Org. Synth. 1969, 49, 6
DOI: 10.15227/orgsyn.049.0006
2-BROMONAPHTHALENE
[Naphthalene, 2-bromo-]
Submitted by J. P. Schaefer, Jerry Higgins, and P. K. Shenoy
1.
Checked by James P. Nelson, Wayland E. Noland, and William E. Parham.
1. Procedure
A
500 ml., three-necked, round-bottomed flask is equipped with a
Trubore stirrer, a
pressure-compensating dropping funnel, and a
reflux condenser with drying tube. The flask is charged with
144 g. of triphenylphosphine (0.55 mole) (Note 1) and
125 ml. of acetonitrile (Note 2) and
(Note 3). The solution is stirred and cooled in an
ice bath and
88 g. of bromine is added dropwise over a period of 20–30 minutes
(Note 4). After the addition of the
bromine (Note 5) is complete, the ice bath is removed and
72 g. (0.50 mole) of β-naphthol (Note 6) in
100 ml. of acetonitrile (Note 7) is added in one portion and the reaction mixture is heated to 60–70° for at least 30 minutes
(Note 8). The flask is now fitted for a simple distillation, stirring is discontinued, and the
acetonitrile is distilled
(Note 9) under aspirator pressure until the
oil bath temperature reaches 110°
(Note 10). After all the
acetonitrile has been removed, the condenser is replaced by a
short, large glass tube (Note 11) connected to a 500-ml. flask half-filled with water, and the oil bath is replaced by a
Wood's metal bath. The bath temperature is now raised to 200–220° and kept at this temperature until all the solid has melted
(Note 12). The mixture is stirred and the bath temperature is raised to 340°
(Note 13) and held at this temperature until evolution of
hydrogen bromide ceases (approximately 20–30 minutes). The Wood's metal bath is removed and the reaction mixture is cooled to approximately 100° and then poured into a
1-l. beaker and cooled to room temperature.
Pentane (300 ml.) (Note 14) is added and the solid is broken into a fine precipitate
(Note 15). The solid is filtered by suction and washed thoroughly with two
300-ml. portions of pentane. The
pentane filtrates are combined, washed with
200 ml. of 20% sodium hydroxide, and dried over anhydrous
magnesium sulfate. The
pentane extract is then passed through a
25 mm. diameter column filled to 35 cm. in depth with alumina; distillation of the
pentane at reduced pressure gives
72–81 g. (
70–78%)
(Note 16) of
2-bromonaphthalene, a white solid melting at
45–50° (reported:
2 55–56.4°)
(Note 17),
(Note 18).
2. Notes
1.
Triphenylphosphine was obtained from M and T Chemicals Inc. and was used without further purification.
2.
The
acetonitrile was
cautiously distilled from
phosphorus pentoxide. The solid
phosphorus pentoxide may cause bumping during the distillation of the
acetonitrile. This can be avoided if the solution is stirred during the distillation.
3.
The
triphenylphosphine is only partially dissolved.
4.
The temperature is kept below 40° and the reaction mixture thoroughly stirred during this addition.
5.
If a small amount of free
bromine remains, as evidenced by color, then a sufficient amount of
triphenylphosphine is added to take up the
bromine.
6.
Practical grade β-naphthol was obtained from Matheson Coleman and Bell and distilled at atmospheric pressure before use.
7.
Warming the
acetonitrile is necessary to dissolve the
β-naphthol.
8.
All the precipitate dissolves at this point. The checkers heated the mixture for 2 hours. The solids appeared to dissolve; then there was some reprecipitation. All solids had not dissolved after 2 hours at 70°.
9.
The checkers encountered severe bumping during distillation of the
acetonitrile. The
acetonitrile may be removed with only moderate bumping if no external heat is applied.
10.
The checkers did not remove all the
acetonitrile at 110°, a factor which contributed to foaming later
(Note 12).
11.
If a tube smaller than ½ inch in diameter is used, it may become plugged later in the reaction.
12.
If temperature is higher than 220°, initial foaming may become troublesome. The checkers heated the solid to 240–270°, since melting did not occur at 200–220°; foaming was encountered.
13.
Evolution of
hydrogen bromide begins at about 280°.
14.
The checkers used
petroleum ether (b.p.
65–67°).
15.
The checkers obtained a somewhat tarry precipitate.
16.
The submitters obtained
85–87 g. (
82–86% yield).
17.
The checkers' product retained solvent. The product was heated for a short period at 120° (20 mm.) and a crystalline solid, free of solvent, was obtained.
18.
Purity was checked by analytical vapor phase chromatography (98–99%). This product can be used for most reactions without further purification. If further purification is desired,
2-bromonaphthalene can be recrystallized from aqueous
methanol (
95% recovery) to give a product melting at
53–55°.
3. Discussion
2-Bromonaphthalene has been prepared from
2-aminonaphthalene by the reaction of
mercuric bromide with the
diazonaphthalene.
2,3 The reaction described in this preparation appears to be fairly general and provides a useful alternative method for introducing
bromine into the aromatic nucleus. Using conditions similar to those outlined, the following have been prepared from the corresponding aryl alcohols:
4,5 α-bromonaphthalene (
72%),
3-bromopyridine (
76%),
2-bromopyridine (
61%),
8-bromoquinoline (48)%,
o-bromotoluene (
72%),
p-chlorobromobenzene (
90%),
p-nitrobromobenzene (
60%), and
p-methoxybromobenzene (
59%). The use of the triphenylphosphinehalogen complex to convert alcohols to alkylhalides is described elsewhere in this series.
6
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
petroleum ether
methanol (67-56-1)
acetonitrile (75-05-8)
sodium hydroxide (1310-73-2)
hydrogen bromide (10035-10-6)
bromine (7726-95-6)
β-naphthol (135-19-3)
α-Bromonaphthalene (90-11-9)
Naphthalene, 2-bromo-,
2-Bromonaphthalene (580-13-2)
Pentane (109-66-0)
magnesium sulfate (7487-88-9)
mercuric bromide (7789-47-1)
o-Bromotoluene (95-46-5)
2-Bromopyridine (109-04-6)
3-bromopyridine (626-55-1)
triphenylphosphine (603-35-0)
2-aminonaphthalene (91-59-8)
diazonaphthalene
8-bromoquinoline (16567-18-3)
p-methoxybromobenzene (104-92-7)
p-chlorobromobenzene (106-39-8)
phosphorus pentoxide (1314-56-3)
p-nitrobromobenzene (586-78-7)
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved