Most of the organic compounds are derived from hydrocarbons and the compounds containing hydrocarbons are classified into Saturated hydrocarbons and Unsaturated hydrocarbons.Unsaturation in organic compounds refer to the presence or double or triple bonds between the carbon atoms in a molecular structure. There are several test for unsaturation to identify if an organic compound is unsaturated. 

In this Chemistry article, learn about the test for unsaturation of an organic compound, their importance, with examples and precautions. 

What is Unsaturation?

Unsaturation in organic compounds is due to the presence of double or triple bonds between the carbon atoms.

The aliphatic hydrocarbons that contain a double bond between the carbon atoms are called alkenes and the hydrocarbons that contain triple bonds are known as alkynes.

Few examples of Unsaturation are Alkenes, Alkynes, Aromatic compounds and Unsaturated fatty acids.

Learn about the basic concepts of organic chemistry for a further insight into the related article. 

Importance of Test for Unsaturation 

Unsaturated compounds are those organic compounds with the presence of one or more double of triple bonds in the compound. The test for unsaturation are important for identifying the presence of unsaturated compounds in the sample.

It provides the information about the structure, composition and chemical properties of that particular organic compound.

Experimental Test for Unsaturation

Let us learn about the two experimental tests: Baeyer’s test for unsaturation and the bromine test for unsaturation. 

Alkaline Potassium Permanganate Test (Baeyer’s Test for Unsaturation)

Baeyer's test is used to determine the presence of a double bond in an unsaturated compound.

Here, an unsaturated compound reacts with a dilute solution of potassium permanganate to form glycols and diols.

Aim

To determine the presence of double bonds between the carbon atoms.

Materials Required

• Potassium Hydroxide solution 
• Solution of Bromine water or Bromine in Chloroform
• Carbon Tetrachloride solution 
• Solution of Potassium Permangenate 
• Distilled water 
• Test Tubes and Test Tube holder

Procedure

Preparation of Reagents 

• Add 1% of Potassium Permanganate solution in an equal volume of 1% of sodium carbonate solution.
• Shake, until completely dissolved.

Alkaline Potassium Permangenate Test (Bayer’s test for Unsaturation) 

• In a test tube add small amount of the given organic compound.
• Dissolve the organic compound in 2ml of distilled water or acetone. 
• Add the Reagent, drop wise, till the solution turns pink. 
• Observe the solution.
• If it turns pink and the colour persists, then it is a saturation compound (negative test).
• If the solution turns pink and the colour does not persist, it stays transparent, then the given organic compound is unsaturated (positive test).

Chemical Reactions

Few examples of chemical reactions for Bayer’s tests of unsaturation are: 

• Ethylene reacts with Potassium Permangenate and water to form Ethlyene Glycol, Manganese Dioxide and Potassium Manganate.

• Alkyne reacts with Potassium Permanganete with water to form Carboxylic acid, Manganese dioxide and Potassium Manganate. 

• Propyne reacts with water in the presence of Potassium Permangenate to form Acetic acid, carbon dioxide, Mangenese dioxide and Potassium Mangenate. 

Bromine Test for Unsaturation 

Aim

To determine the presence of double bonds between the carbon atoms.

Materials Required

• Potassium Hydroxide solution
• Bromine water / carbon tetrachloride solution
• Potassium permangneate solution 
• Sample organic compound 
• Distilled water 
• Test tubes

Procedure

Water Soluble Compounds 

• In a test tube, take the required amount of organic compound.
• Dissolve it in 2ml of distilled water.
• Dropwise, add bromine water.
• If the solution turns orange and persists, then that organic compound is saturated.
• If the solution turns orange and does not persist, then that organic compound is unsaturated. 

Water Insoluble Compounds 

• The given organic compound is added to 1ml of carbon tetrachloride in a test tube.
• Add drops of bromine solution in carbon tetrachloride solution in test tube.
• If the solution turns orange and persists, then that organic compound is saturated.
• If the solution turns orange and does not persist, then that organic compound is unsaturated. 

Gaseous Compounds

• Add 1-2ml of bromine solution in a gaseous compound. 
• Shake the mixture. 
• If the solution turns orange and persists, then that organic compound is saturated.
• If the solution turns orange and does not persist, then that organic compound is unsaturated. 

Precautions

The following are the precautions to be taken for the test for unsaturation of different organic compounds:

• To handle the bromine solution very carefully as it can cause eye irritation and a burning sensation. 
• Avoid inhaling bromine vapours as it can cause headaches, cough, irritation of mucus membranes and watery eyes.
• To completely avoid contact of bromine water and chloroform with skin.
• To ensure that the test for unsaturation of organic compounds is carried out at room temperature.

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