In
organic chemistry, the bromine test is a qualitative test for the presence of
unsaturation (carbon-to-carbon
double or
triple
Triple is used in several contexts to mean "threefold" or a "treble":
Sports
* Triple (baseball), a three-base hit
* A basketball three-point field goal
* A figure skating jump with three rotations
* In bowling terms, three strikes in a row
* In ...
bonds),
phenols and
anilines.
An unknown sample is treated with a small amount of elemental
bromine in an organic solvent, being
as
dichloromethane
Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odour is widely used as a solvent. Although it is not miscible with ...
or
carbon tetrachloride
Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also IUPAC nomenclature of inorganic chemistry, recognised by the IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVAC ...
. Presence of unsaturation and/or phenol or aniline in the sample is shown by disappearance of the deep brown coloration of bromine when it has reacted with the unknown sample. The formation of a brominated phenol (i.e.
2,4,6-tribromophenol
2,4,6-Tribromophenol (TBP) is a brominated derivative of phenol. It is used as a fungicide, as a wood preservative, and an intermediate in the preparation of flame retardants.
Production
Although natural TBP has been identified in ocean sedim ...
) or aniline(i.e.
2,4,6-tribromoaniline) in form of a white precipitate indicates that the unknown was a phenol or aniline. The more unsaturated an unknown is, the more bromine it reacts with, and the less coloured the solution will appear.
["The Systematic Identification of Organic Compounds" R.L. Shriner, C.K.F. Hermann, T.C. Morrill, D.Y. Curtin, and R.C. Fuson John Wiley & Sons, 1997 ]
Should the brown colour not disappear, possibly due to the presence of an alkene which doesn't react, or reacts very slowly with, bromine, the
potassium permanganate test should be performed, in order to determine the presence or absence of the alkene.
The
iodine value is a way to determine the presence of unsaturation quantitatively.
The bromine test is a simple qualitative test. Modern spectroscopic methods (e.g.
NMR and
infrared spectroscopy) are better at determining the structural features and identity of unknown compounds.
References
Chemical tests
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