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

Dehydration of double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O where M(I)Rb(I) and M(II)Mg(II), Mn(II), Co(II), Ni(II), Zn(II) and Cu(II) has been studied by derivatograph. Thermal parameters like activation energy, order of reaction, enthalpy change etc. for each step of dehydration have been evaluated from the analyses of TG, DTA and DTG curves and these parameters are compared with corresponding salt hydrates of the NH₄ and K(I) series. These double salt hydrates are deuterated and studied similarly. Activation energies for the first step of dehydration of these salt hydrates increase with the increase of second ionisation potential of the central metal except for Mg. The nature of dehydration changes in the cases of double salt hydrates of Mg(II) and Ni(II) on deuteration. The order of reaction for each case of dehydration has been found to be unity. The enthalpy change per mole of water varies from 11.4 to 17 kcal.     

Studies on the synthesis and thermal decomposition mechanisms of rare-earth metal (Pr,Nd, Sm) salt hydrates of 3-nitro-1,2,4-triazol-5-one

Three new rare-earth metal (Pr, Nd and Sm) salt hydrates of 3-nitro-1,2,4-triazol-5-one (NTO) were prepared and characterized. The thermal behaviour of the three salt hydrates, M(NTO)₃·nH₂O (M=Pr and Nd,n=9;M=Sm,n=8) were studied by means of TG and DSC under conditions of linear temperature increase. The thermal decomposition intermediates were determined by means of IR, MS and X-ray diffraction spectrometry. The thermal decomposition mechanisms of these hydrates were proposed as follows: We express our thanks to Professor Zhu Chunhua, Associate Professor Fu Xiayun, and Lecturers Fan Tao and Liang Yanjun for their help in this work.     

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.     

Methane hydrate phase equilibrium in the presence of salt (NaCl, KCl, or CaCl2) + ethylene glycol or salt (NaCl, KCl, or CaCl2) + methanol aqueous solution: Experimental determination of dissociation condition

In this communication, we report dissociation conditions of methane hydrates in the presence of salt (NaCl, KCl, or CaCl₂) + ethylene glycol or salt (NaCl, KCl, or CaCl₂) + methanol aqueous solutions at different temperatures. The equilibrium data were generated using an isochoric pressure-search method. These data are compared with some selected experimental data from the literature on dissociation conditions of methane hydrates in the presence of pure water to show the inhibition effects of the above mentioned aqueous solutions.     

Two monosodium salt hydrates of Colour Index Pigment Red 48

We report herein the crystal structures of a monohydrate of Colour Index Pigment Red 48 (P.R.48) (systematic name: monosodium 2‐{2‐[3‐carboxy‐2‐oxo‐1,2‐dihydronaphthalen‐1‐ylidene]hydrazin‐1‐yl}‐4‐chloro‐5‐methylbenzenesulfonate monohydrate), Na⁺·C₁₈H₁₂ClO₆S^?·H₂O, and a dihydrate, Na⁺·C₁₈H₁₂ClO₆S^?·2H₂O. The two monosodium salt hydrates of P.R.48 were obtained from in‐house synthesized P.R.48. Both have monoclinic (P2₁/c) symmetry at 173 K. The crystal packing of both crystal structures shows a layer arrangement whereby N—H…O and O—H…O hydrogen bonds are formed.     

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     

Structure and associated properties of concentrated SiO2 sols in dilute salt solutions

Using the Verwey-Overbeek potential (VO) function the various liquid-state properties of SiO₂ sols in dilute salt solutions have been evaluated under the mean spherical model approximation (MSMA). The structure factors of these SiO₂ sols predicted by this model are compared with results obtained from small-angle neutron scattering experiments by Ramsay et al. Fourier transformation of these structure factors have been performed to obtain the radial distribution functions (RDF), and from these RDF's we computed coordination numbers of the sol particles. The interparticle distanced _c of sol particles has been obtained from the peak position in structure factorS(k) by using the Bragg's equation. The surface potential _s of the oxide sols has been determined from the amplitude (A) of the VO potential. The present calculations clearly indicate some sort of ordering in the sols system. It is gratifying to note that the present theoretical calculations could reproduce the available observed results very satisfactorily with respect to structure factor and other data.     

Phase equilibria of hydrogen sulphide clathrate hydrates in the presence of single or mixed salt aqueous solution

This work reports the dissociation pressures of hydrogen sulphide clathrate hydrates in the presence of single and mixed aqueous solutions of NaCl, KCl and CaCl₂ at different temperatures and various concentrations of salt(s) in aqueous solution. The equilibrium data were generated using an isochoric pressure-search method. These data are compared with some selected experimental data from the literature on the dissociation conditions of hydrogen sulphide clathrate hydrates in the presence of pure water to show the inhibition effects of the aforementioned aqueous solutions. Comparisons between our experimental data and the corresponding literature data show some disagreements in the literature data.     

Dilectric and thermal properties of PEO doped with cadimium chloride salt

The main aim of this research is to investigate the effect of salt concentration on the dielectric properties(AC (σ_AC),permittivity（ε′）,dielectric loss（ε″）,and dielectric relaxation process) and melting behavior of polyethylene oxide （PEO）/CdCl₂ complexes.The dielectric study was carried out over a frequency range 10-335 kHz and a temperature range 25-45℃.The AC conductivity,permittivity and dielectric loss of the PEO/CdCl₂ complexes increase with increasing salt concentration and temperature.Also,it was found that the addition of CdCl₂ salt to PEO host reduced the melting temperature of PEO host.Dielectric results reveal that the relaxation process of these complexes is due to viscoelastic relaxation or non-Debye relaxation at room temperature.Additionally,it was found that relaxation behavior remained viscoelastic at different temperatures and salt concentrations.     

The hydrochloride hydrates of pentylone and dibutylone and the hydrochloride salt of ephylone: the structures of three novel designer cathinones

The structures of the hydrochloride hydrates of pentylone and dibutylone and the hydrochloride salt of ephylone, three new clandestinely-manufactured designer cathinones are described. Pentylone is (±)-1-(1,3-benzodioxol-5-yl)-2-(methylamino)pentan-1-one, dibutylone is (±)-1-(1,3-benzodioxol-5-yl)-2-(dimethylamino)butan-1-one, and ephylone is (±)-1-(1,3-benzodioxol-5-yl)-2-(ethylamino)pentan-1-one. These three drugs have recently appeared in law enforcement seizures of illicit drug materials and are referred to as NPS (new psychoactive substances). The free base pentylone crystallizes as the hydrochloride monohydrate salt with H bonds extending from the protonated amine to the Cl^? anion very close to a center of symmetry, thence to a water of hydration, resulting in an interesting six-sided species of approximately chair conformation whose components are linked by hydrogen bonds. An interesting feature of the dibutylone free base is that it crystallizes as the HCl sesquihydrate salt. Most of the street drugs crystallize as their hydrates; but, unlike most of them, dibutylone HCl^. 1.5H₂O crystallizes as a kryptoracemate in space group P2₁2₁2₁. A kryptoracemic crystal is one whose asymmetric unit contains a racemic pair, but still belongs in a Sohncke space group. The phenomenon was recognized relatively recently and, to date, there are very few drugs identified as crystallizing thus (for more on this topic, see below). In this structure, both independent amine cations have a chloride counter-anion, and they share three water molecules of crystallization, with the chloride anions and the waters forming an interesting H-bonded cyclic array. The free base ephylone crystallizes as the HCl salt and is a brand new substance, not appearing until about November 2015. The packing of all three of these cathinones contains “sandwich” π-π stacking interactions where the phenyl rings of the cations are stacked face-to-face with each other, with distances ranging from 3.531 to 3.862 Å. These compounds are among the most recent examples of cathinone-based stimulants designed to circumvent existing drug laws, and they represent a new danger to recreational drug users.     

Alogliptin and its benzoate salt

The crystal structure of the free base of the antidiabetic drug alogliptin [systematic name: 2‐({6‐[(3R)‐3‐aminopiperidin‐1‐yl]‐3‐methyl‐2,4‐dioxo‐1,2,3,4‐tetrahydropyrimidin‐1‐yl}methyl)benzonitrile], C₁₈H₂₁N₅O₂, displays a two‐dimensional N—H...O hydrogen‐bonded network. It contains two independent molecules, which have the same conformation but differ in their hydrogen‐bond connectivity. In the crystal structure of the benzoate salt (systematic name: (3R)‐1‐{3‐[(2‐cyanophenyl)methyl]‐1‐methyl‐2,6‐dioxo‐1,2,3,6‐tetrahydropyrimidin‐4‐yl}piperidin‐3‐aminium benzoate), C₁₈H₂₂N₅O₂⁺·C₇H₅O₂⁻, the NH₃⁺ group of the cation is engaged in three intermolecular N—H...O hydrogen bonds to yield a hydrogen‐bonded layer structure. The benzoate salt and the free base differ fundamentally in the conformations of their alogliptin moieties.     

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.     

Hydrate inclusion compounds

There are three general classes of hydrate inclusion compounds: the gas hydrates, the per-alkyl onium salt hydrates, and the alkylamine hydrates. The first are clathrates, the second are ionic inclusion compounds, the third are semi-clathrates. Crystallization occurs because the H₂O molecules, like SiO₂, can form three-dimensional four-connected nets. With water alone, these are the ices. In the inclusion hydrates, nets with larger voids are stabilized by including other guest molecules. Anions and hydrogen-bonding functional groups can replace water molecules in these nets, in which case the guest species are cations or hydrophobic moieties of organic molecules. The guest must satisfy two criteria. One is dimensional, to ensure a comfortable fit within the voids. The other is functional. The guest molecules cannot have either a single strong hydrogen-bonding group, such as an amide or a carboxylate, or a number of moderately strong hydrogen-bonding groups, as in a polyol or a carbohydrate.The common topological feature of these nets is the pentagonal dodecahedra: i.e., 5¹²-hedron. These are combined with 5¹²6²-hedra, 5¹²6³-hedra, 5¹²6⁴-hedra and combinations of these polyhedra, to from five known nets. Two of these are the well-known 12 and 17 Å cubic gas hydrate structures,Pm3n, Fd3m; one is tetragonal,P4 ₂/mnm, and two are hexagonal,P6 ₃/mmc andP6/mmm. The clathrate hydrates provide examples of the two cubic and the tetragonal structures. The alkyl onium salt hydrates have distorted versions of thePm3n cubic, the tetragonal, and one of the hexagonal structures. The alkylamine hydrate structures hitherto determined provide examples of distorted versions of the two hexagonal structures.There are also three hydrate inclusion structures, represented by single examples, which do not involve the 5¹²-hedra. These are 4(CH₃)₃CHNH₂·39H₂O which is a clathrate; HPF₆·6H₂O and (CH₃)₄NOH·5H₂O which are ionic-water inclusion hydrates. In the monoclinic 6(CH₃CH₂CH₂NH₂)·105H₂O and the orthorhombic 3(CH₂CH₂)₂NH·26H₂O, the water structure is more complex. The idealization of these nets in terms of the close-packing of semi-regular polyhedra becomes difficult and artificial. There is an approach towards the complexity of the water salt structures found in the crystals of proteins.     

Solute partitioning in polymer–salt ATPS: The Collander equation

The partition coefficients for several solutes (five nitrophenylated-monosaccharides and four proteins) were experimentally determined, at 23 °C, in three different tie-lines of two polymer–salt aqueous two-phase systems (ATPS): UCON-K₂HPO₄ and UCON-NaH₂PO₄. These partition coefficients together with others obtained from the literature for five dinitrophenylated-amino acids were used to investigate the suitability of the Collander equation to correlate partition coefficients in polymer–salt ATPS. This equation was first proposed to describe the linear correlation between partition coefficients of solutes in different water–organic solvent systems. More recently, it was proved that partition coefficients for several biomolecules in polymer–polymer ATPS can also be correlated with this equation. In this work, several correlations were tested: partition coefficients obtained for different tie-lines within the same system and also partition coefficients obtained from different systems. In both cases, a linear relation was observed, despite a less satisfactory correlation was found when different ATPS were compared. Overall, it was demonstrated that the Collander equation can be used to satisfactorily correlate solute partitioning in the studied polymer–salt ATPS.     

Compressibility of Gas Hydrates

Experimental data on the pressure dependence of unit cell parameters for the gas hydrates of ethane (cubic structure I, pressure range 0–2 GPa), xenon (cubic structure I, pressure range 0–1.5 GPa) and the double hydrate of tetrahydrofuran+xenon (cubic structure II, pressure range 0–3 GPa) are presented. Approximation of the data using the cubic Birch–Murnaghan equation, P=1.5B₀[(V₀/V)^7/3?(V₀/V)^5/3], gave the following results: for ethane hydrate V₀=1781 ų, B₀=11.2 GPa; for xenon hydrate V₀=1726 ų, B₀=9.3 GPa; for the double hydrate of tetrahydrofuran+xenon V₀=5323 ų, B₀=8.8 GPa. In the last case, the approximation was performed within the pressure range 0–1.5 GPa; it is impossible to describe the results within a broader pressure range using the cubic Birch–Murnaghan equation. At the maximum pressure of the existence of the double hydrate of tetrahydrofuran+xenon (3.1 GPa), the unit cell volume was 86 % of the unit cell volume at zero pressure. Analysis of the experimental data obtained by us and data available from the literature showed that 1) the bulk modulus of gas hydrates with classical polyhedral structures, in most cases, are close to each other and 2) the bulk modulus is mainly determined by the elasticity of the hydrogen‐bonded water framework. Variable filling of the cavities with guest molecules also has a substantial effect on the bulk modulus. On the basis of the obtained results, we concluded that the bulk modulus of gas hydrates with classical polyhedral structures and existing at pressures up to 1.5 GPa was equal to (9±2) GPa. In cases when data on the equations of state for the hydrates were unavailable, the indicated values may be recommended as the most probable ones.     

Photoisomerization of linear merocyanines in salt solutions

The trans-cis isomerization in the excited state of linear merocyanine L-Mero4 and phenyl substituted linear merocyanine P-L-Mero4 in salt solution and in ionic liquid was investigated using frequency upconversion measurements. Strontium chloride and cesium iodide were added to solvent dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) to vary the ionic strength. The time-resolved fluorescence curves of merocyanines displayed multiple exponential decay behavior. The second temporal component with time constant τ₂ ≈ 2.8 (11) ps of L-Mero4 (P-L-Mero4) in DMSO was assigned to the duration to reach the isomerization equilibrium between the trans and the twisted conformers. The τ₂ increased at higher salt concentrations and was explained by the attachment of salt ions on the polar excited merocyanines decelerating the isomerization rate. The rotational correlation time constants obtained from the anisotropy decay of fluorescence were 360 and 240 ps in neat DMSO for L-Mero4 and P-L-Mero4, respectively, and they increased to 790 and 450 ps in the most concentrated SrCl₂. Using Perrin relation, we estimated the increase in the rotating volume at [SrCl₂] = 536 mM, revealing ≈15 SrCl₂ molecules surrounding L-Mero4 and 7 SrCl₂ on P-L-Mero4. The experimental data indicated that the ion–molecule interaction was stronger with SrCl₂ and on L-Mero4 than on P-L-Mero4.     

Rod-like polyelectrolyte adsorption onto charged surfaces in monovalent and divalent salt solutions

We analyze the adsorption of strongly charged polyelectrolytes onto weakly charged surfaces in divalent salt solutions. We include short-range attractions between the monomers and the surface and between condensed ions and monomers, as well correlations among the condensed ions. Our results are compared with the adsorption in monovalent salt solutions. Different surface charge densities (σ), and divalent (m) and monovalent (s) salt concentrations are considered. When the Wigner-Seitz cells diameter (2R) is larger than the length of the rod, the maximum amount of adsorption scales like n_max ∼ σ^4/3 in both monovalent and divalent solutions. For homogeneously charged surfaces, the maximum adsorption occurs at s* ∼ σ² when s* > ϕ, where ϕ is the monomer concentration, the counterpart for divalent salt solution, m* roughly scales as σ^2.2 when m* > ϕ. The effective surface charge density has a maximum absolute value at m′ < m*. A discrete surface charge distribution and short-range attractions between monomers and surface charge groups can greatly enhance surface charge inversion especially for high salt concentration. The critical salt concentration for adsorption in divalent salt solution roughly scales as m_c ∼ bσ^1.9, where b is the distance between two neighboring charged monomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3642–3653, 2004     

Excluded volume study of a sulfonate-containing polyelectrolyte in salt solutions

Chain characteristics of a linear sulfonate-containing homopolymer, sodium poly(3-methacryloyloxypropane-1-sulfonate), in aqueous salt solutions (ionic strength, C_s = 0.01N to 5N NaCl) have been investigated by light scattering and intrinsic viscosity. The molecular weight (M?_w)–viscosity relation can be well described by the Mark–Houwink and the Stockmayer–Fixman equations. The coil is highly expanded even in the most concentrated NaCl solution (6N), and no 1:1 electrolyte was found to precipitate this polymer. A linear relation was observed between the viscosity expansion factor, α^3η, and (M?_w/C_s)^1/2. Examination of the data in terms of theories for excluded volume and hydrodynamic interaction suggests that the coil experiences dominant hydrodynamic interaction, corresponding to a nondraining coil, and the second virial coefficient and coil expansion at high C^s can be correlated by the Flory–Krigbaum–Orofino equation. Results for this polymer are compared with those for other polyelectrolytes, and are discussed in terms of chain structure, flexibility, and hydrophobicity.     

The initial stage of salt passivation of metals

A theoretical model of the nucleation of a passivating salt layer on the surface S of an anode-dissolving metal was developed. The layer is considered a new phase formed by the mechanism of heterogeneous nucleation, which serves as a related substrate for subsequent growth of the passivating layer. According to experiments, the surface S of real metals is inhomogeneous, that is, anode current density fluctuates on S. It is assumed that, at large current fluctuations, localized regions with volume ΔV _ϕ appear, in which the C _M and C _A concentrations of the M ^z+ and A ⁿ⁻ ions are increased. At fairly large current fluctuations, these concentrations can reach saturation. For this reason, the ΔV _ϕ regions are treated as mother phases, in which A _a M _m salt nuclei are formed with a certain probability. The formation of such ΔV _ϕ volumes and the kinetics of formation of nuclei in them, from which a passivating layer with a finite thickness is formed, are considered.     

Excess interfacial energy change of solid/aqueous salt solution system with increasing salt concentration at a constant charge-determining ion activity based on the Gibbs equation and ionic components of charge

A thermodynamic equation relating the change of interfacial excess (Gibbs) energy in the solid/aqueous salt solution system, caused by a variation of concentration of inorganic salt at a constant charge-determining ion activity, temperature and pressure, is derived. The equation is based on the Gibbs equation and ionic components of charge parameters. On the basis of literature experimental data for the AgI/aqueous KNO₃ and TiO₂/aqueous NaCl systems it was shown that the interfacial excess energy decreases with increasing salt concentration due to variation of the ionic components of charge of the interface.