POTASSIUM BROMATE

1

Potassium Bromate

KBrO

3

[7758-01-2]

BrKO

3

(MW 167.00)

InChI = 1/BrHO3.K/c2-1(3)4;/h(H,2,3,4);/q;+1/p-1/fBrO3.K/q-

1;m

InChIKey = OCATYIAKPYKMPG-RERGACQYCO

(convenient source of molecular bromine;

1a

used for bromination

of deactivated aromatics;

2

used in chemical oscillating reactions

3

)

Physical Data:

mp ≈350

◦

C, dec ≈370

◦

C with evolution of oxy-

gen; d 3.27 g mL

−1

.

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 com-
pounds during storage. Potassium bromate is an analytical stan-
dard for iodometry. Standard solutions are stable indefinitely.

Generation of Bromine and Bromination Reactions. Potas-

sium bromate and Sodium Bromate react with bromide ion in
dilute acid solution.

1

to produce bromine according to eq 1.

(1)

BrO

3

–

+

5 Br

–

+

6 H

+

3 Br

2

+

3 H

2

O

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 keto-

nes,

5,6

3-substituted cyclohexenones,

7

thiophene (in a two-phase

system),

8

organoboranes (to produce an α-bromoorganoborane

which rearranges to the alcohol),

9

cyclopentamethylenediphenyl-

stannane (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 report

12

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,

nitrobenzene

2

has been brominated in 88% yield in this fashion

(eq 2). The reaction is dependent on the concentration of the sulfu-
ric acid. This method is arguably superior to other methods for ni-
trobenzene bromination.

13

(Warning! potassium bromate decom-

poses rapidly in 70% sulfuric acid solution with the evolution of
heat.

2

)

(2)

NO

2

NO

2

Br

KBrO

3

68% H

2

SO

4

rt

88%

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).

50% H

2

SO

4

rt

O

O

Br

O

Br

(3)

+

60%

10%

KBrO

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 phe-

nol 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 reaction

3

and a clock reaction

21

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 mecha-
nism for bromate-driven oscillators controlled by bromide has
appeared.

22

This is still an active area for investigation.

23

1.

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B.; Muthakia, G. K., J. Chem. Soc., Perkin Trans. 2 1987, 1539. (c)
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Perkin Trans. 2 1988

, 1111.

2.

Harrison, J. J.; Pellegrini, J. P.; Selwitz, C. M., J. Org. Chem. 1981, 46,
2169.

3.

Franck, U. F., Angew. Chem., Int. Ed. Engl. 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., J. Am. Chem.
Soc. 1946

, 68, 1831.

6.

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B., J. Heterocycl. Chem. 1987, 24, 1509.

7.

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2153.

8.

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Ser. Khim. 1982

, 10, 2388.

9.

Brown, H. C.; Yamamoto, Y., Synthesis 1972, 699.

10.

Bajer, F. J.; Post, H. W., J. Org. Chem. 1962, 27, 1422.

11.

Poshkus, A. C.; Herweh, J. E.; Magnotta, F. A., J. Org. Chem. 1963, 28,
2766.

12.

Krafft, F.; Merz, V., Chem. Ber. 1875, 8, 1045.

13.

(a) Gottardi, W., Monatsh. Chem. 1968, 99, 815. (b) Gottardi, W.,
Monatsh. Chem. 1969

, 100, 42.

14.

Banerjee, A.; Banerjee, S.; Samaddar, H., J. Indian Chem. Soc. 1979,
56

, 985.

15.

Banerjee, A.; Banerjee, G. C.; Dutt, S.; Banerjee, S.; Samaddar, H., J.
Indian Chem. Soc. 1980

, 57, 640.

16.

Banerjee, A.; Banerjee, G. C.; Adak, M. M.; Banerjee, S.; Samaddar, H.,
J. Indian Chem. Soc. 1981

, 58, 985.

17.

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Org. Prep. Proced. Int. Briefs 1991

, 23, 395.

Avoid Skin Contact with All Reagents

2

POTASSIUM BROMATE

18.

Blackhall, A.; Brydon, D. L.; Javaid, K.; Sagar, A. J. G.; Smith, D. M.,
J. Chem. Res. (S) 1984

, 382.

19.

Broxton, T. J.; Deady, L. W.; McCormack, J. D.; Kam, L. C.; Toh, S. H.,
J. Chem. Soc., Perkin Trans. 1 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., J. Am. Chem. Soc. 1980, 102, 4644.

23.

Koros, E.; Kurin, K. From Phase Transitions Chaos; Gyorgyi, G., Ed.;
World Science: Singapore, 1992; p 128, Chem. Abstr. 21 819u), 1993
118

.

James J. Harrison

Chevron Chemical Company, Richmond, CA, USA

A list of General Abbreviations appears on the front Endpapers