Oxidative cyclization of amidoximes and thiohydroximic acids: A facile and efficient strategy for accessing 3,5-disubstituted 1,2,4-oxadiazoles and 1,4,2-oxathiazoles

A facile and practical protocol has been developed for the synthesis of 3,5-disubstituted 1,2,4-oxadiazoles and 1,4,2-oxathiazoles through oxidative cyclization of amidoximes and thiohydroximic acids, respectively at room temperature. Use of mild reaction conditions, inexpensive reagents, broad substrate scope and good to excellent yield of the products are the salient features of this protocol.     

Bio-inspired oxidative phenolic coupling: Total synthesis of the diarylether heptanoid (±)-pterocarine

The diaryletherheptanoid natural product, pterocarine, is expeditiously synthesized using a bioinspired intramolecular oxidative phenolic coupling of acerogenin G. The cyclization precursor is prepared from a simple cinnamic acid derivative in three high yielding synthetic operations. The key oxidative coupling is inspired by biosynthetic hypotheses; however, the oxidative coupling proceeds with concomitant hydroxylation of the diphenyl ether motif.     

Pyrroles from TosMIC and substituted N-acyl-2,3-dihydro-4-pyridones: A short access to a 4-azaisoindole unit

We investigated the reactions of substituted N-acyl-2,3-dihydro-4-pyridones with TosMIC reagent under various basic conditions to generate novel pyrrole products. These products were then transformed to substituted azaisoindoles in a couple of steps.     

Aerobic oxidative dehydrogenation of N-heterocycles catalyzed by cobalt porphyrin

An efficient catalytic procedure has been developed for the aerobic oxidative dehydrogenation of N-heterocycles by cobalt porphyrin in the absence of any additives. The catalytic system could tolerate various 1,2,3,4-tetrahydroquinoline derivatives and some other N-heterocycles. The corresponding N-heteroaromatics could be obtained in 59–86% yields. The mechanism investigation suggested that the aerobic oxidative dehydrogenation might proceed with imine intermediate through radical paths.     

Gram scale,metal-free and selective aerobic oxidation of alcohol and alkyl benzenes using homogeneous recyclable TAIm[MnO4] oxidative ionic liquid under mild conditions: Microwave/ ultrasonic-assisted to carboxylic acid

A homogeneous catalyst-free system has been developed for the selective oxidation of alcohols and alkyl benzenes to the corresponding carbonyl compounds using a recyclable TAIm[MnO₄] oxidative ionic liquid. The reactions were performed in the presence of previously reported TAIm[MnO₄]/ TAIm[OH] ionic liquids and KMnO₄ at ambient temperature under solvent-free conditions. Benzyl alcohols were selectively transferred to benzaldehydes, while under ultrasonic or microwave irradiation, they oxidized to benzoic acid selectively and directly. Scalability of the process also studied at high scale. Also, the ionic liquid could be readily recycled from the aqueous mixture and reused for several consecutive times without any pre-treatment and loss of catalytic activity. In this work, the highly active and toxic KMnO₄ salt has been transformed into a mild recyclable oxidant reagent with high selectivity towards alcohol oxidation.     

Synthesis and characterization of new polymers derived from 2-methyl-m-phenylenediamine as an effective adsorbent for cationic dye removal

The oxidative polymerizations of 2-methyl-m-phenylenediamine were performed to synthesize PMPDIA-A and PMPDIA-B polymers by H₂O₂ (35% aqueous solution) oxidant in acid-catalyzed ethanol and basic aqueous medium. Furthermore, PMPDIA-E polymer of 2-methyl-m-phenylenediamine was enzymatically synthesized by HRP (horseradish peroxidase) enzyme and H₂O₂ (35% aqueous solution) in dioxane/0.1 M phosphate tampon solution (pH = 7) mixture. The structures of 2-methyl-m-phenylenediamine and polymers were confirmed by FT-IR, NMR and UV–Vis spectrometer measurements. Molecular weight distributions, surface morphologies, thermal and fluorescence properties of polymers were determined from GPC, SEM, TG-DTA, DSC and fluorescence spectra analyses, respectively. CV and UV–Vis analyses were performed to determine the HOMO–LUMO energy levels, electrochemical (E_g′) and optical (E_g) band gaps values of MPDIA, PMPDIA-E, PMPDIA-A and PMPDIA-B. The electrochemical and optical band gaps values of polymers were lower than MPDIA, because of their polyconjugated structures. According to GPC measurements of polymers, the weight average molecular weights were between 5400 and 10400 Da. The fluorescence quantum yield of PMPDIA-E was calculated to be 9.15% in DMSO solution. The adsorption of methylene blue (MB) from aqueous solution on PMPDIA-B was studied. Adsorption isotherms and equilibrium adsorption capacities were determined by the fitting of the experimental data to two well-known isotherm models: Langmuir and Freundlich.     

The thermal stability of highly filled high-density polyethylene quaternary composites: Interactive effects and improved measures

A range of formulations — consisting of high-density polyethylene, surface-coated calcium carbonate, masterbatched carbon black and a stabiliser package — were compared in terms of their thermal stability through the use of several techniques and measures. Notably, calcium carbonate loadings of up to 60 wt% were investigated. The formulations were designed to be I- and D-optimal, based on a quadratic Scheffé polynomial model. Novel and established measures for the thermal stability of the materials were compared, based on data generated using techniques for the determination of oxidative induction time and for studies by time-sweep oscillatory rheometry. For ease of comparison, all tests were performed in air. Fourier-transform infrared spectroscopy was performed on the materials subjected to time-sweep oscillatory rheometry, to ascertain the locality and modes of degradation. Variable effects were found, depending on the technique used. Broadly, strong primary effects were found: positive in the cases of the carbon black and stabiliser pack, negative in the case of calcium carbonate. The latter, however, was offset by the highly synergistic interaction of calcium carbonate with the stabiliser pack. Time-sweep oscillatory rheometry was shown to be a promising method, with it yielding high-quality, comparable results when interpreted using a novel measure.