Submitted by Henry Gilman, Nina B. St. John, and F. Schulze.
Checked by C. R. Noller
1. Procedure
In a
2-l. three-necked flask, fitted with a
mechanical stirrer, a
reflux condenser, and a
separatory funnel, is placed
24.3 g. (1 gram atom) of magnesium turnings (Note
1). The
magnesium is covered with
100 cc. of anhydrous ether, and
10 cc. (15 g., 0.07 mole) of α-bromonaphthalene (Note
2) (with a crystal or two of
iodine) (Note
3) is added to start the reaction. A warm
water bath (45° or higher) is placed under the flask until the reaction starts. The stirrer is started, and a solution of
192 g. (0.93 mole) of α-bromonaphthalene in
500 cc. of anhydrous ether is added to the
magnesium at such a rate that the reaction is vigorous but not violent. The addition requires from one and one-half to three hours. The water bath is again placed under the flask, and stirring and refluxing are continued for one-half hour after the addition of the halide is complete. The Grignard reagent which collects as a heavy oil in the bottom of the flask is dissolved by the addition of
533 cc. of dry benzene (Note
4).
The reaction mixture is then cooled by an ice-salt mixture. The separatory funnel is replaced by a
two-holed rubber stopper containing a
thermometer (bulb immersed in the reaction mixture) and a glass tube drawn out to make a fine capillary (Note
5). When the temperature of the reaction mixture has reached −7°, the condenser is replaced by an
entry tube, 10 mm. in diameter and adjusted so that the end is about 50 mm. above the surface of the reaction mixture (Note
6). The reaction mixture is stirred, and dry
carbon dioxide is added through this tube (Note
7). The rate of flow of the
carbon dioxide is regulated so that the temperature of the reaction mixture does not rise above −2°. The time required for the completion of the reaction varies from one and one-fourth to one and one-half hours. When the reaction is complete, the temperature falls below −7° and does not rise on increasing the rate of flow of
carbon dioxide.
The flask is placed in an
ice bath, and
25 per cent sulfuric acid is added slowly, with stirring, until no further reaction takes place and all the excess
magnesium has dissolved (Note
8). The oily layer is separated, and the water layer is extracted with two
100-cc. portions of ether. The combined
ether-
benzene extracts (Note
9) are shaken with three
100-cc. portions of 25 per cent sodium hydroxide. Each alkaline layer is extracted successively with a
100-cc. portion of ether, and the combined alkaline extracts are then heated to 100° to drive off volatile impurities.
The solution is cooled and acidified strongly with
50 per cent sulfuric acid. The crude
α-naphthoic acid is collected on a
Büchner funnel, washed until free from sulfate, and dried. The yield of crude material melting at
142–155° is
130–135 g. This is dissolved in
400 cc. of hot toluene, a small amount of Filter-Cel is added, and the solution is filtered through a hot Büchner funnel. The filtrate is cooled in an ice bath, filtered with suction, and the filter cake washed with cold
toluene until the filtrate is practically colorless. A light-colored product melting at
159–161° is obtained. The yield is
118–121 g. (
68–70 per cent of the theoretical amount) (Note
10).
2. Notes
1. The finer commercial grade of turnings was used. After the reaction had once started, it proceeded smoothly with any grade of commercial turnings.
3. The checker was more successful in starting the reaction within a reasonable length of time when as much as
0.5 g. of iodine was added.
4. It is necessary to dissolve the Grignard reagent in
benzene to prevent it from solidifying when the solution is cooled. The
benzene should be added to the solution before it cools, as the hardened mass is difficult to redissolve.
5. This is to allow the
carbon dioxide which does not react to escape slowly in order that the pressure in the flask does not become too great.
6. The inlet tube is placed at this distance above the surface of the reaction mixture in order to prevent clogging.
7. The
carbon dioxide from an ordinary commercial
cylinder was dried by passing it through
two wash bottles containing sulfuric acid.
10. A second recrystallization from
toluene gives an almost white product melting at
160.5–162°.
3. Discussion
The procedure described above
8 was developed from the methods of Acree,
1 of Blicke,
1 and of Whitmore and Fox.
1
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved