Organic Syntheses, CV 4, 256
Submitted by Robert E. Buckles and Norris G. Wheeler
1.
Checked by R. S. Schreiber, Wm. Bradley Reid, Jr., and Robert W. Jackson.
1. Procedure
In a
15-cm. evaporating dish is placed
15.4 g. (0.10 mole) of finely powdered biphenyl (Note
1). The dish is set on a
porcelain rack in a 30-cm. desiccator with a
10-cm. evaporating dish under the rack containing
39 g. (12 ml., 0.24 mole) of bromine. The desiccator is closed, but a very small opening is provided for the escape of
hydrogen bromide (Note
2). The
biphenyl is left in contact with the
bromine vapor for 8 hours (or overnight). The orange solid is then removed from the desiccator and allowed to stand in the air under a
hood for at least 4 hours (Note
3). At this point, the product weighs about
30 g. and has a melting point in the neighborhood of
152°. The crude
4,4'-dibromobiphenyl is dissolved in
75 ml. of benzene, filtered, and cooled to 15°. The resulting crystals are filtered, giving a yield of
23.4–24.0 g. (
75–77%) of
4,4'-dibromobiphenyl, m.p.
162–163° (Note
4).
2. Notes
1. The checkers used
Eastman Kodak Company white label grade of biphenyl.
2. If a vacuum desiccator is used, the stopcock can be opened slightly to allow for the escape of
hydrogen bromide.
4.
4,4'-Dibromobibenzyl can be prepared in the same manner.
Eighteen grams (0.10 mole) of finely divided bibenzyl is left in contact with the vapor from
39 g. (12 ml., 0.24 mole) of bromine for 24 hours. The desiccator is put under an opaque cover to keep out light, which causes the formation of
α,α'-dibromobibenzyl. The somewhat sticky reaction product is allowed to stand overnight. The crude product is dissolved in
300 ml. of isopropyl alcohol, filtered, and cooled. A yield of
15.0–17.0 g. (
44–50%) of
4,4'-dibromobibenzyl, m.p.
113–114°, is obtained.
3. Discussion
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