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High vacuum lines

The photocatalytic decomposition of water was carried out in a closed gas circulation system connected to a high-vacuum line. About 200 mg of a powdered catalyst was dispersed in pure distilled water and irradiated through a water filter with an Xe lamp operated at 400 W. Hydrogen and oxygen evolved in the gas phase were analyzed by a gas chromatograph which was directly connected to the reaction system. [Pg.144]

All reactions were performed in evacuated sealed Pyrex tubes of about 80 cm3 volume. Typically, a vessel is thoroughly evacuated on a high vacuum line (pressure <1 x 10 5 Torr) for several hours, then it is sealed off from the line and placed in a muffle furnace preheated to the desired temperature. After two hours the tubes are removed and immediately cooled in liquid nitrogen. Care must be taken in these operations, tubes have been known to explode in the oven and upon removal. Typically, the... [Pg.179]

Materials 1,3-Dioxolane (1) and 1,3-dioxepane (5) were prepared and purified conventionally. Compound 1 contained no impurities detectable by GLC, but 5 contained a trace of tetrahydrofuran (THF) which could not be removed even by distillation on a Fenske column with a reflux ratio of 50 1 4-methyl-l,3-dioxolane (4) was prepared by Astle s method [10]. All monomers were dried preliminarily by storage over LiAlH4 in reservoirs attached to a conventional high-vacuum line fitted only with all-metal valves, and then stored with liquid Na-K alloy until used. Methylene dichloride was purified conventionally, distilled on a Normatron 1.5 m column, dried i.vac. over LiAlH4 on a conventional high-vacuum line, and then stored for 24 h over a fresh sodium film immediately before use, in a reservoir attached to the vacuum line. [Pg.741]

To remove the last traces of water and acetic acid the checkers found it most Convenient to place the residue on a high vacuum line overnight. [Pg.179]

OEP deuterated at the meso positions was obtained by keeping OEP in concentrated D2SO for 24 h (31). All samples were thoroughly degassed by freeze-pump-thaw cycles on a high vacuum line. [Pg.220]

The apparatus is evacuated on a high vacuum line, flamed and sealed off at constriction i. The break-seal on ampoule B is crushed, and the whole unit is rinsed with the solution. The rinsing solution is then returned to B, and the unit is washed by condensing the solvent on the walls which are chilled in the usual way from outside. The required amount of solvent is distilled from 5 to a graduated cylinder, C, and then B is sealed off at P. ... [Pg.156]

Mixing equal concentrations of two separately prepared solutions of colloidal lead and silver particles (each degassed by repeated freeze-pump-thaw cycles on a high-vacuum line and mixed under vacuum) resulted in a slow blue shift of the silver plasmon band from 390 nm to 337 nm and a concomitant broadening... [Pg.109]

Isoprene (99 + %, Aldrich) and styrene (99%, Aldrich) were purified by initial stirring and degassing over freshly crushed Cal on a high vacuum line followed by distillation onto dibutyl-magnesium (Alpha Inorganics). Final purification involved distillation from this solution directly into calibrated ampoules and sealing with a flame. Benzene (Fisher, Certified ACS) was stored over cone. [Pg.118]

Two procedures are given for the treatment of the solution in Section A. In the first the solution is cooled down to — 60 °C, and 20 mL of hexane is added. Careful evaporation under vacuum to 20 mL removes most of the CH2 Cl2. The lilac precipitate is isolated by centrifugation ( 2 min at 1500 rpm) and decanting off the solution. Hexane (20 mL) is added at — 60 °C and the suspension is stirred for 10 min. Centrifugation, decanting, and washing are repeated three times. Then the product is dried at — 20 °C for 8 h on a high-vacuum line (10-3 torr). [Pg.97]

The polymerization vessel is illustrated in Pig. 8. Ampoules A and B contained dilute and concentrated benzene solutions of the seed polymer, respectively, and ampoules C and D contained tetrahydrofuran (or dimethoxyethane) and a benzene solution of the monomer. The polymerization vessel was connected to a high-vacuum line, evacuated, flamed and sealed off. Then the break-seal on ampoule B was crashed, and the whole vessel was washed with the concentrated solution of living polymer. All the solutions were brought to E and the vessel was washed by condensing the benzene using a pad at Dry Ice-methanol temperature. The solvent was distilled into F from E and E was sealed off. The seals on A, C, and D were broken, and the dilute solution of living polymer was collected into G by turning the whole vessel upside down,... [Pg.362]

B. Sealed Tube Preparations. Sealed tube reactions and purifications afford good exclusion of the atmosphere and permit operations at moderate pressures. The latter capability makes it possible to work with highly volatile solvents, such as liquid ammonia, at room temperature. Since the sealed tube is often loaded on a high-vacuum line, the details on these techniques are given in Chapter 9. [Pg.195]

Many vacuum pumps are supplied with a gas ballast valve which is designed to prevent the condensation of moisture and similar condensable materials. This valve bleeds a small amount of air into the pump and as a result the ultimate vacuum and pumping speed of the pump suffer. There is no occasion to use this feature on a pump on a typical chemical high-vacuum line, and it rarely, if ever, is used in typical laboratory rough-pumping systems. [Pg.235]

Figure 1 shows the mixing and irradiation ampules. The solution of Cl2 in CC14 was condensed from the high-vacuum line into the lower part (A), which was then sealed off at 2. The ampules were connected at point 3 to a stock solution of PIB in CC14, a fixed volume of which was allowed to pass into B. Before the solutions of the compounds (separated by break seal 1) were mixed and filled into the irradiation... [Pg.174]

Polysulfanides, in Ru and Os half-sandwich complexes, 5-Gp and 7 5-indenyl compounds, 6, 496 Polysulfide rings, with germanium, 3, 742-743 Polysulfides, in Ru and Os half-sandwich complexes, rjS-Cp and ]5-indenyl compounds, 6, 496 Polysulfido nitrosyl complexes, with chromium, 5, 303 Polytetrafluoroethylene valves, in high vacuum lines, 1, 198 Polythiaether macrocyclic ligands, in hexaruthenium carbido clusters, 6, 1018-1019... [Pg.177]

The most rigorous exclusion of water and oxygen can be accomplished on a high vacuum line. There appears to be a significant psychological barrier that has to be overcome before most workers will go to the trouble of building a suitable vacuum system, so that this approach is regarded as a technique of last resort. [Pg.268]

The home-made heat-flow calorimeter used consisted of a high vacuum line for adsorption measurements applying the volumetric method. This equipment comprised of a Pyrex glass, vacuum system including a sample holder, a dead volume, a dose volume, a U-tube manometer, and a thermostat (Figure 6.3). In the sample holder, the adsorbent (thermostated with 0.1% of temperature fluctuation) is in contact with a chromel-alumel thermocouple included in an amplifier circuit (amplification factor 10), and connected with an x-y plotter [3,31,34,49], The calibration of the calorimeter, that is, the determination of the constant, k, was performed using the data reported in the literature for the adsorption of NH3 at 300 K in a Na-X zeolite [51]. [Pg.286]

The compound has also been obtained by blowing anhydrous hydrazine vapor with a stream of dry nitrogen stepwise into a 5-liter bulb containing an excess of SiH3Br.46 The compound, which is colorless and nonvolatile at -64°, is purified by repeated low-temperature vacuum distillation.9,46 Because the compound may explode if it comes into contact with air, it must be prepared and handled in a Stock-type high-vacuum line. [Pg.21]

All of these operations are accomplished in such a way that monomer never passes through any stopcocks, thereby avoiding contamination by grease. These operations require the use of glass breakseals and several parallel sub-manifolds on the high vacuum line. We are still unhappy about the amount of contamination that must be introduced by the flame-sealing of the final reaction vessel, but it appears to be a source of contamination with which we must live. [Pg.220]


See other pages where High vacuum lines is mentioned: [Pg.683]    [Pg.132]    [Pg.747]    [Pg.89]    [Pg.15]    [Pg.7]    [Pg.219]    [Pg.190]    [Pg.343]    [Pg.102]    [Pg.105]    [Pg.222]    [Pg.53]    [Pg.64]    [Pg.65]    [Pg.259]    [Pg.174]    [Pg.96]    [Pg.215]    [Pg.92]    [Pg.99]    [Pg.105]    [Pg.108]    [Pg.119]    [Pg.128]    [Pg.136]    [Pg.103]    [Pg.46]    [Pg.597]   
See also in sourсe #XX -- [ Pg.268 ]




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High vacuum

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