Showing papers on "Acetonitrile published in 2009"

Solubility-Induced Ordered Polythiophene Precursors for High-Performance Organic Thin-Film Transistors

Abstract: With the aim of enhancing the field-effect mobility of self-assembled regioregular poly(3-hexylthiophene), P3HT, by promoting two-dimensional molecular ordering, the organization of the P3HT in precursor solutions is transformed from random-coil conformation to ordered aggregates by adding small amounts of the non-solvent acetonitrile to the solutions prior to film formation. The ordering of the precursor in the solutions significantly increases the crystallinity of the P3HT thin films. It is found that with the appropriate acetonitrile concentration in the precursor solution, the resulting P3HT nanocrystals adopt a highly ordered molecular structure with a field-effect mobility dramatically improved by a factor of approximately 20 depending on the P3HT concentration. This improvement is due to the change in the P3HT organization in the precursor solution from random-coil conformation to an ordered aggregate structure as a result of the addition of acetonitrile. In the good solvent chloroform, the P3HT molecules are molecularly dissolved and adopt a random-coil conformation, whereas upon the addition of acetonitrile, which is a non-solvent for aromatic backbones and alkyl side chains, 1D or 2D aggregation of the P3HT molecules occurs depending on the P3HT concentration. This state minimizes the unfavorable interactions between the poorly soluble P3HT and the acetonitrile solvent, and maximizes the favorable π–π stacking interactions in the precursor solution, which improves the molecular ordering of the resulting P3HT thin film and enhances the field-effect mobility without post-treatment.

Direct Amide Synthesis from Alcohols and Amines by Phosphine‐Free Ruthenium Catalyst Systems

Abstract: Amides are synthesized directly from alcohols and amines in high yields using an in situ generated catalyst from easily available ruthenium complexes such as the (p-cymene)ruthenium dichloride dimer, [Ru(p-cymeme)Cl 2 ] 2 , or the (benzene)ruthenium dichloride dimer, [Ru(benzene)Cl 2 ] 2 , an N-heterocyclic carbene (NHC) ligand, and a nitrogen containing L-type ligand such as acetonitrile. The phosphine-free catalyst systems showed improved or comparable activity compared to previous phosphine-based catalytic systems. The in situ generated catalyst from [Ru(benzene)Cl 2 ] 2 , an NHC ligand, and acetonitrile showed excellent activity toward reactions with cyclic secondary amines such as piperidine and morpholine.

A porous coordination polymer exhibiting reversible single-crystal to single-crystal substitution reactions at Mn(II) centers by nitrile guest molecules.

Abstract: The porous coordination polymer {[Mn(L)(H2O)](H2O)1.5(DMF)}n (1) containing a water molecule coordinated at the apical position of each distorted octahedral Mn(II) center has been synthesized using the solvothermal technique by reacting Mn(NO3)2·4H2O with a new flexible ligand (LH2) having isophthalic fragment and pyridine donors at the two ends. The coordinated water molecule could be substituted by nitrile guest molecules such as acetonitrile, acrylonitrile, allylnitrile, and crotononitrile (affording compounds 2−5, respectively) without loss of crystallinity. Interestingly, compound 1 selectively captures cis-crotononitrile into its cavity from a mixture of cis and trans isomers. Hence, the cis isomer can be separated from the trans isomer. In each case, 1.5 lattice water molecules and a dimethylformamide (DMF) molecule are also simultaneously replaced by certain numbers of these guest molecules. When these first-generation compounds 2−5 are dipped in DMF at room temperature with the lid of the vial op...

Ru(bpy)3 Covalently Doped Silica Nanoparticles as Multicenter Tunable Structures for Electrochemiluminescence Amplification

Abstract: The electrochemiluminescence (ECL) of doped silica nanoparticles (DSNPs), prepared by a reverse microemulsion method that leads to covalent incorporation of the Ru(bpy)32+, was investigated in acetonitrile and aqueous buffers. The emission was produced for the first time by cation−anion direct annihilation, and the position of ECL maxima indirectly allowed estimation of the E1/2,IOx and E1/2,IRed potentials for Ru(bpy)3 inside DSNPs. The weak ECL emission is most likely generated by an intrananoparticle ruthenium unit annihilation rather than by the electron transfer between a reduced and oxidized DSNP due to the very low diffusivities of the nanoparticles. Thiol-terminated DSNPs were self-assembled on gold substrates, forming compact and stable monolayers which mimic probe−target assays with DSNPs as labels. The ECL intensity obtained by such functionalized substrates in aqueous media, using tripropylamine (TPrA) as coreactant, was surprisingly increased with respect to direct electrochemical oxidation b...

Hydrogen-Bonding Interactions between Water and the One- and Two-Electron-Reduced Forms of Vitamin K1: Applying Quinone Electrochemistry To Determine the Moisture Content of Non-Aqueous Solvents

Abstract: Vitamin K1 (VK1) was shown by voltammetry and coulometry to undergo two chemically reversible one-electron reduction processes in acetonitrile (CH3CN) containing 0.2 M Bu4NPF6 as the supporting electrolyte. The potential separation between the first and second electron-transfer steps diminished sequentially with the addition of water, so that at a H2O concentration of approximately 7 M (∼13% v/v) only one process was detected, corresponding to the reversible transfer of two electrons per molecule. The voltammetric behavior was interpreted on the basis of the degree of hydrogen bonding between the reduced forms of VK1 with water in the solvent. It was found that the potential separation between the first and second processes was especially sensitive to water in the low molar levels (0.001−0.1 M); therefore, by measuring the peak separation as a function of controlled water concentrations (accurately determined by Karl Fischer coulometric titrations) it was possible to prepare calibration curves of peak sep...

Iron(III) Chloride: A VersatileCatalyst for the Practical Synthesis of 3-Sulfenylindoles

Abstract: The direct sulfenylation of indoles with aromatic thiols has been accomplished in the presence of 20 mol% of FeCl 3 in refluxing acetonitrile to produce 3-arylthioindoles in relatively good to excellent yields and with high selectivity. This method works even with 2-unsubstituted indoles.

Ferrocene as a Reference Redox Couple for Aprotic Ionic Liquids

Abstract: The electrochemical behavior of ferrocene has been studied in a number of room temperature ionic liquids. Diffusion-controlled, well-defined anodic and cathodic peaks were found for the Fc/Fc+ (ferrocene/ferrocenium) oxidation/reduction on the gold electrode. Ohmic resistance R between working and auxiliary electrodes was deduced from impedance measurements. Cyclic voltammograms were corrected for the base line current as well as for the ohmic drop (IR). The formal potential 1/2(Epa+Epc) for ferrocene reduction/oxidation in aprotic ionic liquids tested is within a relatively narrow range and may be approximated by the value of 0.527±0.018 V (against the cryptate Ag/Ag+222 in acetonitrile reference). Ferrocene diffusion coefficients, calculated from the peak current dependence on the sweep rate, were of the order of 10−7 cm2 s−1.

Acetal Levulinyl Ester (ALE) Groups for 2′-Hydroxyl Protection of Ribonucleosides in the Synthesis of Oligoribonucleotides on Glass and Microarrays

Abstract: We describe a synthetic strategy that permits both the growth and deprotection of RNA chains that remain attached to a solid polymer support or chip surface. The key synthons for RNA synthesis are novel 5′-O-DMTr 2′-acetal levulinyl ester (2′-O-ALE) ribonucleoside 3′-phosphoramidite derivatives. In the presence of 4,5-dicyanoimidazole (DCI) as the activator, these monomers coupled to Q-CPG solid support with excellent coupling efficiency (∼98.7%). The method was extended to the light directed synthesis of poly rU and poly rA on a microarray through the use of a 5′-O-(2-(2-nitrophenyl)propoxycarbonyl)-2′-O-ALE-3′-phosphoramidite derivative. A two-stage deprotection strategy was employed to fully deblock the RNA directly on the Q-CPG or microarray support without releasing it from the support’s surface: phosphate group deblocking with NEt3 in acetonitrile (ACN) (2:3 v/v; 1 h, r.t.) followed by removal of the 2′-O-ALE groups under mild hydrazinolysis conditions (0.5−4 h, r.t.). This last treatment also remov...

Direct Perfluorination of K2B12H12 in Acetonitrile Occurs at the Gas Bubble−Solution Interface and Is Inhibited by HF. Experimental and DFT Study of Inhibition by Protic Acids and Soft, Polarizable Anions

Abstract: During the optimization of the F2 perfluorination of K2B12H12 in acetonitrile with continuous bubbling of 20/80 F2/N2, it was discovered that (i) HF and other protic acids inhibit each of the 12 fluorination steps (in contradiction to recently published findings) and (ii) the fluorinations appear to take place at the gas bubble−solution interface. Experimental results and DFT calculations suggest that these two phenomena are related by the relative propensities of the various B12H12−xFx2− anions to partition from bulk solution to the interface (i.e., their relative polarizabilities or softness; 0 ≤ x ≤ 12). Relative to the previously reported syntheses of K2B12F12 or Cs2B12F12, the new optimized procedure has the following advantages: (i) the scale was increased 10-fold without sacrificing yield (74% for K2B12F12, 76% for Cs2B12F12) or purity (99.5+%); (ii) the reaction/purification time was decreased from ca. 1 week to 2 days; and (iii) the solvent was changed from anhydrous HF to acetonitrile, allowing ...

Water Structure at Air/Acetonitrile Aqueous Solution Interfaces

Abstract: How is interfacial water organized beneath an acetonitrile monolayer at the air/acetonitrile aqueous solution interface? The method of vibrational sum frequency generation was used to address these issues. It was found that the different water structures expressed at different vibrational spectral regions, i.e. the “ice-like”, the “liquid-like”, and the non-hydrogen bonded “free” OD, responded differently as the acetonitrile bulk concentration was increased. At the bulk acetonitrile concentration that was sufficient to form an acetonitrile monolayer and at higher bulk concentrations, it was observed that there are no longer vibrational resonances that correspond to the oriented collective water vibrations, i.e. the “ice-like” and “liquid-like” structures of water as observed at the air/water interface. The story was different in the free OD vibrational region where a red-shifted resonance was found at acetonitrile concentrations sufficient to form an acetonitrile monolayer. Speculations on the origin of t...

Simulations of Infrared Spectra of Nanoconfined Liquids: Acetonitrile Confined in Nanoscale, Hydrophilic Silica Pores†

Abstract: The infrared spectrum of acetonitrile confined in hydrophilic silica pores roughly cylindrical and 2.4 nm in diameter has been simulated using molecular dynamics. Hydrogen bonding interactions between acetonitrile and silanol groups on the pore wall involve charge transfer effects that have been incorporated through corrections based on electronic structure calculations on a dimer. The simulated spectrum of confined acetonitrile differs most prominently from that of the bulk liquid by the appearance of a blue-shifted shoulder, in agreement with previous experimental measurements. The dominant peak is little changed in position relative to the bulk liquid case, but broadened by ∼40%. A detailed analysis of the structure and dynamics of the confined liquid acetonitrile is presented, and the spectral features are examined in this context. It is found that packing effects, hydrogen bonding, and electrostatic interactions all play important roles. Finally, the molecular-level information that can be obtained a...

Temperature- and solvent-controlled dimensionality in a zinc 6-(1H-benzoimidazol-2-yl)pyridinecarboxylate system

Abstract: Several 0D, 1D, and 3D metal–organic hybrid frameworks of ZnII have been synthesized by using the asymmetric ligand 6-(1H-benzoimidazol-2-yl)pyridinecarboxylic acid (HL) with control of the temperature and solvent in a solvothermal synthesis technique. In DMF, the structure at room temperature confirms that the resulting compound Zn(L)2·2(H2O) (1) is the 0D mononuclear structure, above ∼80 °C, C–N bond cleavage of partial DMF molecules induces the formation of the 1D chain-like compound {[Zn(L)(HCOO)]·2(H2O)}n (2), but on warming up to 120 and 160 °C, due to the decomposition of a large number of DMF molecules, the same reaction, respectively, gives two 3D metal–organic coordination polymers with 3D channels reported previously {[Zn(HCOO)3]−·[H2N(CH3)2]+}n (3) and [Zn(HCOO)2]n (4), in which the 3D channels of 3 contain guest [H2N(CH3)2]+ motifs, while at high temperature the 3D channels of 4 are an open stable system without any guest molecules. Replacing DMF in the above reaction by ethanol or acetonitrile, only 0D compound 1 is obtained in the range from room temperature to 160 °C. However, the same reaction in DMSO provides a 1D wave-like compound {[Zn(L)(DMSO)]·(ClO4)·H2O}n (5), in which the solvent DMSO molecule coordinates to the central metal ZnII ion. Furthermore, in three new complexes 1, 2 and 5, through π⋯π stacking and hydrogen bonding interactions, 3D supramolecular networks are assembled. It is worth noting that the existence of the twelve-membered cyclic water–perchlorate dimers [(ClO4)⋯(H2O)]22− with chair-conformation in the solid state of 5 not only increases the stability of the supramolecular structure, but also results in a stronger fluorescence signal compared with ligand HL, 1 and 2.

Direct synthesis and structural analysis of nitrogen-doped carbon nanofibers.

Abstract: Carbon nanofibers containing a range of nitrogen contents of 1−10 atom % were directly synthesized by catalytic chemical vapor deposition over nickel-based catalysts at 350−600 °C using acetonitrile and acrylonitrile. The nitrogen content was controlled by careful choice of the reaction conditions. The N-doped carbon nanofibers showed herringbone structure with 20−60 nm diameter. X-ray photoelectron spectroscopy was applied to examine the chemical state of nitrogen in carbon nanofibers. Structural features of N-doped carbon nanofibers were examined in X-ray diffraction and electron microscopy. The mechanism for nitrogen including the structure of carbon nanofibers through the catalysis was discussed on the basis of the results.

Diffusion Coefficients of 1-Alkyl-3-methylimidazolium Ionic Liquids in Water, Methanol, and Acetonitrile at Infinite Dilution†

Abstract: The diffusion coefficients of several ionic liquids based on the 1-alkyl-3-methylimidazolium cation, [CnC1Im], with chloride, tetrafluoroborate, and bis(trifluoromethanesulfonyl)imide, [Ntf2], anions were measured, using a Taylor dispersion technique, in three solvents (water, methanol, and acetonitrile) as a function of temperature between (283 and 333) K. The diffusion coefficients vary from 0.57·10−9 m2·s−1 for 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide, [C8C1im][Ntf2], in water to 3.48·10−9 m2·s−1 for 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C2C1im][Ntf2], in acetonitrile. In general, the diffusivities are lower for water, followed by methanol and acetonitrile, and decrease with an increase in the alkyl side chain of the imidazolium-based ionic liquids. These trends do not follow the Stokes−Einstein relation but can be explained by the solute−solvent interactions. The data were correlated using a modified Wilke−Chang equation in which a correction parameter ...

Brønsted-acidic ionic liquid [HO3S(CH2)4MIM][HSO4] as efficient and reusable catalyst for one-pot synthesis of β-acetamido ketones

Abstract: Efficient and convenient synthesis of β-acetamido ketones has been achieved by one-pot reaction of acetophenone, aryl aldehydes, acetyl chloride, and acetonitrile in the presence of 3-methyl-1-(4-sulfonylbutyl)imidazolium hydrogensulfate [HO3S(CH2)4MIM][HSO4], a Bronsted-acidic ionic liquid, as a green and reusable catalyst in solvent-free media at room temperature. The catalyst could be recycled and reused without noticeable decrease in catalytic activity.

Investigation of the reactivity of Pt phosphinito and molybdocene nitrile hydration catalysts with cyanohydrins.

Abstract: Aldehyde- and ketone-derived cyanohydrins were reacted with the nitrile hydration catalysts [PtCl(PR2OH){(PR2O)2H}] (1) and Cp2Mo(OH)(OH2)+ (2) under a variety of hydration reaction conditions. In general, the cyanohydrins were hydrated to the amides rather slowly using these catalysts, but no subsequent hydrolysis of the amide products occurred. Catalyst 2 was much less reactive than catalyst 1, showing at best trace amounts of amide product. Product inhibition-, substrate inhibition-, and cyanide poisoning-tests demonstrated that coordination of cyanide, generated by dehydrocyanation of the cyanohydrins, is responsible for the generally low catalytic activity of 1 and 2 with cyanohydrin substrates. Addition of KCN to reaction mixtures of acetonitrile and 1 gave a linear plot of rate versus cyanide concentration, indicating that binding of cyanide to the catalysts is irreversible. Density functional theory (DFT) calculations showed that, for the hydration reaction catalyzed by 2, the formation of most in...