Thirty-eight grams (0.1 mole) of bis-3,4-dichlorobenzoyl peroxide (Note
1) is added to a boiling solution of
3 g. of m-dinitro-benzene in
800 ml. of dry reagent grade benzene contained in a
1-l. round-bottomed flask, and the resulting solution is boiled under reflux for 40 hours. The solvent is then distilled from the red solution until the residual volume is about 200 ml. (Note
2), and the mixture is allowed to cool. The
3,4-dichlorobenzoic acid which separates is removed by suction filtration, washed with a little cold
benzene, and then with
100 ml. of petroleum ether (b.p.
80–100°). The combined filtrate and washings are further concentrated by distillation (Note
2) to about 60 ml., cooled, and a small second crop of
3,4-dichlorobenzoic acid is removed and washed with a little
benzene followed by a little
petroleum ether. The total yield of acid, m.p.
208–210° (Lit.
2 m.p.
208–209°), is
18.2 g. (
95%) (Note
3). The filtrate and washings are combined (Note
4) and chromatographed on a
column of basic alumina (30 cm. x 3.5 cm.) which is eluted with
petroleum ether (b.p.
40–60°). Solvent is distilled from the eluate (Note
5), and the residual crude
3,4-dichlorobiphenyl is distilled under reduced pressure using a
short air condenser and a
receiver chilled in ice. There is obtained
17.3–18.0 g. (
78–81%) of almost pure
3,4-dichlorobiphenyl (b.p.
146–150° at 2 mm.) which sets to a colorless solid, m.p.
44–47° (Note
6).