β-Nitro derivatives of iron corrolates

Two different methods for the regioselective nitration of different meso-triarylcorroles leading to the corresponding β-substituted nitrocorrole iron complexes have been developed. A two-step procedure affords three Fe(III) nitrosyl products-the unsubstituted corrole, the 3-nitrocorrole, and the 3,17-dinitrocorrole. In contrast, a one-pot synthetic approach drives the reaction almost exclusively to formation of the iron nitrosyl 3,17-dinitrocorrole. Electron-releasing substituents on the meso-aryl groups of the triarylcorroles induce higher yields and longer reaction times than what is observed for the synthesis of similar triarylcorroles with electron-withdrawing functionalities, and these results can be confidently attributed to the facile formation and stabilization of an intermediate iron corrole π-cation radical. Electron-withdrawing substituents on the meso-aryl groups of triarylcorrole also seem to labilize the axial nitrosyl group which, in the case of the pentafluorophenylcorrole derivative, results in the direct formation of a disubstituted iron μ-oxo dimer complex. The influence of meso-aryl substituents on the progress and products of the nitration reaction was investigated. In addition, to elucidate the most important factors which influence the redox reactivity of these different iron nitrosyl complexes, selected compounds were examined by cyclic voltammetry and thin-layer UV-visible or FTIR spectroelectrochemistry in CH(2)Cl(2).     

Enantiopure synthesis of side chain-modified α-amino acids and 5-cis-alkylprolines

A short, concise synthesis of enantiopure, side chain-modified α-amino acids such as 4-oxo-L-norvaline, 6-oxo-L-homonorleucine, and 5-cis-alkyl prolines is described. Knoevenagel condensation of l-aminocarboxylate-derived β-ketoesters with aldehydes followed by reductive decarboxylation results in unnatural α-amino acids in good yield. A fluorescent amino acid is synthesized using a similar protocol. These studies show that aminocarboxylate-derived β-ketoesters are very useful intermediates and the method employed is both general and practical for the preparation of γ(δ)-oxo α-amino acids and alkylprolines.     

ZnO-beta zeolite mediated simple and efficient method for the one-pot synthesis of quinoxaline derivatives at room temperature

A rapid and an efficient one-pot method for the synthesis of quinoxalines catalysed by ZnO-beta zeolite at room temperature is described. This environmentally benign method provides several advantages over methods that are currently employed such as a simple work-up, mild reaction conditions, good to excellent yields, and a process to recover and reuse the catalyst for several cycles with consistent activity.      

Locating automated external defibrillators in a university community

Automated external defibrillators (AEDs) use smart technology to determine whether a victim of cardiac arrest requires defibrillation and will deliver a shock only if one is needed. These portable devices are becoming increasingly more available in such places as airports, shopping malls, and sports facilities. This article reports on a model for determining appropriate locations for AEDs in a university community. Additionally, we describe difficulties encountered when attempting to implement the results obtained from the model.     

Analytical application of poly[dibenzo-18-crown-6] for column chromatographic separation of Nd(III) from Ce(III), U(VI) and other elements

This research is dedicated to the study of analytical application of poly[dibenzo-18-crown-6] for separation of Nd(III) from possible lanthanides, actinides and other metal ions. A simple and efficient column chromatographic method has been developed using poly [dibenzo-18-crown-6] as stationary phase and hippuric acid as a counter ion. The capacity of crown polymer for Nd(III) was found to be 0.55 ± 0.01 mmol/g. Nd(III) was quantitatively separated from Ce(III), U(VI) and other elements in binary as well as multicomponent mixtures. Separation yields were good and reproducible (±2 %). This method has important application for separation of Nd(III) from Ce(III) rapidly and selectively.     

Brönsted acid hydrotrope combined catalysis in water: a green approach for the synthesis of indoloquinoxalines and bis-tetronic acids

The present work describes the applications of Brönsted acid hydrotrope combined catalyst (BAHC) as a mild, efficient and reusable catalyst for synthesis of indoloquinoxalines and bis-tetronic acids in water. Using BAHC, we synthesized many indoloquinoxaline derivatives from isatins and o-phenylene diamine using 10 mol% PTSA in 40% aqueous hydrotropic (NaPTS) solution at room temperature with 83–90% yields. On the other hand, the reaction of tetronic acid with the aldehydes/isatins forms bis-tetronic acids with 83–88% yields through Knoevengel condensation-Michael addition pathway in same BHAC. Moreover, the BAHC can be recycled upto 5th cycles with slight decrease in product yields. The extremely simple operational methodology, green solvent, ambient reaction conditions and high yields render this approach extremely appealing for the synthesis of different heterocyclic compounds.

     

Development of reliable analytical method for extraction and separation of thorium(IV) by Cyanex 272 in kerosene

A simple and selective spectrophotometric method has been developed for the extraction and separation of thorium(IV) from sodium salicylate media using Cyanex 272 in kerosene. Thorium(IV) was quantitatively extracted by 5 × 10⁻⁴ M Cyanex 272 in kerosene from 1 × 10⁻⁵M sodium salicylate medium. The extracted thorium(IV) was stripped out quantitatively from the organic phase with 4.0 M hydrochloric acid and determined spectrophotometrically with arsenazo(III) at 620 nm. The effect of concentrations of sodium salicylate, extractant, diluents, metal ion and strippants has been studied. Separation of thorium(IV) from other elements was achieved from binary as well as multicomponent mixtures such as uranium(VI), strontium(II), rubidium(I), cesium(I), potassium(I), Sodium(I), lithium(I), lead(II), barium(II), beryllium(II) etc. Using this method separation and determination of thorium(IV) in geological and real samples has been carried out. The method is simple, rapid and selective with good reproducibility (approximately ±2%).     

The onset of convection in a nanofluid saturated porous layer using Darcy model with cross diffusion

Linear and nonlinear stability analysis for the onset of convection in a horizontal layer of a porous medium saturated by a nanofluid is studied. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The modified Darcy equation that includes the time derivative term is used to model the momentum equation. In conjunction with the Brownian motion, the nanoparticle fraction becomes stratified, hence the viscosity and the conductivity are stratified. The nanofluid is assumed to be diluted and this enables the porous medium to be treated as a weakly heterogeneous medium with variation, in the vertical direction, of conductivity and viscosity. The critical Rayleigh number, wave number for stationary and oscillatory mode and frequency of oscillations are obtained analytically using linear theory and the non-linear analysis is made with minimal representation of the truncated Fourier series analysis involving only two terms. The effect of various parameters on the stationary and oscillatory convection is shown pictorially. We also study the effect of time on transient Nusselt number and Sherwood number which is found to be oscillatory when time is small. However, when time becomes very large both the transient Nusselt value and Sherwood value approaches to their steady state values.     

Correction to: Brönsted acid hydrotrope combined catalysis in water: a green approach for the synthesis of indoloquinoxalines and bis-tetronic acids

Research on Chemical Intermediates - A correction to this paper has been published: https://doi.org/10.1007/s11164-021-04495-7     

Chromatographic separation of uranium(VI) from other elements using L-valine and poly[dibenzo-18-crown-6]

A selective and effective column chromatographic separation method has been developed for uranium(VI) using poly[dibenzo-18-crown-6]. The separation was carried out in L-valine medium. The adsorption of uranium(VI) was quantitative from 1.0 × 10⁻⁴ to 1 × 10⁻¹ M of L-valine. Amongst various eluents 2.0–8.0 M hydrochloric acid, 1.0–4.0 M sulfuric acid, 1.0–5.0 M perchloric acid, 6.0–8.0 M hydrobromic acid and 5.0–6.0 M acetic acid were found to be efficient eluents for uranium(Vl). The capacity of poly[dibenzo-18-crown-6] for uranium(VI) was 0.25 ± 0.01 mmol/g of crown polymer. Uranium(VI) was separated from number of cations and anions in binary mixtures in which most of the cations and anions show a very high tolerance limit. The selective separation of uranium(VI) was carried out from multicomponent mixtures. The method was extended to determination of uranium(VI) in geological samples. The method is simple, rapid and selective with good reproducibility (approximately ∼2%).