Bromine Water Test (Saturation Test)

The bromine water test is used to assess if an alkene or alkyne does have an unsaturated carbon-carbon bond. The test employs an addition reaction, in which a reactant, in this case, bromine, is introduced to an organic molecule in a way to destroy a double or triple bond. Bromine has an orange-brownish hue in the solution. Therefore, when an alkene or alkyne is available for bromine to interact with, the colour of the solution is erased. Bromine can interact with aromatic chemicals like phenol, but it doesn’t react to alkanes since they only have single bonds. Thus no colour change happens when they’re combined.

What does a bromine water test entail?

A bromine water test is employed to assess if a hydrocarbon is saturated or unsaturated. Since unsaturated hydrocarbons include at most one Carbon-Carbon double bond, which is fragile, an electrophilic addition using halogens, hydrogen halides, or water may be achieved without heat, making it straightforward to check for alkenes. When bromine combines with alkenes (in this example, ethene), the corresponding reaction occurs:

If bromine decolourises, it means that bromine has been used up in the reaction as mentioned above, resulting in the formation of a colourless molecule, showing the existence of an alkene.

Application

Bromine could be utilised in synthetic chemistry as a brominating and oxidising agent.

It could be used in the following ways:

1. Utilising photocatalytic circumstances, brominate alkylbenzenes there at the benzylic location.
2. Electrophilic substitution processes there in the existence of Lewis acid catalysts are used to make brominated aromatic compounds.
3. In the presence of phosphorus trihalides, the bromination of carbonyl compounds at such a carbonyl group through Hell-Volhard-Zelinski reaction.
4. Hofmann rearrangement is used to make isocyanates, carbamates, and amines by interacting primary amides with something like a base.

Bromine water test questions

What does it mean when a bromine water test comes back positive?

This enables us to differentiate between alkenes and alkanes using only a simple chemical test. Bromine water is indeed an orange bromine solution. When this is shaken with an alkene, it turns colourless. Alkenes, but just not alkanes, may decolourise bromine water.

How can you tell whether your water contains bromine?

A simple bromine water test may determine the difference between alkane and alkene. As the bromine interacts with the carbon-carbon double bond, the alkene would convert brown bromine water colourless. In reality, unsaturated molecules with carbon-carbon double bonds can undergo this reaction.

Bromine water test notes

Bromine water, often called the bromide bromate solution of bromine water, is a compound with the chemical formula Br2. Bromine water does have a density of 1.307 g/mL and a molar size of 159.81. Bromine water seems to be a yellow mixed solution with a high oxidation capacity created by mixing diatomic bromine (Br2) with water (H2O). Bromine water is used to identify the substituents present inside organic compounds utilising the halogenation procedure.

Bromine water test (saturation test)

The availability of alkene/alkane functional groups inside the compound may be determined through bromine water testing. Alkene groups react with bromine water and perform an additional reaction, culminating in a decolourised solution, which occurs mainly in the dark. On the other hand, alkane does not interact with bromine water. Hence the colour of bromine water does not change. Enols, aniline, alkenes, phenols, acetyl groups, and glucose are the most often analysed compounds in bromine water. Such a test also determines the presence of an aldehyde functional group in the material. Even during operation, the colour of bromine fluid turns from yellow into neutral.

Conclusion:

This bromine water test determines whether or not hydrocarbons are saturated or unsaturated. Bromine water tests for organic molecules such as phenols, acetyl compounds, alkenes, and even anilines are relatively simple to perform. A colour shift in bromine water even during operation indicates the presence of an unsaturated group of primarily organic compounds. Additionally, bromine water is frequently used to identify the presence of a double covalently linked alkene, which reacts with bromine water to change its colour from brilliant yellow to colourless. Bromine water is also commonly used to check for the presence of an aldehyde group in a compound.