Checked by John D. Roberts and L. K. Montgomery.
1. Procedure
(Note
In a
600-ml. beaker fitted with a
thermometer and mechanical stirrer are placed
150 ml. of concentrated hydrochloric acid and
55 g. (0.32 mole) of o-bromoaniline. After brief stirring, 100 g. of ice is added and the beaker is surrounded by an
ice-salt bath. The solution is then diazotized by the dropwise addition with stirring of a solution of
24.3 g. (0.35 mole) of sodium nitrite in 100 ml. of water, the temperature being kept at 0–5°.
After stirring the diazotized solution for 15 minutes, it is slowly poured through a
glass-wool filter into a solution of
180 g. (3.4 moles) of potassium iodide in 600 ml. of water. After standing overnight, the heavy dark oil is separated, washed successively with
10% aqueous sodium hydroxide, water,
5% aqueous sodium bisulfite and water, and then dried over
magnesium sulfate.
Distillation under reduced pressure gives
o-bromoiodobenzene as a nearly colorless liquid, b.p.
120–121° at 15 mm. Yield
65–75 g. (
72–83%).
A
1-l. flask is fitted with a
reflux condenser,
dropping funnel, and a
sealed mechanical stirrer. A
nitrogen atmosphere is maintained in the flask during the entire reaction period.
In the flask is placed
150 ml. of anhydrous ether, and
5.7 g. (4.1 atomic equivalents) of lithium foil is then added (Note
2). A solution of
56.6 g. (0.2 mole) of o-bromoiodobenzene in
300 ml. of anhydrous ether is added dropwise (Note
3). When a vigorous reaction commences, the stirrer is started and the flask is cooled in ice water to maintain the temperature at about 10°. The reflux condenser is replaced by a thermometer, and the remainder of the
o-bromoiodobenzene solution is added at a rate such that the temperature in the flask remains at about 10° (about 1.5 hours). When this addition is complete,
200 ml. of dry benzene is added; the mixture is stirred at 10° for 1 hour and finally at room temperature for 1 hour. The mixture is then poured through a glass-wool filter on 200 g. of ice.
The organic layer is separated, evaporated on a
steam bath, and the dark semicrystalline residue is distilled with steam to remove
biphenyl. The contents of the steam-distillation flask are then extracted with
ether (Note
4), and the ethereal layer is separated, dried over
magnesium sulfate, and percolated through a
short column of chromatographic alumina (Note
5) and (Note
6). Evaporation of the ethereal solution gives crude
triphenylene which is sublimed at 175–180° and 0.1 mm. pressure. After rejection of an initial sublimate of impure
biphenyl, the sublimed material forms nearly colorless crystals, m.p.
186–194° (Note
7). Yield
8–9 g. (
53–59%). It may be further purified by recrystallization from a mixture of
methylene chloride and
pentane yielding colorless crystals, m.p.
199° (Note
8).
2. Notes
1. Although the procedure described here is still a useful method of preparing
triphenylene, it is in the opinion of the submitters no longer the best available. In their opinion a more nearly pure product and a higher yield (
85%) may be obtained by the reaction of
o-bromofluorobenzene and
magnesium in
tetrahydrofuran2 (private communication from H. Heaney).
2. Slugs of
lithium, coated with paraffin oil, are hammered into thin foil. They are washed free of oil with dry
ether and cut by scissors into slips which are allowed to fall directly into the ether in the reaction flask.
3. By adding
10–20 ml. of the o-bromoiodobenzene solution to the metal before stirring is started, high local concentrations of the dihalo compound which initiate reaction are built up. An induction period of about 10 minutes is usually observed before the vigorous reaction commences.
4. The checkers found that, in view of the limited solubility of
triphenylene in
ether (about 1 g. per 100 ml.), care must be exercised in the extraction to ensure that all the product is removed.
5. The volume of
ether solution must be reduced to approach the solubility limit of the
triphenylene in
ether before the chromatographic procedure.
6. The checkers used a
30-mm. (I.D.) chromatographic column charged with approximately
250 g. of activated (400° for 12 hours), acid-washed, chromatographic aluminum oxide (Merck and Co., Inc.).
7. The contaminant in the product of m.p.
186–194° is present in low concentration and is very probably
o-terphenyl. It is characterized by an absorption near 695 cm.
−1 in the infrared which is absent in the spectrum of pure
triphenylene.
The submitters report that the purity of the product is rather dependent upon the purity of the
lithium used and that results can vary from batch to batch. In addition, they state that side reactions may be catalyzed by traces of heavy metals, that the degree of vigor in the initial reaction may influence the purity of the product owing to local overheating, and that increase in scale of this reaction is deleterious.
8. The checkers carried out this recrystallization by dissolving
triphenylene in a minimum of
methylene chloride maintained at reflux.
Pentane was slowly added to this solution; up to
90% recovery was achieved.
3. Discussion
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