SHORT PAPER
Pyridinium Dichlorobromate: A New Stable Brominating Agent for Aromatic Compunds
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plete, the mixture was allowed to cool down to 0 °C. Cl2 gas was
bubbled into the mixture (fume cupboard), maintaining the temper-
ature between 0–10 °C, until complete precipitation of the complex
took place. Cold CCl4 (200 mL) was added and the resultant yellow
solid was filtered under suction and washed with CCl4 to give pale
yellow crystals (22 g, 96%) of PyHBrCl2; mp140–142 °C.
References
(1) Larock, R. C. Comprehensive Organic Transformation;
Wiley-VCH: New York, 1999, 2nd ed., 619.
(2) Smith, M. B.; March, J. March’s Advanced Organic
Chemistry; Wiley: New York, 2001, 5th ed., 704.
(3) Mitchell, R. H.; Lai, Y. H.; Williams, R. V. J. Org. Chem.
1979, 44, 473.
(4) Eguchi, H.; Kawaguchi, H.; Yoshinga, S.; Nishida, A.;
Nishiguchi, T.; Fujisaki, S. Bull. Chem. Soc. Jpn. 1994, 67,
1918.
IR (KBr): 3200m (NH), 1620m (N=C), 1540m, 1050m, 740s, br,
670s, br cm–1.
1H MNR (CDCl3): = 11.5 (br s, 1 H, NH), 9.1 (m, 2 H), 8.7 (m, 1
H), 8.2 (m, 2 H).
(5) Calo, V.; Ciminale, F.; Lopez, L.; Todesco, P. E. J. Chem.
Soc. C 1971, 3652.
(6) Downs, A. J.; Adams, C. J. Comprehensive Inorganic
Chemistry, Vol. 2; Bailor, J. C.; Emeleus, H. J.; Nyholm, S.
R.; Trotman-Dickenso, A. F., Eds.; Pergamon: Oxford,
1973, 1192.
(7) Obenland, C. O. J. Chem. Educ. 1964, 41, 566.
(8) Rozen, S.; Brand, M.; Lidor, R. J. Org. Chem. 1988, 53,
5545.
(9) Naumann, D.; Lehmann, E. J. Fluorine Chem. 1975, 5, 307.
(10) Heasley, G. E.; Bundy, J. M.; Heasley, V. L.; Arnold, S.;
Gipe, A.; Mckee, D.; Orr, R.; Rodgers, S. L.; Shellhamer, D.
F. J. Org. Chem. 1978, 43, 2793.
(11) Williams, D. M. J. Chem. Soc. 1931, 2783.
(12) Popov, A. I.; Buckles, R. E. Inorg. Synth. 1957, 5, 167.
(13) Chattaway, F. D.; Hoyle, G. J. Chem. Soc. 1923, 123, 654.
(14) Kajigaeshi, S.; Kakinami, T.; Moriwaki, M.; Tanaka, T.;
Fujisaki, S.; Oramoto, T. Bull. Chem. Soc. Jpn. 1989, 62,
439.
(15) Negoro, T.; Ikeed, Y. Bull. Chem. Soc. Jpn. 1984, 57, 2116.
(16) Reeves, W. P.; Lu, C. V.; Schulmeier, B.; Jonas, L.;
Hatlevik, O. Synth. Commun. 1998, 28, 499.
(17) Kajigaeshi, S.; Moriwaki, M.; Tanaka, T.; Fujisaki, S.;
Kakinami, T.; Okamoto, T. J. Chem. Soc. Perkin Trans. 1
1990, 897.
Anal. Calcd for C5H6BrCl2N (230.9): C, 25.97; H, 2.60; BrCl2,
65.37; N, 6.06. Found: C, 26.26; H, 2.72; BrCl2, 64.81; N, 6.15.
Bromination of Aromatic Compounds with 1; General
Procedures
Method A: PyHBrCl2 (1; 5 mmol) was added to a vigorously stirred
solution of the aromatic substrate (5 mmol) in 50% aq MeOH (15
mL) over a period of 5 min. The mixture was stirred at r.t. for the
specified reaction time (Table 1), and then diluted with H2O (50
mL). After complete precipitation of the product, it was filtered in
vacuo and washed with H2O. For liquid products, the aqueous solu-
tion was extracted with Et2O, separated, washed with H2O, dried
(Na2SO4) and evaporated in vacuo (Table 1)
Method B: To a solution of the aromatic substrate (5 mmol) and 1
(1.15 g, 5 mmol) in CH2Cl2 (50 mL), was added anhyd FeCl3 (2.5 g,
15 mmol). The mixture was stirred at r.t. for the specified reaction
time (Table 1), and then diluted with 5% HCl (50 mL). The organic
layer was separated, washed successively with H2O and sat.
NaHCO3 solution, dried (Na2SO4), and evaporated in vacuo
(Table 1).
Method C: A mixture of the aromatic substrate (5 mmol), Ag2SO4
(2.5 g, 8 mmol) and concd H2SO4 (20 mL) was stirred vigorously at
r.t. PyHBrCl2 (1.4 g, 6 mmol) was added over 30 min, and stirred
continuously for the specified reaction time (Table 1). The mixture
was then poured onto crushed ice (70 g) and the resulting solid was
filtered in vacuo. The filtrate and the precipitate were extracted with
Et2O, and the combined extracts were washed several times with
H2O to remove any remaining acid and then evaporated in vacuo
(Table 1).
(18) Derbyshire, D. H.; Waters, W. A. J. Chem. Soc. 1950, 573.
(19) Muathen, H. A. J. Org. Chem. 1992, 57, 2740.
Synthesis 2002, No. 2, 169–171 ISSN 0039-7881 © Thieme Stuttgart · New York