Showing papers on "Acetonitrile published in 2015"

Molecular Catalysis of the Electrochemical and Photochemical Reduction of CO2 with Earth-Abundant Metal Complexes. Selective Production of CO vs HCOOH by Switching of the Metal Center

Abstract: Molecular catalysis of carbon dioxide reduction using earth-abundant metal complexes as catalysts is a key challenge related to the production of useful products—the “solar fuels”—in which solar energy would be stored. A direct approach using sunlight energy as well as an indirect approach where sunlight is first converted into electricity could be used. A CoII complex and a FeIII complex, both bearing the same pentadentate N5 ligand (2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene), were synthesized, and their catalytic activity toward CO2 reduction was investigated. Carbon monoxide was formed with the cobalt complex, while formic acid was obtained with the iron-based catalyst, thus showing that the catalysis product can be switched by changing the metal center. Selective CO2 reduction occurs under electrochemical conditions as well as photochemical conditions when using a photosensitizer under visible light excitation (λ > 460 nm, solvent acetonitrile) with the Co cat...

Standard Reduction Potentials for Oxygen and Carbon Dioxide Couples in Acetonitrile and N,N-Dimethylformamide.

Abstract: A variety of next-generation energy processes utilize the electrochemical interconversions of dioxygen and water as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Reported here are the first estimates of the standard reduction potential of the O2 + 4e– + 4H+ ⇋ 2H2O couple in organic solvents. The values are +1.21 V in acetonitrile (MeCN) and +0.60 V in N,N-dimethylformamide (DMF), each versus the ferrocenium/ferrocene couple (Fc+/0) in the respective solvent (as are all of the potentials reported here). The potentials have been determined using a thermochemical cycle that combines the free energy for transferring water from aqueous solution to organic solvent, −0.43 kcal mol–1 for MeCN and −1.47 kcal mol–1 for DMF, and the potential of the H+/H2 couple, – 0.028 V in MeCN and −0.662 V in DMF. The H+/H2 couple in DMF has been directly measured electrochemically using the previously reported procedure for the MeCN value. The thermochemical approach used for the O2/H2O couple has...

Voltammetric Determination of the Iodide/Iodine Formal Potential and Triiodide Stability Constant in Conventional and Ionic Liquid Media

Abstract: The iodide/triiodide/iodine (I–/I3–/I2) redox system has been the subject of electrochemical investigations for well over half a century and remains a contemporary research interest due to the integral role of the I–/I3– couple in dye-sensitized solar cell (DSSC) technology. In this study, we have calculated the formal potential (E0′) of the I–/I2 process and the stability constant (Kstab) of I3– in two protic solvents (water and ethanol), two aprotic solvents (acetonitrile and propylene carbonate), eight aprotic ionic liquids (AILs), and one protic ionic liquid (PIL) using the voltammetric methodology developed herein. Furthermore, using 1-ethyl-3-methylimidazlium bis(trifluoromethanesulfonyl)imide (abbr. [C2mim][NTf2]) as a “model” ionic liquid-based DSSC electrolyte system, we have also investigated the influence of three common additives/impurities in DSSCs (i.e., tert-butylpyridine, Li+, and water) on the parameters E0′(I–/I2) and Kstab and characterized two analogous redox systems, Br–/Br3–/Br2 and ...

Effect of Organic Solvents on Li+ Ion Solvation and Transport in Ionic Liquid Electrolytes: A Molecular Dynamics Simulation Study

Abstract: Molecular dynamics simulations of N-methyl-N-propylpyrrolidinium (pyr13) bis(trifluoromethanesulfonyl)imide (Ntf2) ionic liquid [pyr13][Ntf2] doped with [Li][Ntf2] salt and mixed with acetonitrile (AN) and ethylene carbonate (EC) organic solvents were conducted using polarizable force field. Structural and transport properties of ionic liquid electrolytes (ILEs) with 20 and 40 mol % of organic solvents have been investigated and compared to properties of neat ILEs. Addition of AN and EC solvents to ILEs resulted in the partial displacement of the Ntf2 anions from the Li+ first coordination shell by EC and AN and shifting the Li–Ntf2 coordination from bidentate to monodentate. The presence of organic solvents in ILE has increased the ion mobility, with the largest effect observed for the Li+ cation. The Li+ conductivity has doubled with addition of 40 mol % of AN. The Li+–NNtf2 residence times were dramatically reduced with addition of solvents, indicating an increasing contribution from structural diffusi...

Strategies for the Hyperpolarization of Acetonitrile and Related Ligands by SABRE

Abstract: We report on a strategy for using SABRE (signal amplification by reversible exchange) for polarizing 1H and 13C nuclei of weakly interacting ligands which possess biologically relevant and nonaromatic motifs We first demonstrate this via the polarization of acetonitrile, using Ir(IMes)(COD)Cl as the catalyst precursor, and confirm that the route to hyperpolarization transfer is via the J-coupling network We extend this work to the polarization of propionitrile, benzylnitrile, benzonitrile, and trans-3-hexenedinitrile in order to assess its generality In the 1H NMR spectrum, the signal for acetonitrile is enhanced 8-fold over its thermal counterpart when [Ir(H)2(IMes)(MeCN)3]+ is the catalyst Upon addition of pyridine or pyridine-d5, the active catalyst changes to [Ir(H)2(IMes)(py)2(MeCN)]+ and the resulting acetonitrile 1H signal enhancement increases to 20- and 60-fold, respectively In 13C NMR studies, polarization transfers optimally to the quaternary 13C nucleus of MeCN while the methyl 13C is har

Electrocatalytic Reduction of Carbon Dioxide: Let the Molecules Do the Work

Abstract: This review summarizes the development of electrochemical CO2 reduction catalysts in the UNC Energy Frontier Research Center for Solar Fuels. Two strategies for converting CO2 to CO or formate have been explored. In one, polypyridyl complexes of Ru(II) have been used to reduce CO2 to CO in acetonitrile and in acetonitrile/water mixtures. In the absence of CO2 water is reduced to H2 by these complexes. With added weak acids in acetonitrile with added water and CO2, reduction to syngas mixtures of CO and H2 is observed. A single polypyridyl complex of Ru(II) has been shown to be both a catalyst for water oxidation and CO2 reduction in an electrochemical cell for CO2 splitting into CO and O2. In parallel, Ir pincer catalysts have been shown to act as selective electrocatalysts for reducing CO2 to formate in acetonitrile with added water and in pure water without competition from electrocatalytic H2 production. Details of the catalytic mechanisms of each have also been investigated.

A fluorescent chemosensor for sequential recognition of gallium and hydrogen sulfate ions based on a new phenylthiazole derivative

Abstract: A new highly selective turn-on fluorescent chemosensor based on 2′-hydroxyphenylthiazole for the detection of gallium and hydrogen sulfate ions in acetonitrile was synthesized and characterized. The mechanism of fluorescence was based on the inhibition of excited state intramolecular proton transfer (ESIPT). The sensor demonstrated high selectivity for gallium as compared to aluminum and other cations and allowed sequential detection of hydrogen sulfate.

Synthesis and Characterization of an Iron Complex Bearing a Cyclic Tetra-N-heterocyclic Carbene Ligand: An Artifical Heme Analogue?

Abstract: An iron(II) complex with a cyclic tetradentate ligand containing four N-heterocyclic carbenes was synthesized and characterized by means of NMR and IR spectroscopies, as well as by single-crystal X-ray structure analysis. The iron center exhibits an octahedral coordination geometry with two acetonitrile ligands in axial positions, showing structural analogies with porphyrine-ligated iron complexes. The acetonitrile ligands can readily be substituted by other ligands, for instance, dimethyl sulfoxide, carbon monoxide, and nitric oxide. Cyclic voltammetry was used to examine the electronic properties of the synthesized compounds.

Fast, high-yield synthesis of amphiphilic Ag nanoclusters and the sensing of Hg2+ in environmental samples

Abstract: We report the high-yield (74%) synthesis of Ag30(Capt)18 (abbreviated as Ag30) in a very time-saving fashion (half an hour). The cluster composition was determined by high-resolution mass spectrometry combined with TG analysis, and the structure was probed by 1D and 2D NMR. Interestingly, the nanoclusters can dissolve in water and methanol, as well as in most organic solvents such as ethanol, acetone, acetonitrile, dichloromethane and ethyl acetate with the assistance of acetic acid. Such a good solubility in a range of various polar solvents was not reported previously in nanoclusters’ research and is important for applications. An important result from this work is that Ag30 can sense a low concentration of Hg2+ in environmental samples (including lake water and soil solution), indicating that Ag30 can be a potential colorimetric probe for Hg2+. The sensing mechanism was revealed to be related to the anti-galvanic reduction process.

Sandmeyer cyanation of arenediazonium tetrafluoroborate using acetonitrile as a cyanide source

Abstract: Palladium-catalyzed cyanation of aryldiazonium tetrafluoroborate using acetonitrile as a non-metallic cyanide source was achieved in the presence of Ag2O under ambient air, eliminating the involvement of highly toxic CuCN used in the traditional Sandmeyer reaction, in which the CN group comes from metallic cyanides. The substrate scope and limitation of this protocol were investigated.

Oxidative C(sp3)–H functionalization of acetonitrile and alkanes with allylic alcohols under metal-free conditions

Abstract: An efficient method for the construction of ketonitriles and α-aryl ketones by tert-butyl peroxybenzoate (TBPB) mediated direct alkylation of acetonitrile and alkanes with α,α-diaryl allylic alcohols has been developed. The reactions involve C(sp3)–H functionalization and radical addition/1,2-aryl migration processes under metal-free conditions.

Submerged liquid plasma for the synchronized reduction and functionalization of graphene oxide.

Abstract: Formation of reduced and functionalized graphene oxide (r-FGO) at ambient temperature and pressure is demonstrated by generating liquid plasma submerged in acetonitrile and graphene oxide solution. The partial restoration of conjugation (sp2 domain) and insertion of fluorophores such as nitrile and amine in r-FGO displays enhanced fluorescence property. Presence of nitrile and amine in r-FGO are confirmed by X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy. Morphology and optical property of r-FGO are studied with transmission electron microscopy, scanning tunneling microscopy and Ultraviolet–visible spectroscopy measurements. The nitrile and amine present in r-FGO undergo a surface-controlled reversible redox reaction and sp2- enriched r-FGO acts as an electrical double layer, providing additional hybrid capacitance or pseudocapacitance. r-FGO shows high cyclic stability with a specific capacitance value of 349 F/g at the scan rate of 10 mV/s. Only marginal reduction of specific capacitance (<10% reduction) is observed at the end of 1000 cycles.

Carbon Dioxide Promoted H+ Reduction Using a Bis(imino)pyridine Manganese Electrocatalyst

Abstract: Heating a 1:1 mixture of (CO)5MnBr and the phosphine-substituted pyridine diimine ligand, Ph2PPrPDI, in THF at 65 °C for 24 h afforded the diamagnetic complex [(Ph2PPrPDI)Mn(CO)][Br] (1). Higher temperatures and longer reaction times resulted in bromide displacement of the remaining carbonyl ligand and the formation of paramagnetic (Ph2PPrPDI)MnBr (2). The molecular structure of 1 was determined by single crystal X-ray diffraction, and density functional theory (DFT) calculations indicate that this complex is best described as low-spin Mn(I) bound to a neutral Ph2PPrPDI chelating ligand. The redox properties of 1 and 2 were investigated by cyclic voltammetry (CV), and each complex was tested for electrocatalytic activity in the presence of both CO2 and Bronsted acids. Although electrocatalytic response was not observed when CO2, H2O, or MeOH was added to 1 individually, the addition of H2O or MeOH to CO2-saturated acetonitrile solutions of 1 afforded voltammetric responses featuring increased current dens...

Enhanced Emission of Polyethyleneimine-Coated Copper Nanoclusters and Their Solvent Effect

Abstract: The solvent-dependent properties of polyethyleneimine (PEI)-capped Cu nanoclusters are discussed in this study. The PEI-encapsulated Cu nanoclusters were dispersed in 12 polar organic solvents, and in water and alcohols, the nanoclusters display similar properties and could be stable in the dark. Moreover, Cu nanoclusters exhibit a blue shift of the emission peak in tetrahydrofuran (THF) and 1,4-dioxane, and the absorption spectra change dramatically. Furthermore, in THF the fluorescence intensity increases significantly over time. Besides, the absorption spectra also display a significant change in acetonitrile, dimethyl sulfoxide, and ethylene glycol monomethyl ether, while the emission bands show no obvious shift. In acetonitrile, THF, and 1,4-dioxane, the solvents look milky under bright light, and the fluorescence colors look more blue under a UV lamp. The solvent effect on the fluorescence and absorption spectra of the PEI-capped Cu nanoclusters in water–THF mixtures at different solvent ratios is d...

Unmasking the Action of Phosphinous Acid Ligands in Nitrile Hydration Reactions Catalyzed by Arene–Ruthenium(II) Complexes

Abstract: The catalytic hydration of benzonitrile and acetonitrile has been studied by employing different arene-ruthenium(II) complexes with phosphinous (PR2OH) and phosphorous acid (P(OR)2OH) ligands as catalysts. Marked differences in activity were found, depending on the nature of both the P-donor and η(6)-coordinated arene ligand. Faster transformations were always observed with the phosphinous acids. DFT computations unveiled the intriguing mechanism of acetonitrile hydration catalyzed by these arene-ruthenium(II) complexes. The process starts with attack on the nitrile carbon atom of the hydroxyl group of the P-donor ligand instead of on a solvent water molecule, as previously suggested. The experimental results presented herein for acetonitrile and benzonitrile hydration catalyzed by different arene-ruthenium(II) complexes could be rationalized in terms of such a mechanism.

Synthesis of functionalized benzoxazines by copper-catalyzed C(sp3)–H bond functionalization of acetonitrile with olefinic amides

Abstract: A copper-mediated oxycyanomethylation reaction of olefinic amides with acetonitrile was developed for the synthesis of important benzoxazine derivatives. The reactions involve the activation of the C(sp3)–H bond of acetonitrile and radical cyclization processes for the construction of new C–C and C–O bonds.

Design and Synthesis of Thermoresponsive Ionic Liquid Polymer in Acetonitrile as a Reusable Extractant for Separation of Tocopherol Homologues

Abstract: We report the design and development of a series of novel ionic liquid polymers (PILs) which possess thermoresponsive properties in organic solvent. The PILs were synthesized via reversible addition–fragmentation chain transfer (RAFT) copolymerization of 1-vinyl-3-butylimidazolium bromide and N-isopropylacrylamide, followed by anion exchange of bromide to amino acid d-alanine. The PILs possessed 0.36–0.76 molar fraction of ionic liquid with number-average molecular weight of 2.70–8.17 kg/mol and polydispersity index ranging between 1.12 and 1.25. The copolymerizations followed first-order reaction kinetics, and they were well-controlled, as indicated by the linear increase of molecular weight with monomer conversion. The PILs were thermoresponsive in acetonitrile with upper critical solution temperatures (UCST) varying from 25.7 to 34.8 °C, owing to the introduction of anion of amino acid. The PILs could be completely precipitated out by lowering the solution temperature. The PIL/acetonitrile solutions we...

From Silylone to an Isolable Monomeric Silicon Disulfide Complex

Abstract: The synthesis and characterization of the first bis-N-heterocyclic carbene stabilized monomeric silicon disulfide (bis-NHC)SiS2 2 (bis-NHC=H2C[{NC(H)C(H)N(Dipp)}C:]2, Dipp=2,6-iPr2C6H3) is reported. Compound 2 is prepared in 89 % yield from the reaction of the zero-valent silicon complex (′silylone′) 1 [(bis-NHC)Si] with elemental sulfur. Compound 2 can react with GaCl3 in acetonitrile to give the corresponding (bis-NHC)Si(S)S→GaCl3 Lewis acid–base adduct 3 in 91 % yield. Compound 3 is also accessible through the reaction of the unprecedented silylone-GaCl3 adduct [(bis-NHC)Si→GaCl3] 4 with elemental sulfur. Compounds 2, 3, and 4 could be isolated and characterized by elemental analyses, HR-MS, IR, 13C- and 29Si-NMR spectroscopy. The structures of 3 and 4 could be determined by single-crystal X-ray diffraction analyses. DFT-derived bonding analyses of 2 and 3 exhibited highly polar SiS bonds with moderate pπ–pπ bonding character.

Acetone as a greener alternative to acetonitrile in liquid chromatographic fingerprinting

Abstract: A considerable amount of chemical waste from liquid chromatography analysis is generated worldwide. Acetonitrile is the most employed solvent in liquid chromatography analyses since it exhibits favorable physicochemical properties for separation and detection, but it is an unwelcome solvent from an environmental point of view. Acetone might be a much greener alternative to replace acetonitrile in reversed-phase liquid chromatography, since both share similar physicochemical properties, but its applicability with ultraviolet absorbance-based detectors is limited. In this work, a reference method using acetonitrile and high-performance liquid chromatography coupled to an ultraviolet photodiode array detector coupled to a corona charged aerosol detector system was developed to fingerprint a complex sample. The possibility of effectively substituting acetonitrile with acetone was investigated. Design of experiments was adopted to maximize the number of peaks acquired in both fingerprint developments. The methods with acetonitrile or acetone were successfully optimized and proved to be statistically similar when only the number of peaks or peak capacity was taken into consideration. However, the superiority of the latter was evidenced when parameters of separation and those related to greenness were heuristically combined. A green, comprehensive, time- and resource-saving approach is presented here, which is generic and applicable to other complex matrices. Furthermore, it is in line with environmental legislation and analytical trends.

Bioinspired Tungsten Dithiolene Catalysts for Hydrogen Evolution: A Combined Electrochemical, Photochemical, and Computational Study.

Abstract: Bis(dithiolene)tungsten complexes, WVIO2 (L = dithiolene)2 and WIVO (L = dithiolene)2, which mimic the active site of formate dehydrogenases, have been characterized by cyclic voltammetry and controlled potential electrolysis in acetonitrile. They are shown to be able to catalyze the electroreduction of protons into hydrogen in acidic organic media, with good Faradaic yields (75–95%) and good activity (rate constants of 100 s–1), with relatively high overpotentials (700 mV). They also catalyze proton reduction into hydrogen upon visible light irradiation, in combination with [Ru(bipyridine)3]2+ as a photosensitizer and ascorbic acid as a sacrificial electron donor. On the basis of detailed DFT calculations, a reaction mechanism is proposed in which the starting WVIO2 (L = dithiolene)2 complex acts as a precatalyst and hydrogen is further formed from a key reduced W–hydroxo–hydride intermediate.