Oxalic acid

About: Oxalic acid is a research topic. Over the lifetime, 11584 publications have been published within this topic receiving 173263 citations. The topic is also known as: ethanedioic acid & H2ox.

Spectrophotometric determination of urinary oxalate with oxalate oxidase prepared from moss.

Abstract: A novel spectrophotometric enzymic procedure for estimating oxalic acid in urine is described. Oxalate oxidase, prepared from moss species, converts oxalic acid to hydrogen peroxide and carbon dioxide. Hydrogen peroxide is determined enzymatically with horseradish peroxidase, by oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline; the resulting indamine due is determined spectrophotometrically at 595 nm. Interfering substances are removed by adsorption to ion-exchange resins and oxidation with charcoal, thus avoiding oxalate recovery problems accompanying oxalate isolation. The procedure is rapid, sensitive, linear, and precise. Results agreed well with those obtained with a widely used chemical technique.

Root exudation of organic acids: importance to nutrient availability and the calcifuge and calcicole behaviour of plants

Abstract: Many vascular plant species are unable to colonize limestone soils and the floristic composition of adjacent limestone and acid silicate soils differs greatly. Low-molecular organic acids (LOAs) in root exudates may greatly affect plant availability of nutrients and it is hypothesized that contrasting exudation of LOAs is a major mechanism controlling the calcicole and calcifuge behaviour of plants. Rhizosphere soil solution from two calcicole and two calcifuge species, grown in a pH-intermediate soil, was expelled by high-speed centrifugation. The concentrations of LOAs in these solutions were determined by an application of ion chromatography using a supported liquid membrane enrichment technique. Concentrations of dicarboxylic (mainly oxalic) and tricarboxylic (mainly citric) acids were much higher in the soil solution of the calcicole species, whereas there was no difference in monocarboxylic (mainly lactic+acetic) acids between rhizosphere soil solutions of the two species categories. A consistent difference in the relative molar proportion of mono-, di- and tricarboxylic acids was also demonstrated among all species, indicating a species specific exudation of LOAs from plant roots. The solubilizing effect of acetic, oxalic and citric acid and their Na-salts on Fe, Mn and phosphate in two limestone soils and in the pH-intermediate soil was also tested. Citric acid and/or Na-citrate were powerful solubilizers of Fe and Mn and oxalic acid and/or Na-oxalate of phosphate, whereas acetic acid and/or Na-acetate was quite weak in this respect. The results from this study strongly support the view that high exudation rates of di- and tricarboxylic LOAs is a major mechanism controlling calcicole behaviour of plants.

Synthesis of magnetite nanoparticles by thermal decomposition of ferrous oxalate dihydrate

Abstract: Two different polymorphs of ferrous oxalate dihydrate were synthesized by precipitation of ferrous ions with oxalic acid: α-Fe(C2O4) · 2H2O with a monoclinic unit cell is obtained after precipitation and ageing at 90 °C, whereas the orthorhombic β-type is formed after precipitation at room temperature. The morphology of the oxalate crystals can be tailored from prismatic crystals of the α-polymorph over star-like aggregates of α/β-mixtures to non-agglomerated crystallites of β-oxalate. Thermal decomposition in air gives hematite at T ≥ 250 °C; if the thermolysis reaction is performed at low oxygen partial pressures (e.g., T = 500 °C and pO2 = 10−25 atm) magnetite is obtained. The synthesized magnetite is stoichiometric as signaled by lattice parameters of a0 = 8.39 A. The thermal decomposition of ferrous oxalate is monitored by thermal analysis, XRD, and IR-spectroscopy. The morphology of the oxalate crystals is preserved during thermal decomposition; the oxalates are transformed into spinel particle aggregates of similar size and shape. The crystallite size of the magnetite particles increases with temperature and is 40 or 55 nm, if synthesized from β-oxalate at 500 °C or 700 °C, respectively. The saturation magnetization of the magnetite particles decreases with decreasing particle size. Since the particles are larger than the critical diameter for superparamagnetic behavior they display hysteresis behavior at room temperature.