Org. Synth. 1923, 3, 41
DOI: 10.15227/orgsyn.003.0041
9,10-DIBROMOANTHRACENE
[Anthracene, 9,10-dibromo-]
Submitted by I. M. Heilbron and J. S. Heaton.
Checked by H. T. Clarke and T. F. Murray.
1. Procedure
To a suspension of 300 g. (1.35–1.43 moles) of anthracene of 80–85 per cent purity in 3 l. of carbon tetrachloride (Note 1), in a 5-l. flask fitted with dropping funnel, stirrer, and reflux condenser, is added slowly 567 g. (182 cc., 3.55 moles) of bromine. The bromination takes place in the cold with separation of the sparingly soluble 9,10-dibromoanthracene; in order to prevent undissolved anthracene from becoming coated over, it is necessary to maintain vigorous stirring throughout the reaction. A tube from the top of the condenser conducts hydrogen bromide to cold water, in which it is absorbed (Note 2). The addition of the bromine occupies about one-half hour; the rate is so adjusted that a minimum of bromine is carried over with the hydrogen bromide.
When all the bromine has been added, the mixture is gently warmed on a steam bath with continual stirring, care being taken not to heat so rapidly as to cause undue loss of bromine by entrainment. Heating is continued until the mixture has boiled gently for one hour. The mixture is then allowed to cool for some hours, without stirring, and the crude dibromoanthracene is filtered off, washed with a little cold carbon tetrachloride, and dried. In this way 270-425 g. of a bright yellow product, which melts (Note 3) at 218–219° (corr.), is obtained. On concentrating the mother liquors, 15–150 g. more of crude material, m.p. about 216° (corr.), can be obtained.
To prepare a purer product, the crude
dibromoanthracene is extracted with
carbon tetrachloride (Note 4) in an apparatus similar to that described on
p. 375, the extraction is carried to the point at which crystals just begin to separate from the boiling solvent, and a fresh quantity of
carbon tetrachloride is then taken. About eight extractions are necessary, 1 l. being used each time. The
9,10-dibromoanthracene so purified consists of brilliant yellow needles melting at
221–222° (corr.)
(Note 5). A further quantity of pure product may be obtained by concentrating the mother liquor and recrystallizing the second crop so obtained. The recovered solvent may be employed for further extractions. The yield amounts to
400–420 g. (
83–88 per cent of the theoretical quantity based on
anthracene of 85 per cent purity).
2. Notes
1.
The reaction may be carried out equally well with a larger proportion of solvent, but if less than the amount indicated is taken, difficulty may arise in stirring.
Carbon disulfide may be employed instead of
carbon tetrachloride, but this solvent presents no essential advantages and it is necessary to use a larger volume for the same amount of
anthracene.
2.
The watery solution of
hydrogen bromide, on fractional distillation, readily yields
48 per cent hydrobromic acid, boiling at
125–126° /760 mm. (p. 26).
3.
The observed melting points of the various products are 5–6° lower than the corrected values.
4.
The crude product may be recrystallized from
toluene, in which it is somewhat more soluble than in
carbon tetrachloride; the color of the product is, however, not quite so light, although the melting point is as high as if
carbon tetrachloride were used. If desired, recrystallization may be effected from
toluene without using the extraction apparatus, in which case about 10 l. of solvent in all will be required; for the filtration of the hot solution, a plug of glass wool, previously wetted with boiling
toluene, may be employed, care being taken to warm the funnel adequately.
The bromination products of the impurities with which commercial anthracene is contaminated appear to be more soluble in carbon tetrachloride than is 9,10-dibromoanthracene; the yield can be slightly increased by fractional recrystallization of the products contained in the original mother liquor, but under laboratory conditions the gain does not compensate for the time involved.
5.
When crystallized from
xylene, samples have been obtained that melt as high as
226° (uncorr.) (E. de Barry Barnett, private communication).
3. Discussion
9,10-Dibromoanthracene can be prepared by the bromination of
anthracene in dilute
carbon disulfide solution.
1
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
HYDROBROMIC ACID,
hydrogen bromide (10035-10-6)
bromine (7726-95-6)
carbon tetrachloride (56-23-5)
toluene (108-88-3)
carbon disulfide (75-15-0)
9,10-Dibromoanthracene,
Anthracene, 9,10-dibromo- (523-27-3)
anthracene (120-12-7)
dibromoanthracene
xylene (106-42-3)
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