Showing papers on "Oxalic acid published in 1991"

Production and Degradation of Oxalic Acid by Brown Rot Fungi

Abstract: Our results show that all of the brown rot fungi tested produce oxalic acid in liquid as well as in semisolid cultures. Gloeophyllum trabeum, which accumulates the lowest amount of oxalic acid during decay of pine holocellulose, showed the highest polysaccharide-depolymerizing activity. Semisolid cultures inoculated with this fungus rapidly converted 14C-labeled oxalic acid to CO2 during cellulose depolymerization. The other brown rot fungi also oxidized 14C-labeled oxalic acid, although less rapidly. In contrast, semisolid cultures inoculated with the white rot fungus Coriolus versicolor did not significantly catabolize the acid and did not depolymerize the holocellulose during decay. Semisolid cultures of G. trabeum amended with desferrioxamine, a specific iron-chelating agent, were unable to lower the degree of polymerization of cellulose or to oxidize 14C-labeled oxalic acid to the extent or at the rate that control cultures did. These results suggest that both iron and oxalic acid are involved in cellulose depolymerization by brown rot fungi.

Chemical and microbiological solubilization of silicates

Abstract: The solubilization of silicates was investigated using kaolin and quartz sand as model substances. The mineral solubilization was studied in the concentration of solubilized Si and Al. The chemical leaching of the silicates was carried out using inorganic and organic acids as well as sodium hydroxide. The process was more effective in the alkine than in the acid pH range. In the acid medium, oxalic acid showed maximum acidity and a tendency to form complex structures, especially with aluminium, and was most effective in leaching. The microbiological influence on solubilization reactions was tested using a number of microorganisms among them acid, alkali and slime-forming species. The highest leaching activity was observed in the case of Thiobacillus thiooxidans, whereas the heterotrophic microorganisms (among them Bacillus mucilaginosus) did not exercise a sollubilizing effect on the silicates. X-ray phase analysis of leached kaolin samples did not show any differences from the non-leached mineral.

Modified enzyme-based colorimetric assay of urinary and plasma oxalate with improved sensitivity and no ascorbate interference: reference values and sample handling procedures.

Abstract: The measurement of oxalate in urine and plasma continues to be difficult, particularly in the presence of ascorbate. We have modified and validated a colorimetric assay involving the use of oxalate oxidase (EC 1.2.3.4). Modification of an HPLC spectrophotometric detector improved sensitivity (to as much as 1000-fold that of conventional spectrophotometers) and allowed measurement of oxalate concentrations less than 1 mumol/L. This provided more than enough sensitivity for measurement of normal concentrations of plasma oxalate. We established reference values for oxalate concentrations in urine and plasma, studied sample handling, and established conditions to avoid ascorbate interference in urine and plasma measurements. Mean analytical recovery of [14C]oxalate from plasma to the filtrate was 86 (SD 10)%; recovery of unlabeled oxalate from filtrate was 87 (SD 9)%. Urinary oxalate excretion rates in apparently healthy controls were 0.11-0.46 mmol/24 h. Plasma concentrations in control subjects were 2.5 (SD 0.7) mumol/L, similar to concentrations determined by recent gas chromatographic and isotope dilution methods. Frozen and acidified urine samples showed no interference from ascorbate when excess ascorbate was avoided. Ingestion of 2 g of ascorbate daily did not increase urinary oxalate in healthy control subjects, but during storage ascorbate was converted to oxalate in all conditions tested.

Dissociation quotients of oxalic acid in aqueous sodium chloride media to 175°C

Abstract: The first and second molal dissociation quotients of oxalic acid were measured potentiometrically in a concentration cell fitted with hydrogen electrodes. The emf of oxalic acid-bioxalate solutions was measured relative to an HCl standard solution from 25 to 125°C over 25o intervals at nine ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and available literature data were treated in the all anionic form by a five-term equation that yielded the following thermodynamic quantities at infinite dilution and 25°C: logK1a=−1.277±0.010, ΔH 1a o =−4.1±1.1 kJ-mol−1, ΔS 1a o =38±4 J-K−1-mol−1, and ΔC p,1a o =−168±41 J-K−1-mol−1. Similar measurements of the bioxalate-oxalate system were made at 25o intervals from 0 to 175°C at seven ionic strengths from 0.1 to 5.0m. A similar regression of the experimentally-derived and published equilibrium quotients using a seven-term equation yielded the following values at infinite dilution and 25°C: logK2a=−4.275±0.006, ΔH 2a o =−6.8±0.5 kJ-mol−1, ΔS 2a o =−105±2 J-K−1-mol−1, and ΔC p,2a o =−261±12 J-K−1-mol−1.

Aluminum(III) speciation with acetate and oxalate. A potentiometric and aluminum-27 NMR study

Abstract: Aluminum (III) hydrolysis and precipitation in the presence of acetic acid and oxalic acid have been studied by combining potentiometric titration and liquid-state {sup 27}Al NMR. The main aluminum species have thus been identified and quantified: unreacted hydrolyzed, complexed monomers, and the Al{sub 13} tridecamer. A solid species appeared when precipitation occurred and was quantified by difference with the other species. The quantitative evolution of these species was followed for pH values up to 5. Acetate forms weak complexes with aluminum. The precipitated phase was hypothesized to be aggregated Al{sub 13}. Oxalate forms strong multiligand complexes to form Al{sub 13} requires higher hydroxyl content. High oxalate contents (L/M > 1) inhibit tridecamer formation and precipitation occurs only at high pH values. With oxalate the precipitated phase seems to be devoid of Al{sub 13} and of a more condensed nature than it is with acetate.

Oxalate patinas on ancient monuments: the biological hypothesis

Abstract: Whewellite and weddellite, calcium oxalate monohydrate and dihydrate respectively, have been found in the form of thin surface layers on limestone and marble monuments and artifacts of various historical periods at different sites. Experimental results indicate that the formation of both minerals must be attributed essentially to the action of oxalic acid secreted by microorganisms (lichens) which live and proliferate on the stone. Oxalic acid attacks the calcium carbonate of the stone surface giving rise to the precipitation of calcium oxalate.

Influence of oxalic acid on the adsorption of cadmium at the goethite surface

Abstract: The adsorption/desorption of oxalic acid and Cd on goethite has been characterized in function of pH in KNO3 medium. Electrophoretic mobilities and pH titrations show that while anion desorbs, cation adsorbs, the maxima of adsorption being in significantly different pH ranges. Adsorption-desorption phenomena of oxalic acid in function of pH are identical in absence or presence of Cd. Contrarily, not only adsorption, but also desorption of Cd is enhanced in presence of oxalic acid. Surface sites are shown to never be saturated even in presence of excess of ligand and cation. So, competition between anions and cations for surface sites is minor. Ligand in solution does not compete with surface sites for the Cd, probably due to the low tendency of oxalic acid to form complexes with Cd. Behavior of Cd in presence of oxalate is discussed and results suggest a surface-binding of Cd via an oxalate-bridge between the surface and the metallic cation.

Preparation of Superconducting Bi-Pb-Sr-Ca-Cu-O Compounds by Oxalate Coprecipitation

Abstract: Bi1.6Pb0.4Sr2Ca2Cu3Oy has been prepared from an ethylene glycol medium that contains starting metal nitrates via homogeneous coprecipitation using triethylammoniumoxalate and oxalic acid. The theoretical estimate on the conditions of oxalate coprecipitation and preliminary characterization of the properties of the Bi1.6Pb0.4Sr2Ca2Cu3Oy obtained after the high-temperature treatment are reported. The preparation of this five-component system of Bi, Pb, Sr, Ca and Cu using triethylammoniumoxalate and oxalic acid has worked successfully in a large-quantity preparation of up to 200 g per batch.

Alkylation of Aromatic Heterocycles with Oxalic Acid Monoalkyl Esters in the Presence of Trivalent Iodine Compounds

Abstract: Aromatic heterocycles containing nitrogen atoms were easily alkylated with the half esters of oxalic acid, which were prepared from alcohols, in the presence of [bis(trifluoroacetoxy)iodo]benzene via radical decarboxylative pathways. This is the first method for the alkylation of aromatic heterocycles with alcohols via the formation of half esters of oxalic acid.

Method of forming rare earth oxide ceramic scintillator with ammonium dispersion of oxalate precipitates

Abstract: A method of forming polycrystalline rare earth oxide ceramic scintillators formed by dissolving a mixture of oxides of the scintillator in an aqueous hydrochloric or nitric acid solution to form a rare earth solution, precipitating oxalates from the rare earth solution, calcining the oxalates to form the respective oxides, cold pressing the oxides to form a compact, and sintering the compact in a reducing atmosphere or vacuum to form the scintillator, the method being improved by precipitating the oxalates by admixing the rare earth solution with an oxalic solution comprised of, oxalic acid and ammonium ions in an amount that disperses the oxalate precipitates.

Prevention of pyrite dissolution in acidic media

Abstract: Three samples of pyrites (n- and p-type semiconductors) were investigated for their corrosion behavior in 1 M H2SO4 using a potentiodynamic polarization technique. The corrosion behavior as influenced by the surface treatment of pyrite by acetyl acetone, methoxy triacetoxy silane (MTS), glycidoxy propyl trimethoxy silane (GPTS), phenyl triacetoxy silane (PTS), humic acid, lignin—NaOH solution, oxalic acid, and benzene was investigated. It was found that the corrosion rate of pyrite in sulfuric acid can be decreased significantly (up to 98%) by acetyl acetone and humic acid treatment. Pyrite is also passivated by PTS, lignin—NaOH solution, benzene, GPTS, and oxalic acid treatment. A mechanism is proposed to explain pyrite passivation due to surface treatment by chemicals used in this study.

Effect of mineral and organic acids on radiation grafting of styrene onto polyethylene

Abstract: A study has been made on the effect of mineral and organic acids on the radiation-induced graft polymerization of styrene onto low-density polyethylene films. Effects of different solvents and dose rate of irradiation on the grafting yield were also investigated. The influence of irradiation time and monomer concentration in the presence and absence of acid on the initial rate and grafting yield was studied. The dependence of the grafting rate on monomer concentration was found to be of the order 1.34 (in absence of acid), 0.61 (in presence of HCl), and 1.25 (in presence of oxalic acid). Such acid enhancement of the radiation grafting process is of practical importance from an economical point of view.

Cellulose solution in water and nmmo

Abstract: A solution of cellulose in water and N-methylmorpholine-N-oxide (NMMO) containing 2 to 44% by weight cellulose is stabilized at 001 to 1%, preferably 01% H 2 O 2 and 001 to 2%, preferably 01% of an H 2 O 2 stabilizer, preferably oxalic acid or a salt thereof during formation of the solution and during heating to prevent discoloration of the cellulose and reduce the composition of NMMO

Evaluation of a dilute chemical decontaminant for pressurized heavy water reactors

Abstract: In this paper a dilute chemical decontamination formulation based on ethylene diamine tetraacetic acid, oxalic acid, and citric acid is evaluated for its efficacy in removing oxide layers in a pressurized heavy water reactor (PHWR). An ion exchange system that is specifically suited for fission product-dominated contamination in a PHWR is suggested for the reagent regeneration stage of the decontamination process. An attempt has been made to understand the redeposition behavior of various isotopes during the decontamination process. The polarographic method of identifying the species formed in the dissolution process is explained. Electrochemical measurements are employed to follow the course of oxide removal during the dissolution process. Scanning electron micrographs of metal coupons before and after the dissolution process exemplify the involvement of base metal in the formation of a ferrous oxalate layer. Material compatibility tests between the decontaminant and carbon steel, Monel-400, and Zircaloy-2 are reported.

Dissolution Kinetics of Nickel Ferrite in Chelating and Reducing Agents

Abstract: As a first step towards developing a decontaminating solution, the dissolution of synthetically prepared nickel ferrite was studied in low concentrations (

The mechanism of thermal eliminations. Part XXVIII [1]: Thermal decomposition of benzoylformic acid

Abstract: The thermal decomposition of benzoylformic acid into carbon dioxide and benzaldehyde is a unimolecular first-order reaction which takes place according to the rate equation log k = 15.3–42,500/4.575 K. At 600 K the reaction takes place 18 times faster than the corresponding decomposition of pyruvic acid into carbon dioxide and acetaldehyde. This is consistent with the 4-center process proposed previously for pyruvic acid, in which a partial negative charge develops on the carbon of the α-carbonyl group in the transition state. Benzoylformic acid is considerably less reactive towards thermal elimination than is oxalic acid, which also accords with the proposed mechanism.

Production of 2,2,6,6-tetramethyl-4-oxopiperidine

Abstract: PURPOSE:To obtain the subject substance in high yield in a short time while producing little by-product by reacting acetone or an acidic condensate of acetone with 2,2,4,4,6-pentamethyl-2,3,4,5-tetrahydropyrimidine in the presence of an iron carboxylic acid salt as a catalyst. CONSTITUTION:The subject substance can be produced by reacting acetone or an acidic condensate of acetone (e.g. diacetone alcohol) with a compound of formula at about 60 deg.C for 5-10hr in the presence of a carboxylic acid iron salt as the reaction catalyst. The carboxylic acid constituting the catalyst is preferably acetic acid, oxalic acid, lactic acid, citric acid, etc., and the amount of the catalyst is preferably 0.01-0.2mol per 1mol of the compound of formula. The above catalyst may be used in combination with a Lewis acid, protonic acid, etc. The subject substance useful as a photo-stabilizer for polymeric material or synthetic intermediate for pharmaceuticals, etc., can be produced in colorless state by the above process in high yield.

Synthesis under ambient pressure of 80 K superconducting YBa2Cu4O8 powders via coprecipitation

Abstract: Sub‐micron homogeneous powders of YBa2Cu4O8 having Tc∼80 K were synthesised from aqueous solutions containing Y, Ba, Cu salts, and oxalic acid as a precipitant via a chemical coprecipitation method using triethylamine as a base. An accelerated formation−within 24 h−of nearly single phase YBa2Cu4O8 powders was achieved. The intragrain critical current density at 5 K and H=1 T was determined to be 3.9×107 A/cm2. This process may have considerable potential in the large‐scale preparation of YBa2Cu4O8.

Double bond isomerization of olefin-containing feeds with minimal oligomerization using permanently surface acidity deactivated zeolite catalysts

Abstract: A method is disclosed for the double bond isomerization of alpha olefin-containing feeds, e.g., conversion of 1-butene-containing hydrocarbon streams to 2-butene-rich product streams, wherein oligomer by-products are minimized. The process uses a catalyst composition comprising a zeolite whose surface has been at least partially deactivated for acid catalyzed reactions by treatment with an aluminum chelating agent, e.g., oxalic acid, which possesses an average cross section diameter greater than that of the zeolite pores.

Analytical applications of oxocarbons. Part 3. Specific spectrophotometric determination of oxalic acid by dissociation of the zirconium(IV)–chloranilate complex

Abstract: Oxalic acid can be determined spectrophotometrically, as it dissociates the chloranilate complex of zirconium(IV) at pH 2. The decrease in the absorbance at 335 nm is proportional to the amount of oxalic acid present. Optimum conditions for the method are described. The sensitivity of the method is high, allowing the determination of 0.035 ppm of oxalic acid. Because of the very high stabilities of the zirconium(IV) complexes of chloranilate or oxalate, few compounds interfere, particularly hydroxy acids. D-Glucose and alditols did not interfere, which could be useful in studies on solutions of biological interest.