Oxalic Acid Complexes Research Articles

Insights into the role of β-MnO2 and oxalic acid complex expediting ozonation: Structural properties and mechanism

The complexation between metal oxides and organic acid plays an important role in the water treatment. However, the mechanism of complex in catalytic ozonation process (HCO) has not been studied yet. In this study, a β-MnO2-oxalic acid (β-MnO2-OA) complex was constructed and used in HCO for pCBA degradation (β-MnO2/OA/O3). The addition of OA enhanced not only k value of β-MnO2/OA/O3 process by 4 times that of ozonation alone, but also had advantageous effects on co-degradation of contaminant and OA. The 90.4 % of pCBA and 65.2 % of OA degradation were achieved at pH 4.0 within 10 mins by the incorporation of OA (10 mg/L) and β-MnO2 (50 mg/L). Systematic characterization techniques (XPS, H2-TPR, and etc.) confirmed the enhanced electron transfer ability and redox property of β-MnO2-OA complex. More oxygen vacancies and reactive oxygen species (ROS) were generated through facilitating oxygen species migration. Besides, sodium pyrophosphate tests demonstrated that Mn3+ was mainly responsible for the formation of β-MnO2-OA complex. Scavenger experiments identified surface-•OH and liquid-•OH as major reactive radicals for pCBA degradation, while other ROS were the radicals involved in OA removal. Finally, a feasible mechanism involving solid–liquid interface reaction was elaborated, which presented a potential strategy improving catalytic ozonation performance.

Enhancing electrochemical lithium-storage properties of hydrated iron oxalate (FeC2O4·2H2O) anode material by combining with dual-states copper

The application of iron oxalate (FeC2O4) as a new high-energy anode material for lithium-ion batteries is astricted by difficulty in obtaining 100 % anhydrous material and inhibitive role of crystal water on lithium storage. Herein, we fabricated the trepang-liked hydrated iron oxalate (FeC2O4·2 H2O) anode materials by combining with dual-states copper and investigated the special function of copper. Because of the differentiated distribution between C2O42- and oxalic acid complexes ([Fe(C2O4)x]-2(x-1) and [Cu(C2O4)x]-2(x-1)), the CuC2O4·xH2O nanosheets with compound state adsorb and imbed on surface of rod-like FeC2O4·2 H2O particles. Meanwhile, copper element with ion state can effectively doped into the crystal structure of FeC2O4·2 H2O, due to the similar three-dimensional crystal structure between transition metal oxalates. In virtue of the differentiated electrochemical behavior of crystal water for iron oxalate and copper oxalate, the copper derivatives (Cu, CuO, Cu2O et al.), formed by the reaction between CuC2O4·xH2O and Li+, exhibit high electrochemical activity and electrical conductivity, which can significantly enhance the lithium storage ability of dihydrate iron oxalate. Hence, hydrated iron oxalate combined with dual-states copper, suggests superior reversible capacity (∼550 mAh g-1 at 0.1 A g-1) and stable long-term cycling performance (∼520 mAh g-1 at 0.5 A g-1 after 200 cycles). This paper provides a novel opportunity to weaken the inhibitive role of crystal water on lithium storage and enhance the electrochemical properties of hydrous oxalate materials.

Recovery and Separation of Vanadium, Nickel, and Molybdenum from the Industrial Waste of a Petroleum Refinery by a Complexation Method

Based on the characteristics of complexation reactions, a novel method for the recovery and separation of vanadium (V), molybdenum (Mo), and nickel (Ni) is proposed. This approach mainly utilizes oxalic acid and hexamethylenetetramine (HMT) as complexing agents to recover and separate V, Mo, and Ni from the roasting slag of the byproduct carbon black from petroleum refineries, which includes the above elements plus iron and calcium. According to the differences in the solubilities of the metallic oxalic acid complexes, V and Mo were selectively leached with efficiencies of 95.49% and 97.74%, respectively, while Ni, iron, and calcium remained in the residue. After decomplexing the V and Mo complexes in the leachate by adding sulfuric acid, the oxalic acid was recycled. Then, the solution containing V and Mo was treated with HMT, and 93.19% of the Mo was complexed and precipitated. Finally, the precipitated Mo complex was dissociated by the addition of calcium oxide to separate and recover Mo and HMT with a Mo recovery efficiency of 95.72%, and HMT was regenerated and used in the following cycles. As a result, the method proposed in this study is an efficient and sustainable way to recover and separate V, Mo, and Ni from the industrial waste of petroleum refineries.

Energetic competition in the complexation affinity of paracetamol with water and oxalic acid

The intermolecular interactions of active pharmaceutical ingredients (APIs) are the driving forces of API molecular activity and stability, in vivo receptor binding, environmental transport, and persistence. In manufacturing, API complexation with another molecule to create stable crystalline structures is pursued, but the formation of more energetically stable complexes can lead to undesired consequences. Density functional theory (DFT) was used to describe the role played by hydrogen bonding in the formation of paracetamol and oxalic acid (PCA-OXA) complexes. PCA-OXA hydrogen bonding sites were investigated to determine strength and overall contribution/competition during the initial stages of the nucleation process. Structural and energetic changes were evaluated for 1:1 PCA-OXA, PCA-Water, and OXA-Water complexes both in vacuum and in water environments via explicit and implicit solvation. Results show significant shortening of the hydrogen bonds within the PCA-OXA complex with large changes in energy in the PCA-OXA complexation mechanism. Two out of the four complexation sites play the largest roles in the initial steps of the nucleation process. In an aqueous environment, little to no energetic competition for PCA hydrogen bonds formation with other molecules is observed. Post Hartree–Fock methods (MP2 and CCSD) were used to calibrate and verify the DFT results.

Synthesis, DFT Calculations, DNA Interaction, and Antimicrobial Studies of Some Mixed Ligand Complexes of Oxalic Acid and Schiff Base Trimethoprim with Various Metal Ions

Mixed ligand metal complexes are synthesized from oxalic acid with Schiff base, and the Schiff base was obtained from trimethoprim and acetylacetone. The synthesized complexes were of the type [M(L1)(L2)], where the metal, M, is Ni(II), Cu(II), Cr(III), and Zn(II), L1 corresponds to the trimethoprim ((Z)-4-((4-amino-5-(3,4,5-trimethoxybenzyl)pyrimidine-2-yl)imino)pentane-2-one) as the first ligand and L2 represent the oxalate anion ( ) as a second ligand. Characterization of the prepared compounds was performed by elemental analysis, molar conductivity, magnetic measurements, 1H-NMR, 13C-NMR, FT-IR, and Ultraviolet-visible (UV-Vis) spectral studies. The recorded infrared data is reinforced with density functional theory (DFT) calculations. Also, the recorded and calculated IR spectra of the complexes suggested that the coordination of Schiff base is a bidentate ligand with Cu and Ni complexes and a tridentate ligand with Co, Cr, and Zn complexes. The electronic structures of the complexes were investigated by DFT calculations, showing several degrees of HOMO-LUMO energy gaps between complexes. The complexes were studied for their DNA interaction activities. The synthesized ligand and its metal complexes were evaluated for antimicrobial properties against bacterial strains of Bacillus subtilis (G+), Enterobacter cloacae (G-), and Staphylococcus aureus (G+). These complexes considered in this study showed good antimicrobial activity.

Photodegradation of cresol red by a non-iron Fenton process under UV and sunlight irradiation: Effect of the copper(II)-organic acid complex activated by H2O2

The copper(II)-organic acid complex activated by H2O2 was known to be a non-iron Fenton process. In this work, photodegradation of cresol red (CR) by a non-iron Fenton process (Cu(II)-Ox- H2O2) using Cu(II)-Oxalic acid (Ox) complex as catalyst was investigated. The results demonstrate that the combination of light and Cu(II)-Ox complex in situ generates H2O2 by producing reactive oxidants through the reaction of Cu(I) with H2O2. The second part, dedicated to the study of capacity of Cu(II)-Ox- H2O2 system to induce the degradation of CR. Kinetics experiments showed that the external supply of H2O2 to the Cu(II)-Ox system was found to further enhance the effectiveness of CR. Here, we further investigate the synergistic effect in different systems (two-component system UV/Cu(II)-Ox, and three-component system UV/Cu(II)-Ox-H2O2 with CR under the same conditions. Parameters such as pH, the initial concentrations of Cu(II), oxalic acid (Ox) and H2O2 were all investigated. Furthermore, the radical scavenging activity studies indicated that •OH was the dominant active species responsible for CR removal, and O2–• could promote CR degradation in Cu(II)-Ox-H2O2 system. These result strongly confirmed the feasibility of non-iron Fenton process (Cu(II)-Ox- H2O2) under excitation by sunlight.

Tunable polymorph and morphology synthesis of iron oxalate nanoparticles as anode materials for lithium ion batteries

Iron oxalate (FeC2O4), a promising anode material for lithium ion batteries (LIBs), is typically crystallized in orthorhombic-type phase. When the synthesis temperature rises, β-FeC2O4·H2O can transform into high-crystalline α-phase. At present, the detail evolution mechanism of crystal structure for two kinds of iron oxalate polymorphs is seldom studied. Through in-depth experiments, the tunable polymorph and morphology of iron oxalate can be obtained by controlling certain conditions. The oxalic acid complex ([Fe(C2O4) x]−2(x−1)), as unstable intermediate state, can change the reaction thermodynamics and kinetics, thus promoting the nucleation and growth of crystals. Higher temperature and longer reaction time would availably reinstitute stable hydrogen bonds and enhance the disordered state between successive stack layers, then resulting in various morphologies and phase-transition process. Due to short diffusion path and stable effective channels for Li+ ions, the mixed state of iron oxalate exhibits higher reversible capacity and more excellent cycling stability. Understanding the phase evolution mechanism of iron oxalate is critical to controllable synthesis, and ultimately, enhancing the performance of future LIBs.

Organic acids combined with Fe-chelate improves ferric nutrition in tomato grown in calcisol soil

Plants developed in calcisol soils have limitations in iron nutrition, so exogenous applications of organic acids plus iron chelate can be an alternative. With the objective of knowing the answer of adding organic acids in the fertilizer solution plus a ferric chelate on the characteristics of the ferric nutrition of tomato plants developed in the calcisol soil the present experiment was established. We conducted the experiment in two stages, in the first stage studied different concentration of some organic acids: citric acid (CA), oxalic acid (OA), salicylic acid (SA), and humic complexes (HCs) combined with a FeEDDHA iron chelate, we included treatment control FeEDTA and FeEDDHA and treatment without iron in the fertilizer solution. In the second stage, we compared the best concentrations of organic acids in combination with FeEDTA iron chelate; we used to treatment control FeEDTA and FeEDDHA, and a control treatment without iron in the fertilizer solution. The best concentrations were CA 10−4 M, OA 10−4 M, SA 10−5 M, and HC 0.4 ml l−1. In the second stage, the addition of CA+FeEDTA and HC+FeEDTA increased SPAD units, chlorophyll and vitamin C contents and fruit quality improved. An increase content of Fe, Zn, and Mn in leaves was presented with treatment CA+FeEDTA and HC+FeEDTA. Addition of CA+FeEDTA improved the oxidation-reduction potential, pH and electrical conductivity (EC) of plant leachates, followed by HC+FeEDTA. Applications of CA and HC in the nutrient solution in combination with EDTA-type chelate improved the characteristics of the ferric nutrition of tomato plants developed in calcisol soil.

Spectral and Thermal Studies on Bivalent Transition Metal Complexes of Oxalic Acid with Morpholine

Morpholinium transition metal oxalates of the formula (MorpH)2[MII(ox)2 (H2O)2].2H2O, where M = Co, Ni have been prepared by the reaction of respective metal nitrates with aqueous solution of morpholinium oxalate salts in appropriate mole ratios. These compounds have been characterized by various physico-chemical techniques like elemental analysis, conductance measurements, UV-Vis, IR, TG-DTA, XRD and SEM studies. The elemental analysis confirms the desired composition of the complexes. Conductance measurements show that all the complexes behave as 2:1 electrolytes, augmenting the non-coordination of morpholiniumcation. Thermal studies show the presence of two coordinated water molecules and two lattice water molecules. Based on the above results, geometry of the complexes is assigned as octahedral. The powder X-ray diffraction patterns of these compounds are similar to one another suggesting that they are isomorphous.Scanning electron micrographs are also observed to evaluate the morphology and particle size of the complexes.

Influence of substituents and cooperativity in doubly hydrogen-bonded complexes of 2-pyridone and oxalic acid

ABSTRACTWe performed a systemic investigation of the substitution and cooperative effects on the O–H···O and N–H···O H-bonds in the complexes of 2-pyridone and its derivatives with oxalic acid. Generally, the electron-withdrawing substituent in 2-pyridone weakens the O–H···O H-bond but strengthens the N–H···O H-bond, while the opposite effect is for the electron-donating group. In addition, the substitution effect is associated with its substitution position in 2-pyridone. The total interaction energy of a chainlike trimer with oxalic acid as a middle molecule exhibits some additivity. When oxalic acid combines with two 2-pyridone/2-pyridinethione molecules, the O–H···O/S H-bond is weakened but the N–H···O H-bond is enhanced. When three oxalic acid molecules are linked by the double O–H···O H-bonds, one H-bond with the middle oxalic acid as the proton donor is weakened and the other H-bond with the middle oxalic acid as the proton acceptor is strengthened.

Forward osmosis for oily wastewater reclamation: Multi-charged oxalic acid complexes as draw solutes

Forward osmosis (FO) has demonstrated its merits in hybrid FO seawater desalination. However, FO may have a potential for other applications if suitable draw solutes are available. In this study, a series of novel draw solutes based on oxalic acid (OA)-transitional metal complexes are presented. Influential factors of FO performance have been systematically investigated by varying the transitional metals, cations of the complex draw solutes as well as the experimental conditions. Compared to NaCl and other recently synthesized draw solutes, the OA complexes show superior FO performance in terms of high water fluxes up to 27.5 and 89.1 LMH under the respective FO and PRO (pressure retarded osmosis) modes, both with negligible reverse solute fluxes. The features of octahedral geometry, abundant hydrophilic groups and ionic species are crucial for the OA complexes as appropriate draw solutes with satisfactory FO performance. Among the synthesized OA complexes, the ammonium salt of chromic complex (NH4-Cr-OA) outperforms others due to the presence of more ionic species in its complex system. NH4-Cr-OA also performs better than the typical NaCl draw solute in FO oily wastewater treatment with higher water recovery and negligible reverse fluxes. Dilute solutions of OA complexes have been reconcentrated through membrane distillation (MD) and reused to new round of FO processes. The OA complexes have demonstrated their suitability and superiority as a novel class of draw solutes for the FO process in this study.

Solid state characterization of azelnidipine–oxalic acid co-crystal and co-amorphous complexes: The effect of different azelnidipine polymorphs

In present study, based on the two polymorphs (α and β form) of azelnidipine (AZE), 12 complexes of AZE and oxalic acid (OXA) were prepared by solvent-assisted grinding (SG) and neat powder grinding (NG) methods at the AZE/OXA molar ratios of 2:1, 1:1, and 1:2. The effect of the different polymorphs of AZE on the micro-structure of the complexes were investigated by powder X-ray diffraction (PXRD), tempreture modulated differential scanning calorimetry and thermogravimetric analysis, cryo-field emission scanning electron microscope system, fourier transform infrared (FTIR), and solid-state nuclear magnetic resonance spectroscopy. β-AZE-OXA co-crystal was produced at β-AZE/OXA molar ratio of 2:1 when SG method was used; while α-AZE was used to produce α-AZE-OXA co-crystal at same condition. However, the other 10 combinations were in co-amorphous forms, including the NG samples with α (or β)-AZE/OXA molar ratios of 2:1, 1:1 (SG and NG), and 1:2 (SG and NG). Although the XRD pattern and IR spectra of the two co-crystals showed no difference, the melting enthalpy and specific heat cp of the β-AZE-OXA co-crystal was higher than that of the α-AZE-OXA co-crystal, indicating that the numbers of solvent molecules which entered the two co-crystal lattices were different. Interestingly, obvious difference occurred in the IR spectra between the α-AZE-OXA and β-AZE-OXA co-amorphous systems. 1745cm−1 wave-numbers, which were assigned to the free CO groups, appeared in the α-AZE-OXA co-amorphous systems even when just a small amount of OXA was introduced, thereby indicating the presence of different intermolecular forces in the two series of co-amorphous forms. The solubility in different media and the dissolution rate in 0.1molL−1 HCl of the 12 complexes were determined. The dramatically improved dissolution rates of the α- and β-AZE-OXA 1:2 (NG) combinations in vitro showed potential in improving the physicochemical properties of AZE by co-amorphous complex formation.

Effective As(III) Removal by A Multi-Charged Hydroacid Complex Draw Solute Facilitated Forward Osmosis-Membrane Distillation (FO-MD) Processes.

Effective removal of As(III) from water by an oxalic acid complex with the formula of Na3[Cr(C2O4)3] (Na-Cr-OA) is demonstrated via an forward osmosis-membrane distillation (FO-MD) hybrid system in this study. Na-Cr-OA first proved its superiority as a draw solute with high water fluxes and negligible reverse fluxes in FO, then a systematic investigation of the Na-Cr-OA promoted FO process was conducted to ascertain the factors in As(III) removal. Relatively high water fluxes of 28 LMH under the FO mode and 74 LMH under the pressure retarded osmosis (PRO) mode were achieved when using a 1000 ppm As(III) solution as the feed and 1.0 M Na-Cr-OA as the draw solution at 60 °C. As(III) removal with a water recovery up to 21.6% (FO mode) and 48.3% (PRO mode) were also achieved in 2 h. An outstanding As(III) rejection with 30-3000 μg/L As(III) in the permeate was accomplished when As(III) feed solutions varied from 5 × 10(4) to 1 × 10(6) μg/L, superior to the best FO performance reported for As(III) removal. Incorporating MD into FO not only makes As(III) removal sustainable by reconcentrating the Na-Cr-OA solution simultaneously, but also reduces the As(III) concentration below 10 μg/L in the product water, meeting the WHO standard.

Hydroxyl radical generation in the photo-Fenton process: Effects of carboxylic acids on iron redox cycling

From the viewpoint of iron redox cycle promoting OH radical generation in the photo-Fenton process, effects of carboxylic acids formed in the proceeding of the degradation of organic pollutants on the photo-Fenton reactions were discussed. To elucidate the contributions of carboxylic acids forming complexes with iron ions to the photo-Fenton process, the Fenton reaction, the photo-Fenton reaction and the Fenton-like reaction composing the photo-Fenton process were individually examined. A kinetic model simulating the dynamic behaviors of iron redox cycle and OH radical generation was developed to quantify the contributions of carboxylic acids, i.e., citric acid, formic acid, malonic acid and oxalic acid. The FeII–oxalic acid complex and FeII–citric acid complex accelerated the rate of iron redox cycle or OH radical generation in the Fenton reaction by 18% and 8%, respectively. The additions of formic acid and malonic acid slightly affected the OH radical generation rate by the Fenton reaction. The photo-Fenton reaction, which is the controlling-step of the photo-Fenton process, was enhanced by oxalic acid and citric acid but largely suppressed by malonic acid. The effect of formic acid on the photo-Fenton reaction was insignificant. These results in the photo-Fenton reaction could be explained by considering the changes in the UV light absorbance with formed FeIII–carboxylic acid complexes. The effects of carboxylic acids on the Fenton-like reaction were little. In the photo-Fenton process, the additions of oxalic acid and citric acid accelerated the iron redox cycle and as a result the OH radical generation by 26% and 11%, respectively. Formic acid insignificantly affected the iron redox cycle and the addition of malonic acid decelerated the iron redox and OH radical generation by approximately 39%.

Oxalic acid complexes: promising draw solutes for forward osmosis (FO) in protein enrichment.

Highly soluble oxalic acid complexes (OACs) were synthesized through a one-pot reaction. The OACs exhibit excellent performance as draw solutes in FO processes with high water fluxes and negligible reverse solute fluxes. Efficient protein enrichment was achieved. The diluted OACs can be recycled via nanofiltration and are promising as draw solutes.

Hydration of a sulfuric acid–oxalic acid complex: acid dissociation and its atmospheric implication

We have investigated structural characteristics and thermodynamics of the hydration of a sulfuric acid–oxalic acid complex using density functional theory to gain insight into the ternary nucleation and its atmospheric implication.

Chemistry of defluoridation by one-pot synthesized dicarboxylic acids mediated polyacrylamide–zirconium complex

Abstract The current report deals with the synthesis of a new and excellent fluoride sorbents using dicarboxylic acids like oxalic acid (Ox) malonic acid (MA) and succinic acid (SA) mediated polyacrylamide–zirconium (PAAm–Zr) and zirconium–oxalic acid (Zr–Ox) complexes by one-pot method. Among the synthesized complexes, Ox–PAAm–Zr and Zr–Ox complexes showed higher (double the times) defluoridation capacity (DC) than the other complexes under batch equilibrium mode. Characterizations of the synthesized complexes were carried out to determine the functional groups, surface morphologies, elemental analysis and crystalline nature. Various equilibrium parameters were optimized. The sorption data were well explained by three commonly used isotherms viz., Freundlich, Langmuir and D–R isotherms. Thermodynamic parameters like ΔG°, ΔH° and ΔS° were calculated and predicted the nature of the fluoride adsorption is spontaneous and endothermic. The mechanism of fluoride removal using Ox–PAAm–Zr complex is ligand-exchange mechanism. Suitable regenerant has been identified in desorption studies and the regeneration ability was tested. Also, the practical viability of the material has been verified with field samples collected from nearby fluoride endemic villages.

Structural Determination of a Novel Polymorph of Sulfathiazole–Oxalic Acid Complex in Powder Form by Solid-State NMR Spectroscopy on the Basis of Crystallographic Structure of Another Polymorph

Two polymorphic forms of a sulfathiazole (STZ):oxalic acid (OXA) 1:1 complex were successfully prepared by different cogrinding methods and characterized by multiple analytical techniques. Rod-milled and ball-milled ground mixtures had different powder X-ray diffraction patterns, showing polymorph formation of the STZ-OXA complex (complex A and complex B). The heat of fusion from differential scanning calorimetry curves and terahertz time-domain spectra helped differentiating the polymorphs. According to infrared spectra, 13C NMR chemical shifts, and the relative intensities of 15N NMR peaks, both polymorphs were salts where the proton of a −COOH group in OXA was transferred to a −NH2 group in STZ. High-resolution 1H NMR and 1H–13C heteronuclear correlation NMR spectra indicated that complex B in powder form had a cocrystal type structure compared to complex A having a clathrate-type structure. Complex B structure suggested by solid-state NMR coincided well with the experimentally determined one, which wa...

Behavior of carboxylic acids upon complexation with beryllium compounds.

A significant acidity enhancement and changes on aromaticity were previously observed in squaric acid and its derivatives when beryllium bonds are present in those systems. In order to know if these changes on the chemical properties could be considered a general behavior of carboxylic acids upon complexation with beryllium compounds, complexes between a set of representative carboxylic acids RCOOH (formic acid, acetic acid, propanoic acid, benzoic acid, and oxalic acid) and beryllium compounds BeX2 (X = H, F, Cl) were studied by means of density functional theory calculations. Complexes that contain a dihydrogen bond or a OH···X interaction are the most stable in comparison with other possible BeX2 complexation patterns in which no other weak interactions are involved apart from the beryllium bond. Formic, acetic, propanoic, benzoic, and oxalic acid complexes with BeX2 are much stronger acids than their related free forms. The analysis of the topology of the electron density helps to clarify the reasons behind this acidity enhancement. Importantly, when the halogen atom is replaced by hydrogen in the beryllium compound, the dihydrogen bond complex spontaneously generates a new neutral complex [RCOO:BeH] in which a hydrogen molecule is lost. This seems to be a trend for carboxylic acids on complexing BeX2 compounds.

The Effects of Interactions of Dicarboxylic Acids on the Stability of the Caffeine Molecule: A Theoretical Study

Abstract The cocrystal formation leads to the improvement of the physicochemical properties of drug substances. Caffeine, as a pharmaceutical compound, forms cocrystals with dicarboxylic acids through OH(acid)···N(caffeine) and CH(caffeine)···O(acid) hydrogen bonds. In the present work, four 2:1 ternary complexes of the caffeine molecule with oxalic, malonic, maleic, and glutaric acids (as cocrystal units) were studied by computational quantum chemistry methods. Also, all ternary complexes were considered in the presence of water molecules. The energy data indicate that the caffeine–oxalic acid complex is the most stable ternary complex with respect to humidity. The results of population analysis, on the basis of the atoms-in-molecules (AIM) and the natural bond orbital (NBO) methods, are in good agreement with the energy data and experimental observations for the caffeine cocrystals.