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).