Tests for Unsaturation

Chemical Test For Unsaturation(Aim Of The Test)

To identify the presence of a useful cluster like a take a look at for unsaturation and saturation in an exceedingly given compound. Hydrocarbons Functional group plays an important role in determining the properties of the organic compounds and their nature. The identification of functional groups is a very vital part of qualitative analysis. Tests for unsaturation can be used to identify the double and triple bonds present in the organic compound. In Organic Unsaturated Hydrocarbons, the bromine test may be a qualitative test for the presence of unsaturation (carbon-to-carbon double or triple bonds), phenols and anilines. 


Theory

Hydrocarbons

Organic compounds containing hydrocarbons(carbon and element bonds). The organic compounds area unit derived from hydrocarbons by the displacement of 1 or additional element atoms by one atom or a bunch of atoms like acid, aldehyde, Hydroxide, and grouping useful teams, etc.


Classification Of Hydrocarbons 

1. Saturated Hydrocarbons

Some examples are methane, ethane, propane and butane.

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Molecular formula 

2. Unsaturated Hydrocarbons

Some examples for alkenes and alkynes are: propene, propyne, butene and butyne.

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Alkenes 

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Alkynes


Unsaturation In An Organic Compound Is Detected By

  1. Alkaline potassium permanganate test (Baeyer’s test)

  2. Bromine Test


Materials Required For The Test

  1. Potassium hydroxide solution

  2. Bromine water solution/ Bromine in CCl4 or chloroform

  3. Carbon tetrachloride/chloroform

  4. Potassium permanganate solution

  5. Sample compound to be tested

  6. Distilled water

  7. Test tubes

  8. Test tube holder


Apparatus Setup

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Precautions

  1. The bromine solution should be handled carefully.

  2. Do not inhale the vapors of bromine and chloroform.

  3. The test should be carried out at room temperature.

  4. Avoid bromine solution in contact with skin.


Procedure

(a) Preparation of Reagents

  1. Alkaline KMnO4 (1%) Dissolve about 1g of potassium permanganate in 100ml of distilled water. To that solution add 10g of anhydrous sodium carbonate. Shake to dissolve it completely.

  2. Bromine in CCl4: Take 5ml of liquid bromine in 100ml of carbon tetrachloride and shake it to dissolve properly.

  3. Bromine Water: Take 5ml of bromine, add 100ml of distilled water, and shake well. Decant off the clear liquid.


(B) Alkaline Potassium Permanganate Test (Baeyer’s Test)

  1. In a test tube, a small amount of the given organic compound is taken to be tested.

  2. In 2ml of water or acetone take in the test tube, the organic compound is dissolved.

  3. Add 1% alkaline potassium permanganate solution dropwise and shake the mixture.

  4. Observe the solution, if pink color persists then it is a saturated compound. The given organic compound is unsaturated if the pink color disappears.


(C) Bromine Test

(i) Water-soluble Compounds:

  1. In a test tube, the given organic compound is taken to be tested

  2. Dissolve it in 2ml of distilled water.

  3. Add bromine water dropwise with constant shaking.

  4. The given organic compound is unsaturated if the orange color of Bromine disappears. When all the pi bonds are broken then the color persists.

  5. The given organic compound is saturated if the color of bromine persists.

(ii) Water-insoluble Compounds:

  1. In a test tube, dissolve the given organic compound in 1ml of carbon tetrachloride.

  2. In the test tube, add bromine with constant shaking in CCl4 dropwise.

  3. The disappearance of orange-red color indicates unsaturation.

  4. Until the brown color persists till then with constant shaking continue the dropwise addition of bromine.

  5. Bring a rod dipped in ammonium hydroxide or blow across the mouth of the test tube. The absence of white fumes confirms unsaturation.

(iii) Gaseous Compounds:

  1. Take a gaseous compound in a jar and add 1-2ml of bromine solution into it.

  2. Shake the mixture well.

  3. The disappearance of the orange-red color of bromine indicates unsaturation.


Observations

  1. Alkaline potassium permanganate test-

         Either disappearance of pink color or pink color persists.

  1. Bromine test-

Either disappearance of orange-red color or orange-red color persists.


Did You Know?

  1. Ethylene (Ethene)

Used in the manufacture of the plastic polyethene. The beginning of the ripening process in many plants is stimulated by the release of ethylene; some unripe (when they are less fragile) plants can be picked, and by exposing to ethylene gas it causes ripening of it once they reach their destination


  1. Tetrachloroethylene

Also called perchloroethylene (“Perc”); an organic solvent that is non-flammable and used in dry cleaning; it is also used as a paint remover, degreaser, and an industrial solvent.


  1. Lycopene

A red pigment found in tomatoes, watermelon, guava, papaya, pink grapefruit, apricots, and rosehips; lycopene may be a good antioxidant and is more readily absorbed from cooked tomatoes and ingredients, especially if the foods contain fat.


  1. Terpenes and Essential Oils

Terpenes are a diverse group of molecules that are biologically

synthesized from isoprene units. They are found in many plants, and often

have distinctive flavors and aromas. They are often components of essential

oils, so named because they need a characteristic “essence” or fragrance.

Many of these molecules are components of common foods and perfumes.

(Lycopene and its related compounds are also terpenes.)

FAQ (Frequently Asked Questions)

1. If The Provided Organic Compound Is An Aldehyde, Then What Test Is Performed To Find The Unsaturation?

Due to its oxidation to carboxylic acid Aldehydes decolorize potassium permanganate (KMnO4) solution. In this case, if the provided organic compound is aldehyde then to find out unsaturation, the Bromine water test can be carried out. The test is as follows

Bromine Water Test:

In a test tube in 2 mL of carbon tetrachloride dissolve 0.1 g or 5 drops of an organic compound and in carbon tetrachloride or bromine water add drop by drop 2% solution of bromine with continuous shaking. Decolourization of bromine solution indicates the presence of unsaturation in organic compounds on performing the test.

2. What Type Of Reaction Takes Place Between Alkenes And Bromine Water?

When alkenes react with bromine then the double bond breaks and each carbon is attached to a bromine atom. The bromine then loses its original red-brown color and gives a colorless liquid. These compounds undergo an addition reaction with bromine water or the solution of bromine in carbon tetrachloride (CCl4), chloroform (CHCl3) or glacial acetic acid. Vicinal dibromide is formed by adding bromine to an alkene. The orange color of the answer of bromine in carbon tet disappears on reaction with an alkene. The reaction is as follows :  

                                 Br H

                                  |   |

H2C=CH2 + Br2 →H-C--CH

                                  |   |

                                 H Br

                           (Colourless)