Kinetics and mechanism of platinum-thallium bond formation: the binuclear [(CN)5Pt-Tl(CN)](-) and the trinuclear [(CN)5Pt-Tl-Pt(CN)5](3-) complex

Formation kinetics of the metal-metal bonded binuclear [(CN)(5)Pt-Tl(CN)](-) (1) and the trinuclear [(CN)(5)Pt-Tl-Pt(CN)(5)](3-) (2) complexes is studied, using the standard mix-and-measure spectrophotometric method. The overall reactions are Pt(CN)(4)(2-) + Tl(CN)(2)(+) <==> 1 and Pt(CN)(4)(2-) + [(CN)(5)Pt-Tl(CN)](-) <==> 2. The corresponding expressions for the pseudo-first-order rate constants are k(obs) = (k(1)[Tl(CN)(2)(+)] + k(-1))[Tl(CN)(2)(+)] (at Tl(CN)(2)(+) excess) and k(obs) = (k(2b)[Pt(CN)(4)(2-)] + k(-2b))[HCN] (at Pt(CN)(4)(2-) excess), and the computed parameters are k(1) = 1.04 +/- 0.02 M(-2) s(-1), k(-1) = k(1)/K(1) = 7 x 10(-5) M(-1) s(-1) and k(2b) = 0.45 +/- 0.04 M(-2) s(-1), K(2b) = 26 +/- 6 M(-1), k(-2b) = k(2b)/K(2b) = 0.017 M(-1) s(-1), respectively. Detailed kinetic models are proposed to rationalize the rate laws. Two important steps need to occur during the complex formation in both cases: (i) metal-metal bond formation and (ii) the coordination of the fifth cyanide to the platinum site in a nucleophilic addition. The main difference in the formation kinetics of the complexes is the nature of the cyanide donor in step ii. In the formation of [(CN)(5)Pt-Tl(CN)](-), Tl(CN)(2)(+) is the source of the cyanide ligand, while HCN is the cyanide donating agent in the formation of the trinuclear species. The combination of the results with previous data predict the following reactivity order for the nucleophilic agents: CN(-) > Tl(CN)(2)(+) > HCN.     

Structural defects in poly(vinylchloride)—III. Degradation of vinyl chloride-phenylacetylene copolymers in solution

Vinylchloride-phenylacetylene copolymers have been prepared and characterized. A known amount of defined defect sites, viz. double bonds, has been introduced into the main chain of the polymer. Thermal degradation behaviour of the copolymers has been studied in trichlorobenzene solution. A strong dependence of the kinetics of dehydrochlorination and polyene formation on the defect concentration has been found. Rate constants and activation parameters have been determined. The effects of different structures have been compared.     

Kinetics of radical polymerization—XLIII. Investigation of the polymerization of methyl acrylate in solution by the rotating sector method

The solvent effect on the chain propagation (k?₂) and chain termination (k₄) rate constants was studied for the polymerization of MA in benzene at 50°. Absolute values of the rate constants were determined from the classical polymerizations published earlier and from rotating sector measurements. The value of k₄ was found constant within the limits of experimental error, while k?₂ greatly depends on the monomer concentration, its variation can be quantitatively described in terms of the hot radical theory.     

Peculiar radon spot in Hungary

For the public, indoor radon is the main source of exposure from ionizing radiation. Radon gas originates from the radioactive decay chain of uranium deposited in rocks or in building materials. In the reviews mostly a rather steady radon exhalation has been assumed. In a village of North-East Hungary, however, high radon concentrations have been measured, differing strongly in neighbouring houses and varying in time, due to the interplay of several geochemical phenomena.     

Typical data of a new microporous material obtained from gels with titanium and silicon

The aim of this work is the synthesis and the characterization of a microporous material obtained from gels with titanium and silicon: NTS (titanosilicate). The structure of NTS zeotype is similar to that of AM-1 and JDF-L1 (titanosilicates). The synthesis were carried out with gels of composition: 3.5Na₂O–yTiO₂–4.48HCl–xSiO₂–110H₂O with 1.0≤x≤12.0 and 0.2≤y≤0.7. The temperature of reaction was 190±2°C.     

Initiated oxidation of polyenes formed in the thermal degradation of PVC

Polyenes formed in the thermal degradation of PVC are readily oxidized in the liquid phase in the presence of a radical initiator. In pure oxygen at a constant rate of initiation, different length polyenes are consumed by a first-order reaction: the rate of consumption is proportional to the polyene length and to the square root of initiator concentration. Applying the relationships given by the theory of chain reactions, we determined the ratio of the rate constant of chain propagation calculated for one double bond k₂ to the square root of the chain-termination rate constant k₄. The value obtained, which is relatively high in comparison to other unsaturated hydrocarbons, reflects very well the high reactivity of polyenes of the degraded PVC sample towards oxidation. Intramolecular chain propagation steps are also likely to play a role in the oxidation of polyenes.     

Application of a time-concentration model of adsorption for determination of the nature of adsorbent-adsorbate interaction

A time-concentration model of chemisorption and hydrophobic adsorption by derivatized cellulose beads allowed discrimination between adsorption processes dominated by stoichiometry and those characterized by nonstoichiometric interactions. This discrimination procedure was applied in estimating the type of interaction in the adsorption process of lactate dehydrogenase by cellulose beads, derivatized with C. I. Reactive Blue 2 or C.I. Reactive Blue 19.     

Differential thermoanalytical studies of frozen ferrous perchlorate solutions

It is inferred from the thermoanalytical data obtained on 0.2–4.0M solutions of Fe(ClO₄)₂ which are frozen under non-equilibrium conditions that the phase containing the solute ions turns into a glassy state below –95°. On the warming of these solutions exothermic and endothermic processes are observed which can be related to the effects observed by the nuclear gamma resonance method.

---

Zusammenfassung Es wurde über thermoanalytische Versuche mit gefrorenen Lösungen von Fe(ClO₄)₂ von 0.2 bis 4.0M Konzentration berichtet, die unter Nichtgleichgewichtsverhältnissen zum Einfrieren gebracht worden waren. Es zeigte sich aus den thermoanalytischen Daten, daß die gelöste Ionen enthaltende Phase in einen glasartigen Zustand unter –95° übergeht. Beim Erwärmen dieser Lösungen beobachtete man exothermische und endothermische Vorgänge, die mit den durch Nukleargamma-Resonanz gefundenen Effekten in Einklang gebracht werden konnten.

---

Résumé L'étude thermoanalytique de solutions congelées de Fe(ClO₄)₂ montre que pour les solutions dont la concentration du soluté varie de 0.2 à 4.0M, et qui sont congelées sous des conditions de non-équilibre, la phase contenant les ions dissous se transforme en un état vitreux au-dessous de –95°. En chauffant ces solutions, on a observé des processus endothermiques et exothermiques qui peuvent être reliés aux effets mis en évidence par la méthode de résonance nucléaire gamma.

---

Fe(ClO₄)₂ 0,2–4,0M. , , , , , –95°C. , , - ( ).

---

---

The authors are indebted to Prof. M. Kaplan (Yale University) and to Dr. L. Keszthelyi for stimulating discussions, and to Mr. I. Klimm, Miss J. Nyeste and Mr. T. Grünstein for their assistance in the measurements.     

Artifacts caused by plastics in chemical experiments: Absorption, degradation, catalysis and irreproducible behavior

In the experimental praxis of our chemical laboratory we have been surprised and impressed by a few uncontrollable results caused by plastics. These materials are generally considered to be chemically more or less unreactive and inert. Absorption and chemical degradation—especially during long use—can activate the surface of silicon rubber, polyethylene or teflon, which are constituents of tubes, reaction vessels, stirring bars and other parts of instruments. In a few cases catalytic activation can be interpreted in terms of the interaction between the microporous surfaces of plastics and reactants. These observations require careful consideration and control of the properties and quality of plastics before using them even in the simplest chemical experiments.

---

, . . — — , , , , , . , . .

     

Comparative study of imidazole hydration: Ab initio and electrostatic calculations vs. Cambridge structural database analysis

We studied geometries and energies of complexes between water and neutral or protonated imidazole by ab initio molecular orbital calculations using the 4-31G basis set with and without the counterpoise correction. Positions of hydration sites and relative binding energies could be also estimated by using the electrostatic field map of imidazole as calculated by our bond increment method. The reliability of the calculations is confirmed by comparing the geometries of the imidazole-water complex to the experimental ones from the Cambridge Structural Database. These were obtained by X-ray diffraction studies on crystals with water bound to a molecule containing the imidazole fragment.