Lewis Acid trapping of an elusive copper-tosylnitrene intermediate using scandium triflate

High-valent copper-nitrene intermediates have long been proposed to play a role in copper-catalyzed aziridination and amination reactions. However, such intermediates have eluded detection for decades, preventing the unambiguous assignments of mechanisms. Moreover, the electronic structure of the proposed copper-nitrene intermediates has also been controversially discussed in the literature. These mechanistic questions and controversy have provided tremendous motivation to probe the accessibility and reactivity of Cu(III)-NR/Cu(II)N(?)R species. In this paper, we report a breakthrough in this field that was achieved by trapping a transient copper-tosylnitrene species, 3-Sc, in the presence of scandium triflate. The sufficient stability of 3-Sc at -90 °C enabled its characterization with optical, resonance Raman, NMR, and X-ray absorption near-edge spectroscopies, which helped to establish its electronic structure as Cu(II)N(?)Ts (Ts = tosyl group) and not Cu(III)NTs. 3-Sc can initiate tosylamination of cyclohexane, thereby suggesting Cu(II)N(?)Ts cores as viable reactants in oxidation catalysis.     

On the number of isomorphism classes of complete translation nets

This note will be contained in the doctoral dissertation of the second author which is written under the supervision of the first author.     

Exclusive \eta production in pp reactions

Angular distributions for the exclusive reaction observed via the decay channel have been measured at GeV, 2.50 GeV and 2.85 GeV (excess energies Q = 324 MeV, 412 MeV and 554 MeV). The polar angle of the shows an anisotropy with respect to the beam direction for the lowest energy, which vanishes for the higher energies. The anisotropy of the pp polar angle increases slightly with the beam energy.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.75.Cs Nucleon-nucleon interactions (including antinucleons, deuterons, etc.) - 14.40.Aq , K, and mesons - 25.40.Ve Other reactions above meson production thresholds (energies > 400 MeV)Y. Bedfer: Present address: DAPNIA/SPhN, CEA Saclay, France.A. Brenschede: Present address: Syngenio AG, StuttgartF. Brochard: Present address: LPHNHE, Ecole Polytechnique 91128 Palaiseau, France.Seonho Choi: Present address: Temple University, Philadelphia, PA, USA.R. Dressler: Present address: Paul Scherrer Institut, Villigen, CH-5232.J. Foryciarz: Present address: Motorola Polska Software Center, Kraków, Poland.H.-W. Pfaff: Present address: d-fine GmbH, Eschborn.     

Determination of dissolved hexavalent chromium in industrial wastewater effluents by ion chromatography and post-column derivatization with diphenylcarbazide

A proposed EPA method for the determination of dissolved hexavalent chromium in drinking water, groundwater and industrial wastewater effluents was developed using existing ion chromatographic techniques. Two solid waste matrices were briefly investigated. Aqueous samples were passed through a 0.45-micron filter and the filtrate was either (1) left unadjusted, (2) adjusted to pH 8 or (3) adjusted to pH 10 prior to analysis by ion chromatography. The method detection limits were 0.3-0.4 micrograms/l. When analyzed within 24 h, the two pH levels and the unadjusted sample yielded ca. 100% recovery of spikes. No oxidation of trivalent chromium to hexavalent chromium was observed at pH 7, 8 or 10 when aqueous samples were spiked with 50 mg/l Cr(III).     

Analysis for aromatic compounds on paper and thin-layer chromatograms by spectrophotophosphorimetry : Application to air pollution

A technique is introduced in spectrophosphorimetric analysis by means of which spectra can be obtained directly on an adsorbent after chromatography. Spectra of the phosphorescent compound, its salts, its reduced or oxidized forms, or its derivatives can be obtained in all types of solvents. Examples of this simple technique are given ; detection limits range from 0.1 ng to mg amounts. A new system for the circular paper Chromatographic separation of aza heterocyclic hydrocarbons using aqueous formamide is described. Many of these heterocyclic compounds can be separated from each other as can the parent compounds from their alkyl derivatives. Air pollution mixtures separated by column and paper chromatography are analysed with the phosphorimetric technique. Spots obtained on the paper chromatograms are analyzed directly in the phosphorimeter. With these techniques benzo-(f) quinoline, benzo(h)quinoline, benz(a)acridine, benz(c)acridine, and hydrocarbons such as phenanthrene and benzo(e)pyrene are readily characterized.