Showing papers on "Acetonitrile published in 1977"

Kinetic and thermodynamic character of reducing species produced on pulse radiolysis of acetonitrile

Abstract: During nanosecond pulse radiolysis of liquid acetonitrile a transient optical absorption was observed in the spectral range 500 to 1500 nm. The extreme reactivity of this species towards solutes capable of accepting electrons allowed its assignment as a reducing entity. In the purest liquid prepared this species had a half-life of some 900 ns. Variable temperature studies showed that this reducing species, having an intense maximum near 1450 nm at + 62°C, was drastically reduced in absorption intensity at –40°C, where the decay character changed and a weak maximum was observed near 550 nm. It was concluded that the two species are different chemical forms of a reducing entity joined by an equilibrium. Tentative identification of the reversible change according to (CH3CN)–+ CH3CN ⇌(CH3CN)–2 with the monomeric anion as the infrared absorbing entity was based on thermodynamic considerations and the effects of adding polar liquids. Quantitative examination of the data allowed a value of –34.9 kJ mol–1 to be extracted for the binding energy of the anion dimer. Measurements of the yields of pyrene and trans-stilbene radical anion formed after pulse radiolysis of appropriate solutions led to the evaluation of G(reducing entity)= 1.03. In addition it was found that O– radicals, formed by reaction between (CH3CN)– and N2O, reacted with acetonitrile via both addition and abstraction routes. Further, in solutions containing tetracyanobenzene (TCNB) and O2, capture of the negative entity by O2 was followed by electron transfer from O–2 to TCNB.

Complexation of the cesium cation by macrocyclic polyethers in various solvents. A cesium-133 nuclear magnetic resonance study of the thermodynamics and kinetics of exchange

Abstract: The formation constants for the complexation of Cs/sup +/ in six solvents by three crown ethers, 18-crown-6, dibenzo-18-crown-6, and dicyclohexyl-18-crown-6, were studied at 25/sup 0/C by cesium-133 NMR techniques. The solvents used, in the approximate order of decreasing first complexation constant for all crown ethers, were pyridine, acetone, propylene carbonate, acetonitrile, N,N-dimethylformamide, and dimethyl sulfoxide. In all solvents, 18-crown-6 formed both 1:1 and 2:1 (ligand to metal) complexes with enough difference between the complexation constants that the second constant could be determined. The formation of 2:1 complexes by the other two crown ethers was also indicated in most solvents but the second complexation constant could only be measured for the dibenzo-18-crown-6 complex in pyridine. In many cases the first complexation constant was too large to measure by the NMR technique so that only lower bounds could be established. The rate of loss of the Cs/sup +/ ion from dicyclohexyl-18-crown-6 and from monobenzo-2,2,2-cryptand in propylene carbonate was measured as a function of temperature. The activation energy for the latter case (15 kcal mol/sup -1/) is substantially larger than for the crown ether complex (8.5 kcal mol/sup -1/). Although the chemical shifts of both Cs/sup +/ and its 1:1 complex with 18-crown-6more » are strongly solvent dependent, the chemical shift of the 2:1 complex is independent of solvent, indicating that in the ''sandwich'' complex the cesium ion is effectively shielded from the solvent.« less

NMR-spectroscopic studies on solvent electrophilic properties, Part II: Binary aqueous-non aqueous solvent systems

Abstract: Acceptor numbers have been determined for binary mixtures of water with acetonitrile (AN), dioxane, acetone (AC), pyridine (PY), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), hexamethylphosphoramide (HMPA), methanol, ethanol andi-propyl alcohol. The electrophilic properties of binary aqueous-non aqueous solvent mixtures are determined both by selective solvation and specific solvent-solvent interactions. The variation of the acceptor number as a function of solvent composition is interpreted in terms of the previously determined nucleophilic and electrophilic properties of the pure components and their specific solvent structure.

Anion and solvent effects on the rate of reduction of triplet excited thiazine dyes by ferrous ions

Abstract: — The lifetimes of the triplet excited states of thionine and methylene blue were measured in aqueous and 50 v/v% aqueous acetonitrile solutions acidified with 0.01 N sulfuric or trifluoromethyl-sulfonic acid. The rate constants for reaction of the triplet excited dyes with ferrous ions were measured in the same solutions. The triplet lifetimes in the absence of added quenchers were insensitive to a change in acid from trifluoromethylsulfonic to sulfuric or to a change in solvent from water to 50v/v% aqueous acetonitrile (τ for triplet thionine ˜7.5 μs, τ for triplet methylene blue ˜4.5 μs). In contrast, the rate constant for reaction of the triplet dyes with ferrous ions increased by nearly a factor of 10 with a change in acid from trifluoromethylsulfonic to sulfuric. In solutions containing sulfate ions this reaction rate constant increased with increasing sulfate concentration and with a change in solvent from water to 50 v/v% aqueous acetonitrile. The results are discussed in terms of the possibility of association of the positively charged reactive ions with sulfate anions. Quenching of the triplet excited dyes by ferric ions or by ground state dye molecules was shown to be negligible at the concentration used for the ferrous ion quenching study.

THE SYNTHESIS OF HIGHLY STABLE o- AND p-QUINONE METHIDES

Abstract: The reactions of 2,4- and 2,6-disubstituted phenols with two molar amounts of 1,3-benzodithiolylium tetrafluoroborate in acetonitrile at room temperature followed by treatment with triethylamine afforded the highly stable quinone methides, 2-(1,3-benzodithiol-2-ylidene)-3,5-cyclohexadien-1-ones and 4-(1,3-benzodithiol-2-ylidene)-2,5-cyclohexadien-1-ones, respectively, in good yields.

Interaction of duroquinone lowest triplet with amines

Abstract: The reaction of the lowest triplet of duroquinone, 3Q, with tertiary amines (triethylamine TEA, diethylaniline DEA, triphenylamine TPA) has been investigated by laser flash absorption spectroscopy in non-polar (cyclohexane or benzene) and polar (acetonitrile) solvents. Three pathways of 3Q deactivation involving an exciplex as intermediate were observed: (i) an electron transfer to 3Q from TPA and DEA in a polar solvent, (ii) a H atom transfer to 3Q from DEA in a non-polar solvent and from TEA in a non-polar or a polar solvent, (iii) a physical quenching of 3Q by TPA in a non-polar solvent with no photoreduction products.

X-Ray structure of tris(acetonitrile)tricarbonylrhenium(I) tetrafluoroborate

Abstract: Reaction of [n-Bu4N]2[Re4(CO)16] with AgBF4 in acetonitrile affords the compound [(CH3CN)3Re(CO)3][BF4]. The latter crystallizes in monoclinic space group P21/c with unit cell dimensions a = 11.021...

Lithium-7, Sodium-23, and Cesium-133 NMR and Far Infrared Study of Alkali Complexes with C222-Dilactam in Various Solvents

Abstract: Nuclear magnetic resonances of alkali nuclei,7Li,23Na, and133Cs, as well as far infrared measurements are used to study alkali complexes of a bicyclic diazapolyoxa ligand—the dilactam of cryptand C222. Measurements were carried out in pyridine, tetrahydrofuran, acetonitrile, nitromethane, dimethylformamide, and aqueous solutions. The complexing ability of the dilactam is similar to, but weaker than, that of the cryptand C222. The limiting chemical shifts of the complexed cations were solvent-dependent, indicating incomplete enclosure of the cation by the ligand. Formation constants of Li+ and Cs+ complexes were calculated from the chemical-shift dependence on the ligand/metal ion mole ratio.

Kinetics of reactions of tris(2,2′-bipyridyl)iron(II) with cyanide and with hydroxide ion in binary aqueous solvent mixtures

Abstract: Rates of reaction of [Fe(bipy)3]2+ with cyanide ion in binary aqueous solvent mixtures containing ethylene glycol glycerol, acetonitrile, dimethyl sulphoxide (dmso), or tris (dimethylamino)phosph ine oxide (tdpo), and with hydroxide ion in binary aqueous solvent mixtures containing t-butyl alcohol, dmso, or tdpo, are reported. Reactivity trends in the various solvent mixtures are discussed and, in the case of the reaction with hydroxide in aqueous dmso, compared with reactivity trends for similar inorganic and organic reactions. Where the existence of the required thermodynamic data on Gibbs free energies of transfer of single ions permits, it is shown that the effect of solvation, and thence chemical-potential, changes for cyanide and hydroxide ions is dominant in determining reactivies in their reactions with [Fe(bipy)3]2+.

Solvation of negative ions by protic and aprotic solvents. Information from gas phase ion equilibria measurements

Abstract: Measurement of the gas phase ion equilibria between ions M and solvent molecules Sl provide binding energies of the complexes M±(S1)n(for n= 1 to ∼6). Comparison of these data with single ion energies of solvation shows that differences in ion solvation in solution are reflected in the binding energies of ion-molecule complexes in the gas phase. The weaker solvation of negative ions (relative to positive ions) observed in liquid aprotic solvents is reflected in the binding energies of negative ion aprotic molecule complexes, a weaker binding being found for the first and subsequent few aprotic molecules. An analysis of the bonding in Cl–(CH3CN) and K+(CH3CN) shows that the weaker bonding to Cl– is due to the very diffuse distribution of the positive pole of the dipole in acetonitrile. In effect the dipole can not come close to the negative ion. Analysis shows a similar picture also for acetone. Experimental results for the bonding between Cl–HR are given for a variety of compounds HR. These show that for RH = protic compounds, like oxygen acids, the hydrogen bond in Cl–HR increases with the acidity of HR. For aprotic compounds, i.e., carbon acids, no relationship between the bond in the complex and the acidity of HR is found. An examination of the solvation of substituted phenoxide ions by protic and aprotic solvents shows that solvation by protic solvents is adversely affected by charge dispersal in the ion, while aprotic solvents are much less sensitive to charge dispersal. The reasons for this important difference in behaviour are examined.

Direct electrochemical synthesis of neutral and anionic chloro- and bromo-complexes of titanium, zirconium, and hafnium

Abstract: Electrochemical oxidation of titanium, zirconium, or hafnium(IV) in the presence of a solution of chlorine or bromine (X) in acetonitrile (L) leads to direct synthesis of MX4L2 species in good yield. These compounds are easily transformed into other neutral adducts. On addition of tetraalkylammonium salts to the solution phase, the products are the salts (R4N)MCl5 or (R4N)2MBr6, except that with titanium Et4NTiBr4 was also formed under some conditions. The advantages of this method are discussed, and a possible reaction mechanism proposed.

Comparison of solvated electron reaction rates in water and ammonia

Abstract: New and literature data of solvated electron reactions in ammonia with some inorganic ions and organic neutral molecules are compared with corresponding data in water. In ammonia only a few reactions with aromatic molecules are diffusion controlled and therefore faster than in water (k ≈ 1 × 1011 and 1 × 1010 M−1 s−1,respectively). After correcting for the electrostatic contribution to the rate constant of the other reactions it is concluded that in general the reactivity of the solvated electron in ammonia is appreciably lower, than in water. For the slow reactions of ammoniated electrons with acetonitrile and dimethylsulfoxide we find activation energies of 7 to 9 kcal/mol and activation volumes of −40 to −60 ml/mol. In these reactions it is suggested that the rate determining step is associated with the collapse of the large electron cavity in liquid ammonia.

Complex formation between sulfur dioxide and halide ions

Abstract: Complex formation between sulfur dioxide and iodide ions in acetonitrile (AN) has been studied by vapour pressure measurements. The enthalpy changes ΔH0 for 1:1 association reactions between SO2 an...

Synthesis, crystal and molecular structure of acetonitrilecarbonyldichloro(cyclo-octa-1,5-diene)ruthenium(II)

Abstract: Reaction of [RuCl2CO(C8H12)]2 with acetonitrile gives [RuCl2CO(MeCN)C8H12](Ia), shown by X-ray diffraction analysis to have octahedral stereochemistry with a trans-OC–Ru–MeCN arrangement. Crystals are monoclinic, space group P21/c, with a= 12.933(2), b= 7.641 (8), c= 13.435(3)A, β= 104.36(2)° and contain one molecule per asymmetric unit. The structure was solved by use of 1 086 film data, and refined to R 0.09. The related complexes [RuCl2CO(L)C8H12](L = acrylonitrile and cyclopropyl cyanide) have also been synthesised.

Kinetics and mechanism of the oxygen-transfer reaction between bis-(diethyldithiocarbamato)dioxomolybdenum(VI) and triphenylphosphine

Abstract: The kinetics of the oxygen-transfer reaction from [MoO2(S2CNEt2)2] to PPh3 in acetonitrile solution have been monitored using stopped-flow techniques at temperatures between 15 and 45 °C. The rate law d[MoIV]/dt=k2[MoVI][PPh3], with k2(25 °C)= 1.1 ± 0.3 dm3 mol–1 s–1, describes the kinetic data obtained, with activation parameters at 25 °C of ΔH‡= 8.4 ± 0.5 kcal mol–1 and ΔS‡=–30 ± 1.6 cal K–1 mol–1.

Anodic Oxidation of Sulfonamides. II. Anodic Oxidation of 4'-Substituted Benzenesulfonanilides in Acetonitrile

Abstract: Anodic oxidation of benzenesulfon-p-anisidide (I), benzenesulfon-p-toluidide (II), and N-methylbenzenesulfon-p-anisidide (III) were investigated by cyclic voltammetry and controlled potential electrolysis at a glassy-carbon anode in acetonitrile. I showed a single anodic wave in the absence of pyridine, and three anodic waves in the presence of pyridine. On electrolysis of I in the absence of pyridine, p-benzoquinone and benzenesulfonamide were formed. On electrolysis of I in the presence of pyridine, N, N'-dibenzenesulfonyl-N-(4'-methoxyphenyl)-5-methoxy-o-phenylenediamine (IV) and 1-(2-benzenesulfonamido-5-methoxyphenyl) pyridinium perchlorate (V) were obtained. Anodic oxidation of II in acetonitrile containing excess of pyridine gave N, N'-dibenzenesulfonyl-N-(p-tolyl)-5-methyl-o-phenylenediamine (VI) and N, N'-dibenzenesulfonyl-5, 5'-dimethyl-2, 2'-biphenyldiamine (VII). The formation of VI and VII was interpreted in terms of one-electron transfer followed by dimerizations of the free radical of II. On electrolysis of III in the presence of pyridine, 1-(N-methyl-3-benzenesulfonamido-6-methoxyphenyl) pyridinium perchlorate (VIII) was formed as the main product. The position of pyridination, which was ortho to the methoxy-group, was explained on the basis of steric factors.