Intramolecular reactions in pseudo-geminally substituted [2.2]paracyclophanes

A selection of pseudo-geminally substituted [2.2]paracyclophanes, the alkynes 6, 7, 10, 11 a, and 11 b and the alkenes 8 and 9 were prepared for the study of intraannular reactions between functional groups in direct juxtaposition. Whereas 9 and 10 provide the corresponding cyclobutane and cyclobutene derivatives on irradiation (12 and 13, respectively), the bis-alkynes 7 and 11 b do not lead to a cyclobutadiene intermediate. In the latter case the "half-closed" butadiene derivative 17 was isolated. A Paterno-Büchi reaction took place on irradiation of 8 and 6, although the oxetene intermediate 21 produced in the second example did not survive the reaction conditions (ring-opening to 22). Bromine addition to 9, 10, and 7 occurred with high stereoselectivity (formation of the dibromides 27, 30, and 33, respectively), and is rationalized by postulating the formation of the cationic intermediates 26, 29, and 32, respectively. To study the interaction of a carbocation with a facing triple bond, the alcohol 34 was prepared from 6. On acid treatment ring closure to the triply-bridged phane 38 took place, accompanied by the hydration of the triple bond to the ketoalcohol 37. In an interesting intraannular [2+3]cycloaddition reaction the bis-acetylene 11 a, on treatment with n-butyl lithium, provided the cyclopentadiene derivative 42. That the two triple bonds of a pseudo-geminal diacetylene can engage in a cyclization reaction leading to the cyclopentadienone complex 44 was also shown by treating 11 b with iron pentacarbonyl.     

Determination of Li, Na, Mg, K, Ca and Fe with ICP-MS using cold plasma conditions

Some important analytes in ICP-MS are interfered by plasma argon or argon species, such as ArO⁺ and ⁵⁶Fe, ⁴⁰Ar and K or Ca. One approach to overcome this interference is the use of reduced forward power and a metal shield inserted between torch and load coil. These so called cold plasma conditions reduce the background caused by argon species and the formerly interfered analytes can be easily detected in the ng/g-range. Other elements in the lower mass region also profit from these conditions even when they are not interfered in normal plasma mode. The limits of detection are improved due to reduced background noise level and enhanced ion transmission. On the other hand, the reduced power fed to the plasma lowers the analytical performance and makes it susceptible to matrix effects. Elements of higher mass generally show higher detection limits compared to normal plasma mode. Received: 30 November 1998 / Revised: 4 February 1999 / Accepted: 8 February 1999     

Carbon Nanotubes Hybrid Hydrogels for Environmental Remediation: Evaluation of Adsorption Efficiency under Electric Field

The performance of Carbon Nanotubes hybrid hydrogels for environmental remediation was investigated using Methylene Blue (MB), Rhodamine B (RD), and Bengal Rose (BR) as model contaminating dyes. An acrylate hydrogel network with incorporated CNT was synthesized by photo-polymerization without any preliminary derivatization of CNT surface. Thermodynamics, isothermal and kinetic studies showed favorable sorption processes with the application of an external 12 V electric field found to be able to influence the amount of adsorbed dyes: stronger interactions with cationic MB molecules (qexp and qexp12 of 19.72 and 33.45 mg g⁻¹, respectively) and reduced affinity for anionic RD (qexp and qexp12 of 28.93 and 13.06 mg g⁻¹, respectively) and neutral BR (qexp and qexp12 of 36.75 and 15.85 mg g⁻¹, respectively) molecules were recorded. The influence of pH variation on dyes adsorption was finally highlighted by reusability studies, with the negligible variation of adsorption capacity after five repeated sorption cycles claiming for the suitability of the proposed systems as effective sorbent for wastewater treatment.     

Measurement and prediction of activity coefficients at infinite dilution (γ), vapor–liquid equilibria (VLE) and excess enthalpies (H) of binary systems with 1,1-dialkyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide using mod. UNIFAC (Dortmund)

Activity coefficients at infinite dilution (γ^∞), vapor–liquid equilibria (VLE) and excess enthalpies (H^E) were measured for alkanes and alkenes in the ionic liquids 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [BMPYR]⁺[BTI]⁻, 1-hexyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [HMPYR]⁺[BTI]⁻ and 1-octyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [OMPYR]⁺[BTI]⁻.     

C?F Activation at Rhodium Boryl Complexes: Formation of 2‐Fluoroalkyl‐1,3,2‐Dioxaborolanes by Catalytic Functionalization of Hexafluoropropene

Fluorinated building blocks by C? F bond cleavage : Catalytic C? F activation reactions that give novel dioxaborolanes have been developed (see scheme). The reactions proceed at room temperature, and catalytic intermediates are presumably rhodium hydride and boryl species.

     

Edge-reinforced random walk on one-dimensional periodic graphs

In the present paper, linearly edge-reinforced random walk is studied on a large class of one-dimensional periodic graphs satisfying a certain reflection symmetry. It is shown that the edge-reinforced random walk is recurrent. Estimates for the position of the random walker are given. The edge-reinforced random walk has a unique representation as a random walk in a random environment, where the random environment is given by random weights on the edges. It is shown that these weights decay exponentially in space. The distribution of the random weights equals the distribution of the asymptotic proportion of time spent by the edge-reinforced random walker on the edges of the graph. The results generalize work of the authors in Merkl and Rolles (Ann Probab 33(6):2051–2093, 2005; 35(1):115–140, 2007) and Rolles (Probab Theory Related Fields 135(2):216–264, 2006) to a large class of graphs and to periodic initial weights with a reflection symmetry.