Potassium Bromate


[7758-01-2]  · BrKO3  · Potassium Bromate  · (MW 167.00)

(convenient source of molecular bromine;1a used for bromination of deactivated aromatics;2 used in chemical oscillating reactions3)

Physical Data: mp ~350 °C, dec ~370 °C with evolution of oxygen; d 3.27 g cm-3.

Solubility: sol 12.5 parts water, 2 parts boiling water; almost insol alcohol.

Form Supplied in: white crystals or granules; widely available. Drying: for analytical work dry at 100-110 °C for 1 h.

Handling, Storage, and Precautions: potassium bromate is a strong oxidizing agent (standard potential 1.44 V). Toxicity is low. Keep from contact with mineral acids and organic compounds during storage. Potassium bromate is an analytical standard for iodometry. Standard solutions are stable indefinitely.

Generation of Bromine and Bromination Reactions.

Potassium bromate and Sodium Bromate react with bromide ion in dilute acid solution1 to produce bromine according to eq 1.

As such, it is a convenient reagent for the bromination of alkenes, phenols, salicylic acid, aniline, and other activated compounds.4 Synthetically useful brominations of methyl ketones,5,6 3-substituted cyclohexenones,7 thiophene (in a two-phase system),8 organoboranes (to produce an a-bromoorganoborane which rearranges to the alcohol),9 cyclopentamethylenediphenylstannane (to form cyclopentamethylenedibromostannane),10 and sulfonylhydrazides (to form sulfonyl bromides)11 have been reported.

Bromination of Deactivated Aromatics.

Potassium bromate in the absence of added bromide is an effective brominating agent. An early report12 that potassium bromate in Sulfuric Acid, in the absence of added bromide, brominated benzene went unnoticed for over 100 years. An efficient procedure for the bromination of deactivated aromatic compounds has appeared.2 For example, nitrobenzene2 has been brominated in 88% yield in this fashion (eq 2). The reaction is dependent on the concentration of the sulfuric acid. This method is arguably superior to other methods for nitrobenzene bromination.13 (Warning! potassium bromate decomposes rapidly in 70% sulfuric acid solution with the evolution of heat.2)

Other deactivated aromatics that can be brominated by this method include benzoic acid,2,14 halobenzoic acids,15 phthalic acid,2 hydroxybenzoic acid,16 halobenzenes,15,17 benzonitrile,16 benzanilide,16 cinnamic and hydrocinnamic acids,16 phenylacetic acid,16 benzophenone,16 acetophenone,2 and 2,5-dimethyl-1,3,4-oxadiazoles.18 In the case of acetophenone, the bromination occured at the aromatic ring and not on the methyl group,19 which is the normal position for attack using molecular bromine (eq 3).

One report in which sodium bromate is used in combination with Bromotrimethylsilane for the bromination of aromatic rings has appeared.20 While activated rings such as anisole and phenol react satisfactorily, deactivated rings do not. Toluene gave the benzyl bromide product instead of the ring brominated product.20

Chemical Oscillators.

Chemical oscillating reactions such as the Belousov-Zhabotinski reaction3 and a clock reaction21 have been reported using potassium bromate/sodium bromate. Chemical oscillations such as these are driven by a combination of bromination and oxidation reactions. A generalized mechanism for bromate-driven oscillators controlled by bromide has appeared.22 This is still an active area for investigation.23

1. (a) Diemente, D. J. Chem. Educ. 1991, 68, 932. (b) Jonnalagadda, S. B.; Muthakia, G. K. JCS(P2) 1987, 1539. (c) Jonnalagadda, S. B.; Simoyi, R. H.; Muthakia, G. K. JCS(P2) 1988, 1111.
2. Harrison, J. J.; Pellegrini, J. P.; Selwitz, C. M. JOC 1981, 46, 2169.
3. Franck, U. F. AG(E) 1978, 17, 1.
4. Day, A. R.; Taggart, W. T. Ind. Eng. Chem. 1928, 20, 545.
5. Winstein, S.; Jacobs, T. L.; Linden, G. B.; Seymour, D.; Levy, E. F.; Day, B. F.; Robson, J. H.; Henderson, R. B.; Florsheim, W. H. JACS 1946, 68, 1831.
6. Culbertson, T. P.; Domagala, J. M.; Peterson, P.; Bongers, S.; Nichols, J. B. JHC 1987, 24, 1509.
7. Shepherd, R. G.; White, A. C. JCS(P1) 1987, 2153.
8. Gol'dfarb, Ya. L.; Dudinov, A. A.; Litvinov, V. P. IZV 1982, 10, 2388.
9. Brown, H. C.; Yamamoto, Y. S 1972, 699.
10. Bajer, F. J.; Post, H. W. JOC 1962, 27, 1422.
11. Poshkus, A. C.; Herweh, J. E.; Magnotta, F. A. JOC 1963, 28, 2766.
12. Krafft, F.; Merz, V. CB 1875, 8, 1045.
13. (a) Gottardi, W. M 1968, 99, 815. (b) Gottardi, W. M 1969, 100, 42.
14. Banerjee, A.; Banerjee, S.; Samaddar, H. JIC 1979, 56, 985.
15. Banerjee, A.; Banerjee, G. C.; Dutt, S.; Banerjee, S.; Samaddar, H. JIC 1980, 57, 640.
16. Banerjee, A.; Banerjee, G. C.; Adak, M. M.; Banerjee, S.; Samaddar, H. JIC 1981, 58, 985.
17. Kosandal, K.; Bhujanga Rao, A. K. S.; Gundu Rao, C.; Singh, B. B. OPP Briefs 1991, 23, 395.
18. Blackhall, A.; Brydon, D. L.; Javaid, K.; Sagar, A. J. G.; Smith, D. M. JCR(S) 1984, 382.
19. Broxton, T. J.; Deady, L. W.; McCormack, J. D.; Kam, L. C.; Toh, S. H. JCS(P1) 1974, 1769.
20. Lee, J. G.; Cha, H. T.; Yoon, U. C.; Suh, Y. S.; Kim, C.; Park, I. S. Bull. Korean Chem. Soc. 1991, 12, 4.
21. Rich, R. L.; Noyes, R. M. J. Chem. Educ. 1990, 67, 606.
22. Noyes, R. M. JACS 1980, 102, 4644.
23. Koros, E.; Kurin, K. From Phase Transitions Chaos; Gyorgyi, G., Ed.; World Science: Singapore, 1992; pp 128-142 (CA 1993, 118, 21 819u).

James J. Harrison

Chevron Chemical Company, Richmond, CA, USA

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