Khashayar Ghandi

A recyclable CuO-catalyzed synthesis of 4(3H)-quinazolinones

This paper describes the synthesis of 2-substituted and 2,3-disubstituted 4(3H)-quinazolinones via a tandem reaction involving anthranilamides and aromatic aldehydes catalyzed by 3 mol% CuO powder under air atmosphere. This new method has several advantages: it uses recyclable and cheap CuO powder as the catalyst and air as the green oxidant, water is the only byproduct, and the solvent is recycled. It is easy to run, has a high atom economy and good to excellent yields. A mechanism for the CuO-catalyzed synthesis of the 4(3H)-quinazolinones is proposed.

Generation and detection of the cyclohexadienyl radical in phosphonium ionic liquids

The formation of the cyclohexadienyl radical, C(6)H(6)Mu, in ionic and molecular solvents has been compared. This is the first time that a muoniated free radical is reported in an ionic liquid. In marked contrast to molecular liquids, free radical generation in ionic liquids is significantly enhanced. Comparison of the hyperfine interactions in the ionic liquid and in molecular solvents and with theoretical calculations, suggests significant and unforeseen solvent interaction with the cyclohexadienyl radical.

Free Radical Formation in Supercritical CO2, Using Muonium as a Probe and Implication for H Atom Reaction with Ethene

This report presents the first observation of an alkyl radical in supercritical CO(2) by any magnetic resonance technique. Muoniated ethyl radical has been detected in muon-irradiated supercritical CO(2) solutions. In the presence of a low concentration of ethene in supercritical CO(2), it is found that the addition of muonium to ethene is the only reaction channel, and that the yield of this process is enhanced compared to conventional solvents. The temperature dependence of the hyperfine coupling constants of the ethyl radical suggests that at a density of 0.3 g/cm(3) both the rotational motion of the methyl group and the electronic structure of the radical are similar to those in the gas phase, and therefore that the local environment around the ethyl radical is similar to the gas phase under these conditions. At higher densities, however, there is a remarkable and unexpected density dependence of the hyperfine coupling constant of the ethyl radical, which has never been observed in any environment. In this regime, the density dependence suggests that supercritical CO(2) has a significant effect on the electronic structure of the free radical. Thus, changing the density of CO(2) offers a possible means of tuning the radical reactivity. In addition, at a density of close to 0.4 g/cm(3), CO(2) molecules cluster around the ethyl radical, and this increases the local density around the ethyl radical by a factor of ~1.5.

Near-diffusion-controlled reactions of muonium in sub- and supercritical water

Rate constants are reported for near-diffusion-controlled reactions of muonium in sub- and supercritical water. Specifically, the spin-exchange interaction of muonium with Ni2 +  and the addition of muonium to hydroquinone were studied as a function of temperature and pressure over a wide range of conditions, from standard to over 400 °C and 400 bar (the critical point of water is at 374 °C, 220 bar). At elevated temperatures the rate constants were found to have values far below those predicted by Stokes–Einstein–Smoluchowski theory. Furthermore, the temperature variation of the isobaric rate constants has a maximum in the subcritical region. The pressure dependence of the rate constants increases with temperature, consistent with the increase in compressibility of the solvent; the effective activation volumes are negative. Various models are explored to interpret the temperature and density dependence of the kinetic data. It is concluded that a key factor in the drop of rate constants at high temperature is the cage effect, in particular the number of collisions between a pair of reactants over the duration of their encounter.

Hyperfine coupling constants of muonium in sub and supercritical water

Abstract Muonium, like the hydrogen atom, is a hydrophobic solute in water under standard conditions. Molecular dynamics simulations suggest that the free atom exists in a transient clathrate-like cage of hydrogen-bonded water molecules. The hyperfine constants of Mu and H are very close to their vacuum values, supporting the picture of an atom “rattling” around in a hole in the liquid. Muonium has now been studied in water over a wide range of temperatures and pressures, from standard conditions to over 400°C and 400 bar (the critical point is at 374°C, 221 bar). Drastic changes occur in the properties of water over this range of conditions, so large changes in the muonium hyperfine constant might well be expected. Surprisingly, the changes are small. The hyperfine coupling constant goes through a minimum in the subcritical region, and then increases toward the vacuum value under supercritical conditions.

Muonium in sub- and supercritical water

Muonium has been studied in muon-irradiated water over a wide range of conditions, from standard temperature and pressure (STP) up to 350 bar and up to 420°C, corresponding to water densities from 1.0 down to 0.1 g cm-3. This is the first report of muonium in supercritical water. Muonium was unambiguously identified from its spin precession frequencies in small transverse magnetic fields. The hyperfine constant was determined and found to be similar to the published values for muonium in water at STP and in vacuum. Muonium was found to be long-lived over the whole range of conditions studied. The fraction of muons which form muonium was found to vary markedly over the density range studied. Correlation of the muonium fraction with the ionic product of water suggests a common cause, such as the rate of proton transfer between molecules involved in the radiolysis of water and the formation of MuOH, which competes with muonium formation.

Nuclear magnetic resonance spectroscopic studies of the trihexyl (tetradecyl) phosphonium chloride ionic liquid mixtures with water

Tetra-alkyl Phosphonium ionic liquids are phosphonium salts with melting points near room temperature. We report the NMR studies of water-trihexyl (tetradecyl) phosphonium chloride ionic liquid mixtures. The proton chemical shifts were used to investigate the intermolecular interactions in mixtures of ionic liquids and water. The OH chemical shifts were found to decrease as the water concentration in the ionic liquid increased, and their rate of change with temperature decreased with water concentration. The CH2 and CH3 chemical shifts were found to move downfield with the increase in temperature, and moved further downfield as water concentration was decreased. The interface of experimental data and the results of quantum calculations suggest a significant binding of phosphonium cations to chloride anion and water molecules. As well, the analysis of the data suggests a possible transformation from cationchloride-water configuration at low water concentrations to cation-water-water at higher water concentrations.

Laser-muon spin spectroscopy in liquids—A technique to study the excited state chemistry of transients

This study introduces laser-muon spin spectroscopy in the liquid phase, which extends muonium chemistry in liquids to the realm of excited states and enables the detection of muoniated molecules by their spin evolution after laser excitation. This leads to new opportunities to study the Kinetic Isotope Effects (KIEs) of muonium/atomic hydrogen reactions and to probe transient chemistry in radiolysis processes involved in muonium formation, as well as muoniated intermediates in excited states.

Selective free radical reactions using supercritical carbon dioxide.

We report herein a means to modify the reactivity of alkenes, and particularly to modify their selectivity toward reactions with nonpolar reactants (e.g., nonpolar free radicals) in supercritical carbon dioxide near the critical point. Rate constants for free radical addition of the light hydrogen isotope muonium to ethylene, vinylidene fluoride, and vinylidene chloride in supercritical carbon dioxide are compared over a range of pressures and temperatures. Near carbon dioxides critical point, the addition to ethylene exhibits critical speeding up, while the halogenated analogues display critical slowing. This suggests that supercritical carbon dioxide as a solvent may be used to tune alkene chemistry in near-critical conditions.

Physicochemical properties of imidazo-pyridine protic ionic liquids

A new class of protic ionic liquids (PILs) were prepared by reacting imidazo-[1,2a]-pyridine (ImPr) with benzene-1,2-dithiol (BDT), oxalic acid (Ox), phthalic acid (Phth), pimelic acid (Pim), and sulfuric acid. [ImPr][HSO4] was determined to be the most thermally stable PIL with a decomposition temperature of 326 °C and could potentially be used as an electrolyte in fuel cells and lithium ion batteries. X-ray crystallography on oxidized [ImPr][BDT] indicated the formation of the first reported disulfide PIL. [ImPr][Pim] and [ImPr][Phth] showed fragile behaviour. A Walden plot indicated ionic behaviour close to ideal for [ImPr][Phth].