A
300-ml., three-necked, round-bottomed flask is equipped with a
mechanical stirrer, a
reflux condenser, and a
pressure-equalizing addition funnel. The condenser is connected in series with two
traps, immersed in liquid
nitrogen, with the exit leading to a
drying tube (Note
1). A line for dry
nitrogen that has a
T-tube joined to a
U-tube containing
mercury is connected to the top of the addition funnel (Note
2). To the flask are added
150 ml. of purified dioxane (Note
3) and
13.6 g. (0.591 g.-atom) of freshly cut sodium (Note
4). The mixture is heated to reflux, and the molten
sodium is broken up with the stirrer. A solution of
20.0 g. (0.118 mole) of 1-bromo-3-chlorocyclobutane (Note
5) in
20 ml. of dioxane (Note
3) is added to the refluxing
dioxane over a 1-hour period; refluxing is maintained for an additional 2 hours (Note
6) and (Note
7). The product in the traps is separated from any
dioxane with the vacuum manifold system shown in
f.htmigure 1 (Note
8). The two traps containing the product are cooled in liquid
nitrogen and connected to one of the
stopcocks on the manifold. A gas storage bulb (
f.htmigure 2) is attached to the other stopcock. All the stopcocks are opened, and the system is evacuated. The stopcock to the pump is then closed, and the
liquid nitrogen bath is removed from the traps and used to cool the gas storage bulb. The traps are warmed slightly, and the
bicyclobutane condenses in the storage bulb, leaving the
dioxane behind, yielding
5–6 g. (
78–94%) (Note
9) of
bicyclobutane.
Figure 1. Vacuum manifold.
Figure 2. Gas storage bulb.