The Teflon Stopcock

A missing Teflon washer or rubber ring. Have it replaced. 

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Reference is again made to the Teflon stopcocks and to the diaphragm type of burette tap which do not require lubrication. 

After the Teflon stopcock is closed, the reaction vessel is transferred to a water bath maintained at 60°. The lower end of the vessel should be immersed to within about 1 in. below the fritted-glass retainer. As refluxing of the bromine proceeds, a liquid layer should accumulate above the fritted-glass retainer. If this does not happen, some bromine should be poured through the bypass arm so that a liquid layer ca. 1 in. thick is maintained on the frit. It is essential that liquid bromine contact the tribromide in order to attain efficient conversion to tetrabromide. As the reaction proceeds, the product, dissolved in liquid bromine, extracts into the lower vessel and deposits there as fine black crystals. 

The Teflon stopcock has a 1 5 taper on its plug to be within the guidelines of gknown as Product Standard. 

Bromosilane (1.46 g, 13.1 mmol) is condensed into the side arm of the reactor (Fig. 17) the Teflon stopcock is closed, and then the reactor is allowed to warm to room temperature. The gaseous bromosilane is allowed to remain in contact with the solid for approximately 30 min. The bottom of... 

A 2.0-g. sample of powdered dicobalt octacarbonyl is placed in a 25-ml. glass reactor in a nitrogen-filled glove bag. The reactor is evacuated then 5 g. of trichlorosilane is condensed from the vacuum system into the reactor which has been cooled to —196°. The Teflon stopcock is closed, the reaction vessel allowed to warm to room temperature, and then the reactants are permitted to stand for 24 hours. Cool the reactor to —42° (diethyl ketone slush), open the Teflon stopcock, and remove the excess silane and noncondensable substances into the vacuum system with pumping. The remaining dry, solid material is then transferred in a nitrogen (or carbon monoxide) filled glove bag to a sublimation apparatus. The solid is then sublimed in vacuo... 

Two grams of powdered dicobalt octacarbonyl are placed in a 20-ml. glass pressure reactor in a nitrogen atmosphere. The reactor is then evacuated and cooled to —196°. Then 4 g. of trimethylsilane, (H3C)3SiH,f are condensed into the reactor, and the Teflon stopcock is closed. The reactor is then allowed to warm to room temperature. After 24 hours the reactor is cooled to —196°, the stopcock opened, and any H2 and CO are... 

In a nitrogen-filled glove bag 10 g. of antimony trifluoride are placed into a 30-ml. glass reactor which is then evacuated and pumped on for 24 hours to provide a final drying at room temperature. The reactor is then cooled to liquid-nitrogen temperature, and 3 g. of hydrogen-chloride-free trichlorosilane is added to the reactor. The Teflon stopcock is then closed... 

Next 2 g. of dicobalt octacarbonyl is placed in a 20-ml. glass reactor in a nitrogen-filled glove bag. After evacuation of the reactor, 1.8 g. of trifluorosilane is condensed and the Teflon stopcock closed. The reaction is allowed to proceed for 24 hours... 

The purified CHaSiCla is then transferred into the SbFa-filled reactor which has been cooled to liquid-nitrogen temperature. The Teflon stopcock is then closed, and the reaction vessel is surrounded by an ice-water bath held in a beaker. The reactor is now most conveniently left overnight, permitting the ice to melt so that the reactor is held at room temperature for a few hours. 

Sample Preparation. Cobalt catalysts were prepared by subliming Co2(C0)g into the pores of dehydrated NaX zeolite in a vacuum line at pressures of 1 x 10- f torr. Argon was flowed over the metal loaded zeolite sample at a pressure of 0.3 torr. A microwave plasma was induced with a static gun and the decomposition of the metal carbonyl precursor occurred for two hours. After total decomposition of the metal carbonyl which can be determined by the color of the plasma, the argon flow was stopped and the sample was sealed off by closing the Teflon stopcocks at both ends of the reactor. The sample was then brought into a drybox and loaded into catalytic reactors or holders for spectroscopic experiments. Further details of this procedure can be found elsewhere (11, 25). Iron samples were prepared in a similar fashion except ferrocene was used as a metal precursor. 

Obtain your unknown licpiid from your instructor. Pour 2 mL of your unknown liquid into the delivery tube above the stopcock. CAUTION Do not inhale the vapor. Open the Teflon stopcock slowly, and allow some of the liquid to enter the flask. The liquid enters the flask very rapidly make certain that vou close the stopcock while there is still about 0.5 mL of licfuid remaining in the delivery tube above the stopcock. If any air also enters the flask at this point, you must start the run again ... 

A student was preparing to do a titration using a buret that required assembly with a Teflon stopcock (see Figure 7.1.2.1). While trying to place the Teflon stopcock onto the long buret tube, the end of the buret broke off and the broken barrel plunged into the student s hand. Stitches were required to close the cut. 

TaCls (35.0 g, 0.098 mol) is added to a 1L round-bottomed flask equipped with Teflon-coated stir bar and a Teflon Y-valve adapter for attachment to the vacuum line. Toluene (400 mL) is vacuum transferred onto the TaCls. On the Schlenk line, under strong Ar purge, the Teflon stopcock is replaced with a septum. (q -CsMcs) Sn(n-Bu)3 (49.9 g, 0.116 mol) is cannula transferred slowly to the stirred suspension of TaCls over a period of 30 min mild exothermicity ensues. Stirring is continued for a further 20 h to give a copious amount of a yellow suspension. The yellow suspension is filtered through a Schlenk frit via cannula transfer and is washed with dry petroleum ether (3x50mL). The residue is dried in vacuum. Yield of (Ti -CsMes)TaCl4 43.5 g (97%). 

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