Dialumenes – aryl vs. silyl stabilisation for small molecule activation and catalysis

Main group multiple bonds have proven their ability to act as transition metal mimics in the last few decades. However, catalytic application of these species is still in its infancy. Herein we report the second neutral NHC-stabilised dialumene species by use of a supporting aryl ligand (3). Different to the trans-planar silyl-substituted dialumene (3Si), compound 3 features a trans-bent and twisted geometry. The differences between the two dialumenes are explored computationally (using B3LYP-D3/6-311G(d)) as well as experimentally. A high influence of the ligand''s steric demand on the structural motif is revealed, giving rise to enhanced reactivity of 3 enabled by a higher flexibility in addition to different polarisation of the aluminium centres. As such, facile activation of dihydrogen is now achievable. The influence of ligand choice is further implicated in two different catalytic reactions; not only is the aryl-stabilised dialumene more catalytically active but the resulting product distributions also differ, thus indicating the likelihood of alternate mechanisms simply through a change of supporting ligand.

Ligand controlled reactivity: a trans-bent and twisted geometry enables dihydrogen activation and enhanced catalytic activity for NHC-stabilised dialumenes.     

Gas chromatographic study of the urinary codeine-to-morphine ratios in controlled codeine consumption and in mass screening for opiate drugs

The urinary codeine-to-morphine ratios in fifteen volunteers administered codeine tablets at intervals were studied by gas chromatography (GC) and compared with one month's GC results for enzyme multiplied immunoassay technique (EMIT)-screened urine specimens in a mass-screening programme for abuse of opiate drugs, particularly heroin. It appears that when M less than 2 and C/M greater than 0 or when M greater than 2 and C/M greater than 0.5, where C and M are codeine and morphine concentrations in micrograms per 10 ml of urine, codeine consumption has to be presumed.     

Sunlight assisted solvent free synthesis of tert-butylperesters

Abstract

A green and efficient methodology has been developed for the direct conversion of aryl aldehydes to the corresponding tert-butyl peresters. The reaction has been carried out in absence of any solvent and the sunlight is used as the green source of energy. In this reaction tetrabutylammonium iodide (TBAI) acts as the mild organo catalyst and tert-butyl hydroperoxide (TBHP) serve as the source of tert-butyl group.     

A water soluble nanostructured platinum (0) metal catalyst from platinum carbonyl molecular clusters: Synthesis, characterization and application in the selective hydrogenations of olefins, ketones and aldehydes

High nuclearity platinum carbonyl cluster anions (Chini's clusters) have been used as precursors to prepare a platinum nanocatalyst. The ionic polyelectrolyte poly(diallyldimethylammonium chloride) has been used as the support material for anchoring [Pt₃₀(CO)₆₀]²⁻ via ion-pairing and subsequent stabilization of the nanoparticles. The polymer-supported material has been studied by spectroscopy (NIR, ¹³C NMR, and IR) and TEM before and after its use as a water soluble hydrogenation catalyst. The nanocatalyst is found to be effective for the chemoselective hydrogenation of olefinic, aldehydic and ketonic double bonds. For most of the substrates isolation of the product and reuse of the catalyst are extremely easy due to the automatic phase separation of the products from the catalyst. The spectral features of the fresh catalyst show retention of the carbonyl ligands and molecular identity of the parent cluster, but after use the carbonyl ligands appear to be lost. TEM of the supported material before and after use as a catalyst shows the presence of platinum nanoparticles with majority (≥70%) of the particles in the range of 2–6 nm. Smaller particles are dominant in the used catalyst and this observation is rationalized on the basis of the known reactivity of Chini's clusters with dihydrogen.     

Solid-state diphotocyclization of iso- and terephthalaldehydes via dihalogen substitution

The supramolecular nonbonded C-H...X interactions between formyl hydrogens and ortho-halogen atoms (Br/Cl) have been exploited to achieve conformational control in the solid state of dimethyl-substituted iso- and terephthaladehydes (1-3) for unprecedented diphotocyclization. It is shown that the dihalogen substitution also contributes to the stability of the benzocyclobutenols relative to their precursor photoenols, so that the solid-state photolysis of dialdehydes 2b, 2c, and 3b leads to diphotocyclization to afford respectable yields of bis-benzocyclobutenols.     

A Jeffrey-fluid model of blood flow in tubes with stenosis

In this paper, we discuss the two-layered Jeffrey-fluid model with mild stenosis in narrow tubes. The blood flow in narrow arteries is treated as a two-fluid model with the suspension of erythrocytes, leukocytes, etc., as a Jeffrey fluid, which is a non-Newtonian fluid, in the core region and plasma, a Newtonian fluid, in the peripheral region. An analytical solution has been obtained for the velocity in the core and peripheral region, volume flow rate, resistance to flow, and wall-shear stress. The effect of Jeffrey-fluid parameters, like the height of stenosis, viscosity, etc., on volume flow rate, resistance to flow (impedance), and wall-shear stress has been discussed graphically. Through the present study, it is found that the wall-shear stress and resistance to flow increases with the increase in height of stenosis and decreases with the increase in the ratio of relaxation time. It is also found that the velocity decreases with an increase in stenosis height in both the core and the peripheral region. A previous result has been also verified.     

Sorptive elimination of fluoride from contaminated groundwater in a fixed bed column: A kinetic model validation based study

The current investigation involves a continuous adsorption experiment in a packed bed column for the sorptive elucidation of fluoride from contaminated groundwater using an activated soil-clay mixture. Through the combination of naturally accessible laterite soil with silica enriched clay (3:1 ratio), a low-cost Al–Si heterogeneous material has been developed. Following detailed characterization, the developed materials were employed in a long-time column process to achieve a high degree of fluoride separation from real-world groundwater. In a packed bed column investigation, the effect of bed height, initial fluoride concentration, and flow rate on the breakthrough properties of the adsorption system were investigated. By using a non-linear regression equation, three model kinetics, such as the Thomas Model, Adams-Bohart Model, and Yoon-Nelson Model, were fitted to validate the column-based experimental data, by analysing the breakthrough curves profiles, and distinct kinetic parameters. The Bed Depth Service Time Analysis (BDST) model was tested to express the effect of bed height on breakthrough curves, as well as to predict the time for breakthrough, and material depletion under optimal conditions. The Thomas and Yoon-Nelson models were identified to be the most appropriate ones for describing the entire breakthrough curve, whereas the Adams-Bohart model was only utilised to predict the first half of the dynamic process. With correlation coefficients (R²) 0.96, the experimental results were well suited to Thomas, Yoon-Nelson, and Adams-Bohart models. Finally, regeneration assessment was carried out where even after four cycles of operation, regenerated adsorbent showed a rejection efficacy of 78% to fluoride that proves the viability of the material and methodology.