ The rates of oxidative degradation of phenol and its oxidation products strongly depend on the dissolved oxygen concentration. The formation of dihydroxybenzenes, trihydroxybenzene and oxalic acid as oxidation intermediates was observed in irradiation experiments with oxygen- and air-saturated solutions, but no significant concentrations of these compounds were observed in experiments with argon-saturated solutions. The depletion rates of NO3− have been reported previously to be slow yielding mainly nitrite and N2O as reaction products. Vacuum-UV irradiation of aqueous solutions containing NO3− and phenols results in the simultaneous mineralization of phenol and depletion of NO3−, yielding mainly NH4+ and, in much lower yields, NO2−. The experimental observations indicate that the nitrogen-containing inorganic ions formed during NO3− depletion promote the oxidation of the dissolved organic matter independent of the presence of oxygen. A possible reaction mechanism is discussed, in which the interaction of O2NOOH, ONOOH, NO. and NO. with organic matter is proposed as being mainly responsible for the overall observed behaviour. The interaction between organic substrates and NO. seems to favour further reduction to NH4+, whereas a one-electron reduction yielding N2O is observed in the absence of organic substrates. The effect of CO32− on these reactions is also discussed. Under continuous irradiation, NH4+ is subsequently re-oxidized. Complete oxidation to NO3− is observed only in experiments with oxygen-saturated solutions. Experiments with air- or argon-saturated solutions show only 30% and 10% NO3− formation respectively due to the simulataneous formation of N2. The reduction of NO3− to NH4+ and the oxidation of NH4+ to NO3− seem to involve a series of common intermediates interrelated by many redox reactions and reaction equilibria where the pH, availability of electrons and the presence of protons or hydrogen donors and molecular oxygen determine their importance.

Selective chemo-catalytic routes for the preparation of β-hydroxypyruvic acid

Abstract: β-Hydroxypyruvic acid was prepared by heterogeneous catalytic liquid phase oxidation of glycerol and derivatives over a bismuth-modified platinum catalyst using air as terminal oxidant. A convenient preparative method is described using sodium glycerate as the starting material under weakly acidic conditions (pH 5–6). A selectivity of 93% towards β-hydroxypyruvic acid at a conversion of sodium glycerate of 95% could be achieved. Dihydroxyacetone as well as glycerol, however, were found to be not a suitable starting material for the preparation of the title compound. Oxidation of these two substrates under the above conditions yields mainly oxalic acid. Glyceric acid may be prepared by oxidation of glycerol with oxygen over Pd C catalyst under alkaline conditions (pH 10), or by liquid phase catalytic oxidation of solketal with oxygen over Pt C catalyst and subsequent removal of the protecting isopropylidene group in acidic medium.

Ethanol increases sensitivity of oxalate oxidase assays and facilitates direct activity staining in SDS gels

Abstract: Oxalate oxidase, and H2O2-generating enzyme, has been characterized from several plants, and is widely used for clinical detection of oxalate Using a germin-like oxalate oxidase from barley leaves, we have developed and optimized novel methods for measuring oxalate oxidase activity As oxalate oxidase is SDS-tolerant, its activity can be detected directly in SDS-PAGE gels in the presence of ethanol This ethanol-dependent method is a hundred times more sensitive than the current methods Furthermore, ethanol also improves the sensitivity of oxalate oxidase assays performed in solution We found at least a 10-fold increase in sensitivity in comparison to a current method The assay in solution is, in addition, useful for detection of oxalate This elevation in sensitivity may be due to the immobilization of the enzyme in protein precipitates as a result of the treatment with ethanol

Reduction of oxalate content of foods by the oxalate degrading bacterium, eubacterium lentum wyh-1

Abstract: Background: Urinary oxalate may contribute far more than urinary calcium to the pathogenesis of urinary calculi. Urinary oxalate may be reduced by restricting the intake of foods high in oxalate. The oxalate content of foods might be reduced by oxalate-degrading bacteria. The purpose of this experiment was to reduce the oxalate content of foods with an oxalate-degrading bacterium which was isolated from the feces of a Japanese male. Methods: An artificial intestinal juice was prepared by modifying Rogosa medium. An infusion of black tea was prepared from a commercial tea bag. The oxalate-degrading bacteria used were Eubacterium lentum WYH-1 which we have isolated. To 5 mL of the above oxalate-containing artificial intestinal juice and infusion of black tea, 0.5 mL of the bacterial culture was added and incubated anaerobically at 37°C. Oxalic acid in the supernatant of the culture medium was assayed by high-performance liquid chromatography. Results: In 24 hours, 1 × 106 cells/mL of Eubacterium lentum WYH-1 decomposed 100% of 1 mg/mL oxalate in the artificial intestinal juice. The oxalate in the black tea infusion (1 mg/mL) was also decomposed completely within 48 hours by 1 × 107 cells/mL of the bacteria. Conclusion: Eubacterium lentum WYH-1 was able to efficiently decompose the oxalate in foods.