Carboxylations of alkali metal phenoxides with carbon dioxide

The reaction mechanism of the Kolbe-Schmitt reaction of phenol and 2-naphthol has been investigated. An alkali metal phenoxide-CO2 complex is not an intermediate that can be easily transformed into a carboxylic acid, such as salicylic acid (SA) and p-hydroxybenzoic acid (pHBA). A direct carboxylation of phenoxide with CO2 takes place even at room temperature, and is competitive with the formation of the CO2 complex. The resulting complex decomposes thermally (above ca. 100 degrees C) to phenoxide, which then undergoes further competitive reactions. Experiments using a carbon-13 labeled complex support a mechanism of direct carboxylation, and not the mechanism via a CO2 complex. The reactivity, C-13 NMR and MOPAC/PM3 calculations suggest a new carbonate-like structure for the CO2 complex.     

Titrimetric determination of microgram amounts of thallium(I) by thiocyanate amplification after precipitation as thallium hexathiocyanatochromate(III)

Summary Thallium (5–200g) is precipitated as Tl₃Cr(SCN)₆. The precipitate is collected, then treated with 10% sodium carbonate solution, and the thiocyanate dissolved is oxidized to sulphate by iodine at pH 8.2. After acidification, the excess of iodine is extracted into chloroform, and the iodide in the aqueous solution is determined by the Leipert amplification procedure. The method provides 76 iodine atoms for each original thallium(I) ion. Copper(II), mercury(II), bismuth, lead and silver interfere seriously, the first three causing negative errors and the other two positive errors.

---

Maanalytische Bestimmung von Mikrogrammengen Thallium(I) durch Vervielfachung mit Thiocyanat nach Fällung als Thalliumhexathiocyanatochromat(III)

Zusammenfassung Thallium (5–200g) wird als Tl₃Cr(SCN)₆ gefällt. Der gesammelte Niederschlag wird mit 10% iger Sodalösung behandelt und das gelöste Thiocyanat mit Jod bei pH 8,2 zu Sulfat oxydiert. Nach Ansäuern wird der Jodüberschuß mit Chloroform extrahiert und das Jodid in der wäßrigen Lösung nach Leipert titriert. Dabei entsprechen 76 Jodatome einem ursprünglichen Thallium(I)ion. Cu(II), Hg(II), Bi, Pb und Ag stören stark und verursachen negative bzw. im Falle Pb und Ag positive Fehler.

     

Polymorph exploration of bismuth stannate using first-principles phonon mode mapping

Accurately modelling polymorphism in crystalline solids remains a key challenge in computational chemistry. In this work, we apply a theoretically-rigorous phonon mode-mapping approach to understand the polymorphism in the ternary metal oxide Bi₂Sn₂O₇. Starting from the high-temperature cubic pyrochlore aristotype, we systematically explore the structural potential-energy surface and recover the two known low-temperature phases alongside three new metastable phases, together with the transition pathways connecting them. This first-principles lattice-dynamics method is completely general and provides a practical means to identify and characterise the stable polymorphs and phase transitions in materials with complex crystal structures.

Using a phonon mode-mapping approach, we recover the known experimental phases of the ternary oxide Bi₂Sn₂O₇ and identify three new metastable phases, highlighting the utility of the method for polymorph prediction on many other complex materials.     

Cathodic stripping voltammetry of copper-complexed reactive dyes at a hanging mercury drop electrode: Reactive violet 5

Reactive Violet 5 and its hydrolysis product, which is produced as a side product in the dyeing process, can be determined in an admixture at sub-ppb levels by cathodic stripping voltammetry because the potentials of their azo reduction peaks are separated sufficiently. For both dyes, at intermediate pH values the azo peak is preceded by a complexed -copper reduction peak at a less negative potential, which aids the identification of the dyes. The use of pH 6 EDTA buffer removes the complexed-copper peak, as does the use of an acidic buffer (pH < 3). This unusual use of EDTA as a pH buffer facilitates the determination of mixtures of the dye and its hydrolysis product.     

Demographic transition and social security policies in France: A welfare analysis

A dynamic computable general equilibrium model with overlapping generations is used to appraise the consequences in France of three social security policies: a 20% cut in the replacement rate (‘TM20’), an increase in retirement age from 60 to 65 (‘RET65’), and the creation of a transitory fund (‘FUND’). These policies are described in three scenarios built up around a baseline scenario, in which the current French public pension system, financed on a pay-as-you-go basis, is maintained. Whatever the scenario, the demographic transition is assumed to be close to that described in official projections, in which the most likely fertility rate between years 1995 and 2050 is supposed to be equal to 1.8 children per woman. The main results are the following: maintaining the current system remains a reasonable option since slump should not occur during the transition period. Nevertheless, this option may seem undesirable because of the demographic risk—the realization of a scenario less favourable than the official one cannot be ruled out—and the lack of equity of the current pensions system. If equity is appraised with respect to a simple actuarial criterion (i.e. the ratio of the present value of pensions received by a generation over the present value of its social contributions), the ‘FUND’ option appears to be the most equitable. The ‘RET65’ option is the least fair since people presently working are worse off. When macroeconomic outcomes (e.g. per capita production or consumption) or social welfare are considered, the scenario in which the legal retirement age is increased seems to dominate all other options, owing to its huge effects. Nevertheless, these results hold under restrictive assumptions, among which the most crucial is full employment being restored quickly. The ‘FUND’ option is the less desirable, owing to ambiguous and small macroeconomic and social welfare effects. Finally, a 20% cut in the replacement rate would have intermediate effects: less additional production or welfare than in the ‘RET65’ scenario, but more than in ‘FUND’; less efficient in struggling against the lack of equity than the latter scenario, but more than the former.     

Coupled pore network model for the cathode gas diffusion layer in PEM fuel cells

Acta Mechanica Sinica - A pore network model (PNM) is developed for gas diffusion layer (GDL) in the cathode side of polymer electrolyte membrane fuel cells (PEMFCs). The model is coupled to...     

Deamination of Some N-Amino Nitrogen Heterocycles Using Preyssler’s Anion

Summary. Some N-aminotriazines and -triazoles were treated with Preyssler’s anion as catalyst in acetic acid to afford the corresponding deaminated triazines and triazoles. The reaction is suggested to proceed via formation of N-nitrosamines with subsequent N–NO bond cleavage.     

A symmetry based investigation of the band gap of SWCNTs

In this paper we use symmetry of Single Walled Carbon Nanotubes (SWCNTs) to generate some types of virtual sub-bands that are lower in number than the real sub-bands obtained through conventional-TB. It is shown that the virtual sub-bands maintain the value of band gap. In obtaining the sub bands, the interactions of the nearest and the second and third-nearest neighbors are taken into account. As the consequence of lower number of sub-bands, a significant reduction in computational effort has occurred and made the approach useful.