A highly efficient catalyst-free protocol for C-H bond activation: sulfamidation of alkyl aromatics and aldehydes

A catalyst-free protocol has been developed for amidation of alkyl aromatics and aldehydes using TsNBr(2)via a nitrene transfer process in the presence of a base in excellent yield within a short time. The reaction was found to be selective for secondary and tertiary benzylic C-H bonds and C-H bonds of aldehydic groups.     

Imidazole-Catalyzed Henry Reactions in Aqueous Medium

2-Nitroalkanols can be efficiently synthesized using imidazole as a mild Lewis basic catalyst in aqueous medium as well as in organic solvents. The products have been found in good yields without purification (> 95% purity by ¹H NMR) for aromatic aldehydes. Additionally, the very mild reaction conditions prevent the particular side reactions such as aldol condensation, Cannizzaro reaction, or dehydration of the 2-nitro alcohols into nitro alkenes even if aromatic aldehydes are used. This report satisfies the criteria for green synthesis in terms of reaction medium and recycling of the catalyst (imidazole).     

Nature of intramolecular transannular interaction in group 13 atranes: a theoretical study

Ab initio molecular orbital (MO) calculations at the MP2/6-31+G* level coupled with quantum theory of atoms in molecules (QTAIM) analysis were carried out on group 13 atranes (M = B, Al, Ga) with special emphasis on the nature of the transannular M···N interaction present in these molecules. Substituents at the equatorial position were found to influence the extent of transannular interaction. Boratrane molecules were found to have the strongest M···N interaction and consequently have higher stabilization energies. QTAIM analysis revealed the presence of significant covalent character in the transannular M···N bonds which decreases down the group.     

SnCl2·2H2O-mediated Barbier-type allylation: A comparative evaluation of the catalytic performance of CuI and Pd(OAc)2

A systematic investigation has been carried out for the allylation of carbonyl compounds under SnCl₂·2H₂O-mediated Barbier-type conditions, using CuI and Pd(OAc)₂ as catalysts. Ketones, which are not reactive under the influence of CuI, however, could be activated by using Pd(OAc)₂ as a catalyst.     

Non-resonant microwave absorption studies of superconducting MgB2 and MgB2 + MgO

Non-resonant microwave absorption (NRMA) studies of superconducting MgB₂ and a sample containing ∼10% by weight of MgO in MgB₂ are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB₂ sample. A linear temperature dependence of the lower critical field H _c1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB₂ + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links. The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB₂ sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong pinning of flux lines. This hysteresis saturates a few degrees below T _c while in the MgB₂ + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning.     

Effect of Cathode and Anode Voltage on an Ion Sheath Thickness in a Magnetically Confined Diffusion Plasma

This article reports about the ion sheath thickness variation occurring in front of a negatively biased plate immersed in the target plasma region of a double plasma device. The target plasma is produced due to the local ionization of neutral gas by the high energetic electrons coming from the source region (main discharge region). It is observed that for an increase in cathode voltage (filament bias voltage) in the source region, the ion flux into the plate increases. As a result, the sheath at the plate contracts. Again, for an increase in source anode voltage (magnetic cage bias), the ion flux to the plate decreases. As a result, the sheath expands at the plate. The ion sheath formed at the separation grid of the device is found to expand for an increase in cathode voltage and it contracts for an increase in the anode voltage of the main discharge region. One important observation is that the applied anode bias can control the Bohm speed of the ions towards the separation grid. Furthermore, it is observed that the ion current collected by the separation grid is independent of changes in plasma density in the diffusion region but is highly dependent on the source plasma parameters. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Iodine as an extremely powerful catalyst for the acetylation of alcohols under solvent-free conditions

Iodine was found to promote quantitative acetylation of alcohols in a very short time with an equimolar amount of acetic anhydride under solvent-free conditions at room temperature.     

The Performance of an Electrorheological Fluid in Dynamic Squeeze Flow: The Influence of Solid Phase Size

This paper is concerned with an experimental investigation of a comparison of the rheological performance of an ER fluid, consisting of a carrier with a range of solid phase sizes, in oscillatory squeeze-flow under DC conditions. The fluid is sandwiched between two parallel plane electrodes, the upper one stationary and the lower one oscillating normal to its plane. It is seen that the dynamic performance of the fluid, in terms of the capacity for the transmission of imposed forces across the fluid, is highly dependent on the size of the dispersed solid phase and has an optimum value which is dependent on the mean value of the interelectrode gap. In addition the paper includes some measurements of the current through the fluid which may help to shed some further light on the mechanism of the ER effect. Finally the implications of the results to vibration control are discussed. Copyright 1999 Academic Press.