Regularities of the formation of the photolysis products in the lead azide-cadmium system

Compared to PbN₆(Ab), the PbN₆(Ab)-Cd system was found to be characterized by a low photolysis rate within the region of intrinsic absorption of PbN₆(Ab) and, at the same time, by a broader range of spectral sensitivity of PbN₆(Ab), up to 510 nm. Preliminary irradiation by 380-nm light resulted in an increase in the photolysis rate. The photolysis rate constants for the PbN₆(Ab)-Cd system were determined. An analysis of the voltammetric characteristics, photocurrent, and contact potential difference made it possible to develop a model of the photolysis of the PbN₆(Ab)-Cd system, including the stages of generation, recombination, redistribution of nonequilibrium charge carriers in the contact field, the photoemission of electrons, formation of the photolysis products, and genesis of the PbN₆(Ab)-Pb(photolysis product)-Cd system. It was demonstrated that the diffusion of anionic vacancies to neutral Pb _n ⁰ sites is the limiting stage of the photolysis of the PbN₆(Ab)-Cd system.     

Intercalation and formation of complexes in the system of lead(II) iodide-ammonia

Interaction between lead(II) iodide and ammonia was studied with the help of an X-ray in situ analysis, DTA-TG analysis, DSC measurements and IR spectroscopy. A two-stage mechanism of the reaction was defined. At the first stage of the reaction two phases with trigonal symmetry and a phase with monoclinic symmetry are developed. At the second stage of the reaction the structure changes lead to formation of a compound with orthorhombic symmetry. The results were discussed along with the data of thermal analysis and IR spectroscopy. The value of enthalpy of formation for the compound PbI₂(NH₃)₄ was determined.     

The photolysis of Chlorocarbonylbis(triphenylphosphine)iridium(I) in chloroform

Under 254 or 313 nm irradiation in chloroform, [IrCl(CO)(PPh3)2] is converted cleanly to [IrCl2(CO)H(PPh3)2] through the addition of HCl, produced photochemically. Under 254 nm irradiation, some of the reaction of [IrCl(CO)(PPh3)2] occurs by direct photolysis of chloroform, though a greater contribution arises from a reaction initiated through absorption of light by the metal complex. Under 313 nm irradiation, essentially all of the reaction is metal-initiated. The linear dependence of the reaction rate on light intensity and on the fraction of light absorbed by the Ir(I) complex as well as the lack of a deuterium isotope effect rule out a radical process. Instead it is proposed that an association complex between excited state [IrCl(CO)(PPh3)2] and CHCl3 leads to dissociation of a chlorine atom from CHCl3, yielding HCl after abstraction of a hydrogen from another CHCl3. HCl then adds to a ground state [IrCl(CO)(PPh3)2] complex.     

Selective gold(I)-catalyzed formation of tetracyclic indolines: a single transition structure and bifurcations lead to multiple products

Several alkynylindoles undergo gold(I)-catalyzed cyclization reactions to form a single isomer in each case. Density functional theory shows why this reaction is favored over the many possible regio- and stereoisomeric reaction pathways. This transformation involves a two-step no-intermediate mechanism with surface bifurcations leading to two or three products. Such bifurcations could explain reactivity in many gold(I)-catalyzed enyne cyclization reactions.     

Electrical conductance,density, and viscosity of the molten system lead(II) dodecanoate/lead(II) oxide

Data are presented for densities, electrical conductances, and viscosities of the molten system lead(II) dodecanoate/lead(II) oxide concentrations up to 0.22 mole fraction of the oxide. Values of ?₀ obtained from extrapolation of graphs of density againts temperature are seen to decrease on adding small quantities of PbO, but to increase on adding further PbO. Results from thermal analysis suggest that this may be due to a change in structure of the liquid phase from small. spherical to long, cylindrical micelles. Over the concentration range studied, molar volumes are linear functions of concentration at any particular temperature. The molar volumes of the system lead(II) carboxylate/lead(II) oxide for the even chain acids C₁₀ to C₁₈ are linear functions of chain length. Arrhenius plots for the electrical conductance of the mixtures show curvature, as in other lead(II) dodecanoate systems. The activation energies for conductance in the low temperature region show a steady decrease with increasing PbO concentration and it is proposed that this arises from increased mobility of the charge carrier. The specific conductance at any temperature decreases with increasing mole fraction of oxide, indicating the oxide to be essentially undissociated in the melt. The activation energy for viscosity shows a dramatic increase on adding small amounts of PbO. This is suggested to arise from a change in the structure of the melt. Studies of the viscosities of the system lead(II) carboxylate/lead oxide as a function of chain length for the even chain acids C₁₀ to C₁₈ suggest a slight decrease in the size of the unit of viscous flow when oxide is present.     

The formation and photolysis of bis(fluorenyl)dimethylzirconium

Bis(fluorenyl)dimethylzirconium has been prepared from fluorene, methyllithium and zirconium tetrachloride by a new and convenient route. The compound was characterized by elemental analysis, proton NMR and mass spectrometry. Photolysis of bis(fluorenyl)dimethylzirconium in solution leads to cleavage of the methyl groups, with formation of methane and a bis(fluorenyl)zirconium-type compound of possible polynuclear nature. Infrared studies using specifically deuterated analogs have shown that this process occurs, at least in part, by intramolecular proton abstraction from theπ-coordinated fluorenyl rings.     

Structuring caused by diazonium-salt photolysis products in poly(oxiethyl methacrylate)

Thermomechanical and holographic methods have been applied to the changes caused in the matrix in poly(oxiethyl methacrylate) POEMA due to photlysis of a diazonium salt dissolved in it, with reference to 2,5-diethoxy-4-N-morpholinophenyldiazonium borofluoride. The measurements on the thermomechanical parameters and on the elastic modulus as a function of temperature indicate that the photolysis does not lead to covalent bonds between the macromolecules. The photolysis mechanism and these data suggest that the D8 groups in the POEMA are esterified by the photolysis products, which leads to a hydrophilic polymer matrix composed of oleophyl parts in the illuminated areas. There are differences in optical parameters between the illuminated and unexposed parts of the POEMA, which can be detected in a hydrophyl solvent, as has been confirmed by holography.Leningrad. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 1, pp. 55–6O, January-February 1991. Original article submitted March 9, 1989.     

Effect of chromium(III) oxide on corundum formation from products of shock-wave synthesis of aluminum oxide

Formation of α-Al₂O₃ in thermal treatment of ultradispersed aluminum oxide powders produced by shock-wave synthesis with addition of Cr₂O₃-(NH₄)₂Cr₂O₇ as a precursor was studied. The acceleration of the conversion of δ-and θ-Al₂O₃ to α-Al₂O₃ upon introduction of additives in the stage of synthesis of aluminum oxide was examined.     

Mesophase formation in lead(II) decanoate

Abstract

Structures of the thermotropic mesophases of lead(II) decanoate are reassigned following optical and X-ray diffraction studies. These results, and those of D.S.C., Raman and ²⁰⁷Pb N.M.R. spectroscopy, indicate formation of a lower temperature mesophase involving mainly increased lateral disorder, and a higher temperature L_α (smectic A) phase resulting from chain disordering and decreased lead-carboxylate interaction. Comparison of experimental thermodynamic data for the phase transitions with theoretical data in the literature indicates that the entropy change for the lower to higher mesophase transition is dominated by the increase in chain disorder.     

Pyrochlore-related phases in the lead oxide-tantalum oxide system

Pyrochlore-related phases in the PbOTa₂O₅ system were reinvestigated. Three such phases are described: cubic Pb_1.5Ta₂O_6.5 with a narrow range of composition, rhombohedral Pb₂₂Ta₁₈O₆₇, and orthorhombic Pb₁₄Ta₁₀O₃₉. A new pyrochlore-related structure is proposed for the orthorhombic phase. There is also a range of rhombohedral solid solution, which may be metastable only. The existence of the previously reported Pb₂Ta₂O₇ is not confirmed.     

Intermolecular interactions governing solubilization in micelles of poly(alkylene oxide) surfactants

Partition coefficients for 39 low-molecular-mass compounds between water and micelles of an ethylene oxide-propylene oxide block copolymer (Pluronic P85) and the monolauryl ether of poly(ethylene oxide) (Brij 35) have been measured by the methods of fluorescence spectroscopy, fluorescence anisotropy, and dialysis kinetics. The tested compounds include aromatic hydrocarbons, phenols, naphthols, xanthene dyes, anthracycline antibiotics, and porphyrins. The multifactor analysis of the partition coefficients in terms of the linear free-energy relationships has been performed. It has been shown that the H-donating ability of compounds facilitates their solubilization in Pluronic micelles and has no effect on solubilization in micelles of monolauryl ether of poly(ethylene oxide). This difference indicates that, when solubilization occurs in Pluronic micelles, the compounds under study appear in a hydrophobic core composed of poly(propylene oxide) blocks.     

Properties of molten carboxylates part 5. A quantitative differential thermal analysis study of mesophase formation in the sytems lead(II)dodecanoate/lead(II) oxide and lead(II)dodecanoate/hendecane

Measurements have been made of the temperatures and enthalpy changes of phase transitions in the systems lead dodecanoate/lead oxide and lead dodecanoate/hendecane. The data have been discussed in terms of the R theory of amphiphylic mesophases. The concepts of the R theory are shown to be useful in the interpretation of phase transitions in molten carboxylate systems.     

Direct observation of spin-forbidden formation of O(D) in the near-UV photolysis of ozone

Time-of-flight measurements have been made of the O(¹D) fragment following the photolysis of ozone in the near-UV. At 321.9 nm fragments are seen with kinetic energies the values of which are those expected from spin-forbidden dissociation with ground state O₂(X³Σ_g⁻) molecules as the co-product. Spin-allowed dissociation of internally excited ozone molecules is also seen to produce translationally cold O(¹D) and O₂(a¹Δ_g) products. The implications for the dissociation of tropospheric ozone are briefly discussed.     

Lead-selective electrodes based on lead(IV) oxide

Lead(IV) oxide electrodes are shown to give near-theoretical calibration slopes for lead(II) ions over the range 10^?3–10^?5 mol l^?1, and to have near-theoretical standard potentials in different acidic media. They are compared with lead sulphide-silver sulphide membrane electrodes and shown to be more tolerant of acidity and copper(II), mercury(II) and iron(III) ions. Iron(II) and manganese(II), however, interfere significantly. Some of the advantages of the lead(IV) oxide electrode are brought out in the determination of the solubility product of lead sulphate; implications for constructing phosphate- and sulphate-sensitive electrodes are mentioned.     

Investigation of lead thiosulfate photolysis in aqueous solutions

A model of photolysis of PbS₂O₃ aqueous solutions has been proposed on the basis of identified photolysis products and semiempirical quantum-chemical calculations. The degradation of PbS₂O₃ starts with the dissociation of the sulfur-sulfur bond in the thiosulfate group via photochemical excitation and transition of the system a whole to the activated state, which is decomposed by the solvent. The interaction of the primary photolysis products with PbS₂O₃ results in the formation of final products.     

Thermal behaviour of the system lead(II) dodecanoate/lead acetate

Data are presented for the heats and entropies of phase changes for the system lead(II) dodecanoate/lead acetate. A phase diagram has also been constructed for the system.Optical observation under a polarising microscope suggests that the phase sequence in this system is the same as in pure lead dodecanoate i.e. crystal → G (smectic) → V₂ (cubic isomorphous) → liquid.The entropy of the V₂ → liquid transition in the mixtures is the same as for pure lead dodecanoate which suggests that addition of lead acetate to lead dodecanoate does not affect the state of aggregation of the soap in the liquid phase.     

Co-photolysis of poly(styrene) and poly(vinylacetophenone)—I. Vacuum photolysis

Films made from blends of poly(styrene) (PS) and poly(vinylacetophenone) (PVAP) (up to 12% mol PVAP) were exposed under high vacuum to long wave u.v. radiation (λ > 300nm). Spectral changes (phosphorescence, NMR and i.r. indicated that PVAP was photolysed: the nature of gaseous products (in order of abundance, methane, carbon monoxide, ethane and acetaldehyde) confirmed that PVAP was undergoing a Norrish Type I decomposition. There was also evidence of photoreduction, OH absorptions appearing in the i.r. The blended films undergo cross-linking but the insoluble material formed after about 10hr contains little carbonyl. The effects of PVPA concentration and molecular weight on the rate of product formation were also investigated. Experiments with poly(α-D-styrene) confirmed that methyl radicals were abstracting H atoms at the α-position in PS. The implications of such reactions in the initiation of photo-oxidation by polymeric ketonic species are discussed.     

Reactive intermediates in the photolysis of cyclopentadienylcobalt(I) dicarbonyl and in the reduction of cyclopentadienylcobalt(III) carbonyl diiodide

Photolysis of (C₅H₅)Co(CO)₂ (I) in toluene or petroleum ether solution at ?78°C generates the unsaturated monocarbonyl species (C₅H₅)Co(CO), which was identified in solution by its IR spectrum. At room temperature, this monocarbonyl can associate with excess I to give (C₅H₅)₂Co₂(CO)₃, or dimerize to (C₅H₅)₂Co₂(CO)₂. The latter is stable as a solid, but in solution it is slowly converted to the insoluble trimer (C₅H₅)₃Co₃(CO)₃. (C₅H₅)₂Co₂(CO)₂ is symmetrically cleaved by phosphines to (C₅H₅)Co(CO)(PR₃), while diolefins bring about unsymmetrical cleavage to give (C₅H₅)Co(diolefin) and (C₅H₅)Co(CO)₂.