3,4-dimethylphenyl benzoate

In the title compound, C15H14O2, the terminal rings form a dihedral angle of 52.39(4)°. The mean plane of the central ester group [r.m.s. deviation = 0.0488Å] is twisted away from the benzene and phenyl rings by 60.10(4) and 8.67(9)°, respectively. In the crystal, molecules are linked by weak C - HO hydrogen bonds, forming C(6) chains which run along [100]

Sodium-mediated magnesiation of thiophene and tetrahydrothiophene : structural contrasts with furan and tetrahydrofuran

Sulfur-containing heterocycles are currently attracting agreat deal of interest in several diverse fields. For instance, substituted tetrahydrothiophenes have received considerable attention due to their extremely wide-ranging chemical and biological applications.These include their use as potent a-glucosidase inhibitors, as an inhibitor of copper amine oxidases and as selective A3 agonists and antagonists. In addition, they have been utilised in chemical transformations, such as catalytic asymmetric epoxidation, catalytic intramolecular cyclopropanation, and asymmetric metal catalysis hydrogenation. From a nanochemical perspective,the adsorption chemistries and physical propertiesof various thiophenes and tetrahydrothiophenes on gold surfaces have recently come to the fore.[7] Polythiophenes are also key compounds in modern materials research, currently utilised in, for example, the fabrication of semi-conducting, fluorescent, and electronic and optoelectronic materials.[8]In this work, metallation (exchange of a hydrogen atom with a metal atom) of the parent heterocycles, tetrahydrothiophene (THT) and thiophene is considered. Metallation is one of the most fundamental reactions in modern day synthesis and is a key tool in the preparation of functionalised aromaticand heterocyclic compounds. It is usually achieved bythe utilisation of commercially accessible organolithiums (or lithium amides); however, these reactions do have theirdrawbacks, including the intolerance of certain functionalgroups, the need for cryoscopic temperatures and the inadvertent reactivity with polar reaction solvents

Numerical modelling of the sound absorption spectra for bottleneck dominated porous metallic structures

Numerical simulations are used to test the ability of several common equivalent fluid models to predict the sound absorption behaviour in porous metals with “bottleneck” type structures. Of these models, Wilson's relaxation model was found to be an excellent and overall best fit for multiple sources of experimental acoustic absorption data. Simulations, incorporating Wilson's model, were used to highlight the relative importance of key geometrical features of bottleneck structures on the normal incidence sound absorption spectrum. Simulations revealed significant improvements in absorption behaviour would be achieved, over a “benchmark” structure from the literature, by maximising the porosity (0.8) and targeting a permeability in the range of 4.0 × 10 −10 m 2 . Such a modelling approach should provide a valuable tool in the optimisation of sound absorption performance and structural integrity, to meet application-specific requirements, for a genre of porous materials that offer a unique combination of acoustic absorption and load bearing capability

Investigation of macrocyclisation routes to 1,4,7-triazacyclononanes : efficient syntheses from 1,2-ditosylamides

Two routes to the synthesis of a cyclohexyl-fused 1,4,7-triazacyclononane involving macrocyclisations of tosamides have been investigated. In the first approach, using a classic Richman-Atkins-type cyclisation of a cyclohexyl-substituted 1,4,7-tritosamide with ethylene glycol ditosylate, afforded the cyclohexyl-fused 1,4,7-triazacyclononane in 5.86% overall yield in four steps. The second, more concise, approach involving the macrocyclisation of trans-cyclohexane-1,2-ditosamide with the tritosyl derivative of diethanolamine initially gave poor yields (< 25%). The well-documented problems with efficiencies in macrocyclisations using 1,2-ditosamides led to the use of a wider range of 1,2-ditosamides including ethane-1,2-ditosamide and propane-1,2-ditosamide. These extended studies led to the development of an efficient macrocyclisation protocol using lithium hydride. This new method afforded 1,4,7-tritosyl-1,4,7-triazacyclononanes in good yield (57-90%) from 1,2-ditosamides in a single step. These efficient methods were then applied to the preparation of a chiral cyclohexyl-fused 1,4,7-tritosyl-1,4,7-triazacyclononane (65-70%). This key chiral intermediate was then converted into a copper(II) complex following detosylation and N-methylation. The resulting chiral copper(II) complex catalysed the aziridination of styrene but it did so in a racemic fashion

Oxidative Addition of Aryl Electrophiles to a Prototypical Nickel(0) Complex: Mechanism and Structure/Reactivity Relationships

Detailed kinetic studies of the reaction of a model Ni-0 complex with a range of aryl electrophiles have been conducted. The reactions proceed via a fast ligand exchange pre-equilibrium, followed by oxidative addition to produce either [(NiX)-X-I(dppf)] (and biaryl) or [Ni-II(Ar)X(dppf)]; the ortho substituent of the aryl halide determines selectivity between these possibilities. A reactivity scale is presented in which a range of substrates is quantitatively ranked in order of the rate at which they undergo oxidative addition. The rate of oxidative addition is loosely correlated to conversion in prototypical cross-coupling reactions. Substrates that lead to Ni-I products in kinetic experiments conditions. produce more homocoupling products under catalytic conditions

A comparison of the manufacture and mechanical performance of porous aluminium and aluminium syntactic foams made by vacuum-assisted casting

This paper compares key aspects of the manufacture and mechanical performance of porous Al, made by replication using salt beads, and structurally similar syntactic metal foams, made by replacing the salt with porous, expanded glass particles. Despite significant increases in stiffness, strength and energy absorbed, power law relationships between properties and relative density demonstrate that adding expanded glass particles is a less efficient route to increasing performance than increasing the metal fraction. That said, merit indices do indicate that 20% savings in mass are possible for stiff beams by substituting aluminium with syntactic metal foams. The manufacturing process for syntactic metal foams is shown to be simpler, driven by the lower thermal mass of the expanded glass particles and no requirement to dissolve a space holder from the structure. The balance of good performance and good manufacturability demonstrated herein, coupled with predicted low costs for raw material and manufacturing, highlights the scope for syntactic metal foams containing weak expanded glass particles to be researched and developed more widely

Compression moulding and injection over moulding of porous PEEK components

A simple and adaptable process for the production of porous PEEK has been demonstrated herein, which uses compression moulding to infiltrate molten PEEK into of a packed bed of salt beads. The process has the capacity to vary the pore size and porosity within the range suitable for materials to replace bone, but compressive testing showed the stiffness to be well below the target to match trabecular bone. This issue was addressed by creating a hybrid structure, integrating “pillars” of solid PEEK into the porous structure, by the injection over-moulding of compression moulded PEEK-salt inserts that contained drilled holes. Good bonding between the moulding and the insert was demonstrated and it was found that as little as 35 mm2 of support, in the form of PEEK “pillars” was required to achieve the target performance

Assessing the potential for multi-functional “hybrid” porous Al-phase change material structures

This study reports the potential for porous aluminium structures, containing porosity in the region of 50–80%, to provide enhancement of the rate of energy capture in phase change materials, whilst being capable of providing a basic mechanical function. The energy stored and the time for thermal exchange between warm water (at 65 °C) and porous aluminium, pure PCM and an Al-PCM hybrid structure was measured. It was observed that the melting of the PCM within the hybrid structure can be greatly accelerated by the continuous, porous aluminium structure. The energy uptake per second was found to follow an approximately linear dependence on the thermal effusivity for the material. This knowledge was used to predict the potential for enhancement of the rate of energy capture, by varying the porosity in the structure, whilst also estimating the detriment to the energy storage density and the mechanical strength. Appreciating this trade off in performance and properties is vital to the design of multi-functional porous structures

The permeability of virtual macroporous structures generated by sphere packing models: comparison with analytical models

Realistic porous structures typical of those made by replication of packed beds of spherical particles have been produced by a novel modelling method. Fluid dynamics simulation of the permeability of these structures agrees well with experimental measurements and similar modelling of structures derived from X-ray tomographic images. By varying the model structures the “bottleneck” flow concept proposed by analytical models in the literature was substantiated, confirming the high dependence of permeability on the size of the windows connecting the pores but also highlighting the need for accurate determination of the connectivity of the pores for these models to be accurate

Pressure-assisted infiltration of molten metals into non-rigid, porous carbon fibre structures

Abstract Mercury intrusion porosimetry has been conducted on a range of non-rigid, porous carbon fibre structures. Comparison with data from gas pressure infiltration experiments in a molten Al-Si alloy shows it to be a useful tool in determining the pressure required to produce Al metal matrix composites with low levels of porosity. Whilst for non-rigid fibre preforms, as studied here, it is difficult to pin-point every aspect of the infiltration process, the method does give an indication of critical aspects of the infiltration behaviour. Preforms made from loose and spread tow can be fully infiltrated at relatively low pressures (12 bar) and although metal can fill the spaces between fibre bundles within textile-based preforms at low pressures, densely-packed bundles are only infiltrated at higher pressures, usually in excess of 50 bar. Mercury intrusion porosimetry could provide a valuable and simple tool in the design of fibre-reinforced metal matrix composites with optimised structures that are easy to manufacture