Isothermal dehydration of copper sulfate pentahydrate and trihydrate

Isothermal dehydrations of the pentahydrate and trihydrate of copper sulfate are studied in the temperature ranges of 47–63°C and of 70.5–86°C respectively. Both dehydration processes involve the loss of two molecules of water in the temperature ranges studied. The topochemical kinetics of the reactions is well described by Avrami-Erofeev equation with x = 2 over the α-range of 0.1–0.9. Activation energies of 104 ± 10 kJ mol⁻¹ and 134 ± 3 kJ mol⁻¹ are evaluated and are approximately equal to the respective values of the heat of reaction. The methods of Jacobs and Kureishy and of Ng in obtaining activation energy from the decomposition curves are also discussed.     

Kinetic study of isopropanol dehydration over silicoaluminophosphate catalyst

The catalytic dehydration of isopropanol has been studied over a solid acid silicoaluminophosphate type SAPO-5. The reaction was processed varying the temperature and weight hourly space velocity, using a fixed bed continous flow reactor. The isopropanol undergoes inter- and intramolecular dehydration, forming propylene and isopropyl ether, respectively. Nevertheless, the catalyst was selective to the olefin, with an activation energy of the order of 46.1 kJ/mol.     

The kinetics of crystallization and dissolution of barium oxalate dihydrate and cadmium oxalate trihydrate

The kinetics of crystallization and dissolution of barium oxalate dihydrate and cadmium oxalate trihydrate have been studied at 25°C by following the changes in conductivity when supersaturated or subsaturated solutions are inoculated with seed crystals. In additive-free solutions, the growth of barium oxalate dihydrate seed crystals follows a rate law second order with respect to supersaturation, and a surface-controlled reaction is proposed. The same kinetic equation may be used to interpret the growth of this salt from supersaturated solutions containing a variety of phosphonate additives. However in these experiments the reaction is preceded by an initial fast surge in the concentration—time profiles. The rate of growth of cadmium oxalate trihydrate crystals varies linearly with supersaturation and this can be explained in terms of a surface diffusion model for growth. The dissolutions of both barium oxalate dihydrate and cadmium oxalate trihydrate follows a rate law in which the rate of reaction is proportional to the undersaturation and evidence is presented for a liquid transport rate-determining step for the dissolution reactions. Although both the crystallization and dissolution of cadmium oxalate trihydrate follow similar first order kinetic equations the appreciable differences in the values of the rate constants suggest that they are not reciprocal processes.     

Kinetic study of the dehydration of modified Y zeolites

The dehydration of ferric exchanged Y zeolites is studied by thermal analysis. Their DTA shows three endotherms in the temperature range 80–450°C. The order of reaction and apparent energies of activation are calculated using various equations. The order of dehydration is nearly one and the apparent energy of activation is 4–8 kcal mole^?1. The effect of heating rate is studied. The energy of activation as determined by the Kissinger and Ozawa method is about 12 kcal mole^?1, which is comparable with the heat of adsorption of water determined by the gravimetric method, and is more acceptable.     

Mechanism of dehydration of magnesium oxalate dihydrate

The isothermal dehydration of magnesium oxalate dihydrate has been studied at various temperatures between 190 and 260°C in the presence of air. The isothermal dehydration curves show the usual sigmoidal character and display an induction period which is highest at 190°C. The dehydration velocity constant (k) values (obtained by the application of Mampel's equation) plotted vs. 1/T according to the Arrhenius equation gave a plot in which two linear sections intersect at ～215°C with activation energies of 12.3 and 18.3 kcal mole^?1 for the lower- and higher-temperature sections, respectively. This behaviour is tentatively explained in terms of a change in the mechanism of dehydration, and not the formation of some new phase other than the dihydrate and the anhydrous oxalate phases present in both the original crystalline oxalate and the sample heated at 200°C for 120 min. X-Ray patterns of the heated oxalate sample left for a few days at room temperature showed a marked sensitivity for rehydration of the anhydrous oxalate phase.     

Donepezilium oxalate trihydrate,a therapeutic agent for Alzheimer's disease

Donepezil, a cholinesterase inhibitor with good central nervous system penetration, has been crystallized as a tertiary amine salt with a disordered oxalate anion to give the title compound, (R,S)‐1‐benzyl‐4‐[(5,6‐dimethoxy‐1‐oxoindan‐2‐yl)methyl]piperidinium hydrogen oxalate trihydrate, C₂₄H₃₀NO₃⁺·C₂HO₄⁻·3H₂O. The indanone and piperidine ring planes are inclined at an angle of 33.4 (1)°. A comparison is made with the piperidinium cation bound in acetyl­cholinesterase in the solid state. The methyl­ene units bridging the indanone–piperidine–benzyl groups determine the mol­ecular shape and conformational features. The structure is stabilized mainly by O—H⋯O and N—H⋯O hydrogen bonds, with water mol­ecules mediating inter­actions between oxalate anions and donepezilium cations.     

Kinetics and thermodynamics of thermal dehydration of magnesium oxalate dihydrate

The kinetics and thermodynamics of the thermal dehydration of crystalline powders of MgC₂O₄ · 2 H₂O were studied by means of thermal analyses both at constant temperatures and at linearly increasing temperatures. The dehydration of the dihydrate is regulated by one of the Avrami-Erofeyev laws. The kinetic parameters from TG at constant temperatures are in good agreement with those from TG at the lowest rate of rising temperatures. The dynamic dehydration kinetics was also examined, using DSC recorded simultaneously with TG at linearly increasing temperatures. The validity of the estimated mechanism and kinetic parameters is briefly discussed.     

Kinetic study of Y, Ba, Cu oxalates and coprecipitated Y-Ba-Cu oxalate

The kinetics of the decomposition of Y, Ba and Cu oxalates and coprecipitanted Y-Ba-Cu oxalate was investigated under a nitrogen atmosphere on the basis of dynamic thermogravimetric data, the average activation energies of the decomposition of Y, Ba and Cu oxalates were obtained from the slopes of the T. Ozawa plot. The average activation energies for the dehydration of these oxalate and coprecipitated Y-Ba-Cu oxalate were also evaluated from the thermogravimetric curves.     

Vibrational studies of calcium oxalate monohydrate (whewellite) and an anhydrous phase of calcium oxalate

The IR spectrum of calcium oxalate monohydrate is re-analysed, and the Raman spectrum presented for the first time. The IR and Raman spectra of an anhydrous phase of calcium oxalate are discussed in relation to the effects of dehydration and compared with the monohydrate.     

A comparative study of methods for precipitating calcium oxalate from homogeneous solution

A PFHS of calcium oxalate has been examined and the optimum conditions for the precipitation established. This method, and two other methods employing PFHS for the gravimetric determination of calcium as the oxalate are compared with the conventional and acetic acid-medium methods. All the methods work well in the absence of magnesium, but the urea hydrolysis procedure, in the absence of an initial precipitate, is recommended as the best method when magnesium is present. Crystal sizes have been measured by microscopy.     

Thermal decomposition of copper(II) glutarate trihydrate. Part I. The mechanism of dehydration of copper(II) glutarate trihydrate

The mechanism of thermal dehydration of copper(II) glutarate trihydrate has been determined from the analysis of the kinetic data for isothermal and non-isothermal dehydration experiments. Microscopic investigations for the dehydration process of a single crystal of copper(II) glutarate trihydrate have been carried out to support the mechanism. The simultaneous DTG—DTA—TG curves of the salt are also described.     

X-ray study of tetrabutylammonium hydroxide trihydrate

Conclusions The crystal lattice parameters were determined for [(C₄H₉)₄N]OH · 3H₂O. Tetrabutylammonium hydroxide trihydrate crystallizes in the rhombic system with the parametersa=13.96, b=11.20, and c=10.50 Å.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2103–2104, September, 1976.     

Simulation of calcium oxalate stone in vitro

Urolithiasis constitutes a serious health problem that affects a significant section of mankind. Between 3% and 14% of the population, depending on the geographical region, suffer from this illness[1]. For example, the incidence of urolithiasis in Florida in the United States of America was 15.7 in 100000 people and increased to 20.8 in 1996. Urolithiasis remains a major medical prob-lem in China, especially in Guangdong Province. A survey in 1997 in Shenzhen City, the most southern city i…     

Kinetic study of the multistep thermal behaviour of barium titanyl oxalate prepared via chemical precipitation method

This study describes the physico-geometrical mechanism and overall kinetics for the multistep thermal dehydration of barium titanyl oxalate tetrahydrate (BTO). The thermal dehydration kinetics of BTO was studied at four different linear heating rates under non-isothermal conditions. The reaction kinetics was performed using differential scanning calorimetry (DSC) and the curves obtained were analysed using different isoconversional model-free equations and the values are found to be compatible with each other. The kinetic deconvolution principle is used for identifying the partially overlapped kinetic processes of the thermal dehydration of BTO, and it occurs in two stages. The overall reaction kinetics parameters calculated via kinetic deconvolution of the sample indicate the multistep nature of the process and the kinetic analysis of the non-isothermal data of this reaction model shows that the reaction is best described by Sestak–Berggren (m, n) empirical kinetic model. The prepared sample was identified and characterized by means of FT-IR, XRD, SEM, and TEM.

     

Metal-ligand-coordinated vesicles and vesicle-assisted preparation of calcium oxalate

A Ca(2+) -ligand-coordinated vesicle phase was prepared from a mixture of tetradecyldimethylamine oxide (C14DMAO) and calcium tetradecylamidomethyl sulfate [(CH3(CH2)13NHCOCH2OSO3)2Ca] in aqueous solution. At the appropriate mixing ratios, Ca(2+) -ligand coordination results in the formation of molecular bilayers because Ca(2+) can firmly bind to the head groups of C14DMAO and (CH3(CH2)13NHCOCH2OSO3)2Ca by complexation which reduces the area of head group. In this system, no counterions in aqueous solution exist because of the Ca(2+) -ligand coordination, and the bilayer membranes are not shielded by salts, i.e., a salt-free but charged molecular bilayer. The structures of the birefringent solutions of (CH3(CH2)13NHCOCH2OSO3)2Ca and C14DMAO mixtures were determined by transmission electron microscopy (TEM) images and rheological measurements, demonstrating that the birefringent sample solutions consist of vesicles. The Ca(2+) -ligand complex vesicle phase was used as a microreactor to prepare calcium oxalate (CaC2O4) crystals. Dimethyl oxalate, as a precursor, can hydrolyze to oxalic acid and methanol. Oxalic acid should precipitate Ca(2+) ions binding to the head groups of C14DMAO and (CH3(CH2)13NHCOCH2OSO3)2Ca to produce CaC2O4 crystals (Ca(2+) + H2C2O4 --> CaC2O4 (downward arrow) + 2H+). The obtained particles were CaC2O4 monohydrate, which were dominated by (020) faces. CaC2O4 precipitates were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FT-IR) analysis. After removal of CaC2O4 precipitates, a new cationic and anionic (catanionic) vesicle phase was constructed through electrostatic interaction between cationic C14DMAOH+ (C14DMAO + H+ --> C14DMAOH+) and anionic CH3(CH12)13 NHCOCH2OSO3-.     

Thermal decomposition of calcium oxalate: beyond appearances

The goal of this study is twofold: to take a fresh look at the decomposition of calcium oxalate and to warn users of thermogravimetric analysis against the hasty interpretation of results obtained. Since the pioneer work of Duval 70 years ago, the scientific community has agreed unanimously as to the decomposition of anhydrous calcium oxalate (CaC₂O₄) into calcium carbonate (CaCO₃) and CO gas, and that of the calcium carbonate into calcium oxide (CaO), and CO₂ gas. We will demonstrate how these reactions, simple in appearance, in fact result from a succession of reactive phenomena involving numerous constituents both solid (CaCO₃, free carbon) and gaseous (CO₂ and CO) produced by intermediary reactions. The mass losses evaluated in the two distinct domains correspond closely to the molar masses of CO and CO₂, respectively. The simple mathematical calculation of that mass loss has simply concealed the existence of other reactions, and, most particularly the Boudouard reaction and that of solid phases between CaCO₃ and C. It just goes to show that appearances can be deceiving.

     

Dissolved urate salts out calcium oxalate in undiluted human urine in vitro: implications for calcium oxalate stone genesis

Hyperuricosuria has long been documented as a predisposing factor to calcium oxalate (CaOx) stone pathogenesis. However, its mechanism is still without sound scientific foundation. Previously, we showed that hyperuricosuria, simulated by the addition of dissolved sodium urate, promotes the crystallization of CaOx. In the present study, we demonstrate that the urate's effect on the crystallization is attributable to its salting out CaOx from solution. Furthermore, analysis of urines revealed that their metastable limit decreased with increases in the product of the prevailing concentrations of calcium and urate: this has implications for CaOx stone genesis. We also outline anti-salting out strategies for future research for the prevention and/or treatment of CaOx calculi.