Thermal studies on dithionate compounds

TG and DTG studies have been carried out on CoS₂O₆ · 6H₂O, NiS₂O₆ · 6 H₂O, CuS₂O₆ · 3.5 H₂O, ZnS₂O₆ · 6 H₂O and CdS₂O₆ · 4H₂O. After partial dehydration, the dithionates of Co(II), Ni(II), Cu(II) and Zn(II) lose water and sulfur dioxide simultaneously to yield the stable metal sulfates in the final step of decomposition. The CdS₂O₆ · 4H₂O dehydrates completely in the first two steps of decomposition with two water molecules being lost in each step. In the third step, it loses only SO₂ to yield CdSO₄. Kinetic parameters are presented for these reactions.

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Zusammenfassung TG- und DTG-Untersuchungen von CoS₂O₆ · 4 H₂O, NiS₂O₆ · 6 H₂O, CuS₂O₆ · 3.5 H₂O, ZnS₂O₆ · 6 H₂O und CdS₂O₆ · 4 H₂O wurden ausgeführt. Nach partieller Dehydratisierung geben die Dithionate von Co(II), Ni(II), Cu(II) und Zn(II) im letzten Schritt des Abbaus gleichzeitig Wasser und Schwefeldioxid unter Bildung der stabilen Metallsulfate ab. CdS₂O₆ · 4 H₂O wird in den ersten beiden Zersetzungsschritten unter Abgabe von je 2 Wassermolekülen vollständing zersetzt. Im dritten Schritt wird nur SO₂ unter Bildung von CdSO₄ abgegeben. Kinetische Parameter dieser Reaktionen werden angegeben.

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CoS₂O₆ · 6 H₂O, NiS₂O₆ · 6 H₂O, CuS₂O₆ · 3.5 H₂O, ZnS₂O₆ · 6 H₂O CdS₂O₆ · 4 H₂O. , , , , . , . , . .

     

Thermal studies on lithium,sodium, potassium and ammonium monomethyl violurates

A study of the ammonium and some alkaline salts of monomethyl violuric acid by TG and DSC is described. These salts form hydrates in all cases and are, with some exceptions, very soluble in water.     

Thermal studies on beryllium,magnesium and calcium hafnyl oxalates

Beryllium hafnyl oxalate tetrahydrate, magnesium hafnyl oxalate tetrahydrate and calcium hafnyl oxalate tetrahydrate abbreviated as BHO, MHO and CHO, respectively, have been prepared in an aqueous medium and characterized by elemental analysis, magnetic susceptibility measurements and infrared spectral data. The thermal behaviour of these compounds in non-isothermal conditions have been investigated by employing TG, DTG and DSC techniques. The intermediates obtained at the end of various thermal decomposition steps were identified on the basis of elemental analysis and infrared spectral studies. The graphical method of Coats and Redfern has been employed to evaluate the kinetic parameters such as apparent activation energy and order of reaction. Heat of reaction for different decomposition steps have been calculated from the DSC curves.     

Vibrational studies of anhydrous lithium,sodium and potassium oxalates

The IR and Raman spectra of sodium oxalate and the IR spectrum of lithium oxalate are re-examined. The Raman spectrum of lithium oxalate is presented for the first time. A recent structural study is used as the basis for the first detailed vibrational study of anhydrous potassium oxalate, phase II.     

Thermal studies on arylsulfinylamines,part II

The thermal characteristics of 13 isomeric arylsulfinylamines (iodosulfinylanilines, dichlorosulfinylanilines and dimethylsulfinylanilines) were examined using a Derivatograph. It was found that some of the arylsulfinylamines underwent thermal degradation.     

Thermal behavior of glutamic acid and its sodium,lithium and ammonium salts

Glutamic acid (H2_glu) and its lithium, sodium and ammonium monosalts were submitted to thermal analysis using thermogravimetry (TG) and differential thermal analysis (DTA). The main goal of these studies was to compare the relative thermal stability and to evaluate the effect of the counter ion in the thermal decomposition pathways. Salts were obtained by direct neutralization of the purified acid with LiOH, NaOH or NH₄OH and were characterized by elemental analysis (C, H and N) and IR spectroscopy. Decomposition occurred after conversion to the pyroglutamic acid or the respective pyroglutamates and ammonium salt loosing NH₃ being converted to H₂glu before decomposition.     

Thermal studies on addition compounds of bis(ethylxathato)nickel(II)

Ni(xanthate)₂, a diamagnetic square planar complex forms 1:1 six-coordinated high-spin paramagnetic adducts with dinitrogen donors in different organic solvents. The thermal studies of these compounds show the loss of trapped solvent(ether) followed by the loss of the addendum leaving behind the parent xanthate complex. In the compounds with 1:3 ratio of Ni(xanthate): dinitrogen donors, the xan^? acts as an anion. The different steps of thermal decomposition in the compounds, Ni(phen)₃xan₂ and Ni(bipy)₃xan₂, can be explained on the basis of the conformational rigidity of the ligands. For the parent compound Ni(xan)₂, its 1:1 and 1:3 adducts as well as the thermal decomposition products (residues) have been analysed by chemical and physical methods. New intermediate complexes with the composition, Ni(phen)₂xan₂, Ni(bipy)S₂ and Ni(bipy)S have been obtained from the decomposition process, leading finally to NiO. The kinetic parameters were calculated using five different methods to check the applicability of these standard methods towards the elucidation of the decomposition mechanism.     

Raman spectroscopic studies on single supersaturated droplets of sodium and magnesium acetate

Raman spectroscopy was used to study structural changes, in particular, the formation of contact-ion pairs in supersaturated aqueous NaCH(3)COO and Mg(CH(3)COO)(2) droplets at ambient temperatures. The single droplets levitated in an electrodynamic balance (EDB), lost water, and became supersaturated when the relative humidity (RH) decreased. For NaCH(3)COO droplet the water-to-solute molar ratio (WSR) was 3.87 without solidification when water molecules were not enough to fill in the first hydration layer of Na(+), in favor of the formation of contact-ion pairs. However, the symmetric stretching vibration band (nu(3) mode) of free -COO(-) constantly appeared at 1416 cm(-1), and no spectroscopic information related to monodentate, bidentate, or bridge bidentate contact-ion pairs was observed due to the weak interactions between the Na(+) and acetate ion. On the other hand, the band of methyl deformation blue shifted from 1352 to 1370 cm(-1) (at RH = 34.2%, WSR = 2.43), corresponding to the solidification process of a novel metastable phase in the highly supersaturated solutions. With further decreasing RH, a small amount of supersaturated solution still existed and was proposed to be hermetically covered by the metastable phase of the particle. In contrast, the interaction between Mg(2+) and acetate ion is much stronger. When WSR decreased from 21.67 to 2.58 for the Mg(CH(3)COO)(2) droplet, the band of C-C-symmetric stretching (nu(4) mode) had a blue shift from 936 to 947 cm(-1). The intensity of the two new shoulders (approximately 1456 and approximately 1443 cm(-1)) of the nu(3) band of free -COO(-) at 1420 cm(-1) increased with the decrease of WSR. These changes were attributed to the formation of contact-ion pairs with bidentate structures. In particular, the small frequency difference between the shoulder at approximately 1443 cm(-1) and the nu(3) band of the free -COO(-) group (approximately 1420 cm(-1)) was proposed to be related to the formation of a chain structure based on the contact-ion pairs of bridge bidentate. The continuous formation of various contact-ion pairs started at higher WSR value (WSR = 15.5) greatly reduced the hygroscopic properties of Mg(CH(3)COO)(2) droplet, so that the WSR of Mg(CH(3)COO)(2) droplets was even lower than that of NaCH(3)COO in the RH range of 40-60%.     

Thermogravimetric studies of binary and ternary systems containing salicylic acid,sodium salicylate,sodium carbonate and sodium hydrogen carbonate. Part II

The mechanism of thermal decomposition of binary and ternary systems containing salicylic acid, sodium salicylate and disodium salicylate sesquihydrate, sodium carbonate and sodium hydrogen carbonate were studied by means of thermogravimetric and differential thermal analysis. The possibility was demonstrated of analyzing ternary systems containing three unreactive or three reactive components. The results can be useful for monitoring the course of the commercial-scale manufacture of sodium salicylate and for checking declared compositions of salicylate mixtures.

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Zusammenfassung Ein Mechanismus der thermischen Zersetzung SalicylsÄure, Natriumsalicylat und Dinatriumsalicylat Sesquihydrat, Natriumcarbonat und Natriumhydrocarbonat enthaltender binÄrer und ternÄrer Systeme wurde mittels Thermogravimetrie und Differentialthermoanalyse untersucht. Die Möglichkeit, drei unreaktive oder drei reaktive Komponenten enthaltende ternÄre Systeme zu untersuchen, wurde gezeigt. Die Ergebnisse können dazu eingesetzt werden den Verlauf der Natriumsalicylatfabrikation im Handelsma\stab zu verfolgen und deklarierte Zusammensetzungen von Salicylatmischungen zu überprüfen.

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Résumé On a étudié par thermogravimétrie et par analyse thermique différentielle le mécanisme de la décomposition thermique de systèmes binaires et ternaires contenant de l'acide salicylique, du salicylate monosodique et du salicylate disodique sesquihydraté, du carbonate de sodium et de l'hydrogénocarbonate de sodium. On montre la possibilité d'analyser des systèmes ternaires comprenant trois composants réactifs ou non. Les résultats peuvent Être utilisés pour commander le déroulement de la fabrication du salicylate de sodium à l'échelle commerciale et pour contrÔler les compositions déclarées des mélanges de salicylates.

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- , , , - . , . .

     

Thermal studies on the sodium salts of aminosalicylic acids

The effect on the stability of the isomers of aminosalicylic acid of formation of their sodium salts has been studied by use of differential scanning calorimetry and thermogravimetry, coupled with evolved gas analysis by Fourier transform infrared spectroscopy. X-ray powder diffraction and infrared spectroscopy provided complementary information. The DSC curves for the sodium salts of all of the isomers showed complex dehydration/decomposition endotherms. From the initial mass losses of the TG curves, the amounts of water per mole of salt were estimated as 0.5, 2.4 and 1.4 moles for the sodium salts of 3-aminosalicylic acid, 4-aminosalicylic acid and 5-aminosalicylic acid, respectively. TG-FTIR results for the sodium salt of 3-aminosalicylic acid showed the evolution of carbon dioxide in three stages: below 150°C, between 200 and 300°C and continuous formation up to 500°C. This behaviour differs from that of 3-aminosalicylic acid itself, which forms CO₂ between 225 and 290°C. For the sodium salt of 4-aminosalicylic acid, the formation of carbon dioxide starts from 250°C and is still being formed at about 650°C. 4-aminosalicylic acid decarboxylates above 150°C. 5-aminosalicylic acid and its sodium salt showed no evolution of carbon dioxide below 600°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal studies on the anation and decomposition of trans-fluoroaquobis(ethylenediamine) and trans-fluoroaquoabis(propylenediamine) dithionate

The anation and decomposition reaction of trans[CrF(H₂O)(aa′)₂]S₂O₆ [aa′ = ethylenediamine (en); 1,3-diaminepropane (tmd)] have been studied by means of ATD, TG and DSC techniques. The first and only perfectly defined step is the anation reaction forming the species cis[CrF(S₂O₆)(aa′)₂]. By means of DSC techniques, the enthalpies of reaction and the activation energies of both reactions have been estimated. The electronic spectra of the resultant products suggest cis configuration. A second step, preceding total decomposition of the complex, involves cis[CrF(S₂O₆)(aa′)₂] → cis[CrF(SO₄)(aa′)₂] + SO₂ which is contaminated by decomposition reactions.     

Ageing studies of magnesium–sodium nitrate pyrotechnic compositions

The ageing characteristics of pyrotechnic compositions are influenced not only by temperature, but also by surrounding effects as humidity and vibrations. In this paper the thermal stability of the pyrotechnic system magnesium–sodium nitrate will be investigated. In an inert helium atmosphere two steps of mass loss, which were not completely separated from each other, were observed in the temperature range from 65 to 265°C: a mass loss of about 15% between 65 and 160°C and about 34% between 160 and 265°C. It is assumed that these two steps are caused by different processes. The separation between the two steps was not or hardly detectable for measurements that were performed in a nitrogen atmosphere. Using MS and FTIR (mass spectrometry/Fourier transform infrared spectroscopy) the evolved gases were analysed. Only above about 170°C evolving gases were detected (which means that during the first step no gases were detectable). The detected gas mainly consists of CO₂, CO and N₂O, with smaller amounts of NO₂, NO and possibly HCN. A third step of mass loss (8–9%) was observed above 314°C. The process which caused this step of mass loss is considered not to contribute significantly to the ageing of the material at much lower temperatures of maximum 80°C, which is of interest in view of the use of the materials.     

Solid-state 25Mg NMR spectroscopic and computational studies of organic compounds. square-pyramidal magnesium(II) ions in aqua(magnesium) phthalocyanine and chlorophyll a

We report a solid-state (25)Mg NMR spectroscopic study of two magnesium-containing organic compounds: monopyridinated aqua(magnesium) phthalocyanine (MgPc.H(2)O.Py) and chlorophyll a (Chla). Each of these compounds contains a Mg(II) ion coordinating to four nitrogen atoms and a water molecule in a square-pyramidal geometry. Solid-state (25)Mg NMR spectra for MgPc.H(2)O.Py were obtained at 11.7 T (500 MHz for (1)H) for a (25)Mg-enriched sample (99.1% (25)Mg atom) using both Hahn-echo and quadrupole Carr-Purcell Meiboom-Gill (QCPMG) pulse sequences. Solid-state (25)Mg NMR spectra for Chla were recorded at (25)Mg natural abundance (10.1%) at 19.6 T (830 MHz for (1)H). The (25)Mg quadrupole parameters were determined from spectral analyses: MgPc.H(2)O.Py, C(Q) = 13.0 +/- 0.1 MHz and eta(Q) = 0.00 +/- 0.05; Chla, C(Q) = 12.9 +/- 0.1 MHz and eta(Q) = 1.00 +/- 0.05. This work represents the first time that Mg(II) ions in a square-pyramidal geometry have been characterized by solid-state (25)Mg NMR spectroscopy. Extensive quantum mechanical calculations for electric-field-gradient (EFG) and chemical shielding tensors were performed at restricted Hartee-Fock (RHF), density functional theory (DFT), and second-order M?ller-Plesset perturbation theory (MP2) levels for both compounds. Computed (25)Mg nuclear quadrupole coupling constants at the RHF and MP2 levels show a reasonable basis-set convergence at the cc-pV5Z basis set (within 7% of the experimental value); however, B3LYP results display a drastic divergence beyond the cc-pVTZ basis set. A new crystal structure for MgPc.H(2)O.Py is also reported.     

Activity coefficients of zinc chloride in the presence of lithium,sodium, and magnesium perchlorates,and magnesium nitrate in aqueous solution at 25°C

The standard potential of the Zn–Hg (sat)/ZnCl₂(M)/AgCl/Ag cell was determined at 25°C using several extrapolation procedures and the value 0.9843 V is proposed for E°. The emf of the Zn–Hg (sat)/ZnCl₂(M), salt (M)/AgCl/Ag cell [salt=NaClO₄, LiClO₄, Mg(ClO₄)₂, Mg(NO₃)₂] have been measured at different concentrations of salt. From these data, the mean ionic activity coefficients of ZnCl₂ are determined and their variations explained with the aid of Pitzer's treatment. It seems necessary to take into account structure in the ionic cospheres in order to explain the observed variations.     

Ab initio molecular orbital studies for compounds of magnesium

Using a 6-311G** basis set with estimation of correlation energy at the MP2 level, structural and energetic data for 40 molecular species containing magnesium have been calculated. For about half the species studied, further energetic data were obtained using Pople's G2 method. Enthalpy changes at 298.15 K were obtained for isogyric reactions and standard enthalpies of formation were derived from these. Comparison of the standard enthalpies of formation with the sparse literature data suggests the MP2/6-311G** standard enthalpies of formation are accurate to ± 15 kJ mol^?1 and the corresponding G2 enthalpies accurate to ± 10 kJ mol^?1. The calculated ΔH [MgN, g] revealed a gross error in the currently accepted value for this function. It is intended that these results will be used to parameterize the semiempirical molecular orbital package, MOPAC, for the element magnesium. © John Wiley & Sons, Inc.     

Imino(phenoxide) compounds of magnesium: Synthesis,structural characterization,and polymerization studies

A plethora of magnesium compounds containing imino(phenoxide) (1–4) and bis(imino)phenoxide (5–10) ligand backbone have been synthesized via the reaction of diethyl magnesium with two equivalent of the corresponding ligand. These compounds were completely characterized by different spectroscopic techniques and elemental analyses. The monomeric nature of the magnesium complexes 3 , 5 , 6 , 9 , and 10 were further confirmed by single crystal X‐ray diffraction studies. The magnesium centers posses distorted trigonal bipyramidal geometry. The controlled hydrolysis compound Mg₇O₈ (C₂₂H₂₈NO₂)₆ ( 11 ) was adequately characterized using ¹H, ¹³C NMR, ESI‐MS, and the biscubane structure was further confirmed by single crystal X‐ray diffraction studies. The Mg₇O₈ core is deeply embedded with the ligand periphery. These compounds (1–10) were found to be active towards the bulk ring opening polymerization (ROP) of lactides, yielding polymers with high number average molecular weight (M_n) and controlled molecular weight distributions (MWDs). In addition, these compounds have been shown to be highly active toward the copolymerization of carbon dioxide with cyclohexene oxide and styrene oxide. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1474–1491     

Chromotropism studies on copper(II) compounds. Part II. Dinuclear copper(II) complexes with triply-bridged hydroxo,acetate, and halo ligands

Abstract

Two triply-bridged dinuclear copper(II) complexes of formula [LCu(μ-OH)(μ-OAc)(μ-X)CuL]X?0.5H₂O where L is a bidentate ligand of N-(pyridine-2-ylmethyl)propane-2-amine and X=Cl, 1 and Br, 2 were synthesized and characterized by elemental analyses, spectroscopic techniques (IR, UV–Vis, EPR), thermal analysis, conductance measurements, and single-crystal X-ray structure determination. The structures of both complexes are similar. The complexes show a distorted square-pyramidal arrangement around each copper(II) ion with a CuN₂O₂X chromophore in which both copper(II) ions are connected by a hydroxo bridge and a triatomic syn-syn carboxylato bridge in equatorial positions and a halide ion bridge at the axial site. The chromotropism behavior of the complexes, including solvato-, thermo-, and halochromism, were investigated in detail. Their halochromism was investigated in the pH range of 2.0–11.0 by visible absorption spectroscopy. The reversible color variations from blue to colorless are attributable to deprotonation and protonation of the ligands. The complexes show reversible thermochromism in solution due to dissociation and recombination of ligands to copper ions.     

Thermal studies on lead(II) salts

The thermal decomposition of synthetic lead(II) hydroxide chloride has been studied between 490 and 520 K over a range of partial pressures of water vapour. The reaction rate is controlled by diffusion of water vapour and Arrhenius parameters have been calculated. The activation energy varies between 92 and 145 kJ mol^?1 and the frequency factor between 10⁹ and 10¹⁵ sec^?1. Water vapour pressure has a profound effect on the reaction rate and a double minimum in the rate is observed. Enthalpimetric data are also presented for the decomposition.     

Thermal studies of lead(II) salts,VI

The kinetics and mechanisms of the thermal decomposition of lead(II) carbonate and lead(II) hydroxide carbonate have been studied over a range of temperatures and partial pressures of carbon dioxide using both isothermal and programmed heating. All stages in each decomposition are diffusion controlled and Arrhenius parameters have been determined. These values for loss of carbon dioxide are all extremely high for a diffusion process, but show a compensation effect, following the equation: logA=–5.02+0.067E The compensation effect is discussed and comparisons with other systems showing such effects are made.

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Zusammenfassung Kinetik und Mechanismus der thermischen Zersetzung von Blei(II)carbonat und Blei(II)hydroxycarbonat wurden bei verschiedenen Temperaturen und CO₂-Partialdrücken sowohl isotherm als auch unter den Bedingungen der programmierten Aufheizung untersucht. Bei allen Zersetzungsschritten ist die Diffusion der geschwindingkeitsbestimmende Schritt; die Arrhenius-Parameter wurden bestimmt. Für einen Diffusionsprozess sind diese Werte extrem hoch, sie zeigen aber einen durch die Gleichung logA=–5.02+0.067E zu beschreibenden Kompensationseffekt, der diskutiert wird. Durch Vergleich mit anderen Systemen wird gezeigt, wie solche Effekte zustande kommen.

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- - , . - - . , , - : log=– 5.02 + 0.067. K .

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We wish to record our thanks to Dr. A. K. Galwey for his interest and the considerable time he has spent discussing the general and particular problems of the compensation effect.