Investigation of dehydration processes III. Thermal dehydration of strontium iodide hydrates

The dehydration phenomena of strontium iodide with different crystal water contents, prepared at room temperature, were studied with thermogravimetry and differential scanning calorimetry. The existence of strontium iodide dihydrate was proved during the dehydration of samples containing less then six moles of crystallization water. Evidence is given for the appearance of a liquid phase in the dehydration of strontium iodide dihydrate. The pertinent enthalpy values are reported.

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Zusammenfassung Die Dehydratisierungserscheinungen von bei Zimmertemperatur hergestelltem Strontiumjodid mit verschiedenem Kristallwasser wurden durch Thermogravimetrie und Differential-Abtastkalorimetrie untersucht. Die Existenz von Strontiumjodid-Dihydrat wurde während der Dehydratisierung von weniger als 6 Mol Kristallwasser enthaltenden Proben bewiesen. Beweis für das Auftreten einer Flüssigphase während der Dehydratisierung von Strontiumjodid-Dihydrat wird erbracht. Die bezüglichen Enthalpiewerte werden angegeben.

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Résumé On a étudié, par thermogravimétrie et analyse calorimétrique différentielle, la déshydratation de l'iodure de strontium contenant diverses sortes d'eaux de cristallisation préparé à température ambiante. On montre l'existence de l'iodure de strontium bihydraté formé lors de la déshydratation d'échantillons contenant moins de six molécules d'eau de cristallisation. On met en évidence l'apparition d'une phase liquide lors de la déshydratation de l'iodure de strontium bihydraté. Les enthalpies respectives sont données.

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We express our thanks to Dr. Gy. Pokol for his assistance in the computations.     

七水氯化镧脱水过程的研究

本文用热分析方法探讨了在不同水蒸气分压下LaCl_3·7H_2O的脱水过程,首次得到了基本分离的LaCl_3·2H_2O,并确定了它的存在条件,同时还发现并制备了尚未见报道的LaCl_3·5H_2O。     

Thermal evolution of microporous nitroprussides on their dehydration process

Divalent transition metal nitroprussides form a family of microporous materials which lose their crystallization water (coordinated and zeolitic) below 100°C and then remain stable up to above 150°C. The dehydration process of representative samples in their stable phases was studied by thermo-gravimetry (TG) and differential scanning calorimetry (DSC). The copper complex dehydrates in a single step through a practically irreversible process. For cadmium and cobalt complexes the water evolution on heating takes place in two stages. The first one, where only zeolitic waters are removed, is dominated by a diffusion mechanism while, during the loss of the strongly bonded waters (second stage) the material framework effect is added. The involved activation energy and its dependence on the conversion degree were estimated evaluating the thermo-gravimetric data according to an isoconversion model.     

The dehydration of copper(II) acetate monohydrate

The thermal dehydration of copper(II) acetate hydrate has been studied between 353 and 406 K, over a range of humidities. The dehydration is controlled by nucleation-and-growth kinetics at low temperatures, with an activation energy of 154 kJ·mol⁻¹, which changes to contracting-disc kinetics at higher temperatures with a lower activation energy of 76 kJ·mol⁻¹. Frequency factors have also been derived; the value for the high temperature process is low (10⁷s⁻¹) and that for the low temperature step is high (10¹⁷s⁻¹). Optical microscopy has been used to clarify the bulk kinetics; there is evidence for a reactive layer at the surface of the decomposing solid. In celebration of the 60^th birthday of Dr Andrew K. Galwey     

Synthesis,characterization, crystal structure and non-isothermal dehydration kinetics of a copper(II) complex

A three-dimensional complex, [CuL₂(H₂O)]₂ (HL?=?3-hydroxy-1-adamantanecarboxylic acid), C₄₄H₆₄Cu₂O₁₄, was synthesized under hydrothermal conditions from CuCO₃?·?Cu(OH)₂ and HL. The crystal structure of the complex was determined by X-ray crystallography and its thermal behavior and IR spectra examined. The non-isothermal dehydration kinetics of the complex were investigated using the Achar differential method.     

Investigation of structural changes of silica particles during dehydration and chemosorption

Investigations have been made of changes in the structures of ultradisperse pyrogenic silica particles by small-angle X-ray scattering during dehydration and chemosorption. It has been established that during dehydration there are abrupt changes in the geometrical dimensions of the particles, caused by breakdown of coordination complexes between surface silicon atoms and water molecules.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 6, pp. 745–748, November–December, 1985.     

Thermal dehydration of some food products and kinetic parameters of this process

Metal poly(vinyl acetates) polymers were obtained by radical polymerization with azodiisobutyronitrile. The thermal stabilities of the metal polymers (M-PVAC) have been studied by thermogravimetry (TG) between 25 and 550°C under nitrogen flow. The decomposition temperature was obtained from the maximum of the first derivative from TG curve. The kinetic parameters of the thermal decomposition were determined by the Arrhenius equation. All these polymers degrade mainly in a single step with a very small second step, probably via a complex reaction. The kinetic data thus obtained show that the thermostabilities decrease in the order: Sb-PVA_c～Ge-PVA_c>Bi-PVA_c～Cd-PCA_c>Ag-PVA_c～PVA_c>Zn-PVA_c> Au-PVA_c>In-PVA_c>Sn-PVA_c>Ga-PVA_c>Pd-PVA_c. Again, the thermal stability is dependent upon the metal incorporated in the backbone polymer. They loose weight after 320°C. The order of reaction from the thermal decomposition of these metal polymers was found to be ?0.5 for the first step and 0 for the second. The pre-exponential factor, the reaction order and the activation energy of the decomposition for metal (PVA_c) have been determined in most of them.     

Micro-Raman studies on the conformational behaviors of monosodium glutamate in dehydration process

The conformational behaviors of monosodium glutamate（MSG） in a dehydration process were studied by Micro-Raman spectroscopy in combination with Hartree-Fock calculations using 6-31+G^* method.The dehydration process of the MSG droplet was performed by decreasing the ambient relative humidity（RH）.The intensity ratio of the 935 cm^-1 band to 884 cm^-1 band(I₉₃₅/ I₈₈₄) kept decreasing when RH decreased.By optimizing the geometries with different fixed dihedral angles,the downtrend of(I₉₃₅/ I₈₈₄) is found to be due to the reduction of MSG molecular volume.     

萃取过程的量热研究 II: 微乳状液形成的滴水量热曲线

采用滴定量热法研究P204钠(钾、铵)-仲辛醇-煤油等体系在滴加水过程中的热量变化, 得到两种不同类型的量热曲线, 在此基础上解释了微乳状液的形成过程和水以两种状态─缔合水和自由水存在, 还以简化的模型定性地讨论了滴水过程中微乳状液颗粒大小的变化。     

Electron microscopic study of dehydration transformations. II. The formation of “superstructures” on the dehydration of goethite and diaspore

It is shown that the satellites observed in the diffraction pattern of the dehydrated single crystal of the mineral goethite, which were previously attributed to a “superstructure,” are better interpreted in terms of small angle scattering by a “texture” of the dehydration product hematite. This texture consists of rows of cavities parallel to the H(003) = G(100) planes with an average distance of 30–50 Å, depending on the stage of the transformation, in a highly twinned hematite matrix. In corundum resulting from the dehydration of diaspore a more isotropic texture is formed and the diffraction pattern exhibits “halos” instead of rows of satellite spots.     

Thermal-Dependent dehydration process and intramolecular cyclization of lisinopril dihydrate in the solid state

The pathway of dehydration and intramolecular cyclization of lisinopril dihydrate in the solid state was investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and a combination of thermal analyzer with Fourier transform infrared microspectroscopy (thermal FT-IR microscopic system). The results indicate that the dehydration from the solid-state lisinopril dihydrate had a two-step process from dihydrate to monohydrate at 76 degrees C and then from monohydrate to anhydrate at 99-101 approximately C, which could be clearly observed from the above three methods. Only the thermal FT-IR microscopic system could give vital information on diketopiperazine (DKP) formation via intramolecular cyclization in anhydrous lisinopril. A new peak at 1670 cm(-1) assigned to the carbonyl band of DKP formation was clearly evidenced. The water of reaction byproduct was liberated at a temperature >157 degrees C and appeared on the IR spectra near 3200-3400 cm(-1). Moreover, the peak at 1574 cm(-1) assigned to carboxylate shifted to 1552 cm(-1) due to the DKP formation. The peak at 1670 cm(-1) related to the DKP formation changed slightly in intensity from 147 degrees C and significantly near 157 degrees C. DSC and TGA methods were poor for use in supplying information on DKP formation in lisinopril. The thermal FT-IR microscopic system is useful from the view point that it can quickly and directly show the solid-state stability of drug.     

A continuous process for solid-state dehydration,amorphization and recrystallization of metoclopramide HCL monohydrate studied by simultaneous DSC-FTIR microspectroscopy

The purpose of this study was to investigate the thermal-induced solid-state characterization of metoclopramide hydrochloride monohydrate (MCP H₂O) by using a combination of differential scanning calorimetry (DSC) and Fourier-transform infrared (simultaneous DSC-FTIR) microspectroscopy. The DSC and thermogravimetric (TG) analyses were also carried out. The result indicates that a continuous process of dehydration, amorphization and recrystallization for MCP H₂O in the solid state was easily evidenced via the thermal responsive IR spectral changes by using this simultaneous DSC-FTIR microspectroscopy. In the heating course, one mole of water was first dehydrated from the MCP H₂O sample beyond 77 °C, was then quickly transformed to an amorphous form due to the appearance of weak broad IR bands, and continuously recrystallized from 148 °C by showing the sharp IR bands. This one-step novel simultaneous DSC-FTIR microspectroscopy might be available for studying the changes in the progressive processes of the thermal-dependent solid-state characterizations of drugs.     

Synthesis of 2-unsubstituted imidazolones from bisamides via a one-pot,domino dehydration/base promoted cyclisation process

A one-pot, domino process was developed as an alternative approach for the preparation of 2-unsubstituted imidazolones. The methodology utilizes readily accessible bisamides, which upon a dehydration/cyclisation sequence produced imidazolones in good yields. The transformation relies on the compatibility of the dehydrating agent and base, and the reaction conditions tolerate various functional groups.     

Chemical mapping of hydration and dehydration process of theophylline in tablets using terahertz pulsed imaging

The purpose of this research is to investigate the topographical pattern of hydration and dehydration (also known as pseudo-polymorphic change) of drug substance in drug product using terahertz (THz) pulsed imaging. Emphasis is placed on (1) applicability of THz pulsed imaging and (2) kinetic analysis in the pseudo-polymorphic change. Either anhydrous or monohydrated form of theophylline was used as the drug substance, leading to initially anhydrous or monohydrated tablets. These tablets were stored at 25°C to keep the relative humidity constant at 84% (anhydrous tablets) or 45% (monohydrated tablets), respectively. The THz pulsed imaging was confirmed to enable visualization that the hydration of the anhydrous form or the dehydration of the monohydrated form began on the surface of the tablets and gradually progressed to the core side in the tablets with storage. Kinetic studies indicated that these pseudo-polymorphic changes followed the phase boundary mechanism. Since the other imaging techniques has been scarcely achieved to show the topographical pattern of pseudo-polymorphic change of drug substances in drug products directly and visually, it is considered that THz pulsed imaging has a potential ability to solve complicated issues in pharmaceutical development.     

Cyclo dehydration reaction of polyhydrazides. II. Kinetic parameters obtained from isothermal thermogravimetry

The kinetics of the thermal conversion reaction of poly-(1,3-phenyl-1,4-phenyl)-hydrazide into poly-(1,3-phenyl-1,4-phenyl)-1,3,4-oxadiazole have been studied with isothermal thermogravimetry in continuation of a study with nonisothermal thermogravimetry described in a previous paper. Although the isothermal measurements are much more time-consuming, they provide some new information and insight about the cyclo dehydration reaction of the polyhydrazide. The physical state of the sample, rubbery or glassy, seems to influence the kinetics considerably. The kinetic parameters determined with the isothermal method for the polymer in its glassy state agree well with the parameters derived from the previously reported nonisothermal measurements, while the kinetic parameters for the expected rubbery state differ considerably. The morphological state or the history of the polymer has also a considerable influence on the kinetics of the isothermal conversion process. The powder form of the polymer has a much lower isothermal conversion rate than the film form.