A.
(Trifluoromethyl)trimethylsilane. A
2-L, three-necked flask is fitted with an
efficient, overhead, sealed mechanical stirrer, a
cold-finger condenser (30-cm in length and 8-cm in diameter) and a
rubber septum (Note
1). The top outlet of the condenser is attached to an
oil bubbler. The flask is flushed with dry
nitrogen and charged with
118.8 g (1.09 mol) of chlorotrimethylsilane (Note
2) in
100 mL of anhydrous benzonitrile (Note
3). The septum is replaced quickly under dry
nitrogen with a
500-mL Ace dry ice gas condenser trap (15-cm in length and 8-cm in diameter) (Note
4). The outlet of the trap is protected from moisture by a tube packed with
potassium hydroxide and the inlet is connected by tygon tubing to a cylinder of
bromotrifluoromethane (Note
5). The
2-L flask is immersed in a
dry ice-acetone bath maintained at −30°C (Note
6) and the condensers are filled with dry ice-acetone mixture (−78°C). The cylinder is opened and 250 mL (d = 1.94 g/mL,
2 485 g, 3.25 mol) of bromotrifluoromethane is condensed into the
500-mL Ace reservoir (Note
7). Stirring is started, and the condensed liquid
bromotrifluoromethane is gradually added to the vessel at −30°C by slowly warming the reservoir to −45°C to −50°C. The resulting white slurry is further cooled to −60°C (Note
6) and (Note
8). The Ace dry ice gas condenser trap is disconnected under dry
nitrogen and replaced with a
600-mL, pressure-equalizing dropping funnel containing a solution of
325.0 g (1.31 mol) of hexaethylphosphorous triamide (Note
9) in
250 mL of dry benzonitrile. This solution is added with stirring at −60°C to the white slurry mixture over a period of 2.5 hr. After the addition is complete, the reaction mixture is stirred for an additional hour at −60°C (Note
10), and then allowed to warm gradually to room temperature (25°C) over a period of 14 hr, during which time it turns clear yellow (Note
11). The condenser and dropping funnel are removed and replaced by a
glass stopper and
joint adapter with its glass tube connected to two,
250-mL, dry ice/acetone-cooled traps; then aspirator vacuum (ca. 20 mm) is applied. The reaction flask is gently warmed to 50°C during which time (3 hr) all the volatile material collects in the cooled traps (Note
12). The cooling baths are removed and the material in the traps is brought to 0°C. The colorless liquid is transferred quickly to a
250-mL separatory funnel, washed rapidly with ice cold water (3 × 100 mL), and the top organic product layer is separated (Note
13). The product is dried over
5 g of anhydrous magnesium sulfate, and the dry liquid is decanted into a
250-mL flask. The product is fractionally distilled through a
15-cm column packed with glass helices. Three fractions are collected. The first minor fraction (bp
45–54°C) and the second major fraction (bp
54–55°C) contain the main quantity of
(trifluoromethyl)trimethylsilane. The third minor fraction (bp 55–65°C) consists mainly of
hexamethyldisiloxane with a small quantity of product
(trifluoromethyl)trimethylsilane (Note
14). The first and second fractions are combined to yield
116.9 g (
75%) of clear liquid product (Note
15) and (Note
16), bp
54–55°C (Note
17).