Mechanochemical reactions on poly (vinyl chloride)

This paper is concerned with molecular phenomena appearing during deformation of poly(vinyl chloride) under tensile stress conditions. By using indirect techniques (reactions with radical acceptors, with vinylic monomers, electron microscopy) the formation of free radicals, appearing as a consequence of splitting of chemical bonds, is evidenced. The amount of reacted radical acceptor or monomer was proved to be related to solution concentration and to the duration of mechanical stress.     

Radiopharmaceuticals prepared with stannous chloride

The preparation of radiopharmaceuticals using stannous chloride has acquired an ever increasing importance. The applicability to a great number of compounds constitutes the basis of interest. The possibility of preparing kits has added to the desirable properties. The stannous ion is a powerful reducing agent, it posseses the quality of coprecipitating with numerous elements and favours the formation of many complexes of relatively low toxicity. The present outline is a panoramic appreciation of the radiopharmaceuticals prepared with the aid of stannous chloride, some brief considerations on quality control have found their way into this exposition.     

Thermal analysis for generating phase diagrams of systems alkali metal chloride/divalent metal chloride

After a historical survey of the application of differential thermal analysis (DTA) for the generation of phase diagrams, particularly those of pseudobinary halide systems, the authors' research work on the systems ACl/MCl₂ (A = NaCs) is reported. In addition to DTA measurements the thermodynamic properties of the ternary compounds A_nMCl_n+2 are investigated by solution calorimetry and EMF measurements dependent on temperature with a newly developed galvanic cell for solid electrolytes. This method is also a useful tool for elucidating phase diagrams, especially for reactions occurring in the solid state.     

Mechanochemical reactions of elastomers with metals

Metal powders were incorporated into various elastomers and the mixtures were subjected to intense shearing in air or a nitrogen atmosphere. The molecular weight after shearing was still relatively high, however; greater than 100 kg/mol. The elastomer was then dissolved and centrifuged to remove the metal particles and the solution was analyzed for reaction products. A strongly ultraviolet (UV)-absorbing species was formed by shearing a styrene–butadiene copolymer (SBR) with iron powder. The concentration increased with the concentration of iron powder in the mixture and the extent of shearing, and it was greater after shearing in a nitrogen atmosphere. These results are attributed to the direct reaction of macromolecular radicals, formed by shearing, with iron powder to yield an iron–polymer compound. Natural rubber (cis-polyisoprene), which absorbed 100–200 μg of iron per gram of polymer, was about as reactive as SBR. Polybutadiene was less reactive, and an ethylene–propylene copolymer did not react with or solubilize a significant amount of iron. Zinc was, in general, solubilized to a somewhat lesser degree than iron, whereas aluminum powder appeared to undergo virtually no reaction with sheared elastomers. The maximum extent of reaction (solubilization) was of the order of one metal atom per final polymer molecule, which was consistent with the proposed mechanism. Moreover, an analogous reaction took place between simple organic radicals and iron particles in suspension.     

Mechanochemical reactions of fluorides with hemin

Hemin has two potential sites to react with fluorides, the peripheral acid groups and the central Fe^III cation. The mechanochemical reactions of hemin with fluorides (LiF, NaF, KF, CsF, NH₄F and AgF) were monitored using X-ray diffraction (XRD), and IR and Mössbauer spectroscopies. LiF and NaF were found inert when milled with hemin, however KF, CsF, NH₄F and AgF react at both hemin sites. At the iron site Cl⁻ is replaced by F⁻ with formation of KCl, CsCl, NH₄Cl, and AgCl, as detected by XRD, while with the peripheral acid groups, fluorides collect the acidic protons to form KHF₂, CsHF₂, NH₄HF and AgHF₂. The reactions of hemin with the reactive fluorides take place first at the iron site and then at the propionic acid groups.     

Termolecular reactions of alkali metal atoms with O2 and OH

Calculations of low-pressure limit, third-order rate constants are presented for the association reactions A + O₂ + N₂ and A + OH + N₂ (A = Li, Na, K) over the temperature range 200–2000 K and a comparison is made with the available experimental data.     

Hydrogenation reactions over alkali metal doped MgO, II

The hydrogenation of benzene, styrene and isoprene over magnesia doped with sodium and potassium vapors has been studied. Neither system displays a catalytic activity towards benzene hydrogenation. The initial rate, turnover number and time of halfdecay for styrene and isoprene hydrogenation have been determined.

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Mechanochemical reactions of telluric acid with alkaline fluorides

The mechanochemical reactions of telluric acid, Te(OH)₆ with alkaline fluorides (Na and K) have been studied using IR and XRD techniques. The reactions lead to the formation of hydrogen-bonding complexes, NaF.Te(OH)₆ and 2KF.Te(OH)₆. The reactions are free from side products such as alkali tellurates, alkali fluorotellurates or HF₂⁻ salts.     

Mechanochemical effects in redox reactions with participation of iron

The processes of deposition of copper, silver, and lead from their aqueous solutions separately on the concave (contracted) and convex (stretched) sides of a bent steel plate have been investigated. The difference in the deposition rate on the opposite sides gives evidence of the existence of the mechanochemical strain sign effect in redox reactions with the participation of iron.     

Mechanochemical reactions of coordination polymers by grinding with KBr

Grinding of a one-dimensional (1-D) ladder coordination polymer (CP), [Zn(μ-CH(3)CO(2))(CF(3)CO(2))bpe] (1), and a hydrogen-bonded 1-D CP, [Cd(CH(3)CO(2))(2)bpe(H(2)O)] (2), with KBr resulted in the exchange of carboxylate by bromide ions and the formation of 1-D zigzag and 2-D CPs respectively.     

Thermal reactions of lead(IV) chloride complexes in the solid state. Part IV. Thermolysis of alkali metal hexachloroplumbates

Alkali metal hexachloroplumbates of general formula M₂(I)PbCl₆, with M(I) = K, Rb, Cs, undergo thermal decomposition on heating to 700 K. The thermal processes in the solid state have been studied by differential thermal analysis (DTA) and thermogravimetry (TG) with a derivatograph. The thermolysis occurs in one step M₂(I)PbCl₆→2M(I)Cl_(s)+PbCl_2(s)+Cl_2(g) The experimental TG and DTG curves were used to estimate the enthalpy of thermal dissociation. Based on these curves the kinetic parameters of thermolysis have been evaluated. In the linearization procedure of the kinetic equation.

the methods of Freeman and Carroll, Coats and Redfern, Horowitz and Metzger and Gorbachev were applied. Sixteen f(α) functions which describe the primary mechanism of thermal decomposition of solid substances—nucleation, growth of nuclei, phase boundary reactions and diffusion processes—were used in the least squares error analysis. The dehydration of calcium oxalate monohydrate was performed to confirm the validity of the analytical and computational procedures. The differences in values of the kinetic and thermodynamic parameters for hexachloroplumbates thermolyses have been discussed. It was found that K₂PbCl₆ showed atypical thermal properties. This is probably caused by the different crystal structure of K₂PbCl₆ as compared with those of Rb₂PbCl₆ and Cs₂PbCl₆, as well as the abnormal course of its thermolysis. The thermal properties of alkali metal hexachloroplumbates have been compared with those for analogous compounds of the type M₂(I)M(IV)X₆ (M(IV) = Pt, Te, Tc; X = Cl, Br).     

Anionic polymerization. III. Polymerization of butadiene with alkali metal alkoxide-modified alkali metal system

A high molecular weight polybutadiene was prepared in hexane solvent by using alkali metal (Li, Na, K) and metal tert-butoxide (Li, Na, K) as a polymerization initiator. The microstructure of polybutadiene varies, depending on the type of modifiers and polymerization and temperatures. The results and mechanistic implications of this study are discussed.     

Chemical studies on the reactions of synthetic 1.13-nm-tobermorite with alkali metal hydroxides at room temperature

Summary The reaction of alkali metal hydroxides (MOH;M=Li, Na, K;c=0.02–1.0M) with synthetic 1.13-nm-tobermorite (Ca₅Si₆H₂O₁₈·4H₂O) at 25±2°C was studied. The results obtained indicate that the reactivity highly depends onpH and cation field strength and to lesser degree on the ionic radius ofM. MOH has negative effects on the crystallinity of the concerned phase in the following order: KOH > NaOH > LiOH. Furthermore, the hydroxides cause swelling of crystals, attributable to the creation of new cavities due to partial hydrolysis of tetrahedral SiO₂(OH)₂ chains in the lattice. Hydrolysisvia cleavage of Si-O-Si bonds facilitates the cation exchange process Ca²⁺ M ⁺ which probably proceeds by a nucleophilic substitution reaction (S_N2). The observed different affinities of 1.13-nm-tobermorite towardsMOH could be used for the separation of these cations.

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Chemische Untersuchung der Reaktion von synthetischem 1.13-nm-Tobermorit mit Alkalimetallhydroxiden bei Raumtemperatur

Zusammenfassung Die Reaktion von Alkalimetallhydroxiden (MOH;M=Li, Na, K;c=0.02–0.1M) mit synthetischem 1.13-nm-Tobermorit (Ca₅Si₆H₂O₁₈·4H₂O) wurde bei 25±2°C untersucht. Die Ergebnisse zeigen, daß die Reaktivität stark vompH-Wert und von der Kationenfeldstärke, hingegen weniger vom Ionenradius des verwendeten Alkalimetalls abhängt.MOH wirkt sich in der Reihenfolge KOH > NaOH > LiOH negativ auf die Kristallinität der betroffenen Phasen aus. Darüber hinaus verursachen Hydroxide eine Schwellung der Kristalle, ausgelöst durch die Erzeugung neuer Hohlräume durch partielle Hydrolyse tetraedrischer SiO₂(OH)₂-Ketten im Kristallgitter. Hydrolyse der Si-O-Si-Bindungen erleichtert den Kationenaustauschprozeß zwischenM ⁺ und Ca²⁺, welcher wahrscheinlich über einen S_N2-Mechanismus verläuft. Die beobachteten Unterschiede in der Reaktivität zwischenMOH und 1.13-nm-Tobermorit eröffnen eine Möglichkeit zur Trennung dieser Kationen.

     

Solubility in the water-Catamine AB-(alkali metal or ammonium chloride) systems

Solubility in ternary aqueous stratifying systems containing Catamine AB (alkylbenzyldimethylammonium chloride [C _n H_{2n + 1}N⁺(CH₃)₂CH₂C₆H₅] · Cl, a cationic surfactant, where n = 10–18) and LiCl, NaCl, KCl, and NH₄Cl inorganic salts was studied for the first time at 25°C. The boundaries of two-phase liquid equilibrium fields were determined. The studied stratifying systems were proposed for use in the liquid extraction of metal ions.     

Mechanochemical interaction of alkali metal metasilicates with carbon dioxide: 2. The influence of thermal treatment on the properties of activated samples

Processes proceeding during the heating of the samples of lithium, sodium, and potassium metasilicates mechanochemically activated in carbon dioxide are studied using thermal analysis, X-ray phase analysis, and IR spectroscopy. Upon the heating of the samples of sodium and potassium metasilicates, the reversal of phases occurs in the sequence according to their appearance during the mechanical treatment in the mill in the atmosphere of carbon dioxide. Hydrocarbonates are first decomposed to neutral carbonates followed by their interaction with silica to form metasilicates. In the course of thermal treatment of lithium sample, the metastable carbonate-silicate phase, which is formed due to the intense mechanosorption of carbon dioxide, is decomposed first. Afterwards, lithium carbonate formed at the final stage of mechanoactivation reacts with SiO₂.     

Single-ion activities and Zn/Zn(II) reactions in alkali chloride solutions

The title subject has been studied through equilibrium potential measurements on the Zn/Zn(II) and the Ag/AgCl electrode vs. SCE and galvanostatic single-step and chronopotentiometric polarization measurements on the former electrode, all in acidified (to pH about 3) solutions of 0.005 M ZnCl₂+0.99 M MeCl (for Me=Li, Na, K, and Cs) at 25°C. It is found that the Zn(II) activity decreases together with the alkali-ion activity along the sequence LiCl>NaCl>KCl>CsCl, that the chloride-ion activity essentially is insensitive to mutual substitutions of alkali ions, and that the Zn/Zn(II) reactions exhibit no other than pure activity effects of such substitutions. The results support that the Zn/Zn(II) electrode reacts in two consecutive steps with Zn(I) as intermediate, and that some sluggishness appears in chemical reactions to and from electroactive Zn(II) species.