In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, ...
, the bromine test is a qualitative test for the presence of
unsaturation (carbon-to-carbon
double
A double is a look-alike or doppelgänger; one person or being that resembles another.
Double, The Double or Dubble may also refer to:
Film and television
* Double (filmmaking), someone who substitutes for the credited actor of a character
* ...
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
* ...
bonds),
phenols
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are ...
and
anilines.
An unknown sample is treated with a small amount of elemental
bromine
Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
in an organic solvent, being
as
dichloromethane or
carbon tetrachloride. 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
In chemistry, the iodine value (IV; also iodine adsorption value, iodine number or iodine index) is the mass of iodine in grams that is consumed by 100 grams of a chemical substance. Iodine numbers are often used to determine the degree of ...
is a way to determine the presence of unsaturation quantitatively.
The bromine test is a simple qualitative test. Modern spectroscopic methods (e.g.
NMR
Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with ...
and
infrared spectroscopy
Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...
) are better at determining the structural features and identity of unknown compounds.
References
Chemical tests
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