Dicobaltoctacarbonyl-mediated synthesis of tricyclic 5,6-diydropyran-2-one derivatives via tandem cycloaddition reaction between cis-epoxyalkynes, a tethered olefin, and carbon monoxide

Cobalt carbonyl complex Co2(CO)8 implemented an intramolecular carbonylation of cis-epoxyalkynes to generate Co2(CO)6-stabilized gamma-lactonyl allene species. For 1,1,2-trisubstituted epoxyalkynes, this Co2(CO)6-allene species reacted with a tethered olefin to give [2+2]-cycloadducts, and with CO and a tethered olefin to produce [2+2+1]-cycloadducts. These resulting cycloadducts have a 5,6-diydropyran-2-one core fused with a cyclobutane and a cyclopentanone ring, respectively. For 1,2-disubstituted cis-epoxyalkyne and 1,1,2-trisubstituted cis-epoxyalkynes bearing a heteroatom constituent, cyclization of the corresponding epoxyalkyne with a tethered alkene is invariably accompanied by incorporation of CO to produce a [2+2+1]-cycloadduct, even in the absence of CO. We have prepared various 1,1,2-trisubstituted and 1,2-disubstituted cis-epoxyalkynes to generalize such cycloaddition pathways. Attempt to use an organic promoter to perform these tandem cycloadditions was unsuccessful because of a competing Pauson-Khand reaction. Cyclization of a 1,2-disubstituted epoxyalkyne with a tethered diene was achieved successfully in one case, but the yield was low (25%).     

The calibration of (multi-) hot-wire probes. 1. Temperature calibration

We study the performance of the classical relation for the correction for ambient temperature drift of the signal of a hot-wire anemometer and the influence of practical assumptions. It is shown that most methods to estimate the operational temperature via the temperature/resistance coefficient lead to underestimation of the operational temperature and thus to overcorrection of signals for temperature drift. We found that, in the presence of a sensible heat flow, temperature fluctuations cannot be sufficiently removed from the hot-wire signal when one relies on temperature/resistance coefficients from literature. When only slow temperature drift is involved, most literature values give a satisfactory temperature correction, but this depends on the specific combination of a probe and a literature reference. Therefore it is generally advisable to calibrate the value. A method that uses a ratio of (measured) resistances as a function of temperature, which does not require estimation of the operational temperature of the wire, is shown to depend crucially on a parasitic resistance of a few tenths of an ohm. This parameter can be found by optimizing its value using data from a collection of velocity calibrations at different temperatures. This additional calibration alone suffices to estimate the operational temperature of the wire via optimization. A quick calibration procedure (15 min) is proposed and tested.     

Parity-dependent rotational rainbows in D2-NO and He-NO differential collision cross sections

The (j', Omega', epsilon') dependent differential collision cross sections of D2 with fully state selected (j = 12, Omega = 12, epsilon = -1) NO have been determined at a collision energy of about 550 cm(-1). The collisionally excited NO molecules are detected by (1+1') resonance enhanced multiphoton ionization combined using velocity-mapped ion-imaging. The results are compared to He-NO scattering results and tend to be more forward scattered for the same final rotational state. Both for collisions of the atomic He and the molecular D2 with NO, scattering into pairs of rotational states with the same value of n = j' - epsilon epsilon'2 yields the same angular dependence of the cross section. This "parity propensity rule" remains present both for spin-orbit conserving and spin-orbit changing transitions. The maxima in the differential cross sections-that reflect rotational rainbows-have been extracted from the D2-NO and the He-NO differential cross sections. These maxima are found to be distinct for odd and even parity pair number n. Rainbow positions of parity changing transitions (n is odd) occur at larger scattering angles than those of parity conserving transitions (n is even). Parity conserving transitions exhibit-from a classical point of view-a larger effective eccentricity of the shell. No rainbow doubling due to collisions onto either the N-end or the O-end was observed. From a classical point of view the presence of a double rainbow is expected. Rotational excitation of the D2 molecules has not been observed.     

Use of a Drying Cartridge in On-Line Solid-Phase Extraction–Gas Chromatography–Mass Spectrometry

A drying cartridge was used and optimized for the in-line elimination of water from the desorption eluent in on-line solid phase extraction–gas chromatography (SPE–GC). The cartridge is essentially a small stainless-steel precolumn packed with a drying agent which can be regenerated by simultaneous heating and purging with a moisture-free gas. The drying cartridge was mounted on an additional valve instead of between the SPE–GC transfer valve and the on-column injector to enable regeneration of the cartridge during the GC run and, thus, to increase sample throughput. Three drying agents were tested, viz. sodium sulfate, silica, and molecular sieves. Although molecular sieves have the highest capacity, silica was preferred because of practical considerations. Large-volume injections were performed through the in-line drying cartridge using a mixture of 23 microcontaminants ranging widely in polarity and volatility. Four solvents were tested. With pentane and hexane, the more polar analytes were retained by the drying cartridge. Ethyl acetate and methyl acetate gave much better (and closely similar) recoveries for all analytes. Because water elimination on the silica cartridge proved to be less critical than with ethyl acetate, this solvent was finally selected. The entire SPE–drying cartridge–GC set-up was combined with mass spectrometric (MS) detection for the determination of a mixture of micropollutants in real-life water samples. With 10-ml tap water samples spiked at the 0.5 μg/l level, for the majority of the test compounds the analyte recoveries generally were 60–106%, and (full-scan) detection limits typically were 0.01–0.03 μg/l. Some very polar analytes such as, e.g. dimethoate, were (partially) sorbed onto the silica packing of the drying cartridge.     

Controlled,micro‐scale film formation of waterborne dispersions

The film formation on a micro‐scale of latex material is described. Waterborne polymer dispersions dried below their Tg are treated by laser or direct heat treatment by means of a tip (diameter 5 µ m) of a micro thermal analysis apparatus (µ ‐TA). Both methods give a linewidth, line thickness and dot‐sizes in the micron range. The layer thickness decreases during fusion of the particles because of the loss of voids during film formation. Non treated areas can be washed away selectively. Laser treatment gives a more smooth surface than direct thermal treatment with a µ‐TA tip. Copyright © 2001 John Wiley & Sons, Ltd.     

Preparation and characterization of the polymer electrolyte system ENR50/PVC/EC/PC/LiN(CF<Subscript>3</Subscript>SO<Subscript>2</Subscript>)<Subscript>2</Subscript> for electrochemical device applications

Polymer electrolytes containing epoxidised natural rubber (ENR50)/poly(vinyl chloride) (PVC) blend as a polymer host, a solvent mixture of ethylene carbonate (EC) and propylene carbonate (PC) as a plasticizer, and lithium imide, LiN (CF₃SO₂)₂, as a salt were studied. Polymer electrolytes that were obtained by solvent cast yielded solid dry rubbery films with a thickness range of 110–125 μm. Impedance spectroscopy, Fourier transform infra red (FTIR) spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were performed on these samples. The prepared solid polymer electrolytes exhibit ionic conductivities in the order 10⁻⁴ S cm⁻¹ at room temperature as expected. However, the physical properties of the electrolytes have improved significantly when optimal composition has been selected. Paper presented at the International Conference on Solid State Science and Technology 2006, Kuala Terengganu, Malaysia, Sept. 4–6, 2006.     

A new homobimetallic arenediyl diplatinum(II) unit as building block for macromolecular synthesis. X-ray crystal structure of [C6H2{CH2NMe2}2-1,5-{PtCl(PPh3)}2-2,4]

Treatment of the diaminobenzene [C₆H₄{CH₂NMe₂}₂-1,3] (NCN-H, 1) with one or two equivalents of cis-PtCl₂(DMSO)₂ leads to exclusive formation of the doubly cycloplatinated species [C₆H₄{CH₂NMe₂}₂-1,5-{PtCl(DMSO)}₂-2,4] (3), which upon addition of triphenylphosphine yields the bisphosphine adduct [C₆H₄{CH₂NMe₂}₂-1,5-{PtCl(PPh₃)}₂-2,4] (4). The X-ray molecular structure of 4 revealed the presence of highly distorted square planar Pt(II) centers which is caused by close proximity of the two phosphine donor ligands. Complexes of type 3 can be regarded as suitable starting materials for the directional build-up of larger macromolecular structures.     

Silver-Mediated Cascade Synthesis of Functionalized 1,4-Dihydro-2H-benzo-1,3-oxazin-2-ones from Carbon Dioxide

A conceptually novel catalytic domino approach is presented for the synthesis of highly functional 1,4-dihydro-2H-1,3-benzoxazine-2-one derivatives. Key to the chemoselectivity is a proper design of the precursor to override thermodynamically favored parasitic cyclization processes and empower the formation of the desired product through Thorpe–Ingold effects. The synthetic diversity of these CO₂-based heterocycles is further demonstrated, and the isolation of a reaction intermediate supports an unusual ring-expansion sequence from an α-alkylidene, five-membered cyclic carbonate to a six-membered cyclic carbamate by N-induced isomerization.