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. The 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 are units 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
Alkaline potassium permanganate test (Baeyer’s test)
Bromine Test
Materials Required For the Test
Potassium hydroxide solution
Bromine water solution/ Bromine in CCl4 or chloroform
Carbon tetrachloride/chloroform
Potassium permanganate solution
Sample compound to be tested
Distilled water
Test tubes
Test tube holder
Precautions
The bromine solution should be handled carefully.
Do not inhale the vapors of bromine and chloroform.
The test should be carried out at room temperature.
Avoid bromine solution in contact with skin.
Procedure
(a) Preparation of Reagents
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.
Bromine in CCl4 : Take 5ml of liquid bromine in 100ml of carbon tetrachloride and shake it to dissolve properly.
Bromine Water : Take 5ml of bromine, add 100 ml of distilled water, and shake well. Decant off the clear liquid.
(b) Alkaline Potassium Permanganate Test (Baeyer’s Test)
In a test tube, a small amount of the given organic compound is taken to be tested.
In 2ml of water or acetone taken in the test tube, the organic compound is dissolved.
Add 1% alkaline potassium permanganate solution dropwise and shake the mixture.
Observe the solution, if the 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:
In a test tube, the given organic compound is taken to be tested
Dissolve it in 2ml of distilled water.
Add bromine water dropwise with constant shaking.
The given organic compound is unsaturated if the orange color of Bromine disappears. When all the pi bonds are broken then the color persists.
The given organic compound is saturated if the color of bromine persists.
(ii) Water-insoluble Compounds:
In a test tube, dissolve the given organic compound in 1ml of carbon tetrachloride.
In the test tube, add bromine with constant shaking in CCl4 dropwise.
The disappearance of orange-red color indicates unsaturation.
Until the brown color persists , with constant shaking, continue the dropwise addition of bromine.
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:
Take a gaseous compound in a jar and add 1-2ml of bromine solution into it.
Shake the mixture well.
The disappearance of the orange-red color of bromine indicates unsaturation.
Observations
1. Alkaline Potassium Permanganate Test-
Either the disappearance of pink color or pink color persists.
2. Bromine Test-
Either disappearance of orange-red color or orange-red color persists.
Did You Know?
1. Ethylene (Ethene)
Used in the manufacture of 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
2. 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.
3. 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.
4. 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.)
5. Phenol
It is an organic compound that is said to be toxic. However, we can see the presence of phenol in the household goods themselves. In the spray cleaners and mouthwash, phenol content is present. Also, phenol when seen in its purest form can be either white or colorless. The phenol can be detected through the scent it has. The phenol sugary-like scent will remind you of the hospital rooms and sterile rooms that you have visited before.
6. Aniline
Aniline is a primary arylamine. For the benzene hydrogens, one amino functional group is substituted. That is how it is formed. The common name of aniline is phenylamine aminobenzene. It is said to be toxic in three ways:
On inhaling
Touching the skin
When ingested
The harm is caused due to affecting the oxygen carrier, haemoglobin in our body. And as a result of that, a condition called methemoglobinemia is caused. The exposure and the time for which you are in contact with aniline determines the severity of the case.
7. Propene
It is an unsaturated organic compound. And it is also called propylene. The simpler alkene present in the family of hydrocarbons is propene. It is the second simplest member. The odour it has is of a faint petroleum one. It contains just one double bond.
8. The Importance of Alkene in Food
Alkenes are called unsaturated hydrocarbons. Since they contain double bonds. It can be seen in the fruits and vegetables that are in the stage of ripening. And the ethylene present in them is what helps them to ripen in an optimum way. So many farmers do use artificial ethylene for properly ripening these fruits and vegetables.
Limonene is an alkene that is present in citrus fruits. And the reason for the flavour that we get in citrus fruits is partly because of the presence of this alkene. When it comes to nutritional forms like vitamins, we can say beta carotene in vitamin A is alkenes.
9. Benzene
Do you know why benzene is not considered as alkene? But regarded as an aromatic compound. It is because benzene doesn’t react that much just like alkenes. It can be said to be mostly inert. The aromatic nature is shown by the delocalization that happens to the pi-electrons present.
FAQs on Chemical Test For Unsaturation
1. What is the difference between saturated and unsaturated hydrocarbons?
The fundamental difference between saturated and unsaturated compounds is the presence and absence of double bonds for carbon respectively. The easy way to detect and find the difference is by testing the compound with a test that will cause a reaction with the double bond present in unsaturated compounds. Thus we can differentiate saturated and unsaturated compounds when given.
2. In organic chemistry, what does the unsaturation test means?
We say the compounds that are having carbon-carbon double bonds to be unsaturated. So through the tests what we prove is whether the carbons are having double bonds or not. So while conducting a bromine test, this is what is getting tested.
Students would conduct a bromine test for the substance and must shake. So if there is a carbon-carbon double bond we can notice that orange-coloured bromine water is colourless.
3. How do we conduct unsaturation tests for alkenes?
There are two tests that we can conduct for alkenes on unsaturation. They are:
Baeyer's test
Bromine solution test
In Baeyer's test, alkenes will react with the potassium permanganate which is an alkaline solution. And thus the colour of potassium permanganate will slowly fade as it forms glycol on the chemical reaction.
If we give an example for Baeyer's test, ethane reacts with the alkaline solution of potassium permanganate to form the ethylene glycol. And as we observe throughout the test we can see that the violet colour of the potassium permanganate goes slowly fading.
4. Why is the unsaturated test given for oxalic acid?
As we know oxalic acid is a saturated one. However, the unsaturated test is given for it. The purpose of unsaturated tests is for finding whether a carbon-carbon double bonding is present or not. And so, for saturated compounds, no such double bond will be present. However, in oxalic acid, there is a double bond present. So it is to be given an unsaturated test and it will show positive as it contains a double bond.
5. Is it possible to conduct an unsaturation test for aromatic compounds?
The unsaturation test is conducted to find whether there is a double bond present between two carbons. And as per the test, we get the result accordingly by the reaction between the compound and bromine. An aromatic compound like benzene and toluene doesn’t come in the category of alkenes. So even if students conduct a test for aromatic compounds, no reaction will be there. Using any additions will only cause molecular instability for the aromatic compound used. For answers to more queries and study materials use the Vedantu app and website.
6. 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.
7. 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
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H Br
(Colourless)
