Synergism of ultrasound and solid acids in intensification of Friedel-Crafts acylation of 2-methoxynaphthalene with acetic anhydride

The Friedel-Crafts acylation of 2-methoxynaphthol is generally carried out by using highly polluting acids such as HF, AlCl(3), BF(3) which are used in more than stoichiometric quantities and are neutralized at the end creating large quantities of waste, corrosion problems and hazard. This paper discusses the use of acid treated clays such as K-10 and Filtrol-24 and cation exchange resins such as Amberlyst-36, Amberlyst-15 and Indion-130 as catalysts at 25 degrees C which have different acid strengths and pore size distributions. The activities were in the following order:Amberlyst-36>Indion-130>Amberlyst-15>K-10clay>Filtrol-24.In the presence of ultrasound, the activities were found to increase by more than a factor of 3 in the case of large porous resins than the clays. The selectivity to 1-acyl-2-methoxynaphthalene was found to remain the same. Utrasonics did not promote isomerisation or direct conversion to 6-acyl-2-methoxynaphthalene.     

Plane Symmetric Viscous Fluid Cosmological Models with Varying <Emphasis Type="Italic">Λ</Emphasis>-Term

Plane symmetric viscous fluid cosmological models of the universe with a variable cosmological term are investigated. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density whereas the coefficient of shear viscosity is to be proportional to rate of expansion in the model. We have also obtained a special model in which the shear viscosity is assumed to be zero. The cosmological constant Λ is found to be a decreasing function of time and a positive which is supported by results from recent supernovae Ia observations. Some physical and geometric properties of the models are also discussed.     

Stimulated Brillouin scattering in magnetized diffusive semiconductor plasmas

Using the hydrodynamical model and following the coupled mode approach, detailed analytical investigation of stimulated Brillouin scattering is performed in an electrostrictive semiconductor. The total induced current density including diffusion current density and the effective Brillouin susceptibility are obtained under off-resonant laser irradiation. The analysis deals with the qualitative behaviour of the Brillouin gain and transmitted intensity with respect to excess doping concentration and magnetic field. Efforts are directed towards optimizing the doping level and magnetic field to achieve maximum Brillouin gain at pump intensities far below the optical damage threshold level. It is found that by immersing a moderately doped semiconductor in a sufficiently strong magnetic field in transverse direction, one can achieve resonant enhancement of Brillouin gain provided the generated acoustic mode lies in the dispersionless regime.     

Magnetoelectric characterization of xNi0.75Co0.25Fe2O4-(1−x)BiFeO3 nanocomposites

Magnetoelectric (ME) nanocomposites containing Ni_0.75Co_0.25Fe₂O₄-BiFeO₃ phases were prepared by citrate sol-gel process. X-ray diffraction (XRD) analysis showed phase formation of xNi_0.75Co_0.25Fe₂O₄-(1−x)BiFeO₃ (x=0.1, 0.2, 0.3 and 0.4) composites on heating at 700 °C. Transmission electron microscopy revealed the formation of powders of nano order size and the crystal size was found to vary from 30 to 85 nm. Dispersion in dielectric constant (ε) and dielectric loss (tan δ) in the low-frequency range have been observed. It is seen that nanocomposites exhibit strong magnetic properties and a large ME effect. On increasing Ni_0.75Co_0.25Fe₂O₄ contents in the nanocomposites, the saturation magnetization (M_S) and coercivity (H_C) increased after annealing at 700 °C. The large ME output in the nanocomposites exhibits strong dependence on magnetic bias and magnetic field frequency. The large value of ME output can be attributed to small grain size of ferrite phase of nanocomposite being prepared by citrate precursor process.     

Hopping type of conduction in (Na0.5Bi0.5)ZrO3 ceramic

Polycrystalline sample with (Na_0.5Bi_0.5)ZrO₃ (NBZ) stoichiometry was prepared using a high-temperature solid-state reaction technique. X-ray diffraction (XRD) analyses indicate the formation of a single-phase perovskite-type orthorhombic structure. AC impedance plot is used as tool to analyse the electrical behaviour of the sample as a function of temperature at different frequency. The AC impedance studies revealed the presence of grain boundary effect and evidence of a negative temperature coefficient of resistance (NTCR) character. Pseudo Cole-Cole and complex electric modulus analyses indicated non-Debye-type dielectric relaxation. The AC conductivity obeys the universal power law. The pair approximation type correlated barrier hopping (CBH) model explains the universal behaviour of the s exponent. The apparent activation energy to the conduction process and minimum hopping distance are discussed.     

Total synthesis of cryptophycin-24 (arenastatin A) via Prins cyclization

A stereoselective synthesis of fragment A of cryptophycin is achieved utilizing the versatile Prins cyclization. Subsequently, the total synthesis of cryptophycin-24 (arenastatin A) has been accomplished by coupling it with the depsipeptide subunit.     

Triflic acid-promoted aza-Prins-Ritter reaction sequence: a novel synthesis of 4-amidopiperidine derivatives

4-Amidopiperidine derivatives have been prepared for the first time in good yields and with high selectivity by means of aza-Prins-Ritter reaction sequence using 1.2 equiv of triflic acid under mild reaction conditions.     

Charge stabilization via electron exchange: excited charge separation in symmetric,central triphenylamine derived,dimethylaminophenyl–tetracyanobutadiene donor–acceptor conjugates

Photoinduced charge separation in donor–acceptor conjugates plays a pivotal role in technology breakthroughs, especially in the areas of efficient conversion of solar energy into electrical energy and fuels. Extending the lifetime of the charge separated species is a necessity for their practical utilization, and this is often achieved by following the mechanism of natural photosynthesis where the process of electron/hole migration occurs distantly separating the radical ion pairs. Here, we hypothesize and demonstrate a new mechanism to stabilize the charge separated states via the process of electron exchange among the different acceptor entities in multimodular donor–acceptor conjugates. For this, star-shaped, central triphenylamine derived, dimethylamine–tetracyanobutadiene conjugates have been newly designed and characterized. Electron exchange was witnessed upon electroreduction in conjugates having multiple numbers of electron acceptors. Using ultrafast spectroscopy, the occurrence of excited state charge separation, and the effect of electron exchange in prolonging the lifetime of charge separated states in the conjugates having multiple acceptors have been successfully demonstrated. This work constitutes the first example of stabilizing charge-separated states via the process of electron exchange.

The significance of electron exchange in stabilizing the charge-separated state is revealed in multi-modular donor–acceptor conjugates.