Reactions of Grignard reagents from 1-halogenoallenes. Allenes—XXXIII

Grignard reagents have been prepared from 1-bromo-3,3-dialkylallenes in ether or tetrahydrofuran. The allenic acids, 4,4-dialkylbuta-2,3-dienoic acids together with 4,4-dialkylbut-2-ynoic acids are formed with carbon dioxide to the exclusion of acids with a terminal acetylene group. Two coupled products, 3,4-diethyl-3,4-dimethylhexa-1,5-diyne and 3-ethyl-3,6-dimethylocta-4,5-dien-1-yne, which are formed as byproducts in reactions of 3-methylpenta-1,2-dienyl magnesium bromide with electrophiles (CO₂, H₂O, Me₂CO), are obtained in high yield by passing oxygen through the solution of the Grignard reagent.     

Toward on-chip X-ray analysis

The possibility of performing chemical analysis and structure determinations with the use of X-rays in a microfluidic chip environment is explored. Externally generated radiation, radioisotope irradiation and on-chip generated X-rays were considered as excitation means for the performance of sample analysis with the techniques of X-ray fluorescence and diffraction. The absorption properties of chip-building materials by different radiation sources are reviewed and data on absorption coefficients calculated, upon which recommendations for optimisations with the use of various X-ray sources may be made. The capabilities and limitations of on-chip X-ray analysis are placed in perspective by preliminary experimental results of diffraction, fluorescence and on-chip X-ray generation experiments.     

Investigations of the lanthanum-europium-copper-oxygen system by X-ray powder diffraction,thermal analysis and europium-151 Mössbauer spectroscopy

Lanthanum-europium-copper oxides of composition La_2?x Eu _x CuO₄ with structures related to those of the high temperature superconducting oxides have been prepared by solid state reactions between the component oxides in air. The X-ray powder diffraction data demonstrate that an orthorhombic to tetragonal structural transformation occurs at compositions betweenx=0.5 andx=0.8. The¹⁵¹Eu Mössbauer spectra show that europium is present in all phases as Eu³⁺. Thermal analysis studies in hydrogen show that a two-step reduction process occurs in the lanthanum-europium-copper oxides with the orthorhombic type structure.¹⁵¹Eu Mössbauer spectroscopy shows that the process does not involve the reduction of the lanthanide ion.     

Synthesis and Characterization of the Reduced Single-Layer Manganite Sr2MnO3.5+x

The nuclear and magnetic structures of polycrystalline Sr₂MnO_3.5 have been determined by the Rietveld analysis of neutron powder diffraction data and electron diffraction techniques. The pure Mn³⁺ single-layered phase crystallizes in the primitive monoclinic space-group P2₁/c with lattice constants a=6.8524(3) Å b=10.8131(4) Å c=10.8068(4) Å β=113.247(4)°. The oxygen defects form an ordered superstructure within the perovskite block layers consisting of interconnected MnO₅ square pyramids, slightly different from those observed for the defect perovskites SrMnO_2.5 and Ca₂MnO_3.5. Magnetic susceptibility studies show a broad transition at ∼280 K, which is attributed to an overall antiferromagnetic ordering of spins, which leads to doubling of the unit cell along [100]. The magnetic unit cell comprises ferromagnetic clusters of four corner-sharing MnO₅ pyramids, which are antiferromagnetically aligned to other similar clusters within the perovskite block layers.     

Synthesis of hydrophilic polymer-grafted ultrafine inorganic oxide particles in protic media at ambient temperature via atom transfer radical polymerization: use of an electrostatically adsorbed polyelectrolytic macroinitiator

A new approach for the surface grafting of polymer chains to colloidal substrates is described. A cationic macroinitiator has been designed for the surface polymerization of a wide range ofhydrophilic methacrylates from ultrafine inorganic oxide sols by atom transfer radical polymerization in protic media at ambient temperature. One advantage of this approach is that it allows one-pot syntheses: the macroinitiator is adsorbed onto the sol, followed by an in situ polymerization. Nonionic, cationic, and betaine monomers can be polymerized directly by this protocol, with reasonably high conversions being obtained, as judged by 1H NMR spectroscopy. Anionic monomers such as sodium 4-styrenesulfonate cannot be polymerized directly due to incompatibility problems with the cationic macroinitiator-coated sol. However, hydroxylated monomers such as glycerol monomethacrylate can be surface-polymerized and then converted to anionic polyelectrolytes by reaction with succinic anhydride under mild conditions. This derivatization was confirmed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic analysis. Thermogravimetry was used to assess the degree of polymer grafting. Higher target degrees of polymerization led to increased grafted polymer loadings, as expected. Particle morphologies and relative degrees of dispersion in aqueous solution were assessed by transmission electron microscopy and dynamic light scattering, respectively. Surface characterization of the polymer-grafted sols was achieved by X-ray photoelectron spectroscopy and aqueous electrophoresis measurements. Most of the data reported in this study concern surface polymerizations from ultrafine silica sols, but some preliminary data for ultrafine tin(IV) oxide sols are also presented. Since most surfaces are negatively charged, this cationic macroinitiator approach can, in principle, be extended to include a wide range of sols, latexes, and planar substrates without requiring a separate surface functionalization step.     

Determination of calcium, potassium, manganese, iron, copper and zinc levels in representative samples of two onion cultivars using total reflection X-ray fluorescence and ultrasound extraction procedure

The chemical characterization of onion cultivar samples is an important tool for the enhancement of their productivity due to the fact that chemical composition is closed related to the quality of the products. A new sample preparation procedure for elemental characterization is proposed, involving the acid extraction of the analytes from crude samples by means of an ultrasonic bath, avoiding the required digestion of samples in vegetable tissue analysis. The technique of total reflection X-ray fluorescence (TXRF) was successfully applied for the simultaneous determination of the elements Ca, K, Mn, Fe, Cu and Zn. The procedure was compared with the wet ashing and dry ashing procedures for all the elements using multivariate analysis and the Scheffé test. The technique of flame atomic absorption spectrometry (FAAS) was employed for comparison purposes and accuracy evaluation of the proposed analysis method. A good agreement between the two techniques was found when using the dry ashing and ultrasound leaching procedures. The levels of each element found for representative samples of two onion cultivars (Yellow Granex PRR 502 and 438 Granex) were also compared by the same method. Levels of K, Mn and Zn were significantly higher in the 438 Granex cultivar, while levels of Ca, Fe and Cu were significantly higher in the Yellow Granex PRR 502 cultivar.