THE PREPARATION OF 2-BROMONAPHTHALENE WINTHROP C. WOLFE and HARRY M. DOUKAS Bureau of Agricultural and Industrial Chemistry, Agricultural Research Center, Beltsville, Maryland
S.ATURWED and unsaturated 2-naphthalene acids have been prepared in this laboratory from 2-bromonaphthalene and tested for plant-growth regulating activity. Because 2-bromonaphthalene is so widely used for introducing specific groups into the naphthalene nucleus, an improvement in the method of preparation of this compound is of considerable interest. The method described here is suitable for the preparation of small or large quantities of 2-bromonaphthalene without the use of any special apparatus. A chromatographic procedure has been used to obtain a product which is sufficiently pure for use in Grignard reactions. 2-Bromonaphthalene is ordinarily prepared by the diazotization of 2-naphthylamine with sulfuric acid and sodium nitrite, followed by the usual treatment with cuprous bromide and hydrobromic acid.= In an alternative method,,proposed by Newman and Wise,%2naphthylamine is first diazotized with hydrochloric acid and sodium nitrite. A stable complex is then formed with mercuric bromide and this complex decomposed by heating to 90°C. Wahl and Basiliosa have recently reported a more satisfactory method, in which the dye intermediate 2-naphthylamine-1-sulfonic acid is first diazotized. The stable diazonium compound is treated with cuprous bromide and hydrobromic acid to obtain 2-bromo-1-naphthalenesulfonic acid. The sulfonic acid group is then removed by sulfuric acid hydrolysis and yields of 77 to 80 per cent of the theoretical value were reported. The method of Wahl and Basilios has been investigated in this laboratory in some detail and was found to give consistent yields of about 65 per cent when a technical grade of 2-naphthylamine-I-sulfonic acid was used as starting material. Four hundred and forty-six grams (2 mols) of 2naphthylamine-1-sulfonic acid (technical grade) is dissolved, with stirring, in 3600 ml. of aqueous sodium hydroxide (2.05 mols) contained in a 2-gallon battery jar or earthenware crock fitted with a mechanical stirrer. An aqueous solution of 138 grams (2 mols) of sodium nitrite is then added, with stirring, and the resulting solution is filtered. One liter of concentrated (37 to 38.5 per cent) hydro' "Organic Syntheses," 2nd ed., John Wiley & Sons, Ine., New Yark, 1941, Call. Vol.1, p. 136. N E U . M A N .M . S., A N D P. H. VISE, J. Am. Chem. Soe., 63, 2847 (1941). \VA*HL.H.. A N D H . DASTLIOS. Bull. SOC. Chim. France. 1947. ' pp. 4824.'
chloric acid and 400 g. of crushed ice are placed in an illsulated 5-gallon battery jar or earthenware crock, fitted with a mechanical stirrer, preferably of the wooden paddle-blade type. The filtered solution of sodium nitrite and sodium salt of 2-naphthylamine-l-sulfonic acid is then siphoned in, with stirring, and the temperature is maintained a t 0-5OC. by adding crushed ice. The reddish-brown precipitate which forms is collected in a large Buchner funnel and washed with about 2 liters of iced water. While the diazotization is in progress, a suspension of cuprous bromide in hydrobromic acid is prepared.& The damp cake of the diazonium compound is added portion-wise and stirred into 1100 ml. of the cuprous bromide (4.8 mols) suspension contained in a 5-gallon jar provided with an efficientmechanical stirrer. After the vigorous evolution of nitrogen has subsided, the mixture is heated to 95-100°C. on a steam bath and filtered hot through a large Buchner funnel. Some cuprous bromide will appear in the filtrate but this does not interfere with the next step in the preparation. The filtrate is poured back into the 5-gallon jar and 450 g. of potassium chloride is added with stirring. The resulting paste is allowed to cool to room temperature, then filtered with suction and washed with 1 liter of 20 per cent aqueous potassium chloride. The reddishbrown precipitate of 2-bromo-1-naphthalenesulfonic acid is air-dried overnight and then transferred to a 5liter round-bottomed flask. A solution of 800 ml. of concentrated sulfuric acid (98 per cent) and 800 g. of crushed ice is prepared and added to the flask, with occasional shaking. A reflux condenser is attached to the flask, which is then placed in a heating mantle. The mixture is gently refluxed for 12 to 16 hours, then cooled to room temperature and poured onto about 2 kg. of crushed ice contained in a 2-gallon jar. The mixture is transferred to a 5-liter separatory funnel, and 2 liters of benzene are used to rinse the solid into the funnel. The mixture is shaken and the benzene layer is separated, then washed with water until the washings are neutral to litmus paper. After the benzene has been removed the product is distilled under reduced pressure. It boils a t 100-101°C./2 mm. and solidifies to a slightly yellow solid which melts a t 56.5-57.3'C. 4 The cuprous bromide is made from 1200 g. (4.8 mols) of copper sulfate ("Organic Syntheses," 1944, Vol. 24, p. 23) using double the quantities, and is suspended in a solution of 300 ml. of 48 per cent hydrobromic acid and 800 ml. of water.
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SEPTEMBER, 1951
The average yield was 239 to 273 g. (58 t o 66 per cent). The product has a slightly yellow color which is not removed by redistillation or recrystallization and which becomes brown on exposure to air or 1ight.l However, a pure white product can be obtained by dissolving 200 This product apparently contains some amine compound. It cannot be used to form a Grignard reagent except in very low yi~ldg.
473
g. of the compound in 600 ml. of normal hexane and passing this solution through n' activated alumina column (8&200 mesh) '/% in. in diameter and 3 to 4 in. in height. The column is then washed with an additional 600 ml. of normal hexane. The 1200 ml. of solution is evaporated to dryness and yields a white product meltis s& ing a t 56.8-57"C. (98 Per cent recovery) ficlently pure for use in Grignard reactions.
