Any special precautions or purifications of the reagents required? Limiting and excess reagent? Why is excess necessary? 4,4'-DIBROMOBIPHENYL [Biphenyl, 4,4'-dibromo-] Submitted by Robert E. Buckles and Norris G. Wheeler1. 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).
Any special precautions or purifications of the reagents required? Limiting and excess reagent? Why is excess necessary?
4,4'-DIBROMOBIPHENYL [Biphenyl, 4,4'-dibromo-]
Submitted by Robert E. Buckles and Norris G. Wheeler1. 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).
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