Gaseous salts of oxygen-containing acids: Thermal stability,structure, and thermodynamic properties

Experimental data and results of quantum-chemical calculations on the structure and thermodynamic properties of gaseous salts of oxygen-containing acids were systematized. A criterion of thermal stability of these compounds was offered and regularities in the atomization enthalpies were established.     

Crystal structure of new carboxylate phosphabetaines and phosphonium salts conjugated with them

Russian Chemical Bulletin - Earlier unknown crystalline forms of three carboxylate phosphabetaines and conjugated with them phosphonium salts differing by β substituent with respect to the...     

Binding of carboxylate and trimethylammonium salts to octa-acid and TEMOA deep-cavity cavitands

In participation of the fifth statistical assessment of modeling of proteins and ligands (SAMPL5), the strength of association of six guests (3–8) to two hosts (1 and 2) were measured by ¹H NMR and ITC. Each host possessed a unique and well-defined binding pocket, whilst the wide array of amphiphilic guests possessed binding moieties that included: a terminal alkyne, nitro-arene, alkyl halide and cyano-arene groups. Solubilizing head groups for the guests included both positively charged trimethylammonium and negatively charged carboxylate functionality. Measured association constants (K _a ) covered five orders of magnitude, ranging from 56 M^?1 for guest 6 binding with host 2 up to 7.43 × 10⁶ M^?1 for guest 6 binding to host 1.     

Thermal properties of molten sulphur-oxyanionic salts

Lithium, sodium, potassium and ammonium bisulphate have been shown by detailed TG/DTA studies to have limited application as molten solvents. By contrast, the eutectic bisulphate systems, ammonium-potassium bisulphate and sodium-potassium bisulphate, appear to be excellent molten solvents in view of their low melting points, long liquid ranges and prolonged thermal stability at 200°. In contrast to previous studies, potassium pyrosulphate has been found to be an excellent molten solvent, provided rigorous preliminary drying procedures have been applied.

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Zusammenfassung An Hand eingehender TG/DTA-Untersuchungen wurde gezeigt, daß die Bisulfate von Lithium, Natrium, Kalium und Ammonium nur eine begrenzte Anwendung als geschmolzene Lösungsmittel finden können. Die eutektischen Bisulfat-Systeme Ammonium/ Kalium Bisulfat und Natrium/Kalium Bisulfat scheinen wegen ihrer niedrigen Schmelzpunkte, ihres weiten Flüssigkeitsbereichs und ihrer dauerhaften Thermostabilität bei 200° ausgezeichnete geschmolzene Lösungsmittel zu sein. Im Gegensatz zu früheren Untersuchungen erwies sich Kaliumpyrosulfat als ein ausgezeichnetes geschmolzenes Lösungsmittel, vorausgesetzt daß vorangehend strenge Trocknungsverfahren angewandt wurden.

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Résumé On montre par une étude TG/ATD approfondie que les hydrogénosulfates de lithium, de sodium, de potassium et d'ammonium n'ont qu'une application limitée en tant que solvants fondus. Les systèmes eutectiques des hydrogénosulfates ammonium/potassium et sodium/potassium paraissent, au contraire, être des solvants fondus excellents, en raison de leurs points de fusion bas, de leurs larges intervalles d'existence à l'état liquide et de leur stabilité thermique prolongée à 200°. Contrairement à des études antérieures, on a trouvé que le pyrosulfate de potassium est un solvant fondu excellent, à la condition d'appliquer un mode opératoire rigoureux lors du séchage préliminaire.

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/ , , , . , - - , 200°. , , , - .

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The authors would like to thank Dr. C. Barraclough and Mr. M. Beyer of the Physical Chemistry Department, Melbourne University, for assistance with the Raman spectra.     

Synthesis of monodisperse iron oxide nanocrystals by thermal decomposition of iron carboxylate salts

Iron oxide (Fe(3)O(4), magnetite) nanocrystals of 6 to 30 nm with narrow size distributions (sigma = 5-10%) were prepared by the pyrolysis of iron carboxylate salts.     

Supramolecular interactions in some organic hydrated 2,4,6-triaminopyrimidinium carboxylate and sulfate salts

Four salts, namely, 2,4,6-triaminopyrimidinium 6-chloronicotinate dihydrate, C₄H₈N₅⁺·C₆H₃ClNO₂⁻·2H₂O, (I), 2,4,6-triaminopyrimidinediium pyridine-2,6-dicarboxylate dihydrate, C₄H₉N₅²⁺·C₇H₃NO₄²⁻·2H₂O, (II), 2,4,6-triaminopyrimidinediium sulfate monohydrate, C₄H₉N₅²⁺·SO₄²⁻·H₂O, (III), and 2,4,6-triaminopyrimidinium 3,5-dinitrobenzoate dihydrate, C₄H₈N₅⁺·C₇H₃N₂O₆⁻·2H₂O, (IV), were synthesized and characterized by X-ray diffraction techniques. Proton transfer from the corresponding acid to the pyrimidine base has occurred in all four crystal structures. Of the four salts, two [(I) and (IV)] exist as monoprotonated bases and two [(II) and (III)] exist as diprotonated bases. In all four crystal structures, the acid interacts with the pyrimidine base through N—H…O hydrogen bonds, generating an R₂²(8) ring motif. The sulfate group mimics the role of the carboxylate anions. The water molecules present in compounds (I)–(IV) form water-mediated large ring motifs. The formation of water-mediated interactions in these crystal structures can be used as a model in the study of the hydration of nucleobases. Water molecules play an important role in building supramolecular structures. In addition to these strong hydrogen-bonding interactions, some of the crystal structures are further enriched by aromatic π–π stacking interactions [(I) and (II)].     

Suppressing carboxylate nucleophilicity with inorganic salts enables selective electrocarboxylation without sacrificial anodes

Although electrocarboxylation reactions use CO₂ as a renewable synthon and can incorporate renewable electricity as a driving force, the overall sustainability and practicality of this process is limited by the use of sacrificial anodes such as magnesium and aluminum. Replacing these anodes for the carboxylation of organic halides is not trivial because the cations produced from their oxidation inhibit a variety of undesired nucleophilic reactions that form esters, carbonates, and alcohols. Herein, a strategy to maintain selectivity without a sacrificial anode is developed by adding a salt with an inorganic cation that blocks nucleophilic reactions. Using anhydrous MgBr₂ as a low-cost, soluble source of Mg²⁺ cations, carboxylation of a variety of aliphatic, benzylic, and aromatic halides was achieved with moderate to good (34–78%) yields without a sacrificial anode. Moreover, the yields from the sacrificial-anode-free process were often comparable or better than those from a traditional sacrificial-anode process. Examining a wide variety of substrates shows a correlation between known nucleophilic susceptibilities of carbon–halide bonds and selectivity loss in the absence of a Mg²⁺ source. The carboxylate anion product was also discovered to mitigate cathodic passivation by insoluble carbonates produced as byproducts from concomitant CO₂ reduction to CO, although this protection can eventually become insufficient when sacrificial anodes are used. These results are a key step toward sustainable and practical carboxylation by providing an electrolyte design guideline to obviate the need for sacrificial anodes.

Selective electrocarboxylation of nucleophilically susceptible organic halides without sacrificial anodes is enabled by inorganic salt additives, which suppress the nucleophilicity of anions in the electrolyte.     

Thermal stability and degradation mechanisms of poly(acrylic acid) and its salts: Part 3—Magnesium and calcium salts

The magnesium and calcium salts of acrylic acid have been polymerised in aqueous solution using ammonium persulphate as initiator. Both polymers were also prepared by the neutralisation of poly(acrylic acid) with metal oxide in the same medium.

The thermal degradation behaviour of magnesium and calcium polyacrylate was studied using thermogravimetry (TG), differential thermal analysis (DTA) and thermal volatilisation analysis (TVA). Degradation products were investigated by IR spectroscopy, mass spectrometry and GC-MS techniques, the volatile product fraction having first been separated by subambient TVA.

The decompositions of these materials show some similarities to the behaviour of the alkali metal salts of poly(acrylic acid) and to that of the alkaline earth metal salts of poly(methacrylic acid), but there are also important differences. Acetone and carbon dioxide are the most important volatile products and, in addition, there are various other carbonyl containing products. More carbon dioxide, resulting from side group scission, is evolved from magnesium polyacrylate than from calcium polyacrylate, because of the lower thermal stability of magnesium carbonate.     

Thermal behaviour of mixed tetravalent metal salts

In contrast with the well-known zirconium and titanium phosphates, products containing these metal ions together are unknown. To investigate the thermal behaviour of such materials, samples were synthetized with various ratios of the two metal ions. The samples were identified by means of X-ray diffraction. Their thermal behaviour was investigated in the temperature interval 25–1000 °C via simultaneous TG, DTG and DTA measurements. The data obtained are presented in this paper.

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Zusammenfassung Im Gegensatz zu den wohlbekannten Zirkonium- und Titanphosphaten sind beide Metallionen gleichzeitig enthaltende Produkte unbekannt. Zur Untersuchung solcher Substanzen wurden Proben mit unterschiedlichen Mengen der beiden Metallionen gefertigt und mittels Röntgendiffraktion identifiziert. Die Proben wurden im Temperaturbereich 25–1000 °C mittels simultaner TG-, DTG- und DTA-Messungen untersucht. Die Ergebnisse werden in dieser Arbeit mitgeteilt.

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Thermal surface ionization of some complex salts

Thermal ionization on the surface of a heated wire is applied to the volatilization products of alkali salts of carboxylic and sulfonic acids, and to quaternary ammonium salts. The mass spectra of the alkali salts exhibit almost exclusively cationized molecules. They provide evidence for the evaporation of intact clustered molecules even under conditions of a slow rate of evaporation of the salts. The method appears to be of interest for selective detection of alkali salts from complex mixtures. With the ammonium salts [R₄N]⁺ ions are formed by thermal surface ionization of intact salt molecules. The evaporation of these molecules could be detected at rather low temperatures.     

Thermal and kinetic analysis of uranium salts

Thermal decomposition of U(C₂O₄)₂·6H₂O was studied using TG method in nitrogen, air, and oxygen atmospheres. The decomposition proceeded in five stages. The first three stages were dehydration reactions and corresponded to removal of four, one, and one mole water, respectively. Anhydrous salt decomposed to oxide products in two stages. The decomposition products in nitrogen atmosphere were different from those in air and oxygen atmospheres. In nitrogen atmosphere UO_1.5(CO₃)_0.5 was the first product and U₂O₅ was the second product, while these in air and oxygen atmospheres were UO(CO₃) and UO₃, respectively. The second decomposition products were not stable and converted to stable oxides (nitrogen: UO₂, air–oxygen: U₃O₈). The kinetics of each reaction was investigated with using Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa methods. These methods were combined with modeling equations for thermodynamic functions, the effective models were investigated and thermodynamic values were calculated.     

Ionic liquids as reaction media for esterification of carboxylate sodium salts with alkyl halides

Ionic liquids based on 1,3-dialkylimidazolinium methanesulfonate have been used as effective reusable reaction media in the esterification of several carboxylate sodium salts with different alkyl halides. Products are easily isolated by extraction with ether, and the protocol is mild and green, compared to the existing methods based on toxic solvents. Proper ‘design’ of the ionic liquid allows us to obtain esters always in quantitative yields.     

Thermal and kinetic analysis of uranium salts

The thermal decomposition kinetics of UO₂C₂O₄·3H₂O were studied by TG method in a flowing nitrogen, air, and oxygen atmospheres. It is found that UO₂C₂O₄·3H₂O decomposes to uranium oxides in four stages in all atmosphere. The first two stages are the same in the whole atmosphere that correspond to dehydration reactions. The last two stages correspond to decomposition reactions. Final decomposition products are determined with X-Ray powder diffraction method. Decomposition mechanisms are different in nitrogen atmosphere from air and oxygen atmosphere. The activation energies of all reactions were calculated by model-free (KAS and FWO) methods. For investigation of reaction models, 13 kinetic model equations were tested and correct models, giving the highest linear regression, lowest standard deviation, and agreement of activation energy value to those obtained from KAS and FWO equations were found. The optimized value of activation energy and Arrhenius factor were calculated with the best model equation. Using these values, thermodynamic functions (??H ^*, ??S ^*, and ??G ^*) were calculated.     

Thermal and kinetic analysis of uranium salts

In this study the thermal decomposition kinetics of uranyl acetate dehydrate [UO₂(CH₃COO)₂·2H₂O] were studied by thermogravimetry method in flowing nitrogen, air, and oxygen atmospheres. Decomposition process involved two stages for completion in all atmosphere conditions. The first stage corresponded to the removal of two?moles of crystal water. The decomposition reaction mechanism of the second stage in nitrogen atmosphere was different from that in air and oxygen atmospheres. Final decomposition products were determined with X-ray powder diffraction method. According to these data, UO₂ is the final product in nitrogen atmosphere, whereas U₃O₈ is the final product in air and oxygen atmospheres. The calculations of activation energies of all reactions were realized by means of model-free and modeling methods. Kissinger?CAkahira?CSunose (KAS) and Flynn?CWall?COzawa (FWO) methods were selected for model-free calculations. For investigation of reaction models, 13 kinetic model equations were tested. The model, which gave the highest linear regression, the lowest standard deviation, and an activation energy value which was close to those obtained from KAS and FWO equations, was selected as the appropriate model. The optimized value of activation energy and Arrhenius factor were calculated using the selected model equation. Using these values, thermodynamic functions (??H*, ??S*, and ??G*) were calculated.     

Thermal stability of Peroxynitrates

Peroxynitrates are thermally unstable intermediates (at ambient temperatures) in the atmospheric degradation of hydrocarbons. In this work, thermal lifetimes of nine peroxynitrates have been measured as a function of temperature and, for two of them, also, as a function of total pressure. In the presence of excess NO, relative concentrations of the peroxynitrates were followed in a 420 I reaction chamber as a function of time by means of longpath IR absorption using a Fourier transform spectrometer. Original data on the unimolecular decomposition rate constants are presented for the peroxynitrates RO₂NO₂ with R = C₆H₁₁, CH₃C(O)CH₂, C₆H₅CH₂, CH₂I, CH₃C(O)OC(H)CH₃, C₆H₅OCH₂, (CH₃)₂NC(O), C₆H₅OC(O), and C₂H₅C(O). Thermal lifetimes at room temperature and atmospheric pressure are very short (in the order of seconds) for substituted methyl peroxynitrates (i.e., R'CH₂O₂NO₂) but rather long for substituted formyl peroxynitrates (i.e., R″C(O)O₂NO₂). Kinetic data from this and previous work from our laboratory are used to derive structure‐stability relationships which allow an estimate of the thermal lifetimes of peroxynitrates from readily available ¹³C n.m.r. shift data. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 127–144, 1999     

Thermal stability of elastomers

Thermal transitions of elastomers are classified and problems concerning their stability are discussed. It is concluded that in the case of general-purpose elastomers no simple correlation exists between the energy of the bonds in the skeleton of a chain and their thermal stability. This also holds for the parameters of the physical structure of the chains. A high tendency to cross-linking, a high concentration of cross-links and their chemical structure give rise to a more perceptible effect.

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Zusammenfassung Thermische Umwandlungen von Elastomeren werden klassifiziert und mit der StabilitÄt von Elastomeren zusammenhÄngende Probleme diskutiert. Es wird gefolgert, da\ bei Elastomeren für allgemeine Verwendungszwecke keine einfache Korrelation zwischen der Energie der Bindungen im Kettengerüst und der thermischen StabilitÄt besteht. Das gilt auch für die Parameter der physikalischen Struktur der Ketten. Der Effekt einer starken Neigung zur Vernetzung, der Netwerkdichte und der chemischen Konstitution der Netzwerkbrücken ist dagegen augenscheinlicher.

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Thermal stability of alcohols

3,3-Dimethylbutanol-2 (3,3-DMB-ol-2) and 2,3-dimethylbutanol-2 (2,3-DMB-ol-2) have been decomposed in comparative-rate single-pulse shock-tube experiments. The mechanisms of the decompositions are The rate expressions are They lead to D(iC₃H₇? H) – D((CH₃)₂(OH) C? H) = 8.3 kJ and D(C₂H₅? H) – D(CH₃(OH) CH? H) = 24.2 kJ. These data, in conjunction with reasonable assumptions, give and The rate expressions for the decomposition of 2,3-DMB-1 and 3,3-DMB-1 are and      

Thermal stability of ketoprofen

The purpose of this investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the ketoprofen—involving active substance’s thermal decomposition—was performed under isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 260; 265; 270; 275; and 280 °C. The thermogravimetry/derivative thermogravimetry data were processed by three differential methods: isothermal–isoconversional, Friedman’s isothermal–isoconversional, and isothermal model-fittings. The obtained results are in good accordance with those obtained under non-isothermal conditions of a previous study, and confirm the necessity for the kinetic parameters to be determined, under different thermal conditions, by the adequate calculation methods.     

Thermal stability of polyurethanes

Summary The combined application of thermogravimetry reactiongas chromatography and gel-permeation chromatography permits to follow the heat degradation of polyurethane polymers in inert gas, air and water-saturated environment. The examinations give information on the rate of thermal degradation, the individual volatile degradation components, the critical points of the polymer chains and on the change of their molecular-weight distribution. Gas chromatographic examinations also permit the identification of the chain-extending components of different types of polyurethanes.