Organic Syntheses, CV 5, 829
Submitted by G. David Mendenhall and Peter A. S. Smith
1.
Checked by Howard A. Harris and Kenneth B. Wiberg.
1. Procedure
A.
o-Aminobiphenyl. A
Parr bottle is charged with
60 g. (0.30 mole) of o-nitrobiphenyl (Note
1),
3 g. of 5% palladium-on-carbon catalyst (Note
2), and
200 ml. of 95% ethanol. The mixture is shaken with
hydrogen under 25–50 p.s.i. until the gas is no longer absorbed (about 70 minutes), the catalyst is filtered from the hot solution and washed with
20 ml. of ethanol, and the filtrates are poured in a thin stream into 1 l. of ice water contained in a
2-l. Erlenmeyer flask (Note
3). After standing for 20 minutes the white solid is filtered with suction, pressed to remove excess water, and allowed to dry in air. The yield of essentially pure
o-aminobiphenyl is
48–51 g. (
94–100%), m.p.
43–45.5°.
B.
o-Amino-p'-nitrobiphenyl. Concentrated
sulfuric acid (400 ml.) is placed in a
1-l. round-bottomed flask fitted with a
mechanical stirrer and a
thermometer. Stirring is begun, and
45.0 g. (0.27 mole) of powdered o-aminobiphenyl is added all at once through a powder funnel. When the amine has dissolved, the flask is placed in an
ice-salt bath and its contents cooled to a temperature between 0° and −5°. A mixture of
30 ml. of concentrated sulfuric acid and
11.0 ml. of fuming nitric acid (density 1.5) is then added dropwise from a
separatory funnel while the temperature is kept below 0°. The addition requires about an hour, and stirring is continued 45 minutes longer. The liquid is poured onto 1.5 kg. of ice in a
4-l. beaker and treated carefully until neutral with a solution of
580 g. (14.5 moles) of sodium hydroxide in 1.5 l. of water cooled to room temperature. The resultant hot suspension of product is allowed to cool nearly to room temperature, filtered with suction, and the orange solid is washed with 500 ml. of water. The crude material is pressed free of excess water and recrystallized from
850–1000 ml. of 95% ethanol (Note
4), giving
32–42 g. (
56–74%) of orange needles, m.p.
156–158.5°.
C.
o-Azido-p'-nitrobiphenyl. Water (100 ml.) is placed in a 1-l. round-bottomed flask equipped with a thermometer and an efficient mechanical stirrer. With stirring,
30 ml. of concentrated sulfuric acid is added, followed by
32.1 g. (0.15 mole) of recrystallized o-amino-p'-nitrobiphenyl. When all the amine has been converted to the white sulfate, 50 ml. more of water is added and the suspension is cooled to 0–5° in an ice-salt bath. A solution of
11 g. (0.16 mole) of sodium nitrite in 30 ml. of water is added dropwise over a period of 15 minutes (Note
5), and the mixture is stirred for 45 minutes longer. A thick precipitate of the sparingly soluble diazonium salt may have separated from the initially clear solution by this time. With strong stirring, a solution of
12 g. (0.17 mole) of sodium azide in 40 ml. of water is run in (Note
6), and stirring is continued for 40 minutes longer. The thick white solid is filtered with suction and washed with 200 ml. of water. After pressing free of excess water, the material is allowed to dry in air in a dark place. The yield of gray-white azide is
35.5–36 g. (
99–100%), m.p.
91.5–92.5° (Note
7).
D.
2-Nitrocarbazole. In a
2-l. round-bottomed flask fitted with a mechanical stirrer, a thermometer, and a short air condenser are placed
35.5 g. (0.15 mole) of powdered o-azido-p'-nitrobiphenyl and
1 l. of o-dichlorobenzene (Note
8). The stirred mixture is heated above 170° for 1 hour by means of a heating mantle, allowed to cool to room temperature, and chilled in a refrigerator (5°) for several hours. The crude product is filtered with suction, washed with
40 ml. of light petroleum, and sucked dry on the filter. There results
26–28 g. of yellow-brown crystals, m.p.
171.5–174°. The filtrate is distilled under aspirator pressure to a volume of 150–200 ml. and chilled as before, to yield an additional
2–3 g., m.p.
171–174°. The total yield is
28–30 g. (
89–96%). The combined crops are dissolved in
400–450 ml. of boiling 95% ethanol with
3–4 g. of Norit® to remove impurities and filtered through a preheated
Büchner funnel. The filtrate on cooling deposits bright yellow needles of product, which are filtered after standing at 5° for several hours. This crop weighs
23–25 g., m.p.
174–175.5°. Concentration of the mother liquor to a small volume (50–70 ml.) and chilling gives a second crop of lesser purity,
1–2 g., m.p.
172–175°. The total yield of recrystallized material is
24–26.5 g. (
77–85%), and the overall yield from
o-nitrobiphenyl is
40–63%.
2. Notes
1. An
Eastman Kodak technical grade of o-nitrobiphenyl was used by the submitters. This is no longer available, and the checkers used the material supplied by K and K Laboratories. Both
o-amino- and o-nitrobiphenyl are available from the Aldrich Chemical Company.
2. The Baker Co. catalyst was used.
3. This carcinogen is more easily handled in a flask than in a beaker. Contact with the skin obviously should be avoided.
4. Recrystallization is best accomplished by adding the compound to boiling
ethanol and filtering. Prolonged heating should be avoided, as the substance gradually decomposes in hot solvent.
5. The
sodium nitrite solution must be added carefully in order to avoid loss of material due to vigorous foaming.
6. This operation should be carried out in a
hood to avoid the unpleasant effects of exposure to
hydrogen azide vapors.
7. The compound may be recrystallized from a large volume of
ethanol, but no increase in yield was noted using recrystallized material in the next step.
8.
Eastman Kodak o-dichlorobenzene of 95% purity was used. Olefin-free kerosene or
decalin may be substituted for the solvent, keeping the reaction temperature between 170° and 190°.
3. Discussion
4. Merits of the Preparation
The decomposition of
o-azidobiphenyls is a convenient and general synthesis for a variety of carbazoles in good yield,
15 especially those not available through direct substitution of
carbazole itself. Many of the required intermediates can be prepared from
o-aminobiphenyl by substitution reactions. The method is also applicable to the preparation of analogs of the
carbazole system in which a heterocyclic ring replaces a
benzene ring, to the preparation of indoles, and to certain analogous aliphatic systems.
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