Facile Conversion of Epoxides to Thiiranes with Ammonium Thiocyanate Catalyzed with Oxalic Acid

Epoxids are efficiently converted to the corresponding thiiranes by ammonium thiocyanate (NH 4 SCN) in the presence of catalytic amounts of oxalic acid with excellent isolated yields under mild and nonaqueous reaction conditions. This conversion performed under both conventional heating and microwave conditions. Distinct rate enhancement is observed under microwave irradiation.     

DFT Calculations of the Elimination Kinetics of Silacyclobutanes and its Methyl Derivatives in the Gas-Phase

Abstract

The gas-phase thermal decomposition kinetics of silacyclobutane (1), 1-methyl- silacyclobutane (2), and 1,1-dimethyl-1-silacyclobutane (3) has been theoretically studied at the B3LYP/6-311G**, B3PW91/6-311G**, and MPW1PW91/6-311G** levels. The B3LYP/6-311G** method was found to give a reasonable good agreement with the experimental kinetics and thermodynamic parameters. The decomposition reaction of compounds 1–3 yields ethylene and the corresponding silene. Based on the optimized ground state geometries using B3LYP/6-311G** method, the natural bond orbital (NBO) analysis of donor-acceptor (bonding–antibonding) interactions revealed that the perturbation energies (E₂) associated with the electronic delocalization from σ_Si1–C2 to σ*_C4–Si1 orbitals increase from compounds 1 to 3. The σ_Si1–C2→σ*_C4–Si1 resonance energies for compounds 1–3 are 1.17, 1.26, and 1.43 kcal/mol, respectively. Also, the decomposition process in these compounds is controlled by σ→σ* resonance energies. Moreover, the obtained order of energy barriers could be explained by the number of electron-releasing methyl groups substituted to the Si_sp2 atom. NBO analysis shows that the occupancies of σ_Si1–C2 bonds decrease for compounds 1–3 as 3 < 2 < 1, and the occupancies of σ*_Si1–C2 bonds increase in the opposite order (3 > 2 > 1). Moreover, these results can fairly explain the decrease of the energy barriers (ΔE_o) of the decomposition reaction of compounds 1 to 3. The calculated data demonstrate that in the decomposition process of the studied compounds, the polarization of the C₃–C₄ bond is the rate determining factor. Analysis of bond orders, NBO charges, bond indexes, synchronicity parameters, and IRC calculations indicate that these reactions are occurring through a concerted and asynchronous four-membered cyclic transition state type of mechanism.     

Quenching effect of l-tyrosine on peroxyoxalate chemiluminescence of berberine as the fluorophore

The present work deals with the first attempt to study the effect of l-tyrosine on the characteristics of the peroxyoxalate chemiluminescence. Berberine was applied as an efficient fluorophore. The investigated parameters include rise and fall rate constant for the chemiluminescence burst, theoretical and experimental maximum intensity, the time needed to reach maximum intensity and the total light yield emission, which is theoretically evaluated using the pooled intermediate model by a computerized non-linear least-squares curve fitting program (KINFIT). Furthermore, based on the observed quenching effect of tyrosine, the Stern–Volmer plot with K _Q value of 7.7 × 10⁴ M^?1 in the quencher concentration range 4 × 10^?6–5 × 10^?5 M. Moreover, this method is applied to determinate tyrosine in biological samples successfully.     

An Efficient One‐Pot Four‐Component Synthesis of Functionalized Imidazo[1,2‐a]pyridines

An efficient one‐pot four‐component protocol for the synthesis of imidazo[1,2‐a]pyridines was developed by condensing ethane‐1,2‐diamine ( 2 ), 1,1‐bis(methylthio)‐2‐nitroethene ( 1 ), aldehydes 3 , and activated methylene compounds in EtOH under reflux conditions (Tables 1–3). The features of this procedure are operational simplicity, good yields of products, in situ preparation of heterocyclic ketene aminals (HKA), and catalyst‐free conditions.     

溶胶-凝胶新方法合成介孔铁酸铜纳米粉体催化剂上CO低温氧化(英文)

Mesoporous CuFe2O4 solid solution nanopowders with high specific surface areas were synthesized by a novel, very simple and inexpensive sol-gel route using propylene oxide as gelation agent, and used as the catalyst in low temperature CO oxidation. The samples were characterized by X-ray diffraction, N2 adsorption-desorption, thermogravimetric/differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and temperature-programmed reduction. The results revealed that the samples have a nanocrystalline structure with crystals in the range of 10 to 25 nm, and that all the catalysts have mesoporous pores. The addition of Cu into iron oxide affected its structural and catalytic properties. The sample containing 15 mol% Cu showed the highest specific surface area and catalytic activity, and showed high catalytic stability in low temperature CO oxidation.     

Pertraction of methylene blue using a mixture of D2EHPA/M2EHPA and sesame oil as a liquid membrane

An experimental study on the pertraction of methylene blue (MB) through a supported liquid membrane (SLM) using a mixture of mono-(2-etylhexyl) ester of phosphoric acid (M2EHPA) and bis-(2-etylhexyl) ester of phosphoric acid (D2EHPA) and sesame oil as the liquid membrane (LM) was performed. Parameters affecting the pertraction of MB such as initial MB concentration, carrier concentration, feed phase pH, and stripping phase concentration were analyzed. Optimal experimental conditions for MB pertraction (permeability of 5.63 × 10^?6) were obtained after a 7 h separation with the MB concentration in the feed phase of 80 mg L^?1, D2EHPA/M2EHPA concentration in membrane phase of 40 vol. %, feed pH of 6, and acetic acid concentration in the stripping phase of 0.4 mol L^?1. Kinetics of transport and stability of the SLM system were also studied and the mass transfer coefficient for this system was evaluated. Scanning electron microscopy (SEM) was used to morphologically characterize the membrane surface.     

Palladium-catalyzed oxidative C–H bond coupling of indoles and benzaldehydes: a new approach to the synthesis of 3-benzoylindoles

A palladium-catalyzed dehydrogenative acylation of indoles using easily accessible aldehydes as the acyl source is described. This reaction provides a new approach for the synthesis of 3-acylindoles.     

A highly diastereoselective five-component synthesis of 1-(alkylimino)-5,5-dicyano-3a-aryloctahydro-3-oxacyclobuta[cd]pentalene-1a,2,5a,5b(2H,3aH)-tetracarboxylates

A novel one-pot, five-component synthesis of 1-(alkylimino)-5,5-dicyano-3a-aryloctahydro-3-oxacyclobuta[cd]pentalene-1a,2,5a,5b(2H,3aH)-tetracarboxylates is described. A mixture of phenacyl bromide, malononitrile, isocyanide, and two equivalents of a dialkyl acetylenedicarboxylate undergoes a novel 1:1:1:2 addition reaction at ambient temperature in absolute ethanol to produce diastereoselectively the title compounds in good yields.     

Introducing Organic Gas Steam-Liquid Extraction as a New Preconcentration Method for Benzene,Toluene, Ethylbenzene and Xylene Determination in Water Samples by Gas Chromatography-Flame Ionization Detection

Journal of Analytical Chemistry - In this study, for the first time, the organic gas steam-liquid extraction by a special hand-made cell was used as a simple and inexpensive preconcentration...     

Solid-Phase Microextraction of Phthalate Esters from Aqueous Media by Functionalized Carbon Nanotubes (Graphene Oxide Nanoribbons) and Determination by GC–FID

Multiwalled carbon nanotubes were exposed to hydrothermal treatment for obtaining graphene oxide nanoribbons (GONRs). The fabricated graphene oxide nanoribbons have been morphologically and compositionally characterized via FE-SEM, XRD, and FT-IR techniques. The as-synthesized GONRs have been used as sorbent phase for headspace solid-phase microextraction of phthalate esters (PEs) from aqueous solutions. In this regard, the GC–FID analysis route has been used for quantification of PEs. The new SPME fiber shows remarkable analytical figures of merit including broad dynamic linear ranges, low limits of detection, as well as good stability and reasonable relative standard deviations for evaluation of PEs. The linearity of the method for analysis of PEs including DnBP, DnPP, DEHP, DEHA, BBP, and DMP was between the range of 0.05–100, 0.05–100, 0.1–100, 0.1–100, 0.2–100, and 0.5–100 μg L^?1, respectively. The limits of detection (based on S/N?=?3) and correlation coefficients were found to be in the range of 0.02–0.2 μg L^?1 and 0.9907–0.9952, correspondingly. The prepared GONR-coated SPME fiber shows larger extraction yield in comparison to pristine MWNTs and commercial PDMS SPME fibers. Furthermore, real sample analysis showed that there is no significant matrix effect for evaluation of PEs from environmental water samples and proposed method could be used for evaluation and determination of PEs from aqueous samples in a precise and accurate manner. The existence of functional groups, π–π interactions, as well as hydrogen bonding between adsorbent phase and PE analytes could be the reason for observing such a high extraction yield.