In a thoroughly dry
500-ml. three-necked round-bottomed flask, equipped with a
mercury-sealed stirrer, a
100-ml. dropping funnel and a
short fractionating column (Note
2), is placed a mixture of
116 g. (2.0 moles) of anhydrous finely powdered potassium fluoride (Note
3) and
200 g. of dry ethylene glycol (Note
4). The fractionating column carries a
thermometer and is connected to a downward double-surface condenser with a
filter flask as
receiver. The round flask is heated at a bath temperature of 160–170°, and
165 g. (1.0 mole) of n-hexyl bromide, b.p.
154–156° (Note
5), is added dropwise during 5 hours; liquid passes over intermittently at 60–90° (temperature at the top of the fractionating column). The bath temperature is allowed to fall to 110–120°, and a slow stream of air is drawn through the apparatus by attaching the side arm of the
filter flask to a
water pump and replacing the
dropping funnel by a narrow-bore tube dipping just below the surface of the liquid; stirring is maintained during this operation. It is advisable to interpose a U-tube cooled in ice between the water pump and the receiver in order to recover any uncondensed liquid. The combined distillates are then distilled at atmospheric pressure through an efficient fractionating column; after a small fore-run
(up to 10 g.) of 1-hexene, the crude
n-hexyl fluoride is collected at
89–92° (
46–48 g.). The crude product is purified by cooling in ice and adding
1-ml. portions of a solution containing 9.0 g. of bromine and
6.0 g. of potassium bromide in 50 ml. of water until the organic layer acquires an orange color; after each addition the mixture is shaken vigorously for a minute or so. The volume of
bromine-potassium bromide solution required is usually less than 5 ml. The aqueous layer is separated, the organic layer is washed with saturated aqueous
potassium bromide solution until color-less and finally with water. The liquid is dried with anhydrous
magnesium sulfate and distilled through an efficient fractionating column; the
n-hexyl flouride is collected at
91–92°. This procedure yields
42–47 g. (
40–45% over-all yield based on the
bromide employed) of a water-white product,
nD20 1.375,
nD25 1.372–1.373,
d420 0.8011. It has been kept for 1 year without change of physical properties and therefore appears to be stable (Note
6).