High vacuum/Schlenk

A metal atom reactor is often used in a variety of "dirty" and "clean" operations. Accordingly, it should be remembered that radiation, adventitious water, oxygen, hydrocarbons, metallic particles and so on, can affect the properties of the isolated products. In the case of minute magnetic structures it is important to determine clearly the role of such agents in affecting volume and surface magnetic properties. Incorporation of a high vacuum Schlenk manifold such as the one described by Wayda in this book, should be considered an important supplement to the VS equipment. 

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). 

Some of the procedures described in the following chapters had to be carried out under an inert atmosphere, nitrogen or argon, to minimize contact with oxygen and moisture. It is then necessary to use Schlenk techniques including the utilization of a vacuum line connected to a high vacuum pump and an inert gas inlet. The use of such equipment requires experience in working under anhydrous conditions. 

Attempts to purify the material further met with little success because of its extreme sensitivity toward oxygen. Recrystallization from ether, for instance, in a modified Schlenk tube (25), with exclusion of air, invariably led to an off-colored product. An attempt to sublime the product in a high vacuum resulted in complete decomposition. Analysis even on the crude product, however, confirmed its identity as a disubstituted derivative of nickel carbonyl. 

The preparation can be carried out in air. A quantity of Re(CO)5(FBF3) (0.85 g, 2.06 mmol) is dissolved in water (15 mL) in a Schlenk flask (25 mL). The solution is filtered into a second flask (25 mL) equipped with a magnetic stirring bar. Aqueous NaOH (2.15 mL of a 1 M solution) is added to the filtrate under stirring. After a few minutes the colorless precipitate is collected on a glass frit and washed several times with water. The solid is dried over P4O10 for 2 days and for 20 h in a high vacuum. Yield 643-693 mg (91-98%). 

A quantity of [Re(CO)4(COOH)]n (0.63 g) is dissolved in acetone (40 mL) in a Schlenk flask (100 mL). The pale yellow solution is filtered quickly, if necessary. After a few minutes a colorless precipitate is formed. The suspension is stirred for 30 to 40 min and the solvent is evaporated in vacuo to 4 mL. The solid is centrifuged off or collected on a glass frit, washed two times each with 2 mL of acetone, and dried in a high vacuum. Yield 344 mg (56%). 

A suspension of trans-Ir(Cl)(N2)(PPh3)2 (1.36 g, 1.74 mmol)5 in 12 mL of dry dichloromethane in a Schlenk tube is cooled to — 25 °C, and a solution of tetrafluoroboric acid in diethyl ether (54%, d = 1.18gem-3) (0.25mL, 1.89 mmol) is added in one portion by means of a plastic micropipette under stirring and under a flush of dry argon. The mixture is stirred for 1 h at — 25 °C. A pale yellow precipitate settles and the brown solution is decanted. The solid is washed 3 to 4 times, each with 8 mL of cold (— 25 °C) dichloromethane until the solid becomes colorless. The solid is then washed three times with 10 mL each of cold (— 20 to — 25 °C) pentane and dried for 8 h at a high vacuum, during which the temperature is raised from — 20 to 0°C. Yield 1.44 g (95%). 

A magnetic stirring bar, runs-Ir(Cl)(CO)(PPh3)2 (520 mg, 0.67 mmol)8 and dry Ag0S02CF3 (173 mg, 0.67 mmol) are placed in a Schlenk tube (60 mL) under an argon atmosphere. The mixture is dried for 2 h under high vacuum. 

After addition of 10 mL of dry dichloromethane, the yellow suspension is stirred magnetically for 3h. The solution is filtered away from the silver chloride through a Schlenk frit under an argon atmosphere into another dry Schlenk tube. To the yellow solution trilluoromethane sulfonic acid (0.058 mL, 0.66 mmol) (distilled at 43 °C in vacuo with an oil pump and stored under argon) is added by means of a micropipette. The mixture is stirred for 1 h. A colorless precipitate forms. Precipitation of the product is completed by addition of 10 mL of pentane. The mixture is centrifuged and the solution decanted. The remaining solid is washed twice with 10 mL of pentane, and dried under high vacuum for 4h. Yield 620 mg (89%). 

Fig. 5.3. Wayda-Dye greaseless vacuum line. This apparatus makes extensive use of metal bellows tubing and O-ring seals. Thus the reaction vessels, filters, and other items can be tilted and manipu lated like Schlenk ware, and high vacuum conditions can be achieved for the removal of atmospheric gases and for baking out residual moisture. Trap to-trap distillation of volatile solvents such as NH) or SO is readily accomplished with this apparatus. This version is not designed for the measurement of volatiles or trap-to-trap separation. (Reproduced from A.L. Way da and J. L. Dye, J. Chent. Educ. 62, 356 (1985) by permission of the copyright owner the Division of Chemical Education of the American Chemical Society.)...

About a 50-ml. quantity of dry ammonia is condensed into the Schlenk tube which is cooled with a Dry Ice-methanol bath. The reaction mixture is stirred with a magnetic stirrer. The Schlenk tube containing the red solution may be left conveniently in the bath overnight. The bath warms up very slowly, and the ammonia can evaporate without further precautions. After removal of ammonia, the yellow solid residue is dissolved in about 30 ml. of water and the solution filtered into an excess of a concentrated solution of sodium tetraphenylborate. The yellow precipitate is collected and dried under high vacuum. The crude product is stirred with several portions of dichloro-methane until the filtrate is almost colorless and only a small quantity of white ammonium tetraphenylborate remains on the filter. Pentane is then added dropwise until no more precipitate separates. After the purification is repeated and the precipitate is dried under high vacuum, the pure product is obtained in about 40% yield, based on CsHsFeCCO Cl. Anal. Calcd. C, 72.55 H, 5.50 Fe, 10.88 N, 2.73. Found C, 73.04 H, 6.05 Fe, 11.04 N, 2.68. 

The reaction described here of methylzinc iodide with sodium hydride, to produce Na[Zn2(CH3)2H3], may be pictured as a combination of the two reaction types named above. Unlike many hydride preparations, the synthesis of sodium trihydridodimethyldizincate(l —) is easily performed using ordinary Schlenk-type bench-top techniques and commercially available starting materials.4 Sodium trihydridozincate( 1 —) is easily prepared by exposing Na[Zn2(CH3)2H3]-xTHF to high vacuum.4... 

Preparation of the in situ Catalyst and Catalytic Reaction. (This is a typical procedure for norbomadiene and phenylacetylene or 1-hexyne). Tris(acetylacetonato)cobalt (7.1 mg, 2.0x10 mmol) and (+)-NORPHOS (13.8 mg, 3.0 x 10 mmol) are dissolved in 1 ml of THF under dry nitrogen, using standard Schlenk techniques. Norbomadiene (1.0 mL, 10.0 mmol) and 10 mmol of phenylacetylene or 1-hexyne are added. The reaction is started by addition of 5 mL of a IM solution of diethylaluminum chloride in hexane. The reaction mixture is kept at 35 °C for 4 h. Then 5 mL of isopropanol are added and the volatile components are removed in vacuum. The oily residue is distilled at 80 °C in high vacuum in a Kugelrohr apparatus. Chemical yield >99% enantiomeric excess 98.4-99.6% for (+)-4-phenyldeltacyclene and 97.6-98.0% for (+)-4-n-butyldeltacyclene. 

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