Dosage de l'acide chlorhydrique en présence d'anhydride sulfureux à l'aide de réactifs solides

Résumé Les phosphates de cadmium, de zinc, de mercure(II) et d'argent absorbent sélectivement l'acide chlorhydrique gazeux en présence d'anhydride sulfureux. Le phosphate d'argent est tout particulièrement recommandé en raison de sa préparation facile à l'état pur, de son action rapide avec changement de coloration et de la précision du dosage du chlorure formé.

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Summary The phosphates of cadmium, zinc, mercury(II) and silver selectively absorb gaseous hydrochloric acid in the presence of sulfurous anhydride. Silver phosphate is especially recommended because of its ready precipitation in the pure state, its rapid reaction with change of color, and the accuracy of the determination of the resulting chloride.

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Zusammenfassung Die Phosphate des Cadmiums, des Zinks, des Quecksilbers(II) und des Silbers absorbieren gasförmigen Chlorwasserstoff selektiv in Gegenwart von Schwefeldioxid. Silberphosphat ist für diesen Zweck besonders zu empfehlen, da es sich leicht rein darstellen läßt, da es rasch unter Farbwechsel reagiert und da sich das dabei entstandene Silberchlorid genau bestimmen läßt.

     

Free-radical functionalisation of vinylcyclopropanes

Free-radical mediated cyclopropane ring opening of 2-silylbicyclo[3.1.0]hexane 1 has been carried out leading to the corresponding trisubstituted cyclopentenes 5 and 6 in good yield with complete 1,2-stereocontrol. [3+2]-Annulation has also been performed by trapping the resulting radical with electron-rich and electron-poor olefins, leading to the corresponding polycyclic compounds. Further studies on the functionalisation of dihydropyridines and pyrroles using this methodology is also described.     

Plasmon resonance microsensor for droplet analysis

Microscale fiber tip sensors based on the plasmon resonance are reported. The fabrication process derived from our previous approach for manufacturing near-field scanning optical microscopy probes has been optimized for sensing applications. A typical tip sensor is a tapered fiber 400 microm in length, coated with a nanoporous thin silver film. The miniaturized geometry of the sensor allows detection in a single droplet of liquid solution (approximately 20 microl). The tip sensor is sensitive for refractive indices between 1.33 and 1.40 with a sensitivity of at least 3 x 10(-4) refractive index unit (RIU)/nm. The Raman scattering enhancement through these microsensors demonstrates the important role played by the localized plasmon resonance. The sensors' linear response covers a large region, interesting for biosensing in aqueous environments such as biomedical applications.     

First study on the enantioselective palladium-catalyzed C-P cross-coupling reaction between an alkenyltriflate and a phosphine-borane

In this article, we report the first example of a palladium-catalyzed asymmetric C-P cross-coupling reaction between a racemic secondary phosphine-borane, methylphenylphosphine-borane 1, and an achiral triflate. The influence of various parameters such as the structure of the chiral ligand, the temperature and the nature of the solvent on the activity and the selectivity of the reaction is reported. Enantiomeric ratios up to 78:22 were obtained using (S,S)-Me-DUPHOSPdCl₂ as catalyst. A kinetic resolution process is proposed to account for this selectivity.     

Localized Electrografting of Vinylic Monomers on a Conducting Substrate by Means of an Integrated Electrochemical AFM Probe

An electrochemical lithographic tool for locally electrografting a non‐conducting organic coating on a conducting substrate with a submicrometer resolution is provided by atomic force scanning electrochemical microscopy (AFM‐SECM). The picture shows the topographic AFM image of the line pattern drawn with an AFM‐SECM tip on a gold surface by direct reduction of an aryl diazonium salt/acrylic acid electrolyte solution.

     

Spin–orbit and dispersion energy effects in XeF

Spin–orbit and dispersion energy contributions to the energy curves of XeF are examined. A rapid variation in the spin–orbit coupling with internuclear separation is found for both the ground and excited states. This result can explain the experimentally observed ordering of the ionic excited states when the spin–orbit perturbation couples ²σ and ²π energy curves obtained by both all-electron and effective core potential (ECP ) calculations at the first-order configuration interaction (FOCI ) level of accuracy. Damped dispersion energy contributions to the ground-state energy curve are shown to be comparable to the charge transfer contribution. The energy curve for XeF is in reasonable agreement with experimental results and a calculation of the analogous XeCl curve confirms the qualitative correctness of the calculation. The energy curves and transition moments were then applied to two problems related to the efficiency of the XeF laser. Photodissociation of the X state provides a means of removing a bottlenecked vibrational level but a calculation of the radiative transition probability between the X and A states finds the cross section is too small to yield rates competitive with collisional deactivation. The bottlenecked state may also be removed by electron dissociative attachment but the calculated energy curves for the X states of XeF and XeF^? do not cross at a low energy indicating a small cross section.     

Hartree-Fock energy curves for XΠ and Σ states of HF

Hartree-Fock energy curves have been calculated for the X²Π and ²Σ⁺ states of HF⁺ and applied to an analysis of the photoelectron spectra of HF. The ²Σ⁺ energy curve is found to have a barrier about 0.07 eV high due primarily to a repulsive ion-quadrupole interaction, and a depth of 0.37 eV. This curve will support two bound states and one shape resonance with a half-width of 0.015 eV. The energy curves are probably accurate to 0.1 eV but the analysis shows that results accurate to within 0.03 eV are required to resolve the experimental questions on the dissociation energy for the ground state of HF. The most recent experimental photoelectron results of Berkowitz (following article) encouraged a model calculation of the vibrational states of the ²Σ⁺ state. Assuming a dissociation energy of 0.45 eV and retaining the barrier three bound and one shape resonance vibrational levels are calculated for HF⁺ in agreement with the results reported by Berkowitz.