Showing papers on "Acetonitrile published in 2001"

Photoalkylation of 10-Alkylacridinium Ion via a Charge-Shift Type of Photoinduced Electron Transfer Controlled by Solvent Polarity

Abstract: A charge-shift type of photoinduced electron-transfer reactions from various electron donors to the singlet excited state of 10-decylacridinium cation (DeAcrH+) in a nonpolar solvent (benzene) is found to be as efficient as those of 10-methylacridinium cation (MeAcrH+) and DeAcrH+ in a polar solvent (acetonitrile). Irradiation of the absorption bands of MeAcrH+ in acetonitrile solution containing tetraalkyltin compounds (R4Sn) results in the efficient and selective reduction of MeAcrH+ to yield the 10-methyl-9-alkyl-9,10-dihydroacridine (AcrHR). The same type of reaction proceeds in benzene when MeAcrH+ is replaced by DeAcrH+ which is soluble in benzene. The photoalkylation of R‘AcrH+ (R‘ = Me and De) also proceeds in acetonitrile and benzene using 4-tert-butyl-1-benzyl-1,4-dihydronicotinamide (ButBNAH) instead of R4Sn, yielding MeAcrHBut. The quantum yield determinations, the fluorescence quenching of R‘AcrH+ by electron donors, and direct detection of the reaction intermediates by means of laser flash p...

An FT-IR study of the adsorption and oxidation of N-containing compounds over Fe2O3-TiO2 SCR catalysts

Abstract: The interaction of NO, ammonia (NH3), hydrazine (N2H4), hydroxylamine (NH2OH), urea (H2NCONH2), acetamide (CH3CONH2) and acetonitrile (CH3CN) on Fe2O3-TiO2 model catalysts was studied. The data support the idea that hydrazine can be intermediate in the oxidation of ammonia to nitrogen, while hydroxylamine-type species, formed at higher temperature, can be intermediate in the oxidation of ammonia to NO. Bronsted acid sites do not appear to be involved in this chemistry.

Synthesis and Excited-State Photodynamics of Perylene−Porphyrin Dyads. 1. Parallel Energy and Charge Transfer via a Diphenylethyne Linker

Abstract: The photophysical properties of a perylene−porphyrin dyad have been examined with the aim of using this construct for molecular photonics applications. The dyad consists of a perylene-bis(imide) dye (PDI) connected to a zinc porphyrin (Zn) via a diphenylethyne linker (pep). In both polar and nonpolar solvents, the photoexcited perylene unit (PDI*) decays very rapidly (lifetimes of 2.5 (toluene) and 2.4 ps (acetonitrile)) by energy transfer to the porphyrin, forming PDI−pep−Zn* in high yield (80%, toluene; 70% acetonitrile), and hole transfer to the porphyrin, forming PDI-−pep−Zn+ in lesser yield (20%, toluene; 30% acetonitrile). In both toluene and acetonitrile, the Zn* excited state subsequently decays with a lifetime of 0.4 ns primarily (80%) by electron transfer to the perylene (forming PDI-−pep−Zn+). In the nonpolar solvent (toluene), the PDI-−pep−Zn+ charge-transfer product has a lifetime of >10 ns and decays by charge recombination primarily to the ground state but also by thermal repopulation of th...

Encapsulation of N2, O2, Methanol, or Acetonitrile by Decamethylcucurbit[5]uril(NH4+)2 Complexes in the Gas Phase: Influence of the Guest on “Lid” Tightness

Abstract: Cucurbiturils are of current interest as encapsulating agents, as catalysts, and as “wheel” components of rotaxanes. Most reports to date have dealt with the 6-mer cucurbituril, 2 but recently synthetic procedures for the higher homologues have been developed. 3 Only a few reports of the methylated 5-mer (Figure 1), decamethylcucurbit[5]uril (C 40H50N20O10, hereafter referred to as mc5), have appeared. 4,5 In solution, mc5 has been reported 5 to be a highly selective host for Pb 2+. Herein we describe the observation of guest@mc5(NH 4)2 complexes (Figure 2) (where guest ) N2, O2, methanol, or acetonitrile) via electrospray ionization Fourier transform mass spectrometry. Further, we show the complex can be opened in the gas phase by use of an ionophore, removing a “lid” cation and releasing the guest, and that the rate of this reaction depends on the size of the guest molecule, which likely influences how strongly the “lid” is attached. All experiments were performed using a Fourier transform ion cyclotron resonance mass spectrometer (model APEX 47e; Bruker Daltonics; Billerica, MA) and a microelectrospray ionization source modified 6 from an Analytica (Analytica of Branford; Branford, MA) design. The instrument was controlled using a MIDAS7 data system (National High Magnetic Field Ion Cyclotron Resonance Facility; Tallahassee, FL). Samples of mc5, obtained from IBC Advanced Technologies (American Fork, UT) about 1 mM in neat water, 50:50 methanol:water, 50:50 acetonitrile:water, or 50:50 ethanol:water, along with 2 mM ammonium acetate (Mallinckrodt; Paris, KY), were electrosprayed. A few samples were sprayed from 50:50 methanold1:D2O (99 and 99.9 atom %, respectively; both from Cambridge Isotope Laboratories; Andover, MA). The complex ions were also allowed to react with 18-crown-6 (Sigma; St. Louis, MO) introduced into the trapping region of the instrument via a direct-exposure probe, with partial pressures typically about 2 × 10-7 mbar. Isolation of reactant ions in the trap was performed using stored waveform inverse Fourier transform (SWIFT) techniques. 8 Reactant and product ion populations were measured as a function of reaction time to determine rate constants. Rate constants were determined both by isolating particular reactant ions, thus studying their reactions individually, and by studying a group of reactant ions concurrently. Molecular models were built usingMacromodel , ver. 7.1 (Schrodinger, Inc.: Portland, OR) and minimized using the MMFF94s force field included withMacromodel . Limited (1000 starting structures) Monte Carlo conformational searches were also carried out using this force field; these tended to find the same minimum-energy structure tens to hundreds of times. These minimum-energy structures were used as the starting point for full geometry optimizations at the semiempirical AM1 level (MacSpartan Pro,ver. 1.0.2; Wavefunction, Inc.: Irvine, CA) and at the ab initio HF/3-21G* level ( Gaussian 98, ver. A.7; Gaussian, Inc.: Pittsburgh, PA). Electrospray of mc5 along with ammonium acetate results in mass spectra composed of peaks corresponding to mc5 with one NH4 attached, mc5 with two NH 4 attached, and the latter with a guest molecule included. The complexity of the resulting mass spectrum depends on the spray solvents employed. We have observed no water inclusion complexes, even when spraying from neat water. Spraying from methanol:water solutions results almost exclusively in observation of doubly charged, doubly NH 4capped complexes with methanol included, whereas spraying from acetonitrile:water (Figure 3) yields peaks corresponding to “empty” doubly charged, doubly capped mc5 as well as guestincluded complexes of N 2, O2 (from air), or acetonitrile. The identity of the methanol guest was verified by spraying from 50: 50 methanold1:D2O, which resulted in a shift of +0.5 m/z for the doubly charged complex ion (allowing for deuteration of the caps). We observed no ethanol guests when spraying from ethanol: water solutions but observed abundant “empty” doubly ammoniated complexes and doubly ammoniated complexes containing N2 or O2. The molecular formulas of the latter two complexes † IBC Advanced Technologies; American Fork, Utah. (1) Jeon, Y.-M.; Kim, J.; Whang, D.; Kim, K. J. Am. Chem. Soc. 1996, 118, 9790-9791. (2) For a recent review, see Mock, W. L. In Comprehensi Ve Supramolecular Chemistry; Vögtle, F., Ed.; Elsevier: New York, 1996; Vol. 2, pp 477 -493. (3) Kim, J.; Jung, I.-S.; Kim, S.-Y.; Lee, E.; Kang, J.-K.; Sakamoto, S.; Yamaguchi, K.; Kim, K.J. Am. Chem. Soc. 2000, 122, 540-541. (4) Flinn, A.; Hough, G. C.; Stoddart, J. F.; Williams, D. J. Angew. Chem., Int. Ed. Engl.1992, 31, 1475-1477. (5) Zhang, X. X.; Krakowiak, K. E.; Xue, G.; Bradshaw, J. S.; Izatt, R. M. Ind. Eng. Chem. Res. 2000, 39, 3516-3520. (6) Shen, N.; Pope, R. M.; Dearden, D. V. Int. J. Mass Spectrom. 2000, 195-196, 639-652. (7) Senko, M. W.; Canterbury, J. D.; Guan, S.; Marshall, A. G. Rapid Commun. Mass Spectrom. 1996, 10, 1839-1844. (8) Chen, L.; Wang, T.-C. L.; Ricca, T. L.; Marshall, A. G. Anal. Chem. 1987, 59, 449-454. Figure 1. Structure of decamethylcucurbit[5]uril, mc5.

Investigation of reduction of Cu(II) complexes in positive-ion mode electrospray mass spectrometry

Abstract: The electrospray ionization mass spectrometry (ESI-MS) behavior of seven Cu(II) complexes with tetradentate ligands has been studied. An unexpected reduction process, in positive ion mode, of the Cu oxidation state was observed, and shown to be due to charge transfer between the metal complex and the solvent molecules in the gas phase. Ion trap collision-induced dissociation experiments and deuterated solvents were used to support the proposed mechanism that is not a common electrochemical redox reaction at the ESI tip, but a gas-phase process. A series of solvents (acetonitrile, methanol, ethanol, propanol and iso-butanol) were tested, and a correlation between ionization energy (IE) and the amount of Cu(I) produced in ESI has been demonstrated for the alcohols, although some other solvent properties should also be taken into account. The electrochemical reduction potential of the complexes in solution is also an important parameter, since complexes more easily reduced in solution are also easier to reduce in the gas phase. Copyright © 2001 John Wiley & Sons, Ltd.

Electrochemical preparation and characterization of conducting copolymers : poly(pyrrole-co-indole)

Abstract: Copolymerization of pyrrole and indole was achieved electrochemically in acetonitrile containing lithium perchlorate as supporting electrolyte. The copolymer compositions can be altered by varying the comonomer feed ratios during preparation. The copolymers were characterized by conductivity measurements, cyclic voltammetry, scanning electron microscopy, UV-visible and IR spectroscopic techniques. A possible scheme for the copolymerization mechanism has been suggested.

Selective oxidation of benzene to phenol in the liquid phase with amorphous microporous mixed oxides

Abstract: Amorphous microporous mixed oxides (AMM) have been investigated as catalysts for the direct oxidation of benzene to phenol with hydrogen peroxide in the liquid phase The catalysts have been prepared by an acidic sol–gel process The most active AMM-catalysts found have been based on Fe as active centre The catalysts have been characterised by a variety of methods including Ar-adsorption isotherms, MAS-NMR, EXAFS, XANES and HRTEM The most promising catalytic system was AMM-Fe 3 Al 3 Si in acetonitrile as solvent The effect of various reaction parameters such as solvent, reaction temperature, molar ratio of benzene:hydrogen peroxide, catalyst concentration, and reaction orders have been studied The iron containing catalysts shows substantial leaching under reaction conditions Among several attempts to stabilise the active centres in the amorphous network doping with Al-ions was most successful The drastic effect of Al on the nature of the active Fe in the amorphous silica framework could be documented by Moessbauer spectroscopy Reaction calorimetry studies revealed that acetonitrile is not an inert solvent but participates directly in the reaction

Solvent effect on the ground and excited state dipole moments of fluorescein

Abstract: The ground-state and excited-state dipole moments of fluorescein were studied at room temperature in n -alcohols (methanol– n -hexanol) and acetonitrile and acetonitrile–benzene solvent mixtures. The excited-state dipole moments were estimated from Lippert's, Bakhshiev's and Chamma–Viallet's equations by using the variation of the Stokes' shift with the solvent dielectric constant and refractive index. Experimental ground-state dipole moments for fluorescein in n -alcohols, acetonitrile and acetonitrile–benzene solvent mixtures were estimated by the Guggenheim–Smith method (GSM). It was determined that dipole moments of the excited-state were higher than those of the ground-state in n -alcohols while they were lower than those of the ground-state in acetonitrile and acetonitrile–benzene solvent mixtures. The solute–solvent interactions on the ground-state and the excited-state dipole moments of fluorescein are discussed.

The role of the solvent in TS-1 chemistry: active or passive? An early study revisited

Abstract: The oxidation of n-hexane with hydrogen peroxide, catalyzed by TS-1 in various solvents, is reported. The initial rate of reaction decreases in the order: t-butanol > t-butanol/water > methanol ≈ acetonitrile ≈ water, whereas the reverse trend was observed for the adsorption of n-hexane in the catalyst. A dual function is postulated for the solvent in relation to its effects on kinetics. It assists the sorption/desorption of reagents/products in TS-1 (passive role) and participates in the catalytic cycle, through interactions with polar species involved in it (active role). A mechanistic pathway for the hydroxylation of paraffinic and aromatic C–H bonds is suggested.

Potential Dependent Orientation of Acetonitrile on Platinum (111) Electrode Surface Studied by Sum Frequency Generation

Abstract: Sum frequency generation, SFG, vibrational spectroscopy is used to investigate the orientation of acetonitrile (CH3CN) at the Pt(111) electrode. Acetonitrile is studied as a function of water concentration and electrode potential to determine how these factors affect the adsorbate structure at the interface. The SFG results indicate acetonitrile orients in response to the electrode potential with the C−C bond, C3 symmetry axis, perpendicular to the surface. The orientation is predominately with the CH3 group toward the metal between 200 and 600 mV and with the CN group toward the metal above 800 mV, (vs NHE, normal hydrogen electrode). The orientation is reversible between 0 and 1400 mV. Addition of water, >0.05x, disrupts the orientation of acetonitrile at the interface. The alignment of acetonitrile along the surface normal is in response to the surface charge at the electrode.

Segmental Mobility in Phosphorus-Containing Dendrimers. Studies by Fluorescent Spectroscopy

Abstract: Steady-state fluorescence spectra and decays of excitations of a phosphorus-containing dendrimer labeled with 12 internal labels and of an iminophosphorane model compound bearing two labels dissolved in acetonitrile, diglyme, 1,4-dioxane, triethylene glycol, and cyclohexanol revealed that the interior of dendrimers contained many solvent molecules, and movements of internally located pyrene labels were not reduced by interactions with the dendrimer core. This conclusion was based on the following findings. A ratio of the intensities of pyrene−pyrene excimer and pyrene monomer emissions (IE/IM) decreased with increasing solvent viscosity but, with exception of acetonitrile solutions, was very close for the dendrimers and for the model. Monomer and excimer emission intensity decays were fitted with two-exponential functions with time constants τ1 and τ2 characterizing formation of pyrene−pyrene excimers and recovery of pyrene moieties in their ground state, respectively. For solvent viscosities varying from...

Covalent attachment of acetonitrile on Si(100) through Si–C and Si–N linkages

Abstract: The covalent binding and adsorption states of acetonitrile on Si(100) have been investigated using temperature programmed desorption (TPD), x-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and density function theory (DFT) calculation. XPS and HREELS results show that acetonitrile chemisorbs on Si(100) in a side-on di-σ binding configuration, forming Si–C and Si–N σ bonds. TPD measurements reveal the presence of two desorption states, β1 and β2 with desorption energies of 29.8 and 24.6 kcal mol−1, respectively. Based on DFT calculations, the β1 state is possibly assigned to di-σ bonded acetonitrile on top of a dimer and/or in an in-row bridging chemisorption, while the β2 state is related to acetonitrile bonded in a cross-row bridging configuration.

Molecular structure of substituted phenylamine alpha-OMe- and alpha-OH-p-benzoquinone derivatives. Synthesis and correlation of spectroscopic, electrochemical, and theoretical parameters.

Abstract: Thirteen C6 para-substituted anilinebenzoquinones derived from perezone (PZ) (2-(1,5-dimethyl-4-hexenyl)-3-hydroxy-5-methyl-1,4-benzoquinone) were prepared to analyze the effect of the substituents on quinone electronic properties. The effect of a hydrogen bond between the α-hydroxy and carbonyl C4−O4 groups was determined in perezone derivatives by substituting electron-donor and electron-acceptor groups such as −OMe, −Me, −Br, and −CN and comparing the −OH (APZs) and −OMe (APZms) derivatives. Reduction potentials of these compounds were measured using cyclic voltammetry in anhydrous acetonitrile. The typical behavior of quinones, with or without α-phenolic protons, in an aprotic medium was not observed for APZs due to the presence of coupled, self-protonation reactions. The self-protonation process gives rise to an initial wave, corresponding to the irreversible reduction reaction of quinone (HQ) to hydroquinone (HQH2), and to a second electron transfer, attributed to the reversible reduction of perezon...

Viscosities and Volumes of Dilute Solutions of Formamide in Water + Acetonitrile and for Formamide and N,N-Dimethylformamide in Methanol + Acetonitrile Mixed Solvents: Viscosity B-Coefficients, Activation Free Energies for Viscous Flow, and Partial Molar Volumes

Abstract: The viscosity B-coefficients and partial molar volumes have been measured for N,N-dimethylformamide and formamide in methanol + acetonitrile solvent systems and for N,N-dimethylformamide in water + acetonitrile mixed solvents. These data are used to calculate the solute contribution to the activation free energy for viscous flow, Δμ≠13, for these systems. It is found that the Δμ≠13 values are simply related to the corresponding enthalpies of transfer.

Unsaturated thiacrown ethers: synthesis, physical properties, and formation of a silver complex.

Abstract: The 6-, 9-, 12-, 15-, 18-, 21-, 24-, and 27-membered unsaturated thiacrown ethers 1−8 were formed by reaction of cis-1,2-dichloroethylene with sodium sulfide in acetonitrile. Crystal structures of 4−8 were determined by X-ray crystallography, and it was found that all sulfur atoms of 5−8 direct to the inside of the ring (endodentate). All of the ORTEP drawings show that there are cavities in these molecules, and the cavity sizes in 4−8 were 1.76, 2.34, 3.48, 4.43, and 5.36 A, respectively. The UV spectra of 4−8 showed absorption maximums at the range of 255−276 nm in acetonitrile, and the absorption maximums of 4−8 were found to shift to longer wavelengths by changing the solvent from acetonitrile to cyclohexane. The cyclic voltammograms of 4−8 indicate that the larger unsaturated thiacrown ethers were oxidized more easily than the smaller systems, and unsaturated thiacrown ethers were oxidized more easily than corresponding saturated systems. The reaction of 4 with silver trifluoroacetate in acetone affo...

Potential-dependent vibrational spectroscopy of solvent molecules at the Pt(111) electrode in a water/acetonitrile mixture studied by sum frequency generation.

Abstract: Sum frequency generation (SFG) vibrational spectra of D2O and/or acetonitrile (CH3CN) on a Pt(111) single-crystal electrode were obtained as a function of applied potential in a 5 mol % water/aceto...

Solvent Effects on Solute Electronic Structure and Properties: Theoretical Study of a Betaine Dye Molecule in Polar Solvents

Abstract: The electronic structure of the betaine dye molecule, pyridinium- N-phenoxide [4-(1-pyridinio)phenolate] including the effects of geometry and polar solvents, has been studied at an ab initio level using the reference interaction site model self-consistent-field (RISM-SCF) method. Acetonitrile (CH3CN) and water (H2O) were selected as polar solvents. We obtain both the optimized solute geometry in solution and the total free energy profile with respect to variation in the torsion angle between the pyridinium and phenoxide rings and analyze the various electronic and solvation contributions. The betaine molecule in the gas phase has a twisted geometry, which is slightly more twisted in solution. In acetonitrile, the calculated structure shows good agreement with earlier semiempirical results for the minimum free energy structure. It is shown that the solute dipole moment is strongly enhanced in polar solution, also in accord with earlier semiempirical calculations. However, in solution, there is relatively ...

About the Keggin Isomers: Crystal Structure of [N(C4H9)4]4-γ-[SiW12O40], the γ-Isomer of the Keggin Ion. Synthesis and 183W NMR Characterization of the Mixed γ-[SiMo2W10O40]n- (n = 4 or 6)

Abstract: The tetrabutylammonium γ-dodecatungstosilicate has been crystallized in a 6/1 acetonitrile/water solvent. An X-ray single-crystal analysis was carried out on [N(C4H9)4]4-γ-[SiW12O40] which crystall...

Cyanides and Nitriles

Abstract: Cyanides are among the most acutely toxic of all industrial chemicals and are produced in large quantities and used in many different applications. However, they cause few serious accidents or deaths. This is partly because the word cyanide is synonymous with a highly poisonous substance and a certain amount of care in handling is thereby ensured. The cyanides and nitriles are a disparate group of substances characterized by the presence of a cyanide (CN) group in their molecular structure. The cyanide group consists of a carbon bonded to a nitrogen. In those cases where the cyanide group is readily available, their toxicity is likely to have similarity to hydrogen cyanide (HCN). The chemical and physical characteristics of the compound will affect the potential availability of the cyanide group and therefore the hazards associated with different chemical species. For purposes of the toxicologist, cyanides and nitriles can be classified into the following groups: The inorganic cyanides include (Group 1) hydrogen cyanide, cyanogen, simple salts of hydrogen cyanide that dissociate readily to release CN−1 ions (such as sodium, potassium, calcium, and ammonium cyanide); (Group 2) halogenated compounds such as cyanogen chloride or bromide; and (Group 3) simple and complex salts of hydrogen cyanide that do not dissociate readily to release CN−1 ions (such as cobalt cyanide trihydrate, cupric and cuprous cyanide, silver cyanide, and ferricyanide and ferrocyanide salts). The organic cyanides include (Group 4) cyanide glycosides produced by plants (such as amygdalin and linamarin); and (Group 5) nitriles [such as acetonitrile (methyl cyanide), acrylonitrile and isobutyronitrile]. Keywords: Cyanides; Nitriles; Bhopal; India; Methylisocyanate release

Synthesis of TMBQ using Cu(II)-substituted MCM-41 as the catalyst

Abstract: Mesoporous MCM-41 molecular sieves substituted with various amounts of Cu(II) and Al(III) were synthesized by the hydrothermal method. The resultant materials were characterized by XRD, XANES, surface area and pore size measurement, EPR and 27 Al solid state NMR. The Cu(II)-substituted MCM-41 was found to be an efficient catalyst in the oxidation of trimethylphenol (TMP) to trimethylbenzoquinone (TMBQ) at mild reaction conditions. The latter is an intermediate in the manufacture of Vitamin E. The optimal activity was obtained when MCM-41 was concomitantly substituted with small amounts of Cu(II) and Al(III). The liquid phase reactions were extremely sensitive to the oxidant and solvent used. With acetonitrile as solvent, hydrogen peroxide and tert-butyl hydrogen peroxide were effective oxidants but with benzaldehyde as solvent, oxygen gas was also an effective oxidant. © 2001 Elsevier Science B.V. All rights reserved.