Application d'un reactif sulfovanadique en milieu acetique anhydre a l'etude analytique de quelques acides α-carbonyles ou α-hydroxyles

(Application of a vanadium(V) reagent in anhydrous acetic acid to the determination of some α-carbonyl or α-hydroxyl carboxylic acids). The reagent is prepared from vanadium pentoxide and sulfuric acid in anhydrous acetic acid medium. The oxidation kinetics of various α-carbonyl (glyoxylic, pyruvic, phenylglyoxylic) and α-hydroxyl (glycolic, lactic, mandelic, gluconic) acids are described. A study of the reaction stoichiometry shows that the immediate reaction, corresponding to the consumption of 2–9 mol V(V) mol^?1 of acid, depending on the acid, is useful quantitatively, except for lactic acid which gives a slow non-stoichiometric reaction.     

Wood elastic characterization from a single sample by resonant ultrasound spectroscopy

The goal of this paper is to propose an experimental method allowing the identification of the complete elastic tensor of anisotropic biological materials such as wood using only one sample. To do so, two complementary methods are used. First, the wood eigen-directions are defined from a sample of spherical shape that is then cut into a cube in a way to perform resonant ultrasound spectroscopy (RUS). The method is successfully applied on a reference beech sample with known orthotropic directions. A comparison of the identified elastic constants with those from the literature and some inferred from ultrasonic transmission measurements is given.     

Preparation and characterization of MgB2 superconductor

The MgB₂ superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties. The upper critical field, irreversibility line and critical current density have been determined using magnetization data. The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition. The surface analysis using X-ray photoelectron spectroscopy shows that MgB₂ is sensitive to atmospheric degradation.     

Functionalization of polymeric organolithium compounds with formaldehyde

Functionalizations of poly(styryl)lithium (PSLi), poly(butadienyl)lithium (PBDLi), and poly(isoprenyl)lithium (PILi) with formaldehyde were investigated in benzene solutions at room temperature. Dimer and unfunctionalized products, in addition to the expected products, were found in the PSLi functionalization with formaldehyde. The byproducts were analyzed by ¹H NMR, ¹³C NMR, size exclusion chromatography (SEC), and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) and showed evidence for Cannizzaro reactions and electron‐transfer reactions. A molecular weight dependence of the dimer formation was found for PSLi functionalizations for number‐average molecular weights of less than 20,000; the dimer formation decreased as the molecular weight increased. Changing the reaction conditions did not eliminate dimer formation in the PSLi functionalization. The reactions of PBDLi and PILi with formaldehyde effected quantitative functionalizations, as determined by SEC, ¹H NMR, ¹³C NMR, MALDI‐TOF MS, quantitative column chromatography, and end‐group titration. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2435–2453, 2003