Bromine Water (500ml) 3%
Bromine water is a highly oxidizing intense yellow to red mixture containing diatomic bromine (Br2) dissolved in water (H2O). It is often used as a reactive in chemical assays of recognition for substances which react with bromine in an aqueous environment with the halogenation mechanism, mainly unsaturated carbon compounds (carbon compounds with 1 or more double or triple bond(s)). The most common compounds that react well with bromine water are phenols, alkenes, enols, the acetyl group, aniline, and glucose.
In addition, bromine water is commonly used to test for the presence of an alkene which contains a double covalent bond which reacts with the bromine water which changes its color from an intense yellow to a colorless solution. Bromine water is also commonly used to check for the presence of an aldehyde group in compounds. In this reaction as well the color of bromine water is changed to colorless from yellow (oxidation process).
In organic chemistry, the bromine test is a qualitative test for the presence of unsaturation (carbon-to-carbon double or triple bonds), phenols and anilines.
An unknown sample is treated with a small amount of elemental bromine 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.
Should the brown colour not disappear, possibly due to the presence of an alkane 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.