Polyaniline-Supported Zinc Oxide (ZnO) Nanoparticles: An Active and Stable Heterogeneous Catalyst for the Friedel–Crafts Acylation Reaction

We report herein the synthesis of zinc oxide (ZnO) nanoparticles incorporating a polyaniline (PANI) matrix in aqueous medium and its catalytic performance toward Friedel–Crafts acylation reactions. The acylation reactions demonstrate that polyaniline/nano-ZnO composites are very active catalysts and are able to activate the reactant at ambient temperature. The obtained nanocatalyst was characterized by Fourier transform–infrared, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller, X-ray diffraction, and particle-size analysis techniques. The catalyst was reusable for five cycles without appreciable loss in activity.     

Flow invariance for solutions to nonlinear nonautonomous partial differential delay equations

We investigate the problem of existence and flow invariance of mild solutions to nonautonomous partial differential delay equations , t?s, us=φ, where B(t) is a family of nonlinear multivalued, α-accretive operators with D(B(t)) possibly depending on t, and the operators F(t,.) being defined—and Lipschitz continuous—possibly only on “thin” subsets of the initial history space E. The results are applied to population dynamics models. We also study the asymptotic behavior of solutions to this equation. Our analysis will be based on the evolution operator associated to the equation in the initial history space E.     

Application of SBA-Pr-SO<Subscript>3</Subscript>H in the synthesis of 2,3-dihydroquinazoline-4(1<Emphasis Type="Italic">H</Emphasis>)-ones: characterization,UV–Vis investigations and DFT studies

An efficient one-pot synthesis of 2,3-dihydroquinazoline-4(1H)-one derivatives 4a–l is described using SBA-Pr-SO₃H as a heterogeneous acid catalyst. The present methodology resulted in various derivatives of 2,3-dihydroquinazoline-4(1H)-one in good yield via a three-component reaction of isatoic anhydride, aldehydes and ammonium acetate. SBA-Pr-SO₃H played a significant role as an efficient mesoporous catalyst due to its pore size of 6 nm. Additionally, UV–Vis spectrum of the products was studied in order to investigate their application as UV absorbers.     

SBA-15-Pr-SO3H catalyzed one-pot synthesis of indole derivatives via Fischer indole pathway

In this work, an efficient, user-friendly, and simple procedure was reported for the preparation of indole derivatives catalyzed by the heterogeneous SBA-15-Pr-SO₃H via Fischer indole pathway. The title compounds were synthesized from various arylhydrazines and ketones in the presence of 3 mol% of the catalyst in the refluxing ethanol.     

Copper(II)-mediated oxidative transformation of vic-dioxime to furoxan: evidence for a copper(II)-dinitrosoalkene intermediate

The mononuclear copper(II) complex [Cu(H(2)L(1))(2)(H(2)O)](ClO(4))(2) (1) (where H(2)L(1) = 1,10-phenanthroline-5,6-dioxime) reacts with copper(II) perchlorate in acetonitrile at ambient conditions in the presence of triethylamine to afford a copper(II) complex, [Cu(L(3))(2)(H(2)O)](ClO(4))(2) (2a), of 1,10-phenanthroline furoxan. A similar complex [Cu(L(3))(2)Cl](ClO(4)) (2) is isolated from the reaction of H(2)L(1) with copper(II) chloride, triethylamine, and sodium perchlorate in acetonitrile. The two-electron oxidation of the vic-dioxime to furoxan is confirmed from the X-ray single crystal structure of 2. An intermediate species, showing an absorption band at 608 nm, is observed at -20 °C during the conversion of 1 to 2a. A similar blue intermediate is formed during the reaction of [Cu(HDMG)(2)] (H(2)DMG = dimethylglyoxime) with ceric ammonium nitrate, but H(2)DMG treated with ceric ammonium nitrate does not form any intermediate. This suggests the involvement of a copper(II) complex in the intermediate step. The intermediate species is also observed during the two-electron oxidation of other vic-dioximes. On the basis of the spectroscopic evidence and the nature of the final products, the intermediate is proposed to be a mononuclear copper(II) complex ligated by a vic-dioxime and a dinitrosoalkene. The dinitrosoalkene is generated upon two-electron oxidation of the dioxime. The transient blue color of the dioxime-copper(II)-dinitrosoalkene complex may be attributed to the ligand-to-ligand charge transfer transition. The intermediate species slowly decays to the corresponding two-electron oxidized form of vic-dioxime, i.e. furoxan and [Cu(CH(3)CN)(4)](ClO(4)). The formation of two isomeric furoxans derived from the reaction of an asymmetric vic-dioxime, hexane-2,3-dioxime, and copper(II) perchlorate supports the involvement of a dinitrosoalkene species in the intermediate step. In addition, the oxidation of 2,9-dimethyl-1,10-phenanthroline-5,6-dioxime (H(2)L(2)) to the corresponding furoxan and subsequent formation of a copper(I) complex [Cu(L(4))(2)](ClO(4)) (3) (where L(4) = 2,9-dimethyl-1,10-phenanthroline furoxan) are discussed.     

Growth kinetics of sulfur nanoparticles in aqueous surfactant solutions

Sulfur is an important element has many practical applications when present as nanoparticles. Despite the practicable applications, limited studies are available in the literature related to synthesis of sulfur nanoparticles. Growth kinetics of colloidal sulfur particles synthesized from aqueous solutions using different surfactants have been studied here. The effects of different parameters such as reactant concentration, temperature, sonication, types of acids, types of surfactants, and even surfactant concentration are studied on the growth kinetics. Since the reaction rate is fast, particle growth depends on the parameters which affect diffusion of sulfur molecules. There is a linear relationship found among the reactant concentration and the particle coarsening rate constant. The growth kinetics was studied in the presence of different surfactants such as nonionic (poly(oxyethylene) p-tert-octylphenyl ether, TX-100), anionic (sodium dodecylbenzene sulfonate, SDBS), cationic (cetyltrimethyammonium bromide, CTAB) and results show the coarsening constant changes according to the following order: water>TX-100>SDBS>CTAB. The particle growth rate also depends on the surfactant concentration, coarsening rate constant decreases with the increase in surfactant concentration and become constant close to the critical micellar concentration (CMC). The coarsening rate constant also highly depends on the types of acid used as catalyst.     

Possibility for mode-locked operation of a femtosecond UV storage ring free-electron laser using a low-loss Fabry–Perot resonator

A storage ring free-electron laser (SR-FEL) is inherently a self-mode-locked optical system. The gain broadening due to electron energy spread affects the small signal gain in order to determine the output coupling. Here, the dependence of the small signal gain, the optimum output coupling, and pulse duration on both electron energy spread and loss of a Fabry–Perot resonator in UV SR-FEL were investigated. It was shown that the output coupling strongly affects the mode-locked pulse duration and the present picosecond pulses can be shortened to femtosecond ones using a proper low-loss resonator.     

Cu(dap)2Cl] as an efficient visible-light-driven photoredox catalyst in carbon-carbon bond-forming reactions

Copper sees the light of day: [Cu(dap)(2)Cl] proved to be an excellent photoredox catalyst for atom-transfer radical addition reactions, as well as for allylation reactions (see scheme), providing an attractive alternative to commonly used iridium- and ruthenium-based catalysts.     

Preparation of various xanthene derivatives over sulfonic acid functionalized imidazolium salts (SAFIS) as novel,highly efficient and reusable catalysts

In this work, some novel sulfonic acid functionalized imidazolium salts (SAFIS), as a new category of ionic liquids, are synthesized by eco-friendly and simple procedures, and used as highly efficient and reusable catalysts to promote the following one-pot multicomponent organic transformations under solvent-free conditions: (i) the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes from β-naphthol (2 eq.) and arylaldehydes (1 eq.), (ii) the preparation of tetrahydrobenzo[a]xanthene-11-ones from β-naphthol, arylaldehydes and dimedone, and (iii) the synthesis of 1,8-dioxo-octahydroxanthenes from dimedone (2 eq.) and aromatic aldehydes (1 eq.). Environmentally benign, simple methodologies, easy workup procedure, clean reaction, short reaction time, high yield and easy preparation of the catalysts are some advantages of this work.