Simple and Highly Efficient Catalytic Thiocyanation of Aromatic Compounds in Aqueous Media

Two simple, mild, and efficient procedures for the thiocyanation of N‐heterocycles, substituted anilines (electron‐rich and electron‐deficient), and N‐substituted aromatic amines at room temperature are reported (Table 3). The first uses H₂O₂ as pollution‐free oxidant and the second H₅IO₆; both with the reagent potassium thiocyanate in H₂O as solvent. These procedures provided the target thiocyanates after a short reaction time in good to excellent yields and high regioselectivity.     

Selectivity effects related to the diversity of active sites operating on nanostructured multifunctional catalysts

The goal of the present study was to gain a better understanding of the selectivity of processes over multifunctional catalysts exhibiting diversity of operating active sites. The concept is that the concurrent performance of different types of active sites may provoke effects on the process selectivity comparable to the effects resulting from the kinetic regularities and activation energies of the occurring reactions. Accordingly, in the kinetic model the authors introduce specific parameters reflecting the contribution of distinct types of active sites, facilitating different reaction routes. Reasons are adduced how suchlike parameters serve to account the impact of various reaction routes occurring on different types of sites. The suggested approach links the deactivation-caused selectivity changes to dissimilarities in the vulnerability of different types of active sites. This work relates the probabilities for action of different types of sites to the size of active-phase islands. Various reaction mechanism patterns are modeled to examine relevant selectivity effects.     

The first report on the synthesis of new hantzsch <Emphasis Type="Italic">N</Emphasis>-Ethyldimetyl Acetal-1,4-dihydropyridines with aldehyde synthon under microwave irradiation

A mixture of ethyl acethylenecarboxylate, various aryl aldehydes and aminoacetaldehyde dimethyl acetal in the presence of silica gel were converted to N-ethyldimethyl acetal-1,4-dihydropyridines using microwave irradiation with good yields.     

Studies of Carbon Dioxide Capture on Porous Chitosan Derivative

Chitosan was modified with 4-formyltriphenylamine to obtain a material with better surface morphology and adsorption profile. Surface morphology and Brunauer–Emmett–Teller (BET) analysis has proved that the chitosan derivative presents higher porosity. CO₂ adsorption analysis results reveal that the triphenyl amine chitosan derivative shows better adsorption than pure chitosan. The results revealed that this material may open new vistas in environmental and industrial applications for carbon dioxide capture, in order to help to reduce the adverse impact of large emissions of the greenhouse gas is the atmosphere.     

Highly Sensitive Electrochemical Hydrogen Peroxide Sensor Based on Iron Oxide‐Reduced Graphene Oxide‐Chitosan Modified with DNA‐Celestine Blue

The present study describes a novel and very sensitive electrochemical assay for determination of hydrogen peroxide (H₂O₂) based on synergistic effects of reduced graphene oxide‐ magnetic iron oxide nanocomposite (rGO‐Fe₃O₄) and celestine blue (CB) for electrochemical reduction of H₂O₂. rGO‐Fe₃O₄ nanocomposite was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X‐ray diffraction (XRD), electrochemical impedance spectroscopy and cyclic voltammetry. Chitosan (Chit) was used for immobilization of amino‐terminated single‐stranded DNA (ss‐DNA) molecules via a glutaraldehyde (GA) to the surface of rGO‐Fe₃O₄. The MTT (3‐(4,5‐Dim ethylt hiazol‐2‐yl)‐2,5‐diphenylt etrazolium bromide) results confirmed the biocompatibility of nanocomposite. Experimental parameters affecting the ss‐DNA molecules immobilization were optimized. Finally, by accumulation of the CB on the surface of the rGO‐Fe₃O₄‐Chit/ssDNA, very sensitive amperometric H₂O₂ sensor was fabricated. The electrocatalytic activity of the rGO‐Fe₃O₄‐Chit/DNA‐CB electrode toward H₂O₂ reduction was found to be very efficient, yielding very low detection limit (DL) of 42 nM and a sensitivity of 8.51 μA/μM. Result shows that complex matrices of the human serum samples did not interfere with the fabricated sensor. The developed sensor provided significant advantages in terms of low detection limit, high stability and good reproducibility for detection of H₂O₂ in comparison with recently reported electrochemical H₂O₂ sensors.     

Application of silica vanadic acid [SiO2-VO(OH)2] as a heterogeneous and recyclable catalyst for oxidative aromatization of Hantzsch 1,4-dihydropyridines at room temperature

A simple method for the oxidative aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines is described using hydrogen peroxide as green oxidant and silica vanadic acid as catalyst in acetonitrile at room temperature. The catalyst can be easily recovered and reused for 15 reaction cycles without considerable loss of activity.     

Porous chitosan–MnO2 nanohybrid: a green and biodegradable heterogeneous catalyst for aerobic oxidation of alkylarenes and alcohols

A porous chitosan–manganese dioxide (PC–MnO₂) nanohybrid was synthesized using an in situ reduction method, in which potassium permanganate solution and nanoporous chitosan acted as precursor and reducing agent. The chemical and structural properties of PC–MnO₂ were characterized using scanning and transmission electron microscopies, X‐ray diffraction, thermogravimetric analysis and Fourier transform infrared spectroscopy. Highly dispersed MnO₂ nanoparticles in a matrix of porous chitosan showed high catalytic activity for selective aerobic oxidation of alkylarenes and alcohols without using any bases or expensive oxidants. Short reaction time, ease of product separation by filtration and recyclability of the catalyst make it environmentally and economically favoured for the synthesis of versatile aldehydes and ketones. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhanced photocatalytic activities of ZnO thin films: a comparative study of hybrid semiconductor nanomaterials

Nanostructure single ZnO, SnO₂, In₂O₃ and composite ZnO/SnO₂, ZnO/In₂O₃ and ZnO/SnO₂/In₂O₃ films were prepared using sol?Cgel method. The obtained composite films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV?CVis spectroscopy. The photocatalytic activities of composite films were investigated using phenol (P), 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 4-aminophenol (4-AP) as a model organic compounds under UV light irradiation. Hybrid semiconductor thin films showed a higher photocatalytic activity than single component ZnO, SnO₂ and In₂O₃ films. The substituted phenols degrade faster than phenol. The ease of degradation of phenols is different for each catalyst and the order of catalytic efficiency is also different for each phenol. The use of multiple components offered a higher control of their properties by varying the composition of the materials and related parameters such as morphology and interface. It was also found that the photocatalytic degradation of phenolic compounds on the composite films and single films followed pseudo-first order kinetics.     

Tetrazoles as carboxylic acid isosteres: chemistry and biology

Tetrazoles are often used as metabolism-resistant isosteric replacements for carboxylic acids in SAR-driven medicinal chemistry analogue syntheses. Tetrazoles have not been found in nature; with rare exceptions, these compounds do not exhibit appreciable biological activity, but they are at the same time resistant to biological degradation. This property makes it possible to use tetrazoles as isosteric substituents of various functional groups in the development of biologically active substances. The tetrazole motif has been used in various drug pharmacophores as a suitable replacement of carboxylic acid moiety and different methods have been used for the synthesis of tetrazoles using different reaction conditions. This review tries to give a vivid look on the different synthetic methods, using catalysts or different reagents for the synthesis of tetrazoles. The biological importance of tetrazoles has also been highlighted.     

Catalytic Synthesis of 5‐Substituted Tetrazoles: Unexpected Reactions and Products

Tetrazoles are incredibly useful organic molecules with a wide range of applications from medicinal chemistry as carboxylic acid isosteres to high energy density materials in space research. In an effort to develop an easy protocol for the synthesis of tetrazoles from nitriles, we used nano‐Ag‐TiO₂ as an efficient heterogeneous catalyst for the reaction of various nitriles and sodium azide to afford 5‐substituted tetrazoles in excellent yields. By this method, a wide variety of aryl nitriles underwent [3 + 2] cycloaddition to afford tetrazoles in excellent yields. Further reaction of tetrazoles with ethylchloroacetate resulted in the formation of expected products, except for a bis‐tetrazole, which underwent ring opening and subsequent reaction to afford an unusual product. The bis‐tetrazole also formed an unusual polymeric sodium complex in aq. NaOH solution. X‐ray crystallography revealed a distorted octahedral geometry for the complex, which forms a three‐dimensional network of chains interlinked by bis‐tetrazole moieties through a network of H‐bonds.