Efficient access to novel hexahydro-chromene and tetrahydro-pyrano[2,3-d]pyrimidine-annulated benzo-δ-sultones via a domino Knöevenagel-hetero-Diels-Alder reaction in water

An efficient catalyst-free, diastereosective synthesis of novel hexahydro-chromene and tetrahydro-pyrano[2,3-d]pyrimidine-annulated benzo-δ-sultones is described. A number of 2-formyl-4-phenyl (E)-2-phenylethenesulfonates were synthesized and underwent a one-pot domino Knöevenagel-hetero-Diels-Alder reaction, respectively, with dimedone and N,N-dimethylbarbituric acid in water, affording the desired products in moderate to excellent yields.     

Kinetic Study and NBO Analysis of the Dehydrogenation Mechanism of Five‐membered Ring Heterocyclic 2,5‐Dihydro‐[furan,thiophene, selenophene

The theoretical study of the dehydrogenation of 2,5‐dihydro‐[furan ( 1 ), thiophene ( 2 ), and selenophene ( 3 )] was carried out using ab initio molecular orbital (MO) and density functional theory (DFT) methods at the B3LYP/6‐311G**//B3LYP/6‐311G** and MP2/6‐311G**//B3LYP/6‐311G** levels of theory. Among the used methods in this study, the obtained results show that B3LYP/6‐311G** method is in good agreement with the available experimental values. Based on the optimized ground state geometries using B3LYP/6‐311G** method, the natural bond orbital (NBO) analysis of donor‐acceptor (bond‐antibond) interactions revealed that the stabilization energies associated with the electronic delocalization from non‐bonding lone‐pair orbitals [LP(e)_X3] to δ*_{C(1)  H(2)} antibonding orbital, decrease from compounds 1 to 3 . The LP(e)_X3→δ*_{C(1)  H(2)} resonance energies for compounds 1 – 3 are 23.37, 16.05 and 12.46 kJ/mol, respectively. Also, the LP(e)_X3→δ*_{C(1)  H(2)} delocalizations could fairly explain the decrease of occupancies of LP(e)_X3 non‐bonding orbitals in ring of compounds 1 – 3 ( 3 > 2 > 1 ). The electronic delocalization from LP(e)_X3 non‐bonding orbitals to δ*_{C(1)  H(2)} antibonding orbital increases the ground state structure stability, Therefore, the decrease of LP(e)_X3→δ*_{C(1)  H(2)} delocalizations could fairly explain the kinetic of the dehydrogenation reactions of compounds 1 – 3 (k ₁ >k ₂ >k ₃ ). Also, the donor‐acceptor interactions, as obtained from NBO analysis, revealed that the (_C(4)C(7)→δ*_{C(1)  H(2)} resonance energies decrease from compounds 1 to 3 . Further, the results showed that the energy gaps between (_C(4)C(7) bonding and δ*_{C(1)  H(2)} antibonding orbitals decrease from compounds 1 to 3 . The results suggest also that in compounds 1 – 3 , the hydrogen eliminations are controlled by LP(e)→δ* resonance energies. Analysis of bond order, natural bond orbital charges, bond indexes, synchronicity parameters, and IRC calculations indicate that these reactions are occurring through a concerted and synchronous six‐membered cyclic transition state type of mechanism.     

Degradation kinetics of electron beam irradiated poly(propylene-co-ethylene) heterophasic copolymer

This study considers the effects of electron beam radiation on degradation kinetics of a poly(propylene-co-ethylene) heterophasic copolymer. Polypropylene heterophasic copolymers are composed of ethylene–propylene rubbery phase dispersed in crystalline polypropylene homopolymer matrix. Electron beam radiation can affect both polypropylene homopolymer matrix and ethylene–propylene dispersed phases simultaneously. Both phases undergo degradation and crosslinking reactions, but degradation is more probable in the polypropylene homopolymer matrix. The aim of this work is to study kinetics of degradation in this material. A high power electron accelerator irradiated raw samples under nitrogen atmosphere. The samples are analyzed using TGA in non-isothermal mode, and the degradation kinetic parameters were determined using Kissinger, Flynn–Wall–Ozawa and Coats–Redfern methods. The kinetic parameters resulted from these methods are compared. Results of kinetics studies show that orders of degradation reactions occurring in nitrogen atmosphere are all less than one. It indicates degradation takes place due to thermal dissociation of the chemical bonds.     

Validation of improved simple method for prediction of activation energy of the thermal decomposition of energetic compounds

This study presents a new simple model for predicting activation energy of the thermolysis of various classes of energetic compounds. The new model can help to elucidate the cause of thermal stability and, therefore, shelf life of some energetic compounds. The methodology assumes that activation energy of an energetic compound with general formula C _a H _b N _c O _d can be expressed as a function of optimized elemental composition as well as the contribution of specific molecular structural parameters. The new correlation has the root mean square and the average deviations of 9.8 and 7.4 kJ mol^?1, respectively, for 86 energetic compounds with different molecular structures. The proposed new method is also tested for 20 energetic compounds, which have complex molecular structures, e.g. 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane, 2,4,6-tris(2,4,6-Trinitrophenyl)-1,3,5-triazine and 1-(2,4,6-Trinitrophenyl)-5,7-dinitrobenzotriazole.     

Determination of abamectin in citrus fruits using SPE combined with dispersive liquid–liquid microextraction and HPLC–UV detection

A new pretreatment method, SPE combined with dispersive liquid–liquid microextraction, was proposed for the determination of abamectin in citrus fruit samples for the first time. In this method, fruit samples were extracted by ultrasound‐assisted extraction followed by SPE. Then, the SPE was used as a disperser solvent in the next dispersive liquid–liquid microextraction step for further purification and enrichment of abamectin. The effects of various parameters on the extraction efficiency of the proposed method were investigated and optimized. Good linearity of abamectin was obtained from 0.005 to 10.0 mg/kg for B_1a and from 0.05 to 10.0 mg/kg for B_1b with correlation coefficient (r²) of 0.998 for B_1a and 0.991 for B_1b, respectively. The LODs were 0.001 and 0.008 mg/kg (S/N = 3) for B_1a and B_1b, respectively. The relative recoveries at three spiked levels were ranged from 87 to 96% with the RSD less than 11% (n = 3). The method has been successfully applied to the determination of abamectin in citrus fruit samples.     

Synthesis,Characterization, X‐ray Structures,and Solution Studies of Nickel(II) Complexes of an Aza‐Crown Macrocycle with a Hydroxyl Pendant‐Armed

The 18‐membered mixed‐donor macrocycle 6,7,8,9,10,11,12,13,20,21‐decahydro‐5H, 19H‐dibenzo[b,m][1,15,5,8,11]dioxatriazacyclooctadecin‐20‐ol ( L ), which contains N₃O₃ donor set, was synthesized. Also two nickel(II) complexes of L have been synthesized and characterized by X‐ray crystallography, FT‐IR, UV‐Vis absorption spectroscopy and elemental analysis. The structure of complexes shows an unexpected anion dependence. Reaction of Ni(ClO₄)₂·6H₂O with L afforded [Ni L ](ClO₄)₂·CH₂Cl₂ complex in which L uses all donor atoms and acts as a hexadentate ligand so forming a mononuclear nickel(II) complex in distorted octahedral geometry. Contrasting with this, when NiCl₂·6H₂0 is used, the product complex [{Ni L Cl}₂(μ‐Cl)₂] is dimeric and consists of two Ni L Cl units bridged by two chloride ions. The coordination geometry of each nickel atom is a distorted octahedral. In this complex L is exo‐coordinated via only three nitrogen atoms to a nickel ion, which is bound to two cis bridging chloride and one non‐bridging chloride too. Also complexing properties of L towards Ni(ClO₄)₂·6H₂O and NiCl₂·6H₂0 have been determined by UV‐Vis titration in methanol. The computer treatment of the data confirmed the 1:1 metal to ligand stoichiometry for two complexes in solution and gave reliable values for corresponding stability constants (logK = 3.00 ± 0.02 with Ni(ClO₄)₂·6H₂O and logK = 3.29 ± 0.06 with NiCl₂·6H₂0).     

Pseudo five-component process for the synthesis of functionalized tricarboxamides using CuI nanoparticles as reusable catalyst

An efficient and multicomponent method has been developed for the synthesis of functionalized tricarboxamides at room temperature using CuI nanoparticles as catalyst. This method involved fivecomponent coupling reactions of Meldrum's acid, isocyanides with aromatic aldehydes and amines at room temperature. Atom economy, wide range of products, excellent yields in short time and mild reaction conditions are some of the important features of this protocol. Notably, this catalyst could be recycled and reused for several times without significantly decreasing the catalytic activity.     

Flat topology and its dual aspects

In this article, a new and natural topology on the prime spectrum is introduced, which behaves completely as the dual of the Zariski topology. It is called the flat topology. The basic and also some sophisticated properties of the flat topology are proved. Specially, various algebraic characterizations for the noetherianess of the flat topology are given. Using the flat topology, then some facts on the structure of the prime ideals of a ring come to light which are not in the access of the Zariski topology.     

Simultaneous Determination of Deltamethrin and Permethrin in Water Samples Using Homogeneous Liquid–Liquid Microextraction via Flotation Assistance and GC-FID

A new method was developed for the simultaneous determination of deltamethrin and permethrin in water samples with homogeneous liquid–liquid microextraction via flotation assistance and gas chromatography–flame ionization detection. A special extraction cell was designed to facilitate collection of the low density solvent extracts. The sample solution was added into the extraction cell, which contained an appropriate mixture of n-hexane (as an extraction solvent) and acetone (as a homogeneous solvent). Air flotation allowed the extraction solvent to be collected from the top of the solution. Under the optimum conditions, good linearity was observed in the range of 1.0–200 μg L^?1 with a correlation coefficient (r ²) greater than 0.9980 for both of the analytes. The limits of detection were 0.2 and 0.3 μg L^?1 for deltamethrin and permethrin, respectively (S/N = 3). The developed method was successfully applied to determine the two pesticides in three different water samples.     

Synthesis,crystal structures and antibacterial studies of oxidovanadium(IV) complexes of salen-type Schiff base ligands derived from meso-1,2-diphenyl-1,2-ethylenediamine

A series of new derivatives and previously reported Schiff base ligands and their oxidovanadium(IV) complexes were synthesized, characterized and tested as potential antibacterial agents against four human pathogenic bacteria. These N₂O₂ type Schiff base ligands were derived from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with different salicylaldehyde derivatives, and their metal complexes were obtained from the reaction of these ligands with bis(acetylacetonato)oxidovanadium(IV). Our studies showed that the metal complexes had moderate antibacterial activity, and this activity was higher than that of the free ligands against both Gram-positive and Gram-negative bacteria. Besides, it was found that the presence of more substituents on the ligands increases the antibacterial activities of both the free ligands and their complexes. The crystal structures of H₂L⁴ and its corresponding complex VOL⁴ were determined by X-ray crystallography.