Sodium Bromide

NaBr

[7647-15-6]  · BrNa  · Sodium Bromide  · (MW 102.89)

(source of bromide ion as nucleophile; precursor to bromine electrophiles)

Physical Data: mp 755 °C; d 3.21 g cm-3.

Solubility: very sol water; sol methanol, ethanol.

Form Supplied in: colorless, odorless crystals, granules, or powder. Drying: is hygroscopic and should be dried at 140 °C for applications that require the anhydrous salt.

Handling, Storage, and Precautions: should be taken directly from the oven when dryness is required. NaBr is of low toxicity.

Source of Bromide Nucleophile.

Sodium bromide is an inexpensive source of bromide anion for service as a nucleophile or nucleophilic catalyst. In alcoholic and dipolar aprotic solvents, NaBr converts the sulfonate esters of primary and secondary alcohols to the corresponding alkyl bromides.1 Sodium bromide cleanly converts primary alkyl chlorides to bromides, provided that a large excess of ethyl bromide or dibromomethane is added as a chloride ion scavenger.2 In the presence of Dowex-50 ion exchange resin, NaBr opens epoxides to bromohydrins.3 Bromotrimethylsilane can be generated in situ from Chlorotrimethylsilane and NaBr, and then used to convert aldehydes and ketones to silyl enol ethers under mild conditions with significant regio- and stereoselectivity.4

Precursor to Bromine Electrophiles.

Chemical or electrochemical oxidation of sodium bromide generates reactive electrophilic bromine species, which can effect a variety of useful transformations. A mixture of NaBr and Peracetic Acid oxidizes secondary alcohols to ketones, primary benzylic alcohols to aldehydes, primary aliphatic alcohols to dimeric esters, and a,o-diols to lactones.5 The reaction conditions, which appear to involve the formation of acetyl hypobromite, provide an inexpensive and less toxic alternative to chromium oxidants. By combining NaBr and NaBrO2, it is possible to generate hypobromite ion without using elemental bromine. This mixture of salts effects the Hofmann degradation of primary amides to generate amines and promotes the bromoform reaction of methyl ketones to generate carboxylic acids.6 Organoboranes are brominolyzed to bromoalkanes or bromoalkenes upon treatment with bromine chloride, which can be generated by reaction of NaBr with Chlorine, Chloramine-T, or N-Chlorosuccinimide.7 This procedure allows the preparation of radiobrominated organic compounds from radioactive NaBr. Sodium bromide is useful as an electrolyte in electrochemical oxidations, generating electrophilic bromine species which can react with organic substrates. Under suitable conditions, alkenes are epoxidized,8 alcohols are oxidized,9 and methyl ketones are converted to methyl esters.10

Miscellaneous Uses.

Raney Nickel modified with tartaric acid and NaBr is an inexpensive catalyst, suitable for the large-scale reduction of methyl ketones and 1,3-dicarbonyl compounds to optically active alcohols in moderate enantiomeric excesses.11


1. (a) Buchman, E. R.; Deutsch, D. H.; Fujimoto, G. I. JACS 1953, 75, 6228. (b) Cason, J.; Correia, J. S. JOC 1961, 26, 3645. (c) Herzog, H. L. OSC 1963, 4, 753.
2. (a) Willy, W. E.; McKean, D. R.; Garcia, B. A. BCJ 1976, 49, 1989. (b) Babler, J. H.; Spina, K. P. SC 1984, 14, 1313.
3. Singhal, G. M.; Zaman, S. S.; Sharma, R. P. CI(L) 1991, 687.
4. (a) Ahmad, S.; Khan, M. A.; Iqbal, J. SC 1988, 18, 1679. (b) Iqbal, J.; Khan, M. A. SC 1989, 19, 515.
5. (a) Morimoto, T.; Hirano, M.; Ashiya, H.; Egashira, H.; Zhuang, X. BCJ 1987, 60, 4143. (b) Morimoto, T.; Hirano, M.; Hamaguchi, T.; Shimoyama, M.; Zhuang, X. BCJ 1992, 65, 703.
6. (a) Kajigaeshi, S.; Nakagawa, T.; Fujisaki, S.; Nishida, A.; Noguchi, M. CL 1984, 713. (b) Kajigaeshi, S.; Nakagawa, T.; Nagasaki, N.; Fujisaki, S. S 1985, 674.
7. (a) Kabalka, G. W.; Sastry, K. A. R.; Knapp, F. F.; Srivastava, P. C. SC 1983, 13, 1027. (b) Kabalka, G. W.; Sastry, K. A. R.; Hsu, H. C.; Hylarides, M. D. JOC 1981, 46, 3113.
8. (a) Torii, S.; Uneyama, K.; Ono, M.; Tazawa, H.; Matsunami, S. TL 1979, 48, 4661. (b) Torii, S.; Uneyama, K.; Matsunami, S. JOC 1980, 45, 16.
9. Inokuchi, T.; Matsumoto, S.; Torii, S. JOC 1991, 56, 2416.
10. Nikishin, G. I.; Elinson, M. N.; Makhova, I. V. AG(E) 1988, 27, 1716.
11. (a) Ito, K.; Harada, T.; Tai, A.; Izumi, Y. CL 1979, 1049. (b) Ito, K.; Harada, T.; Tai, A. BCJ 1980, 53, 3367. (c) Harada, T.; Yamamoto, M.; Onaka, S.; Imaida, M.; Ozaki, H.; Tai, A.; Izumi, Y. BCJ 1981, 54, 2323. (d) Tai, A.; Harada, T.; Hiraki, Y.; Murakami, S. BCJ 1983, 56, 1414. (e) Osawa. T.; Harada, T.; Tai, A. J. Catal. 1990, 121, 7. (f) Sugimura, T.; Yoshikawa, M.; Yoneda, T.; Tai, A. BCJ 1990, 63, 1080.

James S. Nowick

University of California, Irvine, CA, USA

Guido Lutterbach

Johannes Gutenberg University, Mainz, Germany



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