F. A. Vingiello, T. J. Delia,' P. POISS, and D. Farrier2
Virginia Polytechnic Institute Blacksburg, Virginia
An Improved Synthesis of 2-Bromonaphthalene
A n improved synthesis for the large scale preparation of Pbromonaphthalene has been developed. Of the two usual methods of preparation used in our laboratory to prepare this necessary intermediate (I) that of Newman and Wise (2) has been and obviously both Arc1 and ArBr would result from discontinued due to the necessity of using the carcinoits decomposition. genic 2-naphthylamine (3) and due to the rather vigGas chromatographic analysis of the products oborous evolution of gas upon addition to a hot flask of tained using methods A , B, and C (see experimental the complex salt., (C10H7N2Br)2.HgBrt. Just recently section) were consistent with the above statements. we had a violent explosion on attempting to vacuum By altering the method of Wolfe and Doukas to exdry a 5-lh quantity of t,he mercury salt a t 30'. The clude any chloride ion we were able to synthesize 2method of Wolfe and Doukas reported in THIS JOURNAL bromonaphthalene (in comparable yields) that afforded (4), which employs 2-naphthylamine-1-sulfonicacid, is a Grignard reagent in about 85% yield. This is in adaptable to large scale reactions (2 moles) and affords agreement with the value given in Kharasch and Reinyields of about 50%. muth (8). We found, however, that the 2-hromonaphthalenz Preparation of 2-Brornonaphthalene product resulting from this synthesis would only form a Grignard reagent in about 15y0 yield as determined by Method A.5 The method of Newman and Wise was titration (5). I t is interesting to note that a comfollowed exactly using double quantities. Yield: 76.2 mercially prepared 2-bromonaphthalene purchased for On gas chromatographic analyg (52.6%); mp 54-6'. use in this laboratory also formed the Grignard reagent sis' a sample showed only one peak at an elution time in fifteen percent yield. An elemental analysisa was of 17 min, corresponding to 2-bromonaphthalene. obtained on this commercial product which indicated a Melhod B. The method of Wolfe and Doukas was 3: 1 ratio of 2-chloro:2-bromonaphthalene. followed exactly. Yield 197.5 g (47.7%); mp 56.7'; It was reasoned that upon addition of the diazonium analysis calculated for CloH,Br: C, 58.00; H, 3.41; chloride to a solution of CuBr in HBr there would he found:. C, 69.27; H, 4.15. This analysis is consistent equilibration of C1- with CuBr and both CuBr and with 3: 1 ratio of 2-chloro :2-bromonaphthalene. On CuCl would be present. Hence a mixture of 2-chloro gas chromatographic analysis4 a sample showed two and 2-hromonaphthalene would result. peaks, one a t elution time of 11 min, corresponding to Fieser and Fieser state (6) that HC1 is not as satis2-chloronaphthalene, and one a t 17 min, corresponding factory an acidifying agent as H2S04for converting a to 2-bromonaphthalene, The areas traced indicated diazonium salt to a phenol because the diazonium salt 78%2-chloronaphthalene and22y02-bromonaphthalene. group may be replaced in part by halogen. It is also Method C. A solution of 82 g (2.05 moles) NaOH stated in this reference that for preparation of a bromide in a total aqueous volume of 3600 ml was prepared in by the Sandmeyer reaction, the amine is diazotized in a two gallon jar. To this was added, with stirring, H2SO4and the resulting aryldiazonium sulfate treated 446 g (2.00 moles) 2-naphthylamine-1-sulfonic acid. with a solution of CuBr in excess HBr. This suggests An aqueous solution of 138 g (2.00 moles) NaNOz was that the presence of chloride ion during the preparation then added and the solution was filtered through a fluted of an aryl bromide from an amine might cause some of filter paper. The filtrate was then added slowly, with the intermediate diazonium salt to be converted to aryl stirring, to 1 1 of 37% HBr in a five gallon jar. The chloride. temperature was kept below 5'. This was filtered ~vith The proposed mechanism of Cowdry and Davies is suction and the precipitate was washed with 2 1 of ice as follows (7) : water.
Arc1
+ NI + CuCl
c
If the CuCl were replaced by CuBr the bracketed intermediate would be 544 / journal of Chemical Educafion
' Abstracted in part from the PbD theses of T. J. Delia and P. Palss, presented to Virginia Polytechnic Institute in 1961 turd 1962 respectively. Special freshman research participant. 3 Geller Microanralytical Laboratories, Bardonia, N. Y. The gas chromatography data were obtained on a Beckman Model 2-A gas chromatography unit. The column was 6 ft. X I/, in. od, packed with C-22 Firebrick 42/60 mesh coated with Silicone 550 (30%), and was operated at 220'. The samples were 2 pl of a solution of 0.25 g material in 1.0 ml acetone. 5 2-Naphthylamine is available from Pfister Chemical Works, Ridgefield, N. J.
Grignard Reagent Titrotion
Sample from method A
B C
HBOa (mu 10.00 10 .OO 10 .OO
NH~OG 0.834 0.454 0.454
NaOH (ml) 10.10 17.85 12.78
N NaOH 0.806 0.242 0.242
During the above slow addition, CuBr in HBr was prepared exactly as in the literature (9). The damp diazonium salt precipitate was added portionwise with stirring to the CuBr in HBr in a five gallon jar. After a vigorous evolution of Nz, the solution was heated to 9&5" on a steam bath, and filtered while hot. To the filtrate in a 4-1 beaker was added 450 g KBr with stirring. The resulting paste was allowed to cool to room temperature, filtered, washed with 1 1 20% KBr, and air-dried overnight. The air-dried solid was added to 800 ml concentrated H2SOl and 800 g crushed ice in a 5-1 one-neck roundbottom flask equipped with a water condenser and heated under reflux for 14 hr. After cooling to room temperature the mixture was poured onto 2 kg of crushed ice, and extracted with 3 1 of benzene. The benzene layer was washed with water until neutral to litmus paper, concentrated and distilled (4.5 mm): yield 232.3 g (56.2%); bp 122-7". The product was dissolved in 1 1 of n-hexane and allowed to drip through a column packed with 2-in. basic alumina over 2-in. acidic alumina. The column was eluted with a second liter of n-hexane. The solvent was removed in a flash evaporator, and the product was dried overnight in a vacuum desiccator. Yield 229.5 8
Galbraith Laboratories, Knoxville, Tenn.
Aliquot (ml)
Total vol. Grignard (ml)
1 .OO 1 .OO 1.00
180 .O 250.0 300.0
2-BromoGrignard naphthalene reagent (males) formation (%) 0.40 0.40 0.50
90.0 13.8 86.7
g (55.5%); mp 54-6'; analysis calculated for CloH?Br: C, 58.00; H, 3.41; Br, 38.59; found: C, 58.02; H. 3.49; Br, 38.57.8 On gas chromatographic analysis4 a sample showed only one peak at an elution time of 17 min, corresponding to 2-bromonaphthalene. Literature Cited (1) VINGIELLO, F. A,, AND BORKUYEC, A,, J. Am. Chem. Soc., 78, 1240 (1956). M. S., AND WISE, P. H., J . Am. Chem. Soc., 63, (2) NEWMAN, 2847 (1941). (3) HIEGER,I., "Cartrcinogenesis," Academic Press, New York. 1961, p. MI. (4) WOLFE,W. C., AND DOUKAS, H. M., J. CHEM.EDUC.,28,472 (1951). (5) GILMAN,H., ZOELLNER, E. A,, A N D DICKEY,J. B., J . Am. Chem. Soc.. 51.1576 (1929).
(8) KHARASCH, M. S., A N D REINMUTE, O., "Grignard Reactions of Nonmetallic Substances," Prentice-Hall, Inc., New York, 1954, p. 19. J. L., in "Organic Synthesis," Vol. 24, DRAKE, (9) HARTWELL, L., ed., John Wiley and Sons, New York, 1944, p. NATHAN 23. This inv&ination was sumorted bv Research Grant CY-4412 (C3) of the-~ational~ a n & r~ n s t i t k e ,National Institutes of Health.
Volume 40, Number 10, October 1963
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