The reduction of hexanitrocobaltate(III) ion in the presence of hexadecyltrimethylammonium bromide

The influence of cationic surfactant hexadecyltrimethylammonium bromide (CTAB) on the kinetics of the spontaneous reduction of the analytically important compound, sodium hexanitrocobaltate(III), was studied. The spontaneous reduction was monitored spectrophotometrically at pH 2 and 5 and at concentrations of CTAB from 1 × 10⁻⁵ to 5 × 10⁻⁴ M. The mechanism of this process was described using two consecutive first-order reactions. A decrease in the rate constant for reduction at pH 5 in solutions containing CTAB in concentrations of 5.6 × 10⁻⁵ M (critical micelle concentration) compared with its rate in an aqueous solution was observed. These effects could be explained by electrostatic and hydrophobic/hydrophilic interactions between the micellar pseudophase and the hexanitrocobaltate(III) ion. The article is published in the original.     

Study of ion-exchange properties of tin(IV) phosphate modified with sodium hexanitrocobaltate

The interrelation between the chemical composition, structure, and ion-exchange properties of tin(IV) phosphate modified with sodium hexanitrocobaltate was studied. The sorption capacity was increased; the possibilities for lithium, rubidium, and cesium sorption were extended owing to change in the size of cavities in the structure.     

The thermal decomposition of cerium(III) nitrate

The thermal decomposition of anhydrous Ce(NO₃)₃ has been studied. The thermal decomposition reaction is described by the second order kinetic equation, [1/(1–)]–1=kt. The apparent activation energy was determined asE _a=104 kJ mol^–1 while the enthalpy of the reaction was estimated asH _r=111.1 kJ mol^–1. The decomposition reaction differs from that observed for Nd(NO₃)₃.

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Zusammenfassung Die thermische Zersetzung von wasserfreiem Ce(NO₃)₃ wurde untersucht. Die thermische Zersetzung wird durch die Geschwindigkeitsgleichung zweiter Ordnung[1/(1–)]–1=kt, beschrieben. Für die scheinbare Aktivierungsenergie wurde ein Wert von 104 kJ mol^–1 und für die Enthalpie der Reaktion ein Wert von 111,1 kJ mol^–1 ermittelt. Die Zersetzungsreaktion unterscheidet sich von der für Nd(NO₃)₃.

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. : [1/(1–)]– 1=kt. a, 104 · ^–1, H _r, 111.1 · ^–1. .

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The authors wish to thank the Council for Scientific and Industrial Research and the University of Pretoria for financial assistance.     

The thermal decomposition of some Cr(III) complexes

The thermal decomposition reactions of the following chromium(III) complexes were investigated: Cr(CH₃COO)₃·2 H₂O, [C_r3O(CH₃COO)₆(H₂O)₃]Cl·2 H₂O and [Cr₃O(CH₂ClCOO)₆(H₂O)₃]Cl·6H₂O. Simultaneous TG/DTG/DTA were applied nonisothermal conditions. From the recorded curves, the activation energiesE _a were calculated for all the thermal decomposition steps. Appropriate chemical reactions were attributed to the thermal effects, with consideration to the X-ray diffraction and IR spectra results.

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Zusammenfassung Für die Untersuchung der thermischen Zersetzungsreaktion der Chrom(III)-Komplexe Cr(CH₃COO)₃·2H₂O [C_r3O(CH₃COO)₆·(H₂O)₃]Cl2H₂O und [C_r3O(CH₂ClCOO)₆·(H₂O)₃]C₁₆H₂O wurde simultane TG/DTG/DTA unter nichtisothermen Bedingungen eingesetzt. Ausgehend von den aufgezeichneten Kurven wurden für alle Schritte der Zersetzungsreaktion die E_a-Werte berechnet. In Übereinstimmung mit röntgenographischen und IR-spektroskopischen Ergebnissen wurden den thermischen Effekten passende chemische Reaktionen zugeordnet.

     

Catalytic action of metallic salts in autoxidation and polymerization. IX. Polymerization of methyl methacrylate with sodium hexanitrocobaltate(III) in mixed solvent of acetone and water

Polymerization of methyl methacrylate with some cobalt (III) complexes was carried out in various solvents and in mixed solvents of acetone and water or alcohols. Sodium hexanitrocobaltate(III) was found to be an effective initiator in mixed solvent of water and acetone. The kinetic study on the polymerization of methyl methacrylate with Na₃[Co(NO₂)₆] in a water-acetone mixed solvent gave the following over-all rate equation: R_p = 8.04 × 10⁴ exp{ ?13,500/RT} [I]^1/2[M]² (mol/1.?sec). The effects of various additives on polymerization rate and the copolymerization curve with styrene suggest that polymerization proceeds via a radical mechanism. The dependence of the polymerization rate on the square of monomer concentration and the spectroscopic data were indicative of the formation of a complex between initiator and monomer.     

The effects of chromium(III) coordination on the dissociation of acidic peptides

The complexes formed between chromium(III) and synthetic acidic peptides were studied by sustained off-resonance irradiation collision-induced dissociation (SORI-CID) in a Fourier transform ion-cyclotron resonance (FT-ICR) mass spectrometer equipped with electrospray ionization (ESI). Neutral peptides and peptides containing one, two, and multiple acidic residues were studied. Formation of [M + Cr-2H]+ occurred for all peptides. Three noteworthy features were found in the CID spectra of [M + Cr-2H]+. The first is that fewer fragment ions were produced from [M + Cr-2H]+ than from [M + H]+. The reason may be that multiple coordination between chromium(III) and carboxylate or carbonyl groups hinders the production of fragment ions by continuing to bind pieces of the peptide to chromium(III) after cleavage of bonds within the peptide. The second feature is loss of CO from [M + Cr-2H]+ and [y(n) + Cr-H]+. A mechanism involving coordination of chromium(III) with carboxylate groups is proposed to rationalize elimination of CO. The third feature is that chromium(III) is retained in all fragment ions, indicating strong binding of the metal ion to the peptides. The complex [M + 2Cr-5H]+ is formed as the peptide chain length and number of acidic residues increases. Longer peptides have more sites to coordinate with chromium(III) and more conformational flexibility. In addition, formation of [M + Cr-2H]+ from AGGAAAA-OCH(3), which has no carboxylic acid groups, suggests that chromium(III) can coordinate with sites on the peptide backbone, albeit in low abundance. In the negative mode, [M + Cr-4H](-) was only found for peptides containing four or more carboxylic acid groups. This is consistent with deprotonated carboxylic acid groups being involved in chromium(III) coordination and with chromium existing in the 3 + state in the gas-phase ions.     

Oxidation of americium(III) with sodium bismuthate

The oxidation of americium(III) with sodium bismuthate has been investigated in a nitric acid solution. The lower the acidity, the more rapidly the oxidation of americium(III) to americium(VI) proceeds, especially at higher temperatures. Based on this finding, a procedure was developed to oxidize americium(III) completely at low concentrations. The americium(VI) free from the excess oxidant has been found to be stable only at 0°C, irrespective of the acidity, but to be more unstable at the temperature higher than 10°C, especially at lower acidities.     

The thermal decomposition of bismuth(III) compounds used in medicine

The machanisms of thermal decompositions have been studied of the following bismuth(III) salts: benzoate, salicylate, subbenzoate, subsalicylate, subgallate, iodogallate, oxalate, citrate, Na-Bi(III) tartrate and tribromophenolate using thermal and differential thermal analyses. Intermediate products of decomposition have been isolated and identified.     

Infrared multiphoton dissociation of the siderophore enterobactin and its Fe(III) complex. Influence of Fe(III) binding on dissociation kinetics and relative energetics

The dissociation pathways of the siderophore enterobactin and its complex with Fe(III) were examined using infrared multiphoton dissociation (IRMPD). Under experimental conditions (pH = 3.5), both compounds' electrospray spectra exhibited exclusively singly-charged anions. The compositions of the dissociation products were characterized by accurate mass measurements using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The primary dissociation channel for both species was determined to be the loss of one serine group from the precursor molecules. To further investigate the influence of Fe(III) binding on the intramolecular interactions, dissociation kinetics and relative energetics for the loss of this serine group were determined using the focused radiation for gaseous multiphoton energy-transfer (FRAGMENT) method. From the kinetic data, it was found that enterobactin was approximately seven times more reactive than its Fe(III) complex over the range of laser intensities investigated. The relative activation energies, however, exhibited similar values, approximately 7 kcal.mol(-1). These results suggest that at pH = 3.5, Fe(III) interacts with only two of the three serine groups. The results from the present work are believed to be valuable for the characterization of novel siderophores as well as their associated metabolites and synthetic analogues.     

Synthesis and the thermal decomposition of iron(III) tris(oxalato) ferrate(III) tetrahydrate

The paper describes the synthesis and thermal decomposition of Fe[Fe(C₂O₄)₃]4H₂O in air. The compound is completely dehydrated at 170°C and some reduction in the inner sphere iron(III) occurs. At 290°C, a mixture of ferric oxide and ferrous oxalate is obtained. Beyond 420°C, the decomposition is complete and final residue is ferric oxide. A probable reaction mechanism is proposed.     

Kinetics and mechanism of acid catalysed dissociation of some octahedral complexes of cobalt(III) and chromium(III)

Summary The kinetics of dissociation of glycinepentaamminecobalt(III) and tetraaquomonoacetylacetonatochrormium(III) ions in moderately strong perchloric acid media have been investigated spectrophotometrically. From the dependence of the rate on various acidity functions and the observed isokinetic and free energy relationships, both the complexes appear to react by an associative process involving interaction of the conjugate acid form of the substrate complex and H₃O⁺.     

Separation of diastereomers of sodium DL-bis(glycyl-S-alaninato)cobalate (III)

Conclusions The diastereoisomers of sodium DL-bis (glycine-S-alaninato) cobaltate (III) were separated by preparative chromatography on aluminum oxide, in which connection these diastereoisomers have a different absolute configuration of the complex and the same absolute configuration of the dipeptide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 194–196, January, 1973.     

The thermal dissociation of some carbonate minerals

Detailed differential thermal studies on mixtures ofnatural carbonate minerals have confirmed the peak-temperature shifts recently reported for mixtures ofsynthetic carbonates and have established that such shifts can be attributed entirely to dilution effects. The exception, where magnesite in the presence of siderite maintains its peak position, is due simply to the fact that both minerals give similarly sized peaks at approximately the same temperature.

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Zusammenfassung Eingehende differentialthermische Untersuchungen von Gemischen natürlicher Karbonatmineralien zeigten ähnliche Spitzentemperaturverlagerungen wie kürzlich bei Gemischen von künstlichen Karbonatgemischen beobachtet wurden. Solche Verlagerungen sind ausschließlich Dilutionserscheinungen zuzuschreiben. Magnesit behielt zwar in Gegenwart von Siderit seine Spitzenpositionen, wofür jedoch der Umstand verantwortlich ist, daß beide Mineralien ähnliche und bei gleichen Temperaturen erscheinende Spitzen besitzen.

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Résumé L'étude de mélanges de carbonatesnaturels par les procédés thermiques différentiels a confirmé l'observation faite récemment d'un déplacement de la température au sommet du pic pour des mélanges de carbonatessynthétiques. On attribue ces déplacements entièrement aux effets de dilution. La magnésite en présence de sidérite constitue une exception. Dans ce cas, la position du pic reste inchangée du fait que ces deux minéraux donnent des phénomènes sensiblement identiques presque à la même température.

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, , , (1) , , . , , (1), , .

     

Analytical and thermal investigations of new solid Y(III) and La(III) complexes

New compounds with formulae Y(2,4′-bpy)_1.5Cl₃·8H₂O (I), Y(2,4′-bpy)_0.5Br₃·8H₂O (II), La(2,4′-bpy)Cl₃·5H₂O (III) and La(2,4′-bpy)_1.5Br₃·5H₂O (IV) were prepared and characterized by chemical and elemental analysis, IR spectroscopy and powder X-ray diffraction. The thermal properties of compounds in the solid state were studied using TG-DTA techniques under dry air atmosphere. The thermal behavior of investigated compounds was studied in the temperature range 298–1273 K. They are stable up to 323 K. The complexes decompose in several stages, accompanied by endo- and exothermic effects. In all cases, the first step of pyrolysis is partial or total dehydration. When the temperature rises, deamination takes place. The solid final products of decomposition are Y₂O₃ and La₂O₃, respectively. Additionally, for all complexes mass spectrometry was used to analyze principal volatile thermal decomposition and fragmentation products evolved during pyrolysis under dry air atmosphere.