THIONYL BROMIDE 1
O
Thionyl Bromide1
CO2H
SOBr2
(5)
O
CO2H
SOBr2
O
[507-16-4] Br2OS (MW 207.87)
Preparation of Bromides from Alcohols. In the ribonu-
InChI = 1/Br2OS/c1-4(2)3
cleotide series, specific OH replacement has been noted (eq 6).5
InChIKey = HFRXJVQOXRXOPP-UHFFFAOYAY
Other examples of the transformation of OH to Br are illustrated
(brominating agent for alcohols, carboxylic acids, alkenes, and in eqs 7 and 8.6,7 Conversion of an alcohol to a dibromo derivative
ketones) has been reported (eq 9).8
ć% ć%
Physical Data: mp -52 C; bp 68 C/40 mmHg; d 2.688 g cm-3.
HO Br
Solubility: sol benzene, chloroform, carbon tetrachloride. O O
SOBr2
(6)
Form Supplied in: commercially available.
Handling, Storage, and Precautions: less stable than thionyl
OH OH OH OH
chloride and will slowly decompose, even in a stoppered con-
tainer. Stable if kept dry, but reacts violently with water. Ex- OH Br
H H2
SOBr2
tremely destructive to tissue of mucous membranes, upper res-
(7)
( )4N ( )4N
+
Br
piratory tract, eyes, and skin. Reacts vigorously with acetone
to form a lachrymator. Should be handled in a fume hood.
62 g 82 g
Br Br
SOBr2
Thionyl bromide is considerably more reactive than Thionyl
(8)
Br OH Br Br
Chloride and is more difficult to use.2 Unlike thionyl chloride,
CO2Et CO2Et
whose reactions are often carried out in pyridine, thionyl bromide
undergoes a reaction with this solvent to form a nonreactive salt
O O
SOBr2
(eq 1).3
(9)
Br Br
OH
+ +
+ SOBr2 SO2 (1)
+
N N
Br Br3
H H
BrominationÄ…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
Preparation of Acid Bromides from Carboxylic Acids. Al-
Propiophenone gives a mixture of Ä…-bromopropiophenone and
though not often used, thionyl bromide can convert a simple
Ä…-bromo-Ä…-methylpropiophenone. The reaction with unsaturated
organic acid to the acid bromide.4 When the acid is an Ä…,²-
ketones gives addition to the double bond (eq 11).9
unsaturated acid, addition of bromine across the double bond oc-
curs, generally in quantitative yield (eqs 2 and 3).
OO
Br
SOBr2
Br
(10)
CO2HCO2H benzene Br
SOBr2
82%
(2)
Br
OH OH
Br Br
SOBr2
O
(11)
Br
CO2H
SOBr2
(3)
O
O O Br
CO2H
Br
O
Preparation of N-(1-Bromoalkyl)heteroarylium Salts. A
For simple aliphatic acids, formation of the acid bromide is a
general reaction is given in eq 12.10
high yield reaction (eq 4). Simple aromatic carboxylic acids also
form the acid bromides in good yield.
O
SOBr2 +
+ R N (12)
O
SOBr2 R H
N
Br
(4)
RCO2H
Br
R Br
R = Me, 85%; Et, 90%; Pr, 92%; Bu, 90%
Thionyl bromide can function as a dehydrating agent for suit-
1. Mellor, J. W., Comprehensive Treatise on Inorganic and Theoretical
ably positioned dicarboxylic acids (eq 5).
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. 7. Verny, M.; Vessiere, R., Bull. Soc. Chem. Fr. 1968, 2585.
1991, 124, 2013.
8. Saraf, S. D.; Al-Omran, F., Org. Prep. Proced. Int. 1987, 19,
3. See Magee, P. S. In Sulfur in Organic and Inorganic Chemistry; Senning, 455.
A., Ed.; Dekker: New York, 1971; Vol. 1, p 283.
9. Al-Mousawi, S. M.; Bhatti, I.; Saraf, S. D., Org. Prep. Proced. Int. 1992,
4. Saraf, S. D.; Zaki, M., Synthesis 1973, 612. 24, 60.
5. Kikugawa, K.; Ichino, M., Tetrahedron Lett. 1971, 87. 10. Anders, E.; Tropsch, J. G., Bull. Soc. Chim. Belg. 1987, 96, 719.
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.
Bradford P. Mundy
(b) Frazer, M. J.; Gerrard, W.; Machell, G.; Shepherd, B. D., Chem. Ind.
Colby College, Waterville, ME, USA
(London) 1954, 931.
A list of General Abbreviations appears on the front Endpapers