Showing papers on "Acetonitrile published in 2017"

Copper-Catalyzed Three-Component Carboazidation of Alkenes with Acetonitrile and Sodium Azide.

Abstract: A copper-catalyzed three-component reaction of alkenes, acetonitrile, and sodium azide afforded γ-azido alkyl nitriles by formation of one C(sp3 )-C(sp3 ) bond and one C(sp3 )-N bond. The transformation allows concomitant introduction of two highly versatile groups (CN and N3 ) across the double bond. A sequence involving the copper-mediated generation of a cyanomethyl radical and its subsequent addition to an alkene, and a C(sp3 )-N bond formation accounted for the reaction outcome. The resulting γ-azido alkyl nitrile can be easily converted into 1,4-diamines, γ-amino nitriles, γ-azido esters, and γ-lactams of significant synthetic value.

Local Proton Source in Electrocatalytic CO2 Reduction with [Mn(bpy–R)(CO)3Br] Complexes

Abstract: The electrochemical behavior of fac-[Mn(pdbpy)(CO)3 Br] (pdbpy=4-phenyl-6-(phenyl-2,6-diol)-2,2'-bipyridine) (1) in acetonitrile under Ar, and its catalytic performances for CO2 reduction with added water, 2,2,2-trifluoroethanol (TFE), and phenol are discussed in detail. Preparative-scale electrolysis experiments, carried out at -1.5 V versus the standard calomel electrode (SCE) in CO2 -saturated acetonitrile, reveal that the process selectivity is extremely sensitive to the acid strength, producing CO and formate in different faradaic yields. A detailed spectroelectrochemical (IR and UV/Vis) study under Ar and CO2 atmospheres shows that 1 undergoes fast solvolysis; however, dimer formation in acetonitrile is suppressed, resulting in an atypical reduction mechanism in comparison with other reported MnI catalysts. Spectroscopic evidence of Mn hydride formation supports the existence of different electrocatalytic CO2 reduction pathways. Furthermore, a comparative investigation performed on the new fac-[Mn(ptbpy)(CO)3 Br] (ptbpy=4-phenyl-6-(phenyl-3,4,5-triol)-2,2'-bipyridine) catalyst (2), bearing a bipyridyl derivative with OH groups in different positions to those in 1, provides complementary information about the role that the local proton source plays during the electrochemical reduction of CO2 .

Controlling Excited State Single versus Double Proton Transfer for 2,2'-Bipyridyl-3,3'-diol: Solvent Effect

Abstract: In this work, we theoretically investigate the sequential excited state double proton transfer (ESDPT) mechanism of a representative intramolecular hydroxyl (OH)-type hydrogen molecule 2,2′-bipyridyl-3,3′-diol (BP(OH)2). We mainly adopt three kinds of different polar solvents (nonpolar cyclohexane (CYH), polar acetonitrile (ACN), and moderate chloroform (CHCl3)) to explore solvent effects on this system. Two intramolecular hydrogen bonds of BP(OH)2 are testified to be strengthened in the S1 state, which provides possibility for ESDPT process. Explorations of charge redistribution and potential energy surfaces (PESs) reveal ESDPT process. Searching transition state (TS) structures in different polar aprotic solvents, we successfully regulate and control the stepwise ESDPT behaviors of BP(OH)2 through solvent polarity.

Metal-Assisted Ligand-Centered Electrocatalytic Hydrogen Evolution upon Reduction of a Bis(thiosemicarbazonato)Cu(II) Complex

Abstract: In this study, we report the electrocatalytic behavior of the neutral, monomeric Cu(II) complex of diacetyl-bis(N-4-methyl-3-thiosemicarbazonato), CuL1, for metal-assisted ligand-centered hydrogen evolution in acetonitrile and dimethylformamide. CuL1 displays a maximum turnover frequency (TOF) of 10 000 s–1 in acetonitrile and 5100 s–1 in dimethylformamide at an overpotential of 0.80 and 0.76 V, respectively. The rate law is first-order in catalyst and second-order in proton concentration. Gas analysis from controlled potential electrolysis confirms CuL1 as an electrocatalyst to produce H2 with a minimum Faradaic efficiency of 81% and turnover numbers as high as 73 while showing no sign of degradation over 23 h. The H2 evolution reaction (HER) was probed using deuterated acid, demonstrating a kinetic isotope effect of 7.54. A proton inventory study suggests one proton is involved in the rate-determining step. Catalytic intermediates were identified using 1H NMR, X-ray photoelectron, and UV–visible spectro...

Visible-light Homogeneous Photocatalytic Conversion of CO2 into CO in Aqueous Solutions with an Iron Catalyst.

Abstract: An iron-substituted tetraphenyl porphyrin bearing positively charged trimethylammonio groups at the para position of each phenyl ring catalyzes the photoinduced conversion of CO2 . This complex is water soluble and acts as a molecular catalyst to selectively reduce CO2 into CO under visible-light irradiation in aqueous solutions (acetonitrile/water=1:9 v/v) with the assistance of purpurin, a simple organic photosensitizer. CO is produced with a catalytic selectivity of 95 % and turnover number up to 120, illustrating the possibility of photocatalyzing the reduction of CO2 in aqueous solution by using visible light, a simple organic sensitizer coupled to an amine as a sacrificial electron donor, and an earth-abundant metal-based molecular catalyst.

Highly selective and sensitive detection of 4-nitrophenol and Fe3+ ion based on a luminescent layered terbium (III) coordination polymer

Abstract: A luminescent terbium(III)-based coordination polymer, [Tb(BTEC)0.5(HCOO)(H2O)2] (1) has been successfully synthesized by solvothermal reaction of Tb(NO3)3·6H2O with 1,2,4,5-tetracarboxylic acid (H4BTEC) in N,N-dimethylformamide (DMF) and H2O at 160 °C. Compound 1 possesses dimeric [Tb2(BTEC)4(HCOO)2(H2O)4] building blocks which are linked by BTEC linkers to generate a two-dimentional honeycomb layer. 1 shows intense characteristic green emission in both solid state and organic solvents including acetone, ethanol, acetonitrile, benzene, dichloromethane, methanol, tetrahydrofuran, dimethyl sulfoxide and water at ambient temperature. Strong emission of 1 could be highly and selectively quenched by 4-nitropenol (4-NP) even in the coexistence of other competing nitroaromatics such as 2,4,6-trinitrophenol, 2,6-dinitrotoluene, nitrobenzene, 4-nitrotolune, 4-bromophenol, phenol, bromobenzene, and 1,2-dimethylbenzene. In addition, 1 exhibited superior selectivity and sensitivity towards Fe3+ ion over other metal ions including Al3+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Ni2+, K+, Mg2+, Mn2+, Pd2+ and Zn2+ ions. The possible detection mechanisms have been proposed. More interestingly, the trace amounts of 4-NP and Fe3+ ions were selectively detected using visual luminescent test papers based on 1, which could further contributes a credible potential sensing application of coodination polymers for the biological and environmental concerns.

Strong Blue Emissive Supramolecular Self-Assembly System Based on Naphthalimide Derivatives and Its Ability of Detection and Removal of 2,4,6-Trinitrophenol.

Abstract: Two simple and novel gelators (G-P with pyridine and G-B with benzene) with different C-4 substitution groups on naphthalimide derivatives have been designed and characterized. Two gelators could form organogels in some solvents or mixed solvents. The self-assembly processes of G-P in a mixed solvent of acetonitrile/H2O (1/1, v/v) and G-B in acetonitrile were studied by means of electron microscopy and spectroscopy. The organogel of G-P in the mixed solvent of acetonitrile/H2O (1/1, v/v) formed an intertwined fiber network, and its emission spectrum had an obvious blue shift compared with that of solution. By contrast, the organogel of G-B in acetonitrile formed a straight fiber, and its emission had an obvious red shift compared with that of solution. G-P and G-B were employed in detecting nitroaromatic compounds because of their electron-rich property. G-P is more sensitive and selective toward 2,4,6-trinitrophenol (TNP) compared with G-B. The sensing mechanisms were investigated by 1H NMR spectroscopic...

Synthesis of a new fluorescent cyanide chemosensor based on phenothiazine derivative

Abstract: A new phenothiazine derivative containing two dicyano-vinyl groups as the cyanide receptor on both sides was synthesized and fully characterized. The chemosensor showed an intramolecular charge transfer (ICT) absorption band at 494 nm and emission band at 633 nm in acetonitrile solution. Upon titration with different concentrations of cyanide anion both absorption and emission bands decreases in a ratiometric manner. This optical response for cyanide anion is due to the nucleophilic Michael addition of CN− on the α-position of the dicyano-vinyl groups present in the chemosensor in both sides and thus converting these electron acceptors to anionic electron donors and consequently breaking the conjugation, which ultimately affect the ICT and the fluorescence of the chemosensor. The result indicated that the chemosensor showed high sensitivity with a fast response of less than 50 s and selectivity toward cyanide anion with a detection limit as low as 3.2 × 10−9 M, which is the lowest ever reported. The chemosensor reaction mechanism with CN− was studied by 1H NMR and 13C NMR, FTIR and mass spectroscopies.

Crystal Morphology and Interfacial Stability of RS-Ibuprofen in Relation to Its Molecular and Synthonic Structure

Abstract: The key intermolecular (synthonic) interactions, crystal morphology, and surface interfacial stability of the anti-inflammatory drug RS-ibuprofen are examined in relation to its bulk crystal and surface chemistry, and to rationalize its growth behavior as a function of the crystallization environment. The OH···O H-bonding dimers between adjacent carboxylic acid groups are calculated to be the strongest bulk (intrinsic) synthons, with other important synthons arising due to interactions between the less-polar phenyl ring and aliphatic chain. Morphological prediction, using the attachment energy model, predicts a prismatic faceted shape, in good agreement with the shape of the experimentally grown crystals from the vapor phase. Crystals grown from solution are found to have higher aspect ratios, with those prepared in polar protic solvents (EtOH) producing less needle-like crystals, than those prepared in less polar and aprotic solvents (toluene, acetonitrile, and ethyl acetate). Though the anisotropy facto...

Gold Nanoparticles Supported on Alumina as a Catalyst for Surface Plasmon-Enhanced Selective Reductions of Nitrobenzene

Abstract: Au nanoparticles supported on alumina (Au/Al2O3) with average particle size of 3.9 ± 0.7 nm and surface plasmon band centerned at 516.5 nm were prepared by deposition–precipitation method, and their photocatalytic activities for the reduction of nitrobenzene using either formic acid in acetonitrile (method A) or KOH in 2-propanol (method B) were investigated. Even at room temperature, the Au/Al2O3 was found to be highly active and selective for conversion of nitrobenzene to aniline when used with formic acid in acetonitrile or to azobenzene when performed with KOH in 2-propanol under irradiation with green light-emitting diode (517 nm).

Photochemical Processes in a Rhenium(I) Tricarbonyl N-Heterocyclic Carbene Complex Studied by Time-Resolved Measurements.

Abstract: We carried out time-resolved infrared (TR-IR) and emission lifetime measurements on a Re(I) carbonyl complex having an N-heterocyclic carbene ligand, namely, fac-[Re(CO)3(PyImPh)Br], under photochemically reactive (in solution in acetonitrile) and nonreactive (in solution in dichloromethane) conditions to investigate the mechanism of photochemical ligand substitution reactions. The TR-IR measurements revealed that no reaction occurs on a picosecond time scale and the cationic product, namely, fac-[Re(CO)3(PyImPh)(MeCN)]+, is produced on a nanosecond time scale only in solution in acetonitrile, which indicates that the reaction proceeds thermally from the excited state. Because no other products were observed by TR-IR, we concluded that this cationic product is an intermediate species for further reactions. The measurements of the temperature-dependent emission lifetime and analysis using transition-state theory revealed that the photochemical substitution reaction proceeds from a metal-to-ligand charge tr...

Chalcone based ion-pair recognition towards nitrates and the application for the colorimetric and fluorescence turn-on determination of water content in organic solvents

Abstract: This article describes a novel ion-pair recognition mode of a molecular probe (C-1) bearing chalcone moiety. C-1 can bind to metal nitrates selectively (metal = Zn2+, Ni2+, Co2+, Cd2+) with remarkable color change from yellow to purple. The mechanism was investigated via experimental and theoretical approaches. The results show that C-1 coordinate with metal ions by stoichiometric ratio 2:1, the nitrate anion binds with metal ion via electrostatic interaction, and binds with ligand via supramolecular interactions. Furthermore, the selected two-component sensor, C-1/Ni(NO3)2, can detect water content in acetone, acetonitrile, ethanol and isopropanol with low detection limit by both colorimetric and fluorescence turn-on approach. The sensor has favorable linear relationships with water content within the range 0–10% in the above four solvents, and the detection limit in acetone, acetonitrile, ethanol and iso-propanol is 0.20%, 0.38%, 0.24% and 0.09%, respectively, showing great potential for water content monitoring.

A DFT Investigation of the Mechanism of Propene Ammoxidation over α-Bismuth Molybdate

Abstract: The mechanisms and energetics for the propene oxidation and ammoxidation occurring on the (010) surface of Bi2Mo3O12 were investigated using density functional theory (DFT). An energetically feasible sequence of elementary steps for propene oxidation to acrolein, propene ammoxidation to acrylonitrile, and acrolein ammoxidation to acrylonitrile is proposed. Consistent with experimental findings, the rate-limiting step for both propene oxidation and ammoxidation is the initial hydrogen abstraction from the methyl group of propene, which is calculated to have an apparent activation energy of 27.3 kcal/mol. The allyl species produced in this reaction is stabilized as an allyl alkoxide, which can then undergo hydrogen abstraction to form acrolein or react with ammonia adsorbed on under-coordinated surface Bi3+ cations to form allylamine. Dehydrogenation of allylamine is shown to produce acrylonitrile, whereas reaction with additional adsorbed ammonia leads to the formation of acetonitrile and hydrogen cyanide....

Anionic optical devices based on 4-(nitrostyryl)phenols for the selective detection of fluoride in acetonitrile and cyanide in water

Abstract: Four compounds, 4-(4-nitrostyryl)phenol (1a), 4-(2,4-dinitrostyryl)phenol (2a), [4-(4-nitrostyryl)phenoxy]triisopropylsilane (3), and [4-(2,4-dinitrostyryl)phenoxy]triisopropylsilane (4), were synthesized and characterized. The three-dimensional molecular structures of compounds 3 and 4 were solved using X-ray crystallography. Compounds 1a and 2a were used in an acid-base strategy for the detection of fluoride and cyanide in acetonitrile. With the addition of small amounts of water the systems were able to detect only cyanide. Compounds 1a and 2a were also able to selectively detect cyanide in pure water, in the presence of a micellar concentration of cetyltrimethylammonium bromide, which is required to adjust the acidity constants of the compounds for the detection of the anion. Compounds 3 and 4 were used in a chemodosimeter approach for the selective detection of fluoride in acetonitrile. The fluoride attacks the silicon centers of 3 and 4 and through a nucleophilic substitution at the silicon (SN2@Si) their corresponding colored phenolate species are immediately released as leaving groups. This process is effective in acetonitrile for the detection of fluoride, which is a strongly nucleophilic analyte under these experimental conditions. Paper test strips were prepared, containing compounds 1a and 2a, and in tests with aqueous solutions of different anions it was verified that only CN− changes the color of the modified paper.

Solvent-Mediated Reversible Structural Transformation of Mercury Iodide Coordination Polymers: Role of Halide Anions

Abstract: Solvothermal reactions of HgX2 with 2,2′-(1,2-phenylene)-bis(N-pyridin-3-yl)acetamide, L, in ethanol afforded [Hg(L)X2]n (X = Cl, 1; Br, 2; I, 3), which are isostructural one-dimensional (1D) zigzag chains, while layering reactions of a ethanoic solution of L with a methanoic solution and an acetonitrile solution of HgI2, respectively, gave 1D helical chains [Hg(L)I2·MeOH]n, 4, and [Hg(L)I2·MeCN]n, 5. In marked contrast to 1 and 2, the iodide-containing 3 is able to exhibit reversible structural transformation with 4 and 5 by adsorption and desorption of methanol and acetonitrile, suggesting the importance of N–H---X and Hg---X interactions in the evaluation of structural transformation. Moreover, complexes 4 and 5 exhibit reversible crystal to crystal transformation triggered by solvent exchange. Complexes 3–5 represent a unique example that the solvents show a significant effect on folding and unfolding of the HgI2 single-stranded helical coordination polymers.