Showing papers on "Oxalic acid published in 1992"

Formation of hydrogen peroxide and depletion of oxalic acid in atmospheric water by photolysis of iron(III)-oxalato complexes

Abstract: The generation of hydrogen peroxide (H 2 O 2 ,) and the depletion of oxalic acid by photochemical/chemical cycling of Fe(III)/Fe(II)-oxalato complexes in sunlight has been studied under the conditions typical for acidified atmospheric water. H 2 O 2 is produced though the reduction of oxygen by intermediates formed from photoreactions of Fe(III)-oxalato complexes. The rate of H 2 O 2 formation increases with sunlight intensity, and with oxalate and Fe(III) concentration within the concentration range used

Production of citric and oxalic acids and solubilization of calcium phosphate by penicillium bilaii

Abstract: An isolate of Penicillium bilaii previously reported to solubilize mineral phosphates and enhance plant uptake of phosphate was studied. Using agar media with calcium phosphate and the pH indicator alizarin red S, the influence of the medium composition on phosphate solubility and medium acidification was recorded. The major acidic metabolites produced by P. bilaii in a sucrose nitrate liquid medium were found to be oxalic acid and citric acid. Citric acid production was promoted under nitrogen-limited conditions, while oxalic acid production was promoted under carbon-limited conditions. Citric acid was produced in both growth and stationary phases, but oxalic acid production occurred only in stationary phase. When submerged cultures which normally produce acid were induced to sporulate, the culture medium shifted toward alkaline rather than acid reaction with growth.

Determination of organic mercury species in soils by high-performance liquid chromatography with ultraviolet detection

Abstract: Reversed-phase high-performance liquid chromatography with ultraviolet detection was optimized for the simultaneous separation and quantification of nine organic mercury compounds: methyl-, ethyl-, phenyl-, methoxyethyl-, ethoxyethyl-, benzoic and tolylmercury, mersalylic acid and nitromersol. The nine compounds were successfully separated on octadecylsilane columns (200 × 3 mm i.d.) by gradient elution with a methanol–water mixture ranging from 30 to 50% v/v. The detection limits for the various compounds are in the range 7.0–95.1 µg dm–3. For the extraction of five organomercurials from spiked soils, eight different extraction solutions were tested to differentiate between the total content and the available/soluble fraction of the analytes. Ammonium acetate solutions (1 mol dm–3) and water proved to be suitable agents for the estimation of the available and soluble fractions of methyl-, ethyl-, benzoic, methoxyethyl- and ethoxyethylmercury. For the determination of the total content of methyl- and benzoic mercury in soils, solutions of potassium iodide (1 mol dm–3)–ascorbic acid (0.1 mol dm–3) and oxalic acid (1 mol dm–3) provided recoveries in the range 53–81%. None of the solutions tested is suitable for the extraction of ethyl-, methoxyethyl- and ethoxyethylmercury.

Matrix isolation and ab initio studies of oxalic acid

Abstract: Rotamerization and UV photochemical decomposition of oxalic acid were studied in various matrices and ab initio calculations in this paper. Two conformers, cTc (2 intramolecular hydrogen bonds) and cTt (one intramolecular hydrogen bond) and their conversion energy from one form to the other were observed and studied. Full Xe arc irradiation decomposes matrix oxalic acid. For 6 oxalic acid conformers other spectra are calculated and assigned along with their potential energy distributions. 25 refs., 8 figs., 11 tabs.

Extrarenal clearance of oxalate increases with progression of renal failure in the rat.

Abstract: Oxalic acid is an end product of metabolism, and no significant degradation of oxalate occurs in mammals. The sole route of oxalate excretion is believed to be via the kidney. The extrarenal clearance of oxalate in control rats (N = 16) and in 5/6 nephrectomized rats (N = 25) with renal insufficiency was investigated. [14C]oxalic acid, approximately 2 microCi/day, was infused sc by a mini osmotic pump over 4 days. Excretion of 14C was measured in urine, in feces, and in expired CO2. The 14C content of kidney, heart, liver, muscle and bone was also determined at the time the animals were killed. Plasma oxalate was determined by an enzymatic method and by an isotopic dilution procedure. Creatinine clearance in the controls was 1.82 +/- 0.1 mL/min (mean +/- SE) compared with 0.31 +/- 0.04 mL/min (P

Olefin oligomerization with surface modified zeolite catalyst

Abstract: A method for producing substantially linear hydrocarbons by oligomerizing a lower olefin at elevated temperature and pressure which comprises contacting the lower olefin under oligomerization/polymerization conditions with constrained intermediate pore siliceous acidic zeolite, e.g., ZSM-22, -23 or -35, having Bronsted acid activity; wherein the zeolite has acidic pore activity and wherein the zeolite surface is rendered substantially inactive for acidic reactions. The zeolite surface can be inactivated by contact with dicarboxylic acid, e.g., oxalic acid. The olefin oligomers may be used as alkylating agents to prepare biodegradable alkylbenzenes and alkylphenylsulfonates.

Charge density studies on small organic molecules around 20 K: oxalic acid dihydrate at 15 K and acetamide at 23 K

Abstract: Collecte de donnees de diffraction RX a haute resolution afin d'obtenir des donnees precises et des densites de charge experimentales. Affinements conventionnel et multipolaire. Generation des cartes de densite de deformation par des syntheses de Fourier X-X et comparaison avec les distributions statiques obtenues par la methode multipolaire. Les resultats sont egalement compares avec ceux obtenus precedemment. Analyse du changement de resolution de la densite de deformation due a une precision accrue

Incapability of Gluconobacter oxydans to produce tartaric acid.

Abstract: The dependence of tartaric acid production by Gluconobacter oxydans ssp. oxydans ATCC 19357 and G. oxydans ssp. suboxydans ATCC 621 on vanadate was investigated. It was found with both organisms that tartaric acid could only be produced in a medium containing vanadate (NH(4)VO(3)). A proposed intermediate of the tartaric acid metabolism in G. oxydans, 5-ketogluconic acid, was tested on its reactivity in the presence of the oxidizing catalyst vanadate. It could be shown that 5-ketogluconic acid and the catalyst vanadate, but not the activity of G. oxydans, were responsible for the formation of tartaric acid. G. oxydans was not able to produce tartaric acid by itself. The stereochemical identity of the formed tartaric acid could be identified as the L-(+)-type. Oxalic acid was formed from 5-ketogluconic acid with vanadate in the absence and in the presence of G. oxydans. The ratio of oxalic acid to tartaric acid was 1:1.

Process for the photochemical and thermal stabilisation of polyamide fibre material with a copper complex having fibre-affinity and an oxalic acid diarylamide

Abstract: Process for the photochemical and themal stabilisation of polyamide fibre material with a copper complex having fibre-affinity and an oxalic acid diarylamide Abstract of the Disclosure There is disclosed a process for the photochemical and thermal stabilisation of polyamide fibre material as claimed in claim 1. The fibre materials treated by the inventive process are distinguished by good fibre affinity and enhanced photochemical and thermal stability.

Selective extraction and determination of metals in organic stream sediments

Abstract: The effects of pre-treatment (drying, homogenizing and ashing temperature) on metal leachability and the effectiveness of extractants for metals and arsenic are described Nine organic stream sediment samples were collected from non-polluted and two from polluted catchment areas Buffered 1 mol dm–3 ammonium acetate at pH 45, buffered 1 mol dm–3 ammonium acetate with a chelating 002 mol dm–3 ethylenediaminetetraacetic acid agent at pH 55 and 35, and 02 mol dm–3 ammonium oxalate with 02 mol dm–3 oxalic acid at pH 30, were used separately to extract mobile and hydromorphic Al, As, Cd, Co, Cu, Cr, Fe, Pb, Mn, Ni and Zn for determination Hot 6 mol dm–3 hydrochloric acid, hot 725 mol dm–3 nitric acid and hot aqua regia[HCl—HNO3(3 + 1)] leaches were used in the determination of the total element content

A Rapid Acid‐Oxalate Extraction Procedure for the Determination of Active Fe‐oxide Forms in Calcareous Soils

Abstract: Extraction with acid NH4-oxalate is widely used to estimate the content of “active” forms of Fe oxides in soil. In calcareous soils, this extraction presents some problems (pH change, production of CO2), which have been circumvented by decalcifying the soil before extraction. However, because of its tediousness, this procedure cannot be applied for routine purposes. In this paper, we describe a rapid procedure in which the soil is treated with oxalic acid before oxalate extraction to neutralize the active calcium carbonate equivalent. The method is simple and provides a useful estimation of the content of active Fe forms that are not occluded in the coarse particles and aggregates of carbonate.

Selective surface dealumination of zeolites using dicarboxylic acid

Abstract: A process for the selective surface dealumination of a zeolite having a Constraint Index greater than 1 by contacting the zeolite with dicarboxylic acid, such as oxalic acid.

Electrochemical and in situ atomic force microscopy and scanning tunneling microscopy investigations of titanium in oxalic acid solution

Abstract: The growth of an oxide film and the dissolution of the metal were studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) for titanium electrodes which had been pretreated by a chemical polishing procedure. Images were obtained with a gas–solid interface and under an aqueous solution containing 0.1 M oxalic acid. The electrochemical polarization of titanium in 0.1 M oxalic acid is qualitatively the same as observed in chloride or sulfate medium, and the dissolution reaction in oxalic acid appears to follow the same monolayer coverage mechanism as in the other media. The titanium specimen is polycrystalline and the presence of grain boundaries between individual crystallites is observed by AFM. In situ microscopy indicates that both the rate of growth of oxide and the dissolution of the metal are dependent on the crystallographic face of the titanium. AFM and STM show that the growth of titanium (IV) oxide or hydrous oxide has the appearance of hemispherical domes which grow togeth...

A process for the dealumination of zeolite beta

Abstract: A process for the dealumination of a zeolite having the structure of zeolite Beta by contacting the zeolite with dicarboxylic acid, such as oxalic acid.

Reduction of urinary oxalate by combined calcium and citrate administration without increase in urinary calcium oxalate stone formers.

Abstract: Oxalic acid seems to play a far greater role in the formation of calcium oxalate stone than calcium. Three grams of calcium lactate and 3 g of sodium potassium citrate were administered to 46 urolithiasis patients, whose stones were mainly composed of calcium oxalate. Urinary oxalate level was reduced significantly without raising urinary calcium level by the administration of the two drugs for two weeks. The reduction of urinary oxalic acid was particularly remarkable in patients without hypercalciuria. The mechanism of action of these drugs was discussed.

Synthesis of fine-particle titanates by the pyrolysis of oxalate precursors

Abstract: Fine-particle MTiO3, where M=Ca, Sr, Ba or Pb, were prepared by the pyrolysis of MTiO(C2O4)2·4H2O in the presence of a redox mixture containing NH4NO3 and oxalic acid dihydrazide at 350 °C. The redox mixture, having a low ignition temperature, not only pyrolyses the oxalate precursor but also produces large quantities of gases, which results in a fine, foamy oxide product. The exothermicity of the redox reaction provides the heat required for the decomposition of the oxalate, and the gases evolved create the foamy nature of the product and help to dissipate the heat, which inhibits the sintering of MTiO3. Metal titanate powders obtained by the pyrolysis of the oxalates are of submicrometre size and have a high surface area (18–42 m2g−1). The sintered BaTiO3 and PbTiO3 showed spontaneous polarization of 12 and 26 µC cm−2, respectively, for a field strength of 120 kV cm−1.