Org. Synth. 1969, 49, 44
DOI: 10.15227/orgsyn.049.0044
ARYLBENZENES: 3,4-DICHLOROBIPHENYL
[Biphenyl, 3,4-dichloro-]
Submitted by D. H. Hey and M. J. Perkins
1.
Checked by K. K.-W. Shen and K. B. Wiberg.
1. Procedure
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).
2. Notes
1.
The
bis-3,4-dichlorobenzoyl peroxide may be prepared as follows.
3,4 To a
2-l. beaker containing 400 ml. of water which is cooled to 0–5° in an
ice bath is added slowly
40 g. (0.51 mole) of sodium peroxide. A
dropping funnel containing
167.6 g. (0.8 mole) of 3,4-dichlorobenzoyl chloride in 400 ml. of dry toluene is supported over the beaker. The peroxide solution is cooled and stirred vigorously while the
toluene solution is added drop-wise over a 1-hour period. The solution is stirred for an additional 2 hours. The precipitate is filtered using a suction funnel, washed with 600 ml. of cold water, and dried in air overnight. There is obtained
114 g. (
75%) of
bis-3,4-dichlorobenzoyl peroxide, m.p.
135° dec. The crude product is purified by dissolving it in
chloroform and precipitating by the addition of
methanol, m.p.
139° dec.
2.
Solvent removal may conveniently be carried out with a
rotary evaporator to obviate bumping caused by separation of the
dichlorobenzoic acid from the boiling solution.
3.
In syntheses of other arylbenzenes, in which the acid by-product is more soluble, it may be extracted from the reaction mixture with aqueous
sodium bicarbonate or removed in the subsequent chromatography.
4.
At this point the solvent is largely
petroleum ether. Appreciable quantities of
benzene in the mixture to be chromatographed tend to carry some of the
dinitrobenzene through the alumina.
5.
After removal of the solvent from the eluate, almost pure white
3,4-dichlorobiphenyl crystallizes, m.p.
44–48°. It may be purified by recrystallization from
methanol as an alternative to vacuum distillation.
6.
The product may be freed from a trace (
~1%) of
biphenyl present as an impurity by recrystallization from
methanol which raises the melting point to 47–48°. The literature values range from
46°5 to
49–50°.
6
3. Discussion
3,4-Dichlorobiphenyl has been prepared by the arylation of
benzene using the Gomberg procedure starting with
3,4-dichloroaniline,
5 and using the acid-catalyzed decomposition of
1-(3,4-dichlorophenyl)-3,3-dimethyltriazene in
benzene.
6 The arylation procedure given above, which utilizes a diaroyl peroxide as the aryl radical source, provides a route arylbenzenes which involves simple operations and gives a good yield of pure product. In the absence of the nitro compound, the mode of action of which has been discussed in terms of two somewhat different mechanisms,
7,8 the yields of aroic acids and arylbenzenes are commonly below 50%,
9 and the arylbenzene may be contaminated with aryldihydrobenzenes.
10 The present procedure has been used to prepare a variety of simple arylbenzenes in isolated yields ranging from 70 to 90%. If a nitro substituent is present in the peroxide, high yields are obtained without the addition of further nitro compound.
9
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
petroleum ether
Benzene (71-43-2)
methanol (67-56-1)
chloroform (67-66-3)
sodium bicarbonate (144-55-8)
toluene (108-88-3)
Biphenyl (92-52-4)
sodium peroxide
3,4-Dichlorobiphenyl,
Biphenyl, 3,4-dichloro- (2974-92-7)
bis-3,4-dichlorobenzoyl peroxide
3,4-dichlorobenzoic acid (51-44-5)
3,4-dichlorobenzoyl chloride (3024-72-4)
dichlorobenzoic acid (50-45-3)
dinitrobenzene (528-29-0)
3,4-dichloroaniline (95-76-1)
1-(3,4-dichlorophenyl)-3,3-dimethyltriazene
m-dinitro-benzene (99-65-0)
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