which is best analytical tool to confirm presence of bromin in a organic solution?
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Answer:
Bromine water, also called Bromide bromate solution or Bromine solution with the chemical formula Br2. The molecular weight of bromine water is 159.81 and the density is 1.307 g/mL. Bromine water is a yellow mixture solution with high oxidizing property, prepared by dissolving diatomic bromine (Br2) in water (H2O).
Bromine water solution can be prepared in the chemistry lab by direct mixing of fumes of bromine and water. But it is not safe, so the more convenient method of preparation of bromine water solution is breaking of sodium bromide (NaBr) in the presence of bleach and hydrochloric acid (HCl).
Bromine Water
Bromine water is used to identify the functional group present in the organic compound by halogenation mechanism.
Bromine water test (saturation test)
The bromine water test is a qualitative test, used to identify the alkene or alkane functional groups present in the compound. Alkene groups react with bromine water in the dark condition and undergo an addition reaction, to give a decolourized solution. On the other hand, alkane doesn’t react with bromine water and the colour of the bromine water remains the same. Enols, alkenes, aniline, glucose, phenols and acetyl groups are the most common compounds to undergo bromine water test. The test also identifies the presence of an aldehyde group in the compound. During the process, the colour of the bromine water changes from yellow to colourless.
The reaction between bromine water and different functional groups are as given below:
1. Alkane
Alkane does not react with the bromine water solution and the dark yellow colour of bromine solution remains as such.
CH3 + CH2 + CH2 + CH3 → No reaction
2. Alkene
Alkene undergoes an addition reaction. For example, ethene reacts with bromine water to give 1,2 dibromo ethanes.
Addition Reaction Of Ethene
The reaction takes place at room temperature if the reactants are in the gaseous state (ethene). Colour of the bromine water solution is decolourized as it reacts with ethene.
But, liquid alkenes like cyclohexene react with bromine water solution in the presence of tetrachloromethane.
3. Phenols
Phenols undergo substitution reactions in the presence of bromine water to give a brominated compound. During the process, bromine water is decolourized and gives white precipitate.
Bromination of phenol
The mechanism of the reaction is given below,
Mechanism - Bromination Reaction of Phenol
4. Aniline
Aniline or phenylamine reacts with bromine water. During the reaction, a white precipitate is formed along with decolouration of brome water.
Bromination Reaction Of Aniline
5. Enol
Bromination of Enol
Enols undergo the bromine water test and brominated ketone is formed.
6. Glucose
The bromine water test is a simple test to distinguish between glucose and fructose. The Glucose undergoes oxidation reaction to give glucuronic acid on reaction with the bromine water solution. Since bromine water is a mild oxidizing agent, fructose fails to undergo an oxidation reaction.
Oxidation reaction of glucose
7. Ketones
A reaction between the ketone and bromine water is an electrophilic alpha substitution reaction, adjacent to the carbonyl group and gives the colourless solution of brominated compounds.
8. Aldehydes
Aldehyde reacts with bromine water and undergoes an oxidation reaction to give a colourless solution.