THIONYL BROMIDE

1

Thionyl Bromide

1

SOBr

2

[507-16-4]

Br

2

OS

(MW 207.87)

InChI = 1/Br2OS/c1-4(2)3
InChIKey = HFRXJVQOXRXOPP-UHFFFAOYAY

(brominating agent for alcohols, carboxylic acids, alkenes, and

ketones)

Physical Data:

mp −52

◦

C; bp 68

◦

C/40 mmHg; d 2.688 g cm

−3

.

Solubility:

sol benzene, chloroform, carbon tetrachloride.

Form Supplied in:

commercially available.

Handling, Storage, and Precautions:

less stable than thionyl

chloride and will slowly decompose, even in a stoppered con-
tainer. Stable if kept dry, but reacts violently with water. Ex-
tremely destructive to tissue of mucous membranes, upper res-
piratory tract, eyes, and skin. Reacts vigorously with acetone
to form a lachrymator. Should be handled in a fume hood.

Thionyl bromide is considerably more reactive than Thionyl

Chloride and is more difficult to use.

2

Unlike thionyl chloride,

whose reactions are often carried out in pyridine, thionyl bromide
undergoes a reaction with this solvent to form a nonreactive salt
(eq 1).

3

N

H

+

N

H

+

Br

–

SOBr

2

Br

3

–

SO

2

(1)

+

+

Preparation of Acid Bromides from Carboxylic Acids. Al-

though not often used, thionyl bromide can convert a simple
organic acid to the acid bromide.

4

When the acid is an α,β-

unsaturated acid, addition of bromine across the double bond oc-
curs, generally in quantitative yield (eqs 2 and 3).

CO

2

H

CO

2

H

Br

Br

(2)

SOBr

2

CO

2

H

CO

2

H

O

Br

Br

O

O

(3)

SOBr

2

For simple aliphatic acids, formation of the acid bromide is a

high yield reaction (eq 4). Simple aromatic carboxylic acids also
form the acid bromides in good yield.

O

R

Br

(4)

R = Me, 85%; Et, 90%; Pr, 92%; Bu, 90%

SOBr

2

RCO

2

H

Thionyl bromide can function as a dehydrating agent for suit-

ably positioned dicarboxylic acids (eq 5).

CO

2

H

CO

2

H

O

O

O

(5)

SOBr

2

Preparation of Bromides from Alcohols.

In the ribonu-

cleotide series, specific OH replacement has been noted (eq 6).

5

Other examples of the transformation of OH to Br are illustrated
in eqs 7 and 8.

6,7

Conversion of an alcohol to a dibromo derivative

has been reported (eq 9).

8

O

HO

OH OH

O

Br

OH OH

(6)

SOBr

2

H
N

OH

(7)

H

2

N

Br

( )

4

( )

4

+

Br

–

62 g

82 g

SOBr

2

Br

Br

OH

CO

2

Et

Br

Br

Br

CO

2

Et

(8)

SOBr

2

O

OH

O

Br

Br

(9)

SOBr

2

Bromination α to a Carbonyl Group. Aromatic ketones with

active methylene protons can be brominated with thionyl bromide.
There is an example of dibromination of a methyl ketone (eq 10).

8

Propiophenone gives a mixture of α-bromopropiophenone and
α

-bromo-α-methylpropiophenone. The reaction with unsaturated

ketones gives addition to the double bond (eq 11).

9

(10)

O

O

Br

Br

benzene

82%

SOBr

2

OH

O

OH

O

Br

Br

Br

(11)

SOBr

2

Preparation of N-(1-Bromoalkyl)heteroarylium Salts.

A

general reaction is given in eq 12.

10

O

R

H

N

N

(12)

R

Br

+

+

Br

–

SOBr

2

1.

Mellor, J. W., Comprehensive Treatise on Inorganic and Theoretical
Chemistry

; Longmans: London, 1936; Vol. X, p 662.

Avoid Skin Contact with All Reagents

2

THIONYL BROMIDE

2.

Maquestiau, A.; Anders, E.; Mayence, A.; Eynde, J.-J. V., Chem. Ber.
1991, 124, 2013.

3.

See Magee, P. S. In Sulfur in Organic and Inorganic Chemistry; Senning,
A., Ed.; Dekker: New York, 1971; Vol. 1, p 283.

4.

Saraf, S. D.; Zaki, M., Synthesis 1973, 612.

5.

Kikugawa, K.; Ichino, M., Tetrahedron Lett. 1971, 87.

6.

(a) Elderfield, R. C.; Kremer, C. B.; Kupchan, S. M.; Birstein, O.; Cortes,
G., J. Am. Chem. Soc. 1947, 69, 1258; see also earlier papers in this series.
(b) Frazer, M. J.; Gerrard, W.; Machell, G.; Shepherd, B. D., Chem. Ind.
(London) 1954

, 931.

7.

Verny, M.; Vessiere, R., Bull. Soc. Chem. Fr. 1968, 2585.

8.

Saraf, S. D.; Al-Omran, F., Org. Prep. Proced. Int. 1987, 19,
455.

9.

Al-Mousawi, S. M.; Bhatti, I.; Saraf, S. D., Org. Prep. Proced. Int. 1992,
24

, 60.

10.

Anders, E.; Tropsch, J. G., Bull. Soc. Chim. Belg. 1987, 96, 719.

Bradford P. Mundy

Colby College, Waterville, ME, USA

A list of General Abbreviations appears on the front Endpapers