Attachment to a vacuum line

Today, the glassware required consists of either a round-bottom flask or a Schlenk tube serving as the reaction chamber. This chamber is equipped with a magnetic stirbar and a Teflon high-vacuum valve (or glass stopcock) which provides for easy vacuum control after attachment to a vacuum line (Fig. 8.7). 

In preparation for the next experiment, invert the column and extrude the silicic acid by applying gentle pressure. Clean the column with a long-handled brush, wash with water and acetone, and dry by attaching to a vacuum line. 

Antimony pentafluoride (4.94 g, 22.8 mmole) is added, in a good dry box, to side B of the reaction flask using an all-glass syringe. Elemental mercury (2.74 g, 13.7 mmole) is added to side A. The reaction vessel is fitted at E and F with Nupro or similar metal valves, removed from the dry box, and attached to a vacuum line that has been thoroughly flamed before use. Approximately 10 mL of sulfur dioxide is transferred to side B by cooling with liquid N2, and the... 

A diethyl ether solution containing 20 mmoles of methyllithium is placed in a 50-mL reaction vessel equipped with a stopcock and standard taper joint. The vessel is attached to a vacuum line stopcock equipped with a mercury blow-out manometer,3 and the contents are frozen at -196° (liquid nitrogen) prior to evacuation of the vessel. 

Fig. 4.3. Solvent storage tubes with Teflon valves, (a) The O-ring joint on the sidearm allows attachment to a vacuum line equipped with O-ring joints, (b) Same basic design as in (a) with a straight sidearm. This design is easily connected to a Schlenk line via Tygon or other flexible tubing that fits over the sidearm.

A typical arrangement of components in a tensimetric titration is presented in Fig. 9.5, which shows the previously discussed tensimeter and a calibrated bulb attached to a vacuum line.2 The sample container on the tensimeter is fitted with a small reciprocating stirrer which consists of a thin glass rod connected to a glass-encased headless nail or glass-encased bundle of soft iron wire. This stirrer is driven by an external solenoid, the field of which is switched on and off by a current-interrupting device, the details of which are laid out in Fig 9.6. The size of the calibrated bulb is chosen so that it will contain the desired amount of gas for each addition at a pressure which is convenient and accurately measured (e.g., 100-500 torr). The calibration procedure and steps used dispensing gas from such a bulb are described in Section 5.3.G. 

For the FTIR measurements (Bruker IFS28 resolution 2 cm-1 MCT detector), the samples, pressed into self-supporting pellets, were placed into a quartz IR cell equipped with KBr windows attached to a vacuum line (residual pressure 1 x 10 6 Torr). Thermal treatments were carried out in situ. To decrease the scattering of the IR beam, severely affecting the transparency of the samples in the in the 4000-3000 cm-1 range, a system of condenser mirrors were placed between the IR cell and the detector. 

Approximately 0.5-1.0 ml. of NTO is run into a sample tube, and the tube is quickly capped with a 12/30 outer joint glass cap. Next, the tube is immersed in LN2 to freeze the NTO. The cap is removed, and the taper joint is attached to a vacuum line as quickly as possible. Still frozen, the tube is pumped out and sealed off with a torch at the junction between the NMR tube proper and the taper joint Samples so prepared may be stored indefinitely without deterioration or accumulation of moisture. 

Since the data-acquisition time for a given S/N scales inversely with the square of the number of molecules sampled, high pressures and large tube volumes are desirable. NMR tubes are produced in a range of diameters, and the largest of these that is compatible with the instrument probe design should be chosen. Tubes of 5-, 10-, and 15-mm diameter with an in-line Teflon valve, which permits easy attachment to a vacuum line via i-in. or -in. Ultra-Torr fittings and which can be spun in the normal way, are available from various suppliers. 

Anionic polymerization of IPTMSK and styrene was carried out at -78 °C in a Schlenk flask attached to a vacuum line. The reaction was carried out in benzene or benzene-THF (tetrahydrofuran) with an n-butyllithium-18-crown-6 complex as the initiator. The reaction was carried out under argon atmosphere and was quenched by injecting methanol into the polymerization mixture. 

A flask containing 5.6 g (7.1 mmole) of carbonylchlorobis(triphenylphos-phine)iridium(I) suspended in 50 mL of benzene and equipped with a magnetic stirrer is attached to a vacuum line, frozen in liquid nitrogen, and evacuated. Trimethylphosphine (2.2 g, 28.4 mmole) is condensed into the flask, which is then closed off from the line and allowed to warm to room temperature with stirring. The resulting suspension is filtered (in air) and the solid is washed with benzene to remove traces of yellow color and then dried in vacuum. The yield of [Ir(CO)-(P(CH3)3)4]C1 is 4.0 g (98%). 

A column (about 25 mm od X 300 mm long), packed loosely with glass wool and lead cyanamide (about 25 g, Alfa Inorganics Inc., Beverly, MA ), is attached to a vacuum line and evacuated for about 2 hours. lodogermane (GeH3l 0.10l... 

The tube is allowed to warm to room temperature. The mixture liquefies and the pressure decreases, probably because of the formation of HBr addition compounds. After liquefaction it is safe to heat the tube in an oil bath to 100°. As reaction proceeds a second liquid layer of dimethylamine hydrobromide forms and reaction is complete within 36 hours. The tube is then cooled to -45° and attached to a vacuum line (10 torr) for 3 hours to remove excess HBr. Each of the bromo fluoro cyclotriphosphazenes can then be isolated by allowing the tube to warm to room temperature and distilling the products into a trap held at -196°. Alternatively, the products can be vacuum distilled using conventional apparatus, but recovery is more efficient by the former method. The yield of P3N3Br3F3 is 3.8 g (70%) and that of P3N3Br2F4 is 4.5 g (90%). 

Lightly lubricate the glass joint with vacuum grease to prevent polymer from forming between the glass surfaces, close the tube with a vacuum stopcock and attach to a vacuum line. 

Hydride transfer reactions. A known amount of trlphenylmethyl hexafluoroantlmonate was placed In an NMR tube attached to a vacuum line. After 30 minutes vacuum drying of the salt, the desired amount of nltromethane-d3 gnd model compound was distilled In and the NMR tube sealed off. The reactions were carried out at room temperature and the products were not Isolated. 

Sodium Hexafluorouranate(V) Uranium pentafluoride (2.00 g) and dried NaF (0.25 g) are combined in a 250-mL flask in a drybox. The flask is then attached to a vacuum line, and approximately 150 mL of dry acetonitrile is vacuum transferred into the flask. (The acetonitrile can be dried by distillation from P4O10 or CaH2.) The mixture is allowed to warm to room temperature. With stirring, the NaF gradually dissolves over a period of 12 hours. The solvent is removed in vacuo, quantitatively yielding NaUF6 in the rhombohedral form (X-ray powder diffraction). The potassium salt is prepared similarly. 

Immediately after the addition of trimethylaluminum is completed, external heating is begun and the crude product is distilled at 55-60° onto the sodium fluoride in flask D. The pure product is redistilled at about 56° from sodium fluoride into the receiving flask F. This flask is taken from the system, quickly fitted with an adapter equipped with a stopcock, and attached to a vacuum line for transfer into a storage vessel. ( Caution. Some flaming of the product may occur when the receiving flask is removed from the apparatus however, rapid and careful work should prevent any serious problems.) Extreme caution must be exercised in the disposal of the pyrophoric residues in flask B. 

Figure 1.3.11 Typical two- and three-electrode cells used in electrochemical experiments, a) Two-electrode cell for polarography. The working electrode is a dropping mercury electrode (capillary) and the N2 inlet tube is for deaeration of the solution. [From L. Meites, Polarographic Techniques, 2nd ed., Wiley-Interscience, New York, 1965, with permission.] (Jb) Three-electrode cell designed for studies with nonaqueous solutions at a platinum-disk working electrode, with provision for attachment to a vacuum line. [Reprinted with permission from A. Demortier and A. J. Bard, /. Am. Chem. Soc., 95, 3495 (1973). Copyright 1973, American Chemical Society.] Three-electrode cells for bulk electrolysis are shown in Figure 11.2.2.

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