Synthetic studies towards the novel diterpenoid rameswaralide: RCM mediated acquisition of the tricyclic core

A synthetic approach towards the novel anti-inflammatory diterpenoid rameswaralide from the cis-Corey lactone involving a tandem RCM and Diels-Alder reaction has been conceived and endeavors so far have led to the acquisition of the BCD ring fragment of the natural product.     

Liquid chromatographic properties of aromatic sulfur heterocycles on a Pd(II)-containing stationary phase for petroleum analysis

Polycyclic aromatic sulfur heterocycles (PASHs) can show very poor reactivities in catalytic hydrodesulfurization processes in refineries, especially those in high-boiling fractions and distillation residues. An insight into the structural features of the most recalcitrant PASHs is essential for developing more efficient catalysts and improving refinery processes. The very high complexities of such mixtures necessitate fractionation of the samples into smaller subsets according to defined criteria. A stationary phase containing a palladium(II)-complex was previously shown to be efficient for separating PASHs in lighter petroleum fractions. Here we characterize this ligand exchange chromatographic phase using a large number of sulfur aromatic model compounds that were synthesized for the purpose. In general, compounds containing thiophene rings that are not condensed with other aromatic systems are weakly retained and elute in a first fraction with the polycyclic aromatic hydrocarbons. Thiophene rings condensed with other aromatic rings are more strongly retained and elute in a later fraction with a more polar eluent. If the sulfur is in a non-aromatic ring, the compound is irreversibly retained by the Pd(II) ions. Some steric effects are seen in compounds with alkyl or aryl substituents close to the sulfur atom but in general they do not interfere strongly with the complexation. Thus it seems possible to separate groups of aromatic sulfur compounds according to their complexation properties. For instance, such fractionated samples can be studied much more easily by mass spectrometric techniques.     

Rational design of thermogravimetric experiments to determine intrinsic char gasification kinetics

The Boudouard reaction is an important heterogeneous reaction that takes place inside the gasifier during char gasification. To evaluate the gasification performance of solid fuels, it is important to know the intrinsic rate of the Boudouard reaction of that particular fuel. Incorrect determination of this rate results in error when used for modelling or gasifier scaling purposes. The thermo-gravimetric analyser (TGA) is an instrument that is widely used for gasification studies, particularly to explore the intrinsic gasification kinetics of coal or biomass char in a controlled environment. As in a real gasifier environment, several experimental parameters in TGA experiments can influence the intrinsic reactivity of the sample char; however, this is rarely discussed in the literature. It is essential to carefully differentiate the physical effects from the pure chemical reaction and to consider their interactions to obtain reliable kinetic parameters. No systematic experimental procedures to minimize the effects of the rate-influencing parameters during TGA experiments are available in the literature. This article presents an analysis for this purpose and demonstrates the variation in the gasification rate when the experimental conditions are not properly optimized. A mathematical model is also presented to explain the possible diffusional interactions with chemical kinetics during un-optimized TGA experiments.     

Auto-correlation measurements and integral time scales in three-dimensional turbulent boundary layers

Auto-correlation, time and length scales of the three components of turbulence and power spectra in a three-dimensional turbulent boundary layer developing on a yawed flat plate have been obtained. The measurements indicate that close to the wall, in the region of turbulence production, there is a marked disparity among the time scales but as the outer edge of the boundary layer is approached, the scales become comparable to one another. Also, the behaviour of the length scales and the power spectra across the boundary layer is presented.Nomenclature Boundary layer thickness where Q/Q _e=0.995 - E _u(f) one dimensional frequency spectra - f frequency in Hz - k ₁ wave number defined as k ₁=2f/Q - L length scale defined as: time scale times local mean velocity - Q local mean velocity - Q _e free stream velocity - R _u, R _v, R _w Auto-correlation coefficients of u, v and w respectively as defined in equation (1) - T _u, T _v, T _w the time scales of u, v and w fluctuations as defined in equation (2) - delay time - u fluctuating velocity component in x-direction - v fluctuation velocity component in y-direction - w fluctuation velocity component in z-direction - x coordinate axis in the streamwise direction - y coordinate axis normal to the surface - z coordinate axis normal to the x-direction and parallel to the wall     

Phenanthridine synthesis via [2+2+2] cyclotrimerization reactions

A concise synthesis of phenanthridines via a microwave-assisted [2+2+2] cyclotrimerization reaction has been developed.