Showing papers on "Acetonitrile published in 2002"

Polarizable Continuum Model (PCM) Calculations of Solvent Effects on Optical Rotations of Chiral Molecules

Abstract: A new theory of solvent effects on the optical rotations of chiral molecules is presented. The frequency-dependent electric dipole−magnetic dipole polarizability, βαβ(ν), is calculated using density functional theory (DFT). Solvent effects are included using the polarizable continuum model (PCM). DFT/PCM calculations of sodium D line specific rotations, [α]D, have been carried out for seven conformationally rigid chiral organic molecules (fenchone, camphor, α-pinene, β-pinene, camphorquinone, verbenone, and methyloxirane) for a diverse set of seven solvents (cyclohexane, carbon tetrachloride, benzene, chloroform, acetone, methanol, and acetonitrile). The predicted variation in [α]D for the solvents cyclohexane, acetone, methanol, and acetonitrile are in excellent agreement with experiment for all seven molecules. For the solvents carbon tetrachloride, benzene, and chloroform, agreement is much poorer. Since only electrostatic solute−solvent interactions are included in the PCM, our results lead to the con...

Synthesis, characterization, and reactivity of arylpalladium cyanoalkyl complexes: selection of catalysts for the alpha-arylation of nitriles.

Abstract: A new coupling process, the palladium-catalyzed alpha-arylation of nitriles, was developed by exploring the structure and reactivity of arylpalladium cyanoalkyl complexes. Complexes of 1,2-bis(diphenylphosphino)benzene (DPPBz), 1,1'-bis(di-i-propylphosphino)ferrocene (D(i)()PrPF), racemic-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP), and diphenylethylphosphine (PPh(2)Et) were prepared. Coordination to palladium through the alpha-carbon was observed for DPPBz-ligated complexes and for complexes of primary and benzylic nitrile anions. However, the anion of isobutyronitrile was coordinated to palladium through the cyano-nitrogen when the complex was ligated by D(i)()PrPF. The isobutyronitrile anion displaced a phosphine ligand to form a C,N-bridged dimer when generated from PPh(2)Et-ligated palladium. These results suggest that the nitrile anion preferentially coordinates to palladium through the carbon atom in the absence of steric effects. Thermolysis of the arylpalladium cyanoalkyl complexes led to reductive elimination that formed alpha-aryl nitriles. The high yields and short reaction times observed for BINAP-ligated complexes suggested that BINAP-ligated palladium catalysts might be appropriate for the arylation of nitriles. Initial results on a palladium-catalyzed process for the direct coupling of aryl bromides and primary, benzylic, and secondary nitrile anions to form alpha-aryl nitriles in good yields are reported.

Structural and density functional studies of uranium(III) and lanthanum(III) complexes with a neutral tripodal N-donor ligand suggesting the presence of a U-N back-bonding interaction.

Abstract: The crystal structures of two trisiodide octacoordinated uranium(III) complexes of tris[(2-pyrazinyl)methyl]amine (tpza), which differ only by the ligand occupying the eighth coordination site (thf or MeCN), and of their lanthanum(III) analogues have been determined. In the acetonitrile adducts the M-N(pyrazine) distances are very similar for U(III) and La(III), while the U-N(acetonitrile) distance is 0.05 A shorter than the La-N(acetonitrile) distance. In the [M(tpza)I(3)(thf)] complexes in which the monodentate acetonitrile ligand, a weak pi-acceptor ligand, is replaced by a thf molecule, a sigma-donor only, the mean value of the distance U-N(pyrazine) is 0.05 A shorter than the mean value of the La-N(pyrazine) distance. Since we are comparing isostructural compounds of ions with very similar ionic radii, these differences indicate the presence of a stronger M-N interaction in the U(III) complexes and therefore suggest the presence of a covalent contribution to the U-N bonding. The selectivity of the tpza ligand toward U(III) complexation (with respect to that of La(III)) in the presence of sigma-donor-only ligands has been quantified by the value of K(U(tpza))/K(La(tpza)) measured to be 3.3 +/- 0.5. The analysis of the metal-N-donor ligand bonding was carried out by a quasi-relativistic density functional theory study on small model compounds, of formula I(3)M-L (M = La, Nd, U; L = acetonitrile, pyrazine) and I(3)M-(pyrazine)(3) (M = La, U). The structural data obtained from geometry optimizations on these systems reproduce experimental trends, i.e., a decrease in the M-N distance from La to U, combined with an increase of the C-N distance in the acetonitrile derivatives. A detailed orbital analysis carried out on the resulting optimized complexes did not reveal any orbital interaction between the trivalent lanthanide cations (Ln(3+)) and the N-donor ligands. In contrast, a back-donation electron transfer from 5f U(3+) orbitals to the pi* virtual orbital of the ligand was observed for both acetonitrile and pyrazine. Evaluation of the total bonding energy between the MI(3) and L fragments shows that this orbital interaction leads to a stabilization of the uranium(III) system compared to the lanthanide species.

Electrochemical Polymerization and Characterization of Poly(3-(4-fluorophenyl)thiophene) in Pure Ionic Liquids

Abstract: The electrochemical oxidation of 3-(4-fluorophenyl) thiophene (FPT) at a platinum electrode in pure 1-ethyl-2,3-dimethylimidazolium bis ((trifluoromethyl)sulfonyl) amide, EDMITFSI, and 1,3-diethyl-5-methylimidazolium bis ((trifluoromethyl)sulfonyl) amide, DEMITFSI, yielded an electroactive polymer. This polymer (PFPT) was similar to that prepared from common nonaqueous media such as tetraethylammonium tetrafluoroborate/acetonitrile, but it was characterized by slower ion insertion kinetics. A rapid loss of electroactivity of the polymer was observed upon cycling in pure ionic liquid, and that was attributed to gradual deswelling of the polymer. X-ray photoelectron spectroscopy measurements demonstrated that the doping processes of PFPT when cycled in pure ionic liquid were similar to those occurring in acetonitrile-based electrolyte and involved the incorporation of the anions (TFSI-) of the ionic liquid when the polymer was oxidized to the p-doped state. The expulsion of these anions and the incorporatio...

Ferrocene-containing carbohydrate dendrimers.

Abstract: Aliphatic amines, incorporating one or three (branched) acylated beta-D-glucopyranosyl residues, were coupled with the acid chloride of ferrocenecarboxylic acid and with the diacid chloride of 1,1'-ferrocenedicarboxylic acid to afford four dendrimer-type, carbohydrate-coated ferrocene derivatives in good yields (54-92%). Deprotection of the peracylated beta-D-glucopyranosyl residues was achieved quantitatively by using Zemplen conditions, affording four water-soluble ferrocene derivatives. When only one of the two cyclopentadienyl rings of the ferrocene unit is substituted, strong complexes are formed with beta-cyclodextrin in H2O, as demonstrated by liquid secondary ion mass spectrometry (LSIMS), 1H NMR spectroscopy, electrochemical measurements, and circular dichroism spectroscopy. Molecular dynamics calculations showed that the unsubstituted cyclopentadienyl ring is inserted through the cavity of the toroidal host in these complexes. The electrochemical behavior of the protected and deprotected ferrocene-containing dendrimers was investigated in acetonitrile and water, respectively. The diffusion coefficient decreases with increasing molecular weight of the compound. The potential for oxidation of the ferrocene core, the rate constant of heterogeneous electron transfer, and the rate constant for the energy-transfer reaction with the luminescent excited state of the [Ru(bpy)3]2+ complex (bpy = 2,2'-bipyridine) are strongly affected by the number (one or two) of substituents and by the number (one or three) of carbohydrate branches present in the substituents. These effects are assigned to shielding of the ferrocene core by the dendritic branches. Electrochemical evidence for the existence of different conformers for one of the dendrimers in aqueous solution was obtained.

Selective interaction of lower rim calix[4]arene derivatives and bivalent cations in solution. Crystallographic evidence of the versatile behavior of acetonitrile in lead(II) and cadmium(II) complexes.

Abstract: The interaction of lower rim calix(4)arene derivatives containing ester (1) and ketone (2) functional groups and bivalent (alkaline-earth, transition- and heavy-metal) cations has been investigated in various solvents (methanol, N,N-dimethylformamide, acetonitrile, and benzonitrile). Thus, 1 H NMR studies in CD 3 -OD, C 3 D 7 NO, and CD 3 CN show that the interaction of these ligands with bivalent cations (Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Hg 2+ , Pb 2+ , Cd 2+ ) is only observed in CD 3 CN. These findings are corroborated by conductance measurements in these solvents including benzonitrile, where changes upon the addition of the appropriate ligand (1 or 2) to the metal-ion salt only occur in acetonitrile. Thus, in this solvent, plots of molar conductance against the ligand/metal cation ratio reveal the formation of 1:1 complexes between these ligands and bivalent cations. Four metal-ion complex salts resulting from the interaction of 1 and 2 with cadmium and lead, respectively, were isolated and characterized by X-ray crystallography. All four structures show an acetonitrile molecule sitting in the hydrophobic cavity of the ligand. The mode of interaction of the neutral guest in the cadmium(II) complexes differs from each other and from that found in the lead(II) complexes and provides evidence of the versatile behavior of acetonitrile in binding processes involving calix(4)arene derivatives. The thermodynamics of complexation of these ligands and bivalent cations in acetonitrile is reported. Thus, the selective behavior of 1 and 2 for bivalent cations is for the first time demonstrated. The role of acetonitrile in the complexation process in solution is discussed on the basis of 1 H NMR and X-ray crystallographic studies. It is suggested that the complexation of 1 and 2 with bivalent cations is likely to involve the ligand-solvent adducts rather than the free ligand. Plots of complexation Gibbs energies against the corresponding data for cation hydration show a selectivity peak which is explained in terms of the predominant role played by cation desolvation and ligand binding energy in complex formation involving metal cations and macrocycles in solution. A similar peak is found in terms of enthalpy suggesting that for most cations (except Mg 2+ ) the selectivity is enthalpically controlled. The ligand effect on the complexation process is quantitatively assessed. Final conclusions are given highlighting the role of the solvent in complexation processes involving calix(4)arene derivatives and metal cations.

Electrochemical oxidation of tetrabutylammonium salts of aliphatic carboxylic acids in acetonitrile

Abstract: Departamento de Qui ´mica del Centro de Investigacion y Estudios Avanzados del I.P.N., C. P. 07360,D. F., Me´xicoThe anodic oxidation of a series of tetrabutylammonium aliphatic carboxylates has been performed in acetonitrile on glassy carbonelectrodes. The electrochemical behavior was studied without the interference of the anodic oxidation of the solvent. The cyclicvoltammetry analysis shows that the electron transfer and the decarboxylation are stepwise. The coulometric analysis shows thatthe overall mechanism is monoelectronic. However preparative scale electrolysis shows the intervention of two electron-transfersteps leading to carbocations, which then react with the acetonitrile and the carboxylate itself to form N-acylamides as principalproducts. Two types of adsorption of the carboxylate ions and the alkyl carbocations were proposed to occur selectively, namely,on a small fraction of active sites or on the functional groups existing on the glassy carbon surfaces.© 2002 The Electrochemical Society. @DOI: 10.1149/1.1450616# All rights reserved.Manuscript submitted August 8, 2001; revised manuscript received October 18, 2001. This was Paper 1193 presented at theSan Francisco, California, Meeting of the Society, September 2–7, 2001. Available electronically February 8, 2002.

Dielectric relaxation and underlying dynamics of acetonitrile and 1-ethyl-3-methylimidazolium triflate mixtures using THz transmission spectroscopy

Abstract: We use terahertz (THz) transmission spectroscopy to obtain the frequency dependent complex dielectric functions for pure acetonitrile, pure 1-ethyl-3-methylimidazolium triflate (emim triflate, a room temperature molten salt), and mixtures of the two liquids. The behavior of the pure liquids is modeled with either two (acetonitrile) or three (emim triflate) Debye relaxations. We then discuss the interactions of the molten salt and solvent based on the modified Debye relaxations evident in the mixtures. We determine that at low molten salt concentrations, the mixtures behave like electrolyte solutions of a crystalline salt dissolved in a solvent. At higher molten salt concentrations, the behavior is that of a mixture of two liquids.

Oxidative dehydrogenation and ammoxidation of ethane and propane over pentasil ring Co-zeolites

Abstract: The activity of Co-zeolites with MFI, BEA, FER, MOR topologies was studied in ethane and propane oxidative dehydrogenation and ammoxidation in a through-flow arrangement and temperature range 350–500 °C. The products of oxidative dehydrogenation of paraffins were corresponding olefins, CO and CO 2 , in the propane reaction only a small part was cracked to ethylene and methane. Besides CO and CO 2 , the ammoxidation of ethane yielded ethylene and acetonitrile, and of propane brought propylene and acetonitrile too. Presence of ammonia increased substantially the paraffin conversion as well as selectivity and yield of the sum of olefin and nitrile for CoH-BEA and CoH-MFI zeolites, while with CoNa-zeolites the paraffin conversion and selectivity were similar. The sequence in activity in both the oxidative dehydrogenation and ammoxidation (in TOF values per Co ion in conversion of paraffins and yields of olefin and olefin+acetonitrile) of Co-zeolites (more pronounced for ammoxidation) Co-BEA>CoMFI⪢Co-MOR>Co-FER is ascribed to the location of prevailing amount of Co ions in β cationic position of pentasil ring zeolites, i.e. at the exposed site at the intersection of straight and sinusoidal channel in ZSM-5, and in open channels of beta-zeolite, in contrast to Co-β ions in MOR and FER structures occurring in the narrow interconnected channels and in eight-member ring channel, respectively. Formation of acetonitrile at propane ammoxidation can be attributed to interaction of ammonia with double bond of propylene at β position, as suggested in literature, as well as to the observed easy decomposition of acrylonitrile to acetonitrile in the presence of ammonia.

Dynamics of polar solvation in acetonitrile–benzene binary mixtures: Role of dipolar and quadrupolar contributions to solvation

Abstract: While dynamics of polar solvation have been tabulated for a wide range of pure polar solvents, substantially less is known about the dynamic response of solvent mixtures. Here, results for polar solvation dynamics are presented for the nonassociating mixture of a dipolar solvent, acetonitrile, and a quadrupolar solvent, benzene. The solvation response observed is sensitive to the mixing of the pure solvents, affecting both the inertial and diffusive components of the solvation response function. Addition of acetonitrile to benzene increases the amplitude of the inertial response. At high benzene mole fractions, the diffusive relaxation reveals a slow component attributed to translational diffusion of the acetonitrile.

Hydrocarbon Oxidations with Hydrogen Peroxide Catalyzed by a Soluble Polymer‐Bound Manganese(IV) Complex with 1,4,7‐Triazacyclononane

Abstract: Soluble manganese(IV) complexes with polymer-bound 1,4,7-triazacyclononanes as ligands (compound 2) catalyze the oxidation of alkanes by hydrogen peroxide in acetonitrile at room and lower temperatures. The corresponding alkyl hydroperoxides are the main products. The presence of a relatively small amount of acetic acid is obligatory for this reaction. The oxidation of alkanes and olefins exhibits some features (kinetic isotope effect, bond selectivities) that distinguish this system from an analogous one based on the dinuclear Mn(IV) complex 1.

Electron localization in liquid acetonitrile

Abstract: Time-resolved one- and two-pulse laser dc photoconductivity has been used to observe two kinds of reducing species, anion-1 and anion-2, in liquid acetonitrile. At 25 C, the standard enthalpy of conversion from anion-1 to anion-2 is -44.3 {+-} 3.6 kJ/mol and the conversion time is 3 ns. The high-temperature form, anion-1, absorbs in the IR and migrates >3.3 times faster than any other ion in acetonitrile. This rapid migration has a low activation energy of 3.2 kJ/mol (vs 7.6 kJ/mol for other ions). Anion-1 rapidly transfers the electron to acceptors with high electron affinity, with rate constant up to 10{sup 11} M{sup -1} s{sup -1}. The low-temperature form, anion-2, absorbs in the visible and exhibits normal mobility and electron-transfer rates, ca. 1.5 x 10{sup 10} M{sup -1} s{sup -1}. It reacts, by proton transfer, with two hydrogen-bonded molecules of water and/or aliphatic alcohols. Laser photoexcitation of these two solvent anions in their respective absorption bands leads to the formation of CH{sub 3} and CN{sup -}. We present arguments indicating that anion-2 is a dimer radical anion of acetonitrile, whereas anion-1 is a multimer radical anion that may be regarded as a 'solvated electron'.

Inhomogeneity of Mixing in Acetonitrile Aqueous Solution Studied by Small-Angle X-ray Scattering

Abstract: Acetonitrile aqueous solution has an upper critical solution temperature (UCST) at 272 K at c = 0.38 (c represents the mole fraction of acetonitrile). To study quantitatively how the mixing scheme ...

Microwave activation of electrochemical processes: enhanced electrodehalogenation in organic solvent media.

Abstract: The effect of high-intensity microwave radiation focused into a “hot spot” region in the vicinity of an electrode on electrochemical processes with and without coupled chemical reaction steps has been investigated in organic solvent media. First, the electrochemically reversible oxidation of ferrocene in acetonitrile and DMF is shown to be affected by microwave-induced thermal activation, resulting in increased currents and voltammetric wave shape effects. A FIDAP simulation investigation allows quantitative insight into the temperature distribution and concentration gradients at the electrode | solution interface. Next, the effect of intense microwave radiation on electroorganic reactions is considered for the case of ECE processes. Experimental data for the reduction of p-bromonitrobenzene, o-bromonitrobenzene, and m-iodonitrobenzene in DMF and acetonitrile are analyzed in terms of an electron transfer (E), followed by a chemical dehalogenation step (C), and finally followed by another electron-transfer...

Lead as its own luminescent sensor.

Abstract: Lead (II) in polar organic solvents such as acetone, acetonitrile, and propylenecarbonate with excess bromide generates the highly luminescent lead−halide cluster Pb4Br113-. This in situ sensor does not rely on a host−guest relationship and, thus, is intrinsically selective and sensitive, allowing for the detection of lead at nanomolar concentrations. The cluster's emission maximum and relaxation kinetics are temperature dependent and indicate a close spacing of intralead and intracluster electronic energy levels.

Solvent Effects on the Oxidative Electrochemical Behavior of cis-Bis(isothiocyanato)ruthenium(II)-bis-2,2‘-bipyridine-4,4‘-dicarboxylic Acid

Abstract: The redox properties of cis-[Ru(dcbpyH2)2(NCS)2] ([Ru(dcbpyH2)2(NCS)2]; dcbpyH2 = 2,2‘-bipyridine- 4,4‘-dicarboxylic acid) have been investigated in various solvents by combining electrochemical techniques (cyclic voltammetry (CV) and spectroelectrochemistry), mass spectrometry, digital simulation techniques, and semiempirical quantum chemical calculations. The electrochemical study has shown that while in polar solvents such as acetonitrile and ethanol the complex undergoes, following oxidation, the rapid loss of SCN ligands, forming the corresponding solvato complexes. In the less polar solvent tetrahydrofuran, a reversible oxidative CV behavior is observed at relatively low scan rates. On the basis of the CV and spectroelectrochemical studies and supported by quantum chemical calculations, a complex parallel ECE mechanism is proposed, comprising the loss of the SCN ligands in their pristine (anionic) form, which is initiated by the metal-centered oxidation process.

Preferential solvation of a hydrophobic probe in binary mixtures comprised of a nonprotic and a hydroxylic solvent: A view of solute-solvent and solvent-solvent interactions

Abstract: The fluorescence of pyrene, a hydrophobic probe, was investigated in binary mixtures comprising a nonprotic [acetonitrile, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and tetrahydrofurane (THF)] and a protic (water, methanol, ethanol, propan-2-ol, and butan-1-ol) solvent. The variation in I/III values, the intensity ratios between the first and third bands in vibronic fine structures of the emission spectra, along with the variation in the more polar component was studied for each binary mixture. A preferential solvation (PS) model was adapted from the literature and successfully applied to the experimental data. In the mixtures containing acetonitrile, pyrene is always preferentially solvated by the nonprotic component. However, the extent of PS by acetonitrile diminishes with a decrease in the polarity of the protic cosolvent. These results were explained by the fact that pyrene is a highly hydrophobic probe. Thus, a replacement of the more polar protic cosolvent for one which is more hydrop...

Hydrogen Bonding between Phenol and Acetonitrile

Abstract: The present work aims to resolve theoretically the puzzling effect of downshifting of the νOH stretching mode of phenol, complexed with acetonitrile, as the latter concentration increases, via performing a thorough search of the potential energy surface of the interaction of phenol with acetonitrile at the modest MP2/6-31+G(d,p), MP2/6-31G(d), and B3LYP/6-31+G(d,p) computational levels. We postulate and firmly approve that, besides the conventional σ hydrogen-bonded structure of phenol with one acetonitrile molecule, there exists the novel, although less favorable, structure with π-type hydrogen bonding. Such bonding becomes crucial as the second acetonitrile molecule is added to the 1:1 complex of phenol and acetonitrile, and furthermore, its substantial stabilization in polar solvents provides an explanation of the mentioned controversial issue that has stood unclear during the last four decades.

Unique 2:1 complex with a trans-chelating bis-pyridine ligand.

Abstract: The trans-chelating ligand 1,2-bis(2‘-pyridylethynyl)benzene (1) was prepared in a single step by a Sonogashira cross-coupling reaction. Treatment of 1 with trans-bis(acetonitrile)palladium chloride provides the complex [Pd(1)Cl2] while treatment with tetrakis(acetonitrile)palladium(II) tetrafluoroborate provides the 2:1 complex [Pd(1)2](BF4]2. The structural, spectroscopic, and thermal properties of 1 and its Pd(II) complexes are examined.