Transformations of pyridiniums derived from amino-alcohols and from diamines : Novel ring closures

Pyridiniums derived from amino alcohols cyclise to ethers or rearrange to aldehydes on heating. Monopyridiniums from diamines can be acylated or converted into ureas or thioureas: these products cyclise on heating in solution to give dihydro-thiazoles, -4H-thiazines, -oxazoles, -4H-oxazines, or tetrahydro-3H-thiazepines.     

Synthesis of benzophenone tetracarboxylic dianhydride and pyromellitic dianhydride incorporated biscitraconimides and their thermal polymerization

Biscitraconimides incorporated with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) were synthesised. Their curing behavior as well as thermal stabilities were investigated. The intermediate amic acids were prepared by the reaction of 4-amino 4′-citraconamic acid diphenyl sulphone, 4-amino 4′-citraconamic acid diphenyl ether, and 12-amino 1-citraconamic acid dodecane with BTDA and PMDA, respectively. Six amic acids formed were then imidized by cyclocondensation with acetic anhydride. The imide monomers were obtained and these were cured at 225–240°C. The thermal stabilities of the polymers so formed were investigated and compared. © 1996 John Wiley & Sons, Inc.     

Raman and DFT study of static,dynamic interactions and isotope effect in pyridazine + H2O/D2O systems

Polarized Raman and density functional theory (DFT) approach have been applied to study the static and dynamic properties of pyridazine (PRD) in H₂O(W) and D₂O(D) environment. The possible hydrogen bonded (HB) complexes of PRD with H₂O in gas phase and in the water solvation (using IEF-PCM and Onsager models) have been calculated using a B3LYP functional and 6-31+G(d,p)/6-311++G(d,p) basis sets. The static interaction in the PRD + H₂O complex leads to a blue shift in all the Raman modes of PRD and red shift in the O–H modes of water. The IEF-PCM solvation model gives the Raman wavenumbers closest to the experimental values. Raman spectra of ～962 and 1061 cm^?1 mode of PRD in the mixture of PRD + H₂O and PRD + D₂O at different mole fractions of PRD (x) have been measured. A difference in the wavenumber shift of the two modes of PRD is observed experimentally when PRD is diluted with H₂O and D₂O. The wavenumber shift at maximum dilution (x = 0.1), however, takes the same value in both H₂O and D₂O. In view of the similar chemical properties of H₂O and D₂O, the difference in the trend of the wavenumber shift is not trivial. It has been explained on the basis of relative values of dipole moments of H₂O, D₂O, and conjugated molecules of PRD with H₂O/D₂O calculated theoretically and the role of larger diffusive property of H₂O compared to D₂O. The dynamical process in the mixture of PRD+ H₂O/D₂O is discussed by studying the variation of the linewidth with concentration. A theoretical model, which is based on the fact that the concentration in microscopic volume fluctuates, fits the experimental results nicely.     

On the use of the dual-process Langmuir model for correlating unary equilibria and predicting mixed-gas adsorption equilibria

A new model has been developed for predicting mixed-gas adsorption equilibria from multicomponent gas mixtures based on the dual-process Langmuir (DPL) formulation. It predicts ideal, nonideal, and azeotropic adsorbed solution behavior from a knowledge of only single-component adsorption isotherms and the assertion that each binary pair in the gas mixture correlates in either a perfect positive (PP) or perfect negative (PN) fashion on each of the two Langmuir sites. The strictly PP and strictly PN formulations thus provide a simple means for determining distinct and absolute bounds of the behavior of each binary pair, and the PP or PN behavior can be confirmed by comparing predictions to binary experimental adsorption equilibria or from intuitive knowledge of binary pairwise adsorbate-adsorbent interactions. The extension to ternary and higher-order systems is straightforward on the basis of the pairwise additivity of the binary adsorbent-adsorbate interactions and two rules that logically restrict the combinations of PP and PN behaviors between binary pairs in a multicomponent system. Many ideal and nonideal binary systems and two ternary systems were tested against the DPL model. Each binary adsorbate-adsorbent pair exhibited either PP or PN behavior but nothing in between. This binary information was used successfully to predict ternary adsorption equilibria based on binary pairwise additivity. Overall, predictions from the DPL model were comparable to or significantly better than those from other models in the literature, revealing that its correlative and predictive powers are universally applicable. Because it is loading-explicit, simple to use, and also accurate, the DPL model may be one of the best equilibrium models to use in gas-phase adsorption process simulation.     

Cyclohexanol dehydrogenation over Cu-loaded TiO2 photocatalyst under solar illumination

Abstract  

The liquid-phase selective dehydrogenation of cyclohexanol has been investigated using two classes of catalyst containing either Cu₂O or CuO on TiO₂ under solar light in deaerated conditions at room temperature using acetonitrile medium in a batch reactor. The effect on dehydrogenation of three conditions, cyclohexanol concentration, copper loading on TiO₂, and amount of catalyst, were investigated. The maximum yield of cyclohexanone obtained was 40%. The catalysts were characterized by XRD, UV–DRS, TEM, SEM–EDAX, and XPS. It was found that 1% (w/w) Cu₂O/TiO₂ was 100% selective for photocatalytic dehydrogenation of cyclohexanol.     

BCN: A Graphene Analogue with Remarkable Adsorptive Properties

A new analogue of graphene containing boron, carbon and nitrogen (BCN) has been obtained by the reaction of high‐surface‐area activated charcoal with a mixture of boric acid and urea at 900 °C. X‐ray photoelectron spectroscopy and electron energy‐loss spectroscopy reveal the composition to be close to BCN. The X‐ray diffraction pattern, high‐resolution electron microscopy images and Raman spectrum indicate the presence of graphite‐type layers with low sheet‐to‐sheet registry. Atomic force microscopy reveals the sample to consist of two to three layers of BCN, as in a few‐layer graphene. BCN exhibits more electrical resistivity than graphene, but weaker magnetic features. BCN exhibits a surface area of 2911 m² g^?1, which is the highest value known for a B_xC_yN_z composition. It exhibits high propensity for adsorbing CO₂ (≈100 wt %) at 195 K and a hydrogen uptake of 2.6 wt % at 77 K. A first‐principles pseudopotential‐based DFT study shows the stable structure to consist of BN₃ and NB₃ motifs. The calculations also suggest the strongest CO₂ adsorption to occur with a binding energy of 3.7 kJ mol^?1 compared with 2.0 kJ mol^?1 on graphene.     

Quantum tunneling and back reaction

We give a correction to the tunneling probability by taking into account the back reaction effect to the metric of the black hole spacetime. We then show how this gives rise to the modifications in the semiclassical black hole entropy and Hawking temperature. Finally, we reproduce the familiar logarithmic correction to the Bekenstein–Hawking area law.     

Shower age in correlation with zenith angle

The variation of lateral shower age parameter with zenith angle for different shower size ranges is studied. The observed variation is in agreement with the electron-photon cascade theory and with the other EAS observations. It is found that up to zenith angle 30°, shower ‘age’ is practically independent of zenith angle. So it is difficult to correlate the reported high ‘age’ value of the excess showers from the direction of plausible point sources with zenith angle. The change in the value of shower age with atmospheric depth is studied and is found to be consistent with the prediction of cascade theory and simulation results. From the study of the variation of shower age with shower size for two different zenith angle intervals it is found that the shower age decreases with size but the rate of change of shower age decreases at higher sizes.     

Effect of incident shock wave strength on the decay of Richtmyer–Meshkov instability-introduced perturbations in the refracted shock wave

The effect of incident shock wave strength on the decay of interface introduced perturbations in the refracted shock wave was studied by performing 20 different simulations with varying incident shock wave Mach numbers (M ~ 1.1? 3.5). The analysis showed that the amplitude decay can be represented as a power law model shown in Eq.7, where A is the average amplitude of perturbations (cm), B is the base constant (cm^?(E?1), S is the distance travelled by the refracted shockwave (cm), and E is the power constant. The proposed model fits the data well for low incident Mach numbers, while at higher mach numbers the presence of large and irregular late time oscillations of the perturbation amplitude makes it hard for the power law to fit as effectively. When the coefficients from the power law decay model are plotted versus Mach number, a distinct transition region can be seen. This region is likely to result from the transition of the post-shock heavy gas velocity from subsonic to supersonic range in the lab frame. This region separates the data into a high and low Mach number region. Correlations for the power law coefficients to the incident shock Mach number are reported for the high and low Mach number regions. It is shown that perturbations in the refracted shock wave persist even at late times for high incident Mach numbers.