Answer to Question #9969 in Organic Chemistry for Brayden

Question

How to separate Biphenyl from benzene and bromobenze? The solvent used is diethyl ether, which can easily be evaporated off. The melting point of biphenyl is a lot higher (approx. 70 C) than the other two, so once the solvent has been removed will biphenyl precipitate out? or will it still be solvated by the other two compounds? I know that benzene boils off at 60 C but bromobenzene doesn't until 150 C, so what would the easiest way to isolate biphenyl be? Thanks for the help

Answer 1

Biphenyl mp 69 bp 255

Bromobenzene mp -30 bp 156

Benzene mp 5.5 bp 80

How much biphenyl do you have? If biphenyl is major product, bromobenzene and benzene are impurities, the follow method is appropriate. Just evaporates the diethyl ether and filtered off the biphenyl (wash the precipitate with small amount appropriate solvent and to dry in vacuum). If amounts of biphenyl, bromobenzene and benzene are equal, evaporate benzene and bromobenzene in vacuo (ca.10-50 torr) with moderate warming (ca.100 C). Then distill the biphenyl in high vacuum(ca. 10^-2 torr - 10^-3 torr).