A reaction vessel as shown in
f.htmig. 1 is made from Pyrex tubing (Note
1). The vessel is evacuated and the stopcock closed. A
500-ml. round-bottomed, two-necked flask equipped with a
gas inlet and a
cold finger condenser containing dry ice is charged with
1 g. of finely powdered 4,4'-bis(dimethylamino)benzophenone (Michler's ketone) (Note
2), (Note
3). A
butadiene tank is connected to the gas inlet, and about
250 ml. (160 g., 3.0 moles) of butadiene is collected in the flask (Note
4). The
butadiene is cooled to dry ice temperature. The reaction vessel is immersed to the filling level shown in
f.htmig. 1 in a slurry of dry ice and
acetone. A
4-in. length of Tygon tubing is attached between the inlet of the reaction vessel and one neck of the flask containing the
butadiene. The other neck of the flask is stoppered, and the flask is tipped to fill the connecting tube and the neck of the stopcock with
butadiene. At the same time the stopcock is opened. The flask is shaken to ensure that the suspended Michler's ketone will be swept into the reaction vessel by the
butadiene. After the vessel is filled with
butadiene the stopcock is closed, the connecting tube removed, and the vessel transferred to a
Dewar flask filled with liquid
nitrogen. When the
butadiene is frozen, the vessel is evacuated with a
high-vacuum pump and sealed off below the stopcock with a torch (Note
5). The reaction vessel is fitted with cooling water hoses and a
450-watt Hanovia medium-pressure mercury arc lamp, and then the
butadiene is allowed to thaw and come to room temperature (Note
6). The mixture is irradiated for 72 hours, the water jacket dried, and the vessel weighed (
Caution! (Note
6). The reaction vessel is then frozen in a Dewar flask containing a dry ice-acetone mixture, and the seal is cautiously broken. The
cooling bath is removed, and the reactor is allowed to come to room temperature. The reaction mixture is removed, the vessel cleaned (Note
7), and weighed again to determine the amount of starting material. The reaction mixture is distilled and the fraction boiling between 109° and 111° (uncor.) is collected (Note
8). The yield is
96–104 g. (
60–65%) of 99% pure (by gas chromatography)
trans-1,2-divinylcyclobutane,
n25D 1.4429–1.4431, the impurities being
butadiene and
1,5-cyclooctadiene (Note
9).
Fig. 1.
A,
4-mm. stopcock;
B, thickened for easy sealing;
C, water inlet;
D, water outlet;
E, this seal can be replaced by a ground glass joint for higher-boiling materials than
butadiene;
F, filling level;
G, the cooling water tube indicated by the dotted lines will permit a higher flow rate if shaped as an oval or rectangle;
H, reaction well;
I, lamp well;
J, cooling water jacket.