Sulfur isotope fractionation during incorporation of sulfur nucleophiles into organic compounds

(34)S enrichment is shown to occur during sulfurization reactions and for the first time conclusively attributed to an isotope equilibrium effect rather than selective addition of (34)S enriched nucleophiles.     

Cordierite-based refractory ceramics from natural halloysite and peridotite: Insights on technological properties

Cordierite-based ceramics were fabricated from Moroccan natural halloysite clay by using a simple and low-cost manufacturing method. To this end, peridotite and halloysite samples, collected from Beni Bousera and Melilla sites, Morocco, were used as raw materials for ceramics manufacturing. A starting mixture was prepared (76.08 wt% of clay and 23.92 wt% of peridotite), molded and heated to the desired temperature (1250, 1300 and 1350 °C) to fabricate cordierite ceramic specimens. Both raw materials (peridotite and halloysite) and final ceramics were analyzed using routine characterization techniques including chemical analysis by XRF, mineralogical analysis by XRD, thermogravimetric analysis, and morphological characteristics using scanning electron microscopy (SEM). The prepared ceramics were investigated regarding their mineralogical composition, thermal and technological properties, chemical resistance, and microstructural characteristics. Our results indicated that peridotite sample is mainly composed of silica (40.25 wt%) and magnesia (38.05 wt%) while halloysite is consisted essentially of silica (38.00 wt%) and alumina (34.13 wt%). This was confirmed by XRD, TG-DTA and FTIR analyses. The prepared ceramic specimens at different sintering temperatures (i.e., 1250, 1300 and 1350 °C) have regular cylindrical forms, displaying good ceramic properties. This is consolidated with the main technological tests including porosity (4.56–3.11%), bulk density (2.45–2.78 g/cm³), shrinkage (6.51–10.31%), indirect tensile strength (20.35–27.60 MPa), and low linear thermal expansion coefficient (3.05–2.18 × 10^?6/°C). Cordierite specimen prepared at 1350 °C provided the best ceramic sample with the highest technological properties, good chemical resistance and thermal properties. Thus, naturally abundant halloysite and peridotite deposits are potential candidates for cordierite-based ceramic manufacture. Therefore, the achieved results have provided cost-effective ceramic bricks with physical, thermal and mechanical properties that are favorable to be used as refractory bricks.     

Rate Enhancement Effects in the Dabco Catalysed Synthesis of Hydroxyalkenoate Esters

Marked acceleration of the catalytic coupling of aldehydes with methyl acrylate is achieved by varying either the aldehyde or the catalytic system. Rapid and efficient formation of heterocyclic derivatives with significant synthetic potential is described.     

Stereoselective synthesis of enantiopure analogues of (−)-cephalotaxine

The asymmetric total synthesis of three analogues of (?)-cephalotaxine with structural modification of the aromatic ring was achieved in 16 steps and acceptable overall yields. The procedure used was quite similar to that reported by our group for the total synthesis of (?)-cephalotaxine in 2004. The enantiopure spiranic compound 4 is a common intermediate on which various aromatic groups can be introduced. Unexpected and interesting different chemical behaviors were observed during these syntheses.     

Mass-spectral behavior of 2-azatriptycene and its derivatives

The mass-spectral behavior of 11 aromatic and partially hydrogenated 2-azatriptycenes was investigated. It was established that the principal fragmentation pathway for these compounds is the formation of [M-nH] ⁺ and [M-nH]²⁺ ions (n = 1–6), as well as pseudoretrodiene fragmentation of the heterocyclic ring with the elimination of the atoms in the 2 and 3 positions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1399–1402, October, 1981.     

Omega chrome black blue G as a colorimetric reagent for the microdetermination of various cations

Summary Omega Chrome Black Blue G has been found to be a suitable colorimetric reagent for the detection of cobalt and for the determination of copper, cobalt, cadmium, lead and magnesium. The effects of time, p_H, temperature, and foreign ions on the absorbancy are investigated. The reagent is practically suitable for the determination of microgram amounts of cobalt in presence of nickel and other ions which evoke a red colour.The reagent is not suitable for the determination of nickel, calcium, strontium, and zinc.     

Electric and dielectric properties of some gamma-irradiated cabal glasses

Electrical conductivity and dielectric properties have been studied for the glass system CaO---B₂O₃---Al₂O₃ in the temperature range 40–200°C. The substitution of 5% B₂O₃ by CaO or replacing 5% CaO by Na₂O or MgO cause a decrease in the conductivity, but the decrease obtained by soda is greater than that of magnesia. The activation energies of the tested glasses were calculated. All the glasses investigated showed a dielectric constant almost independent of temperature at fixed frequency. The effect of subjecting the glass to a constant dose of gamma-rays changes both the electrical conductivity and dielectric constant. The experimental results were discussed in relation to the specific conduction mechanism in such glasses. Also the effect of varying glass composition or temperature on the mobility or migration of current carrier was considered. The possible creation of induced defects in glass on irradiation was evaluated.