Oxalic acid

About: Oxalic acid is a(n) research topic. Over the lifetime, 11584 publication(s) have been published within this topic receiving 173263 citation(s). The topic is also known as: ethanedioic acid & H2ox.

Structural Features of Oxide Coatings on Aluminum

Abstract: The structural features of the porous type of anodic oxide coating applied to aluminum have been investigated with the electron microscope. These coatings consist of close‐packed cells of oxide, predominately hexagonal in shape, each of which contains a single pore. Pore size is a function of the electrolyte used and is independent of forming voltage. Wall thickness and barrier thickness are primarily a function of forming voltage and are affected to a minor degree by the electrolyte type. Pertinent dimensions of anodic coatings formed in sulfuric acid, oxalic acid, chromic acid, and phosphoric acid electrolytes are presented, and formulas are given for calculating the cell size and pore volume of these coatings.

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

Fungal production of citric and oxalic acid: importance in metal speciation, physiology and biogeochemical processes.

Abstract: The production of organic acids by fungi has profound implications for metal speciation, physiology and biogeochemical cycles. Biosynthesis of oxalic acid from glucose occurs by hydrolysis of oxaloacetate to oxalate and acetate catalysed by cytosolic oxaloacetase, whereas on citric acid, oxalate production occurs by means of glyoxylate oxidation. Citric acid is an intermediate in the tricarboxylic acid cycle, with metals greatly influencing biosynthesis: growth limiting concentrations of Mn, Fe and Zn are important for high yields. The metal-complexing properties of these organic acids assist both essential metal and anionic (e.g. phosphate) nutrition of fungi, other microbes and plants, and determine metal speciation and mobility in the environment, including transfer between terrestrial and aquatic habitats, biocorrosion and weathering. Metal solubilization processes are also of potential for metal recovery and reclamation from contaminated solid wastes, soils and low-grade ores. Such ‘heterotrophic leaching’ can occur by several mechanisms but organic acids occupy a central position in the overall process, supplying both protons and a metal-complexing organic acid anion. Most simple metal oxalates [except those of alkali metals, Fe(III) and Al] are sparingly soluble and precipitate as crystalline or amorphous solids. Calcium oxalate is the most important manifestation of this in the environment and, in a variety of crystalline structures, is ubiquitously associated with free-living, plant symbiotic and pathogenic fungi. The main forms are the monohydrate (whewellite) and the dihydrate (weddelite) and their formation is of significance in biomineralization, since they affect nutritional heterogeneity in soil, especially Ca, P, K and Al cycling. The formation of insoluble toxic metal oxalates, e.g. of Cu, may confer tolerance and ensure survival in contaminated environments. In semiarid environments, calcium oxalate formation is important in the formation and alteration of terrestrial subsurface limestones. Oxalate also plays an important role in lignocellulose degradation and plant pathogenesis, affecting activities of key enzymes and metal oxidoreduction reactions, therefore underpinning one of the most fundamental roles of fungi in carbon cycling in the natural environment. This review discusses the physiology and chemistry of citric and oxalic acid production in fungi, the intimate association of these acids and processes with metal speciation, physiology and mobility, and their importance and involvement in key fungal-mediated processes, including lignocellulose degradation, plant pathogenesis and metal biogeochemistry.

Pharmaceutical Cocrystallization: Engineering a Remedy for Caffeine Hydration

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.