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Showing papers on "Oxalic acid published in 2005"


Journal ArticleDOI
TL;DR: In this paper, a systematic crystal engineering study was performed on the model pharmaceutical compound caffeine to prepare a cocrystal that, unlike caffeine, is physically stable at all relative humidities (RH).
Abstract: A systematic crystal engineering study was performed on the model pharmaceutical compound caffeine to prepare a cocrystal that, unlike caffeine, is physically stable at all relative humidities (RH). Six cocrystal materials containing caffeine with one of several dicarboxylic acids are described herein. Methods of cocrystallization included solution growth, neat solid-state grinding, and grinding with solvent-drop addition. Crystal structures are reported for a total of five cocrystals containing caffeine (with oxalic acid, malonic acid, maleic acid, and glutaric acid), including two recently reported polymorphic caffeine cocrystals. In each of these structures, a predicted intermolecular hydrogen-bonding motif is observed. The stability with respect to RH is evaluated for the six cocrystal materials. The cocrystal with oxalic acid exhibits complete stability to humidity over a period of several weeks. Other cocrystals demonstrate lesser degrees of stability with respect to humidity.

617 citations


Journal ArticleDOI
TL;DR: The fungus Beauveria caledonica was highly tolerant to toxic metals and solubilized cadmium, copper, lead, and zinc minerals, converting them into oxalates, suggesting that a ligand-promoted mechanism was the main mechanism of mineral dissolution.
Abstract: The fungus Beauveria caledonica was highly tolerant to toxic metals and solubilized cadmium, copper, lead, and zinc minerals, converting them into oxalates. This fungus was found to overexcrete organic acids with strong metal-chelating properties (oxalic and citric acids), suggesting that a ligand-promoted mechanism was the main mechanism of mineral dissolution. Our data also suggested that oxalic acid was the main mineral-transforming agent. Cadmium, copper, and zinc oxalates were precipitated by the fungus in the local environment and also in association with the mycelium. The presence of toxic metal minerals often led to the formation of mycelial cords, and in the presence of copper-containing minerals, these cords exhibited enhanced excretion of oxalic acid, which resulted in considerable encrustation of the cords by copper oxalate hydrate (moolooite). It was found that B. caledonica hyphae and cords were covered by a thick hydrated mucilaginous sheath which provided a microenvironment for chemical reactions, crystal deposition, and growth. Cryo-scanning electron microscopy revealed that mycogenic metal oxalates overgrew parental fungal hyphae, leaving a labyrinth of fungal tunnels within the newly formed mineral matter. X-ray absorption spectroscopy revealed that oxygen ligands played a major role in metal coordination within the fungal biomass during the accumulation of mobilized toxic metals by B. caledonica mycelium; these ligands were carboxylic groups in copper phosphate-containing medium and phosphate groups in pyromorphite-containing medium.

255 citations


Journal ArticleDOI
TL;DR: The mechanism of ozonation likely develops through formation of iron-oxalate complexes that further react with ozone without the participation of hydroxyl radicals, and is supported through an Eley-Rideal mechanism that involves a surface reaction between non-adsorbed ozone and adsorbed oxalic acid.

227 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated two buckwheat cultivars, Jiangxi (Al resistant) and Shanxi (al sensitive), which showed significant variation in their resistance to Al stress.
Abstract: Oxalic acid secretion from roots is considered to be an important mechanism for aluminum (Al) resistance in buckwheat (Fygopyrum esculentum Moench). Nonetheless, only a single Al-resistant buckwheat cultivar was used to investigate the significance of oxalic acid in detoxifying Al. In this study, we investigated two buckwheat cultivars, Jiangxi (Al resistant) and Shanxi (Al sensitive), which showed significant variation in their resistance to Al stress. In the presence of 0 to 100 μm Al, the inhibition of root elongation was greater in Shanxi than that in Jiangxi, and the Al content of root apices (0–10 mm) was much lower in Jiangxi. However, the dependence of oxalic acid secretion on external Al concentration and the time course for secretion were similar in both cultivars. Furthermore, the variation in Al-induced oxalic acid efflux along the root was similar, showing a 10-fold greater efflux from the apical 0- to 5-mm region than from the 5- to 10-mm region. These results suggest that both Shanxi and Jiangxi possess an equal capacity for Al-dependent oxalic acid secretion. Another two potential Al resistance mechanisms, i.e. Al-induced alkalinization of rhizosphere pH and root inorganic phosphate release, were also not involved in their differential Al resistance. However, after longer treatments in Al (10 d), the concentrations of phosphorus and Al in the roots of the Al-resistant cultivar Jiangxi were significantly higher than those in Shanxi. Furthermore, more Al was localized in the cell walls of the resistant cultivar. All these results suggest that while Al-dependent oxalic acid secretion might contribute to the overall high resistance to Al stress of buckwheat, this response cannot explain the variation in tolerance between these two cultivars. We present evidence suggesting the greater Al resistance in buckwheat is further related to the immobilization and detoxification of Al by phosphorus in the root tissues.

175 citations


Journal ArticleDOI
TL;DR: This study investigates the nutrient extraction efficiency of three individual organic acids commonly identified in root exudates, i.e. citric, malic and oxalic acid, and demonstrates the context dependent nature of nutrient release by organic acids.
Abstract: Calcareous soils are frequently characterized by the low bioavailability of plant nutrients. Consequently, many vascular plant species are unable to successfully colonize calcareous sites and the floristic composition of calcareous and acid silicate soils has been shown to differ markedly. The root exudation of oxalate and citrate has been suggested to play a pivotal role in same nutrient acquisition mechanisms operating in calcareous soils. The aim of this study was therefore to investigate the nutrient extraction efficiency of three individual organic acids commonly identified in root exudates, i.e. citric, malic and oxalic acid. Our results clearly demonstrate the context dependent nature of nutrient release by organic acids. The degree of P extraction was highly dependent on which organic acid was added, their concentration and pH, and their contact time with the soil. P is generally more efficiently extracted by organic acids at a high pH and follows the series oxalate > citrate > malate. The opposite relationship between pH and extraction efficiency was apparent for most other cations examined (e.g. Zn, Fe), which are more efficiently extracted by organic acids at low pH. A serious constraint to the ecological importance of organic acid exudation in response to P deficiency is, however, their very low P mobilization efficiency. For every mol of soil P mobilized, 1000 mol of organic acid has to be added. It can, however, be speculated that in a calcareous soil with extremely low P concentrations it is still beneficial to the plants to exude organic acids in spite of the seemingly high costs in terms of carbon.

164 citations


Journal ArticleDOI
TL;DR: Overall, this study shows the possible use of bioleaching for the extraction of metal resources from spent catalysts and demonstrated the advantages of buffer-stimulated excretion of organic acids by A. niger inBioleaching of the spent catalyst.

161 citations


Journal ArticleDOI
TL;DR: In this paper, two rice husk samples of different origin, one from the state of Andhra Pradesh (APRH) in the central part of India and the other from Kerala (KRH) the southern most part of the country, were compared for optical properties.
Abstract: Rice husk, an agro waste material, contains about 20% ash which can be retrieved as amorphous, chemically reactive silica. This silica finds wide applications as filler, catalyst/catalyst support, adsorbent and a source for synthesizing high performance silicon and its compounds. Various metal ions and unburned carbon influence the purity and color of the ash. Controlled burning of the husk after removing these ions can produce white silica of high purity. The present paper deals with the investigation carried out on two rice husk samples of different origin, one from the state of Andhra Pradesh (APRH) in the central part of India and the other from Kerala (KRH) the southern most part of the country. Leaching the husk with acetic and oxalic acids was attempted for the first time and the improvement in properties of the ash was studied. The husk samples were also treated with hydrochloric and nitric acids of different concentrations for comparison. The ashes produced by controlled burning of these samples before and after acid treatment, were characterized for the optical properties in addition to the chemical and physical nature. The APRH ash was found to be inferior to the KRH ash in all properties. Pretreatment of the husks with the organic acids improved the properties of ashes and the effect was comparable to that achieved by mineral acid leaching. Amorphous, reactive and high purity silica with high surface area and pore volume and good optical properties could be prepared from both the husks under specific conditions.

159 citations


Journal ArticleDOI
TL;DR: In this article, a three-phase fixed-bed FBR with a commercial catalyst based on copper oxide was used to analyze the variables affecting significantly the copper leaching, and it was found that temperature has almost negligible influence in the range studied (70-160°C).
Abstract: Catalytic wet oxidation of phenol as a model pollutant has been performed in a three phase fixed-bed reactor (FBR) by using a commercial catalyst based on copper oxide in order to analyze the variables affecting significantly the copper leaching. It has been found that temperature has an almost negligible influence in the range studied (70–160 °C). On the contrary, an important effect of the pH value was noticed. The copper leaching reduces when the pH of the solution fed to the reactor increases, being almost negligible at pH ≥ 5. Moreover, the composition of the reaction media also influences the leaching. Higher copper concentrations than those expected by the effect of the acid aqueous media have been measured in the reactor effluent when phenol, catechol, hydroquinone, p -benzoquinone and maleic acid are present in the reaction media. On the contrary, oxalic acid has a negative influence on the leaching, since it captures the copper in solution to form copper oxalate which precipitates on the catalyst surface. For a previously acidified medium, the acetic and formic acids do not have any other effect on the copper leaching. It has been also demonstrated that as copper in solution decreases, so does phenol conversion, because the homogeneous catalysis contributes significantly to the oxidation reactions even in fixed-bed reactors.

141 citations


Journal ArticleDOI
TL;DR: Five case reports of fatal EG-poisoning are presented, and the literature concerning clinical presentation and diagnosis, pathological findings, treatment and prevention are reviewed.

104 citations


Journal ArticleDOI
TL;DR: Yttria-doped ceria powder was prepared from oxalate precursors, and compacts of such powders were sintered to high density (98%) at 1400°C (4 h).
Abstract: Yttria-doped ceria powder was prepared from oxalate precursors. The oxalate coprecipitation bath parameters were closely monitored and found to influence the sintering behavior of the subsequently obtained oxide powders strongly. The use of concentrated (Ce,Y) metal nitrate solutions and dilute neutralized oxalic acid for coprecipitation were identified as the most-important parameters. Following calcination at 700°C, compacts of such powders were sintered to high density (98%) at 1400°C (4 h). Ball milling of the powder further reduced the sintering temperature. Dry milling, for tape-casting applications of the powder in particular, was more effective than wet milling. Tape-cast membranes were fired at 1400°C (2 h), with resulting densities of 98%.

103 citations


Journal ArticleDOI
TL;DR: In this article, polyaniline and polypyrrole films were electropolymerized onto iron from aqueous oxalic acid and phosphoric acid solutions, respectively.

Journal ArticleDOI
TL;DR: In this paper, anodic oxidation of 4,6-dinitro- o -cresol (DNOC) has been studied in a cell of 100 ml with a boron-doped diamond anode and a graphite cathode, both of 3-cm 2 area.

Journal ArticleDOI
TL;DR: A fungus, termed strain A, was able to utilize 1,4-dioxane and many kinds of cyclic ethers as the sole source of carbon and was identified as Cordyceps sinensis from its 18S rRNA gene sequence.
Abstract: By using 1,4-dioxane as the sole source of carbon, a 1,4-dioxane-degrading microorganism was isolated from soil. The fungus, termed strain A, was able to utilize 1,4-dioxane and many kinds of cyclic ethers as the sole source of carbon and was identified as Cordyceps sinensis from its 18S rRNA gene sequence. Ethylene glycol was identified as a degradation product of 1,4-dioxane by the use of deuterated 1,4-dioxane-d8 and gas chromatography-mass spectrometry analysis. A degradation pathway involving ethylene glycol, glycolic acid, and oxalic acid was proposed, followed by incorporation of the glycolic acid and/or oxalic acid via glyoxylic acid into the tricarboxylic acid cycle.

Journal ArticleDOI
TL;DR: Data from six genotypes of Actinidia chinensis suggest that oxalate is not a sink for excess ascorbic acid but that Oxalate formation is regulated, and that no ascorBic acid was found in the seed.
Abstract: Ascorbic acid and total oxalate were measured in fruit from six genotypes of Actinidia chinensis. Ascorbic acid was separated from oxalate in fruit extracts by HPLC and quantified from absorbance at 245 nm, whereas oxalate was measured enzymatically in the HPLC eluate. Levels of whole fruit mean ascorbic acid in the different genotypes ranged from 98 to 163 mg/100 g of fresh weight (FW), whereas mean oxalate varied between 18 and 45 mg/100 g of FW. Ascorbic acid was highest in the inner and outer pericarp, whereas oxalate was concentrated in the skin, inner pericarp, and seed. Essentially no ascorbic acid was found in the seed. Each tissue clustered separately when the tissue ascorbic acid and oxalate data were normalized to the whole fruit level of ascorbic acid and oxalate in that genotype and plotted against each other, suggesting that oxalate is not a sink for excess ascorbic acid but that oxalate formation is regulated.

Journal ArticleDOI
TL;DR: In this article, the in situ ATR-FT-IR was used to study catalytic photooxidation on TiO2 (Degussa P-25) of oxalic acid at pH 3.7 and of catechol at pH 6.2.

Journal ArticleDOI
TL;DR: In this article, the authors used the FTIR-ATR spectra of an illuminated Degussa P-25 film deposited onto the ATR crystal to follow the photocatalytic oxidation of oxalic acid in acidic media.

Journal ArticleDOI
Peter Warneck1
TL;DR: In this paper, a box model is used to explore the detailed chemistry of C2 and C3 organic compounds in the marine troposphere by tracing the individual reaction paths resulting from the oxidation of ethane, ethene, acetylene, propane, propene and acetic acid.
Abstract: A box model is used to explore the detailed chemistry of C2 and C3 organic compounds in the marine troposphere by tracing the individual reaction paths resulting from the oxidation of ethane, ethene, acetylene, propane, propene and acetic acid. The mechanisms include chemical reactions in the gas phase and in the aqueous phase of clouds and aerosol particles at cloud level under conditions resembling those in the northern hemisphere. Organic hydroperoxides are found to be important intermediate products, with subsequent reactions leading partly to the formation of mixed hydroxy or carbonyl hydroperoxides that are readily absorbed into cloud water, where they contribute significantly to the formation of multifunctional organic compounds and organic acids. Organic hydroperoxides add little to the oxidation of sulfur dioxide dissolved in the aqueous phase, which is dominated by H2O2. Next to acetaldehyde and acetone, glycol aldehyde, glyoxal, methyl glyoxal and hydroxy propanone are prominent oxidation products in the gas and the aqueous phase. Acetaldehyde is not efficiently converted to acetic acid in clouds; the major local sources of acetic acid are gas-phase reactions. Other acids produced include hydroperoxy acetic, glycolic, glyoxylic, oxalic, pyruvic, and lactic acid. The mechanism of Schuchmann et al. (1985), which derives glycolic and glyoxylic acid from the oxidation of acetate, is found unimportant in the marine atmosphere. The principal precursors of glyoxylic acid are glyoxal and glycolic acid. The former derives mainly from acetylene and ethene, the latter from glycolaldehyde, also an oxidation product of ethene. The oxidation of glyoxylic acid leads to oxalic acid, which accumulates and is predicted to reach steady state concentrations in the range 30–90 ng m−3. This is greater, yet of the same magnitude, than the concentrations observed over the remote Pacific Ocean.

Journal ArticleDOI
TL;DR: A kinetic model that describes the removal of organic pollutants by an ozone/UV process is described and was verified by experimental data on concentrations of oxalic acid and hydrogen peroxide under various experimental conditions.
Abstract: A kinetic model that describes the removal of organic pollutants by an ozone/UV process is described. Oxalic acid, which reacts with a very low rate constant with ozone and relatively high rate con...

Journal ArticleDOI
TL;DR: In this article, the influence of different halides on electrochemical incineration of oxalic acid was studied and experiments were initially carried out at a Pt electrode in alkaline media, in which case, in the absence of mediating effects, a slow electroxidation was observed.
Abstract: The influence of different halides on electrochemical incineration of oxalic acid was studied. Experiments were initially carried outat a Pt electrode in alkaline media, in which case, in the absence of mediating effects, a slow electroxidation was observed.However, with halides, the rate of the electrochemical incineration was increased significantly, following the order F

Journal ArticleDOI
TL;DR: In this paper, a substitution polyaniline, poly(o-toluidine) was synthesized by an oxidative chemical polymerization method using Acetic, formic and oxalic acids as dopants during the polymerization process.

Journal ArticleDOI
TL;DR: In this paper, the degradation of phenol and its chlorinated derivatives with ozone is studied and the HPLC analysis is used to identify intermediates and final products formed during ozonation.
Abstract: The degradation of phenol and its chlorinated derivatives with ozone is studied. The studied compounds are phenol (Ph), 4-chlorophenol (4-CPh) and 2,4-dichlorophenol (2,4-DCPh). The kinetic performances of each phenolic compound and their model mixture are examined. The pH influence on the decomposition dynamics for different phenolic compounds in the range 2–12 is investigated. The increase of the decomposition rate under increasing pH was observed. In the pH range studied, phenol and chlorophenols ozonation proceeds rapidly. The UV absorbency is used for the preliminary control of the degree of decomposition. The HPLC analysis is used to identify intermediates and final products formed during ozonation. It is shown that the basic intermediates are muconic and fumaric acids, malonic and maleic acids, catechol and hydroquinone. The final products are oxalic acid and formic acid. In the case of alkaline media, the principal final product is oxalic acid. Furthermore, intermediates and final decomposition pr...

Journal ArticleDOI
TL;DR: In this article, the authors used three commercial active carbons (AC) as catalysts for catalytic wet oxidation of phenol as a model pollutant and found that all the AC tested showed high catalytic activity in both phenol conversion and mineralization.

Journal ArticleDOI
TL;DR: In this article, polyaniline coatings were electrodeposited from an oxalic acid solution onto iron and their electrochemical activity and corrosion protection properties were studied as a function of pH.
Abstract: Polyaniline coatings were electrodeposited from an oxalic acid solution onto iron and their electrochemical activity and corrosion protection properties studied as a function of pH. It was found that the coating (emeraldine salt) had a limited effect on the corrosion protection of iron in acidic solutions. However, in an alkaline borate solution, where the conducting polyaniline was converted to the emeraldine base, the coating had a clear beneficial effect on the local breakdown of iron by chloride anions; much higher pitting potentials were recorded following a 2 h immersion period for the polyaniline-coated substrate relative to the uncoated electrode. Relatively small anions, such as acetates, nitrates and borates, were transported readily across the polymer interface. However, the emeraldine base inhibited the transport of the much larger ethylenediamine tetraacetate (EDTA) species to the iron interface, preventing complexation of the iron by EDTA.

Journal ArticleDOI
TL;DR: In this paper, photo-Fenton (PF) reaction was used to degrade oxalic acid (ox) at relatively high concentrations (0.032 m) and the results indicated that, at a fixed iron concentration, H 2 O 2 increased the initial HP reaction rate and reduced the TOC 95.

Journal ArticleDOI
TL;DR: Hydrogen peroxide evolution during the vacuum-ultraviolet (V-UV, 172 nm) photolysis of water is considerably affected by the presence of oxalic acid (employed as a model water pollutant) and striking differences are observed in the absence and in the Presence of dioxygen.
Abstract: Hydrogen peroxide evolution during the vacuum-ultraviolet (V-UV, 172 nm) photolysis of water is considerably affected by the presence of oxalic acid (employed as a model water pollutant) and striking differences are observed in the absence and in the presence of dioxygen.


Journal ArticleDOI
TL;DR: In this paper, a simple route for synthesis of nanocrystalline N-doped titania by calcination of acidified TiCl 3 in presence of urea and oxalic acid was demonstrated.

Journal ArticleDOI
15 Oct 2005
TL;DR: This work evaluated the rates of kaolinite dissolution induced by three kinds of low-molecular-weight organic acid, i.e., citric, oxalic, and malic acids, under far-from-equilibrium conditions.
Abstract: Kaolinite is a dominant clay mineral in the soils in tropical and subtropical regions, and its dissolution has an influence on a variety of soil properties. In this work, kaolinite dissolution induced by three kinds of low-molecular-weight organic acid, i.e., citric, oxalic, and malic acids, was evaluated under far-from-equilibrium conditions. The rates of kaolinite dissolution depended on the kind and concentration of organic acids, with the sequence R(oxalate)>R(citrate)>R(malate). Chemical calculation showed the change in concentration of organic ligand relative to change in concentration of organic acid in suspensions of kaolinite and organic acid. The effect of organic acid on kaolinite dissolution was modeled by species of organic anionic ligand. For oxalic acid, L(2-)(oxalic) and HL(-)(oxalic) jointly enhanced the dissolution of kaolinite, but for malic and citric acids, HL(-)(malic) and H2L-(citric) made a higher contribution to the total dissolution rate of kaolinite than L(2-)(malic) and L(3-)(citric), respectively. For oxalic acid, the proposed model was R(Si)=1.89x10(-12)x[(25x)/(1+25x)]+1.93x10(-12)x[(1990x1)/(1+1990x1)] (R2=0.9763), where x and x1 denote the concentrations of HL(oxalic) and L(oxalic), respectively, and x1=10(-3.81)xx/[H+]. For malic acid, the model was R(Si)=4.79x10(-12)x[(328x)/(1+328x)]+1.67x10(-13)x[(1149x1)/(1+1149x1)] (R2=0.9452), where x and x1 denote the concentrations of HL(malic) and L(malic), respectively, and x1=10(-5.11)xx/[H+], and for citric acid, the model was R(Si)=4.73x10(-12)x[(845x)/(1+845x)]+4.68x10(-12)x[(2855x1)/(1+2855x1)] (R2=0.9682), where x and x1 denote the concentrations of H2L(citric) and L(citric), respectively, and [Formula: see text] .

Journal ArticleDOI
TL;DR: In this paper, a comparative study on the catalytic behavior of Mo-V-Te-Nb-O and MoV-VTe-O catalysts prepared from Te6+ or Te4+-containing precursors is presented.

Journal ArticleDOI
TL;DR: In this article, a kinetic study of the electrochemical oxidation of ferulic acid (3methoxy-4-hydroxycinnamic acid) by direct electron transfer at treated gold disk was combined with results of electrolyses in order to produce total degradation into CO2 and H2O at Ta/PbO2 anode.
Abstract: A kinetic study of the electrochemical oxidation of ferulic acid (3-methoxy-4-hydroxycinnamic acid) by direct electron transfer at treated gold disk was combined with results of electrolyses in order to produce total degradation into CO2 and H2O at Ta/PbO2 anode. The oxidation of ferulic acid at gold electrode was studied by cyclic voltammetry. At low concentration, ferulic acid shows one irreversible anodic peak. The peak current shows adsorption characteristics. For ferulic acid concentrations higher than 0.02 mmol dm−3, the voltammogram shows two anodic peaks. The effect of experimental conditions on the ratio of these two peaks was examined. The proposed mechanism is based on the hypothesis of two-electron oxidation of ferulic acid molecule involving a three intermediate cation mesomers. Hydrolysis of these mesomers leads to the formation of caffeic acid, methoxyhydroquinone and 3,4-dihydroxy-5-methoxycinnamic acid. Then ferulic acid was quantitatively oxidised by electrolysis on lead dioxide to produce, via intermediate aromatic compounds, maleic acid, oxalic acid and formic acid whose oxidation leads to carbon dioxide.