Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. VI

Non-isothermal studies of the dehydration of double salt hydrates of the type K₂AB₄·M(II)SO₄·6H₂O where AB₄BeF^2?₄ or SeO^2?₄ and M(II)Mg(II), Co(II), Ni(II), Cu(II) or Zn(II) and their D₂O analogues were carried out. Thermal parameters like activation energy, order of reaction, enthalpy change, etc., for each step of dehydration were evaluated from the analysis of TG, DTA and DTG curves. These parameters were compared with the corresponding double sulphate, i.e., K₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues. The role of divalent cation on the thermal properties of dehydration of the salt hydrates and also the effect on the thermal properties due to deuteration were discussed. The order of reaction was always found unity. The values of ΔH were within ～11-～19 kcal mol^?1     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. V

Non-isothermal thermal studies of the dehydration of the double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues were carried out where M(I) = TI(I) and M(II) = Mg(II), Co(II), Ni(II), Cu(II) or Zn(II). Thermal parameters like activation energy, order of reaction, enthalpy change, etc. were evaluated from the analysis of TG, DTA and DTG curves. These thermal parameters were compared with those of other series, like NH₄(I), K(I), Rb(I) and Cs(I) studied earlier. On deuteration the nature of dehydration altered in the case of Tl₂Zn(SO₄)₂·6H₂O only. The thermal stability of the salt hyd discussed in relation to the salt hydrates of other series. The role of divalent cation on the thermal properties of dehydration of salt hydrates is also discussed. The order of reaction was always found unity. The values of ΔH were within ≈12–≈16 kcal mol^?1.     

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.

---

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.

---

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.

---

. , , . . .

---

---

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

Thermal and calorimetric investigations on crystalline hydrates of barium hydroxide and their deuterated analogues

The thermal decompositions of Ba(OH)₂ · 8H₂O, Ba(OH)₂ · 8D₂O, Ba(OH)₂ · H₂O and Ba(OH)₂ · D₂O were studied and the phase transitions were identified by DSC and DTA methods. The corresponding enthalpy changes were determined and compared with those calculated from the thermodynamic data. A decrease of the thermal stability was demonstrated for the deuterated crystal hydrates in comparison with the normal ones.

---

Zusammenfassung Die thermische Zersetzung von Ba(OH)₂ · 8H₂O, Ba(OH)₂ · 8D₂O, Ba(OH)₂ · H₂O und Ba(OH)₂ · D₂O wurde untersucht. Phasenübergänge wurden mittels DSC und DTA ermittelt. Die entsprechenden Enthalpieveränderungen wurden bestimmt und mit den aus thermodynamischen Daten berechneten Werten verglichen. Die deuterierten Kristallhydrate sind thermisch weniger stabil als die leichtes Kristallwasser enthaltenden Verbindungen.

---

()₂ · 8₂, ()₂ · 8D₂O, Ba(OH)₂·H₂O Ba(OH)₂·D₂O. , . .

     

The use of protium and deuterium analogues in mechanistic studies of thiazole syntheses

The mechanisms of two reactions which give isomeric thiazol-5-yl ketones have been elucidated by work with substrates containing pairs of acyl groups and their deuterium-substituted analogues.     

Raman studies of molten salt hydrates: the beryllium and aluminium nitrate-water systems

Raman spectra of the liquid systems Be(NO₃)₂ · 20H₂O, Be(NO₃)₂ · 4H₂O, Al(NO₃)₃·20H₂O, and Al(NO₃)₃ · 9H₂O have been recorded. The spectra are analysed in terms of vibrational modes arising from water, the nitrate ion, the aquated metal ions and hydrolysis products. For the concentrated beryllium system, though not for the aluminium system, the spectra suggest a significant degree of proton transfer from [Be(OH₂)₄]²⁺ to NO₃^?. Solvent-separated metal-nitrate ion pairs appear to be present in all the systems studied.     

Effects of temperature, salt, and deuterium oxide on the self-aggregation of alkylglycosides in dilute solution. 2. n-Tetradecyl-beta-D-maltoside

The effects of salt, temperature, and deuterium oxide on the self-aggregation of n-tetradecyl-beta-d-maltoside (C(14)G(2)) in dilute solution have been investigated by static light scattering, dynamic light scattering (DLS), small-angle neutron scattering (SANS), tensiometry, and capillary viscometry. SANS data show that the micelles can be described as relatively flexible polymer-like micelles with an elliptical cross section, at least at temperatures between 35 and 50 degrees C. The micelles grow in one dimension with increasing temperature and concentration. DLS and viscometry data suggest that the micelle size reaches a maximum at 60-70 degrees C. Comparison of DLS data in D(2)O and H(2)O shows that the micelles are larger in the former case. The effect of salt on the micelle size was found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreases according to the sequence SO(4)(2)(-) > Cl(-) > NO(3)(-) > I(-) > SCN(-), where I(-) and SCN(-) act as salting-in anions. From tensiometric data, it can be concluded that the temperature effects on micelle morphology do not correlate directly with those on unimer solubility. Rather, the temperature effect on the hydrocarbon chain conformation seems to be decisive for the micelle morphology. At constant temperature, on the other hand, the effect of salt and deuterium isotope is attributable to changes in effective headgroup area, including intermolecular interactions and water of hydration.     

Effects of temperature, salt, and deuterium oxide on the self-aggregation of alkylglycosides in dilute solution. 1. n-nonyl-beta-D-glucoside

The influence of salt, temperature, and deuterium oxide on the self-aggregation of n-nonyl-beta-D-glucoside (beta-C9G1) in dilute solution has been investigated by static and dynamic light scattering, neutron scattering, and tensiometry. Scattering data show that the micelles can be described as relatively stiff, elongated structures with a circular cross section. With a decrease of temperature, the micelles grow in one dimension, which makes it surprising that the critical micelle concentration (cmc) shows a concomitant increase. On the other hand, substitution of D2O for H2O causes a large increase in micelle size at low temperatures, without any appreciable effect on cmc. With increasing temperature, the deuterium effect on the micelle size diminishes. The effects of salt on the micelle size and cmc were found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreased according to the sequence SO4(2-) > Cl- > Br- > NO3- > I- > SCN-, whereas the effect on cmc displays the opposite trend. Here, I- and SCN are salting-in anions. Similarly, the effects of cations decrease with increasing polarizability in the sequence Li+ > Na+ > K+ > Cs+. At high ionic strength, the systems separate into two micellar phases. The results imply that the size of beta-C9G1 micelles is extremely sensitive to changes in the headgroup size. More specifically, temperature and salt effects on effective headgroup size, including intermolecular interactions and water ofhydration, are suggested to be more decisive for the micelle morphology than the corresponding effects on unimer solubility.     

Kinetic studies on the dehydration of trans-dichlorotetrammine-cobalt (III) iodate dihydrate

Summary The dehydration of trans-[Co(NH₃)₄Cl₂)IO₃·2H₂O was studied isothermally by t.g.a. In the 0.1 < α < 0.8 range, where α is the fraction of the reaction complete, most of the runs gave the best fit to a second order rate law. Early stages of the reaction appear to follow a rate law based on reaction order while later stages (0.3 < α < 0.5) appear to be controlled by diffusion of H₂O. The reaction in the 0.1 < α < 0.3 range gave a best fit to a third order rate law, while the 0.3 < α < 0.5 range gave the best fit to a three dimensional control rate law. The activation energy for the overall reaction was ca. 103 kJ mol⁻¹. For α < 0.3 the activation energy was ca. 79.9 kJ mol⁻¹, but for 0.3 < α < 0.5 it was ca. 110 kJ mol⁻¹.     

Effect of grinding on the dehydration behavior of nedocromil sodium hydrates

Nedocromil sodium has a number of known hydrate states, a monohydrate, a trihydrate and a heptahemihydrate, including an amorphous state. Effect of grinding on the hydration states of nedocromil sodium crystals was studied. After grinding the trihydrate, heptahemihydrate was observed in the ground sample, even though, the water content in the ground sample was not sufficient to cover the heptahemihydrate’s hydration level. On the other hand, in the ground heptahemihydrate, trihydrate was existed. Apparent activation energies (ΔE) for hydrates, monohydrate→anhydrate, trihydrate→monohydrate and heptahemihydrate→amorphous(anhydrate), were calculated using TG data. ΔE for the dehydration of heptahemihydrate was significantly lower than that of other hydrates. Obtained ΔE data explained the inter-conversion behavior of nedocromil sodium induced by grinding.     

Studies on the dehydration and decomposition of calcium and dicalcium magnesium aconttate hydrates

The thermal decomposition of calcium and dicalcium magnesium aconitate hydrates were studied by TG/DTG, DTA, EGA, SEM and other physico-chemical techniques. The decomposition proceeds in four stages: dehydration; oxidation of the carboxylic acid portion of the salt; complete fragmentation of the hydrocarbon portion; and finally, decarboxylation of the metal carbonate to the oxide. The crystal morphologies of the hydrate and anhydrous salts of each compound are very similar. Tricalcium aconitate consists of well-developed twinned crystals and stellate clusters intergrown with flat platy crystals. On the other hand, dicalcium magnesium aconitate crystals are monoclinic with well-developed pinacoidal faces. The activation energy,E _d (43±2 kJ mol^?1 water), calculated from Borchardt and Daniels' method, for the dehydration process of calcium aconitate trihydrate is of the same order of magnitude as some simple metal salt hydrates. The rate constant, k_d increased from 0.04/min at 238°C to greater than 0.86/min at 295°C. It is concluded that the dehydration process is due to cation bound water.     

Sealed tube differential thermal analysis studies of some nickel(II) salt hydrates

Sealed and open tube DTA curves are reported for nickel sulfate, nitrate, ammonium sulfate, chloride, acetate, formate and perchlorate hydrates. The endothermic peaks for the sealed tube reactions were smaller than those found for the open tubes, due to the lack of water vaporization in the former. With the exception of NiSO₄-(NH₄)₂SO₄-6H₂O, the peaks for the sealed and open tube reactions appeared at about the same initial peak temperature. The sealed tube reaction intervals (T_f-T_i) were shorter than those found for the open tube.     

Thermal dehydration and structural models of two new vanadyl sulfate hydrates

The preparation of a new modification of vanadyl sulfate trihydrate, VOSO₄ · 3H₂O, is described. In the course of its thermal dehydration, another new phase, VOSO₄ · 2H₂O, is observed as an intermediate. Crystal data for the two compounds are: VOSO₄ · 3H₂O, orthorhombic, a = 8.980 ± 0.006, b = 9.026 ± 0.009, c = 7.776 ± 0.003 Å, space group P2₁2₁2; VOSO₄ · 2H₂O, monoclinic, a = 8.913 ± 0.027, b = 8.93 ± 0.09, c = 7.80 ± 0.06 Å, β = 92.4 ± 0.6°. From the topotaxy of the dehydration reaction, structural models for the two phases are deduced. They consist essentially of VOSO₄ layers similar to those in α-VOSO₄ and interlayer water.     

Kinetic studies on the linkage isomerization and dehydration of silver hexacyanocobaltate(III) hexadecahydrate

Summary Heating Ag₃[Co(CN)₆]·16H₂O results in dehydration and complete conversion of the Ag⁺ NC -Co³⁺ linkages to Ag⁺ -CN -Co³⁺. These processes have been studied kinetically. The dehydration process follows an R1, one dimensional contraction, rate law and has an activation energy of 28.7 kJ mol^–1. The linkage isomerization process was studied nonisothermally by means of DSC. It follows an Avrami rate law with an index of about 1.5. These results are interpreted in terms of processes known for other solid state reactions.     

DSC study of melting and solidification of salt hydrates

Most salt hydrates, especially those proposed for thermal-energy-storage applications, melt incongruently. In static systems, this property often leads to differences between the enthalpy of fusion and enthalpy of solidification. By means of differential scanning calorimetry (DSC), these differences have been determined for several salt hydrates. For Na₂SO₄ · 10 H₂O, the enthalpy of solidification at or near the peritectic temperature is never more than 60% of the enthalpy of fusion; further cooling leads to a second phase transition at a temperature corresponding to eutectic melting of mixtures of ice and this hydrate. This asymmetrical melting and freezing behavior of Na₂SO₄ · 10 H₂O decreases its potential as an energy-storing medium and also limits its usefulness for temperature calibration of DSC instruments. Sodium pyrophosphate decahydrate, Na₄P₂O₇ · 10 H₂O, although in some ways a higher temperature analog of Na₂SO₄ · 10 H₂O, exhibited a smaller discrepancy between the enthalpies of fusion and of solidification; its relatively high transition temperature permits a more rapid solidification reaction than is the case for Na₂SO₄ · 10 H₂O. For Mg(NO₃)₂ · 6 H₂O, a congruently melting compound, the magnitude of ΔH of crystallization equalled ΔH of fusion, even when supercooling occurred; a solid-state transition at 73°C, with ΔH = 2.9 cal g^?1, was detected for this hydrate. MgCl₂ · 6 H₂O, which melts almost congruently, exhibited no disparity between ΔH of crystallization and ΔH of fusion. CuSO₄ · 5 H₂O and Na₂B₄O₇ · 10 H₂O exhibited marked disparities. Na₂B₄O₇ · 10 H₂O formed metastable Na₂B₄O₇sd 5 H₂O at the phase transition; this was derived from the transition temperature and verified by relating the observed ΔH of transition to heats of hydration. Peritectic solidification of hydrates can be viewed as a dual process: crystallization from the liquid solution and reaction of the lower hydrate (or anhydrate) with the solution; where ΔH of solidification appears to be less in magnitude than the ΔH of fusion, the difference can be attributed to slower reaction rate between solution and the lower hydrate. New or previously unreported values for ΔH of fusion obtained in this study were, in cal g^?1: Mg(NO₃)₂ · 6 H₂O, 36; Na₄P₂O₇ · 10 H₂O, 59; CuSO₄ · 5 H₂O, 32; Na₂B₄O₇ · 10 H₂O, 33.     

Application of DTA for investigation of hydration and dehydration of crystal hydrates

The results of the investigation of the hydration processes of the dehydration products of magnesium carbonate trihydrate are shown. The DTA curve was used to calculate the functionQ(t). It was found that the results were in good agreement with the equation , whereQ is the heat evolved during the hydration timet;Q ₀,Q _f are the same for the initial and final products, respectively,k ₁ andk ₂ are the hydration constants.

---

Zusammenfassung Die benutzte Methode wurde am Beispiel der Untersuchung des Hydrationsvorganges der Dehydratisierungsprodukte des Magnesiumkarbonat-Trihydrats demonstriert. Zur Errechnung der FunktionQ(t) dienten die DTA-Kurven. Die Ergebnisse folgten gut der Gleichung , woQ die freigesetzte Wärme während der Hydratationszeitt, Q ₀,Q _f dieselbe für die Anfangs- und Endprodukte,k ₁,k ₂ die Hydratationskonstanten bedeuten.

---

Résumé Pour illustrer la méthode employée, on communique les résultats se rapportant à l'étude du phénomène d'hydration des produits de déshydratation du carbonate de magnésium trihydraté. On calcule la fonctionQ(t) à l'aide des courbes d'A.T.D. Les résultats obtenus sont en bon accord avec les valeurs de l'équation oùQ est la chaleur dégagée pendant le temps d'hydratationt, Q ₀ etQ _f sont les valeurs correspondantes pour les produits initiaux et finals,k ₁ etk ₂ les constantes d'hydratation.

---

. Q(t) (). , , ,t,Q ₀ Q _f — , ,k ₁ k ₂ — .

     

Water vapor pressure and thermodynamics of dehydration of Group 2 perchlorate hydrates

The limits of existence for Group 2 perchlorate hydrates are defined. The water vapor pressure is measured over the crystal hydrates Mg(ClO₄)₂·2H₂O, Ca(ClO_{4 2}·4H₂O, Sr(ClO₄)₂·3H₂O, Sr(ClO₄)₂·2H₂O, Sr(ClO₄)₂·H₂O, Ba(ClO₄)₂·3H₂O, and Ba(ClO₄)₂·H₂O. The water vapor pressure and thermodynamics constants of dehydration depend directly on the electron-acceptor strength of the cation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1467–1473, July, 1990.     

EPR studies of reduced Zn-chlorins and their isotope substituted analogues

Radical anions of Zn-chlorin, Zn-octaethylchlorin complexes and their ¹⁵N and deuterium substituted analogues have been studied by EPR spectroscopy and the INDO molecular orbital method in the unrestricted Hartree-Fock procedure. Parameters of experimental spectra, determined by using the iterative least-squares fitting method, have been compared with those calculated on the basis of spin density distribution. A satisfactory agreement between the experimental hyperfine coupling constants and theoretical ones for the systems studied has been obtained.     

Mechanochemical destruction of crystalline hydrates of cobalt and zinc acetylenedicarboxylates during dehydration

Upon the dehydration in vacuo, crystals of cobalt and zinc acetylenedicarboxylates (CoADC?2H₂O and ZnADC?2H₂O) remain stable only to a certain minimum content of coordination water. Once this content is reached, gaseous decomposition products are abruptly released giving rise to chemically reactive moieties that can initiate the solid-phase polymerization of metal-containing monomers. During the dehydration, stretching and bending bands of carboxyl groups become broader and are shifted, which is indicative of the appearance of a mechanical strain in the crystals. Besides, the removal of one water molecule from the coordination sphere of Zn²⁺ leads to a strong shift of the Zn—O stretching band to lower frequencies. At the moment of an extensive release of gaseous products (CO₂ and H₂O), the deformation gradients increase so that narrow reflections of the crystalline phase are absent in the X-ray powder diffraction pattern. The development of strains in the crystals is facilitated also by the accumulation of free CO₂ molecules in the solid phase, as evidenced by the appearance of the bands at 2338 and 655 cm^–1 in the IR spectra. The energy of dehydration of crystalline hydrates estimated by quantum chemical calculations (DFT) is 150—200 kJ mol^–1. This high energy can lead to mechanochemical activation of the destruction of the crystal and coordination structures of CoADC?2H₂O and ZnADC?2H₂O upon their dehydration.