Freeze-pump-thaw method

Figure 18.9 Glass vessel for the preparation and degassing of solutions by the freeze-pump-thaw method. The degassed solution is gravity-transferred to the electrochemical cell by rotating the container 180°. [From Ref. 38, with permission.]...

B. Saturated Hydrocarbons. Purging and freeze-pump-thaw methods are effective in degassing paraffins. Distillation with the elimination of the first fractions produces dry solvent. Molecular sieves may also be used to remove water. Distillation from sodium-benzophenone ketyl is highly effective in obtaining very low levels of water and oxygen. Commercial grades of hydrocarbons are often contaminated with olefins, which can be eliminated by several washings... 

Commercial chloroiodomethane was passed through a short column of oven dried basic alumina (activity 1) into a flame dried Schlenk flask containing copper wire, and then was degassed via the freeze-pump-thaw method. The reagent was stored under an atmosphere of Ar in the Schlenk flask, which was covered with aluminium foil. 

ClCI- Ch CI was distilled over calcium hydride and then was degassed via the freeze-pump-thaw method. 

All solvents must be freshly distilled over sodium/benzophenone ketyl or freshly degassed using the freeze/pump/thaw method. Solutions of Ni(COD)2 are far more sensitive to oxygen than the solid form and were not used in these studies. Ni(COD)2 and BINAP must be stirred together at a concentration of not less than 0.02 M for a period of about 4 hours which produces a deep burgundy... 

Oct-l-ene (3.4 g, 0.03 mol), haloalkane (0.06 mol) and [RuCl2(PPh3)3] (0.01 g, 1 X 10 mol) were loaded into a glass tube with a restriction in the neck to facilitate sealing. The reaction mixture was degassed three times by the freeze-pump-thaw method and the tube was then sealed under vacuum. The tube was then heated to the desired temperature in an oven for times varying between 1.5 and 20 h, after which time it was opened and the contents analyzed by GLC. 

Sample Treatment. Research grade isobutylene (99.5 mole % purity) was used after degassing by the freeze-pump-thaw method for most experiments. The only impurity detected by gas chromatographic analysis was 0.02% isobutane. C8 and Ci2 compounds which were used as gas chromatographic standards were obtained from the Chemical Samples Co. (Cleveland). Research grade rare gases were used. 

Alkenyl carbene complex was dissolved in benzene at a concentration of 0.002 M. The red solution was deoxygenated by the freeze-pump-thaw method (four cycles) and heated in an oil bath to 100°C. The solution turned from red to yellow during the reaction. After the completion of the reaction, the solvent was removed, and the residue was taken up in CH2Cl2/ether, and stirred in air overnight. The mixture was then loaded on silica gel and chromatographed to give 40% of p-methoxy phenol derivative and 21% of m-methoxy phenol derivative. 

To an approximately 0.33 M solution of the carbene complex in dry benzene was added a threefold excess of 1-pentyne. The resulting solution was deoxygenated by the freeze-pump-thaw method (-196°C/25°C, three cycles). The flask was back-filled with argon at... 

Dihromo-l,l,3,3-tetra-/hutyl-l,3-dimethyltrisilane (4.02 g, 7.99 mmol) and KCs (2.35 g, 17.3 mmol) were added to a round-bottom flask in a glove box. Dry, degassed DME (30 mL, degassed by freeze—pump—thaw method) was introduced by vacuum transfer to this reaction mixture at 78°C. Afterward the reaction mixture was allowed to warm to room temperature with stirring over 5 h. 

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