Distinguish Acetaldehyde and Acetone | Difference between Acetone and Acetaldehyde

Acetaldehyde and acetone can be distinguished because acetaldehyde is an aldehyde and acetone is a ketone. Aldehydess and ketones show different reactions with same reagents because there is a difference in their structure.


acettaldehyde and acetone

See aldehyde and ketone identifying full tutorial

Both acetaldehyde and acetone are colourless liquids at room temperature. So we cannot identify distinguish and acetone from looking their colour or physical state. Therefore, we have to go for some reactions to distinguish acetaldehyde and acetone. remember that, acetaldehyde is an aldehyde compound and acetone is a ketone compound.



Distinguish acetaldehyde and acetone

Acetaldehyde and acetone have differences when they react with some compounds. Note that, acetaldehyde can be oxidized easily to acetic acid. But acetone cannot be oxidized easily like acetaldehyde. We use this characteristic to identify acetaldehyde and acetone.


Acidic potassium permanganate (H+ / KMnO4) solution is added to acetaldehyde and acetone separately to see, what will be oxidized. When oxidation reduction reaction occur, purple colour of H+ / KMnO4 is changed to colourless or light pink.


Acetaldehyde oxidation by acidic potassium permanganate

Acetaldehyde is oxidized by H+ / KMnO4 to ethanoic acid. We can see the colour change.



acetone is not oxidized by H+ / KMnO4. So there is no change of colour of acetone with H+ / KMnO4.


So, we can identify acetaldehyde and acetone by H+ / KMnO4.



Acetaldehyde can be oxidized by following reagents also. And a colour change or physical change can be seen when those oxidizing agents react with acetaldehyde.

  • H+ / K2CrO4: yellow colour is changed to green
  • H+ / K2Cr2O7: orange colour is changed to green


Acetone to acetaldehyde

If we can prepare ethanol from acetone, we can easily prepare acetaldehyde from ethanol. When ethanol is oxidized by PCC, acetaldehyde is given. PCC is used to oxidize primary alcohols to aldehydes. So our target should be preparing ethanol from acetone. Also note that, number of carbon is reduced by one in this organic conversion


Acetone reduction to 2-propanol

When ketones react with LiAlH4 in ether medium, secondary alcohols are given. Therefore when acetone reacts with LiAlH4 to give 2-propanol.


2-propanol oxidizing to propene

When alcohol is heated with a dehydrator, alkene is given as a product. As dehydratoros, concentrated sulfuric acid, alumina or diphosphorus pentoxide can be used. When 2-propanol and a dehydrator is heated, propene is given.


Propene to ethanoic acid

When propene reacts with hot acidic potassium permanganate, propene is oxidized and give ethanoic acid and carbon dioxide as products. Propne molecule is broken to two parts in this reaction.


Ethanoic acid to ethanol

Carboxylic acids are reduced to alcohols by LiAlH4. Again, ethanoic acid is treated with LiAlH4 in ether medium to get ethanol as the alcohol product.


Ethanol to acetaldehyde

PCC reacts with ethanol and produce acetaldehyde as the product.



Questions


Why acetaldehyde and acetone cannot be distinguished by LiAlH4

Acetaldehhyde and acetone are reduced to ethanol and 2-propanol respectively by LiAlH4. There is no significant difference in ethanol and 2-propanol in their colour. Because both acetaldehyde and acetone react with LiAlH4, acetaldehyde and acetone cannot be distinguished by LiAlH4.



What is incorrect statement about, acetaldehyde and acetone can be identified by

  • Acidic potassium permanganate
  • Lithium aluminium hydride (LiAlH4)
  • Ammoniacal Silver Nitrate Solution
  • Fehling's solution

Statement two is incorrect. Both acetaldehyde and acetone are reduced by LiAlH4 to ethanol and 2-propanol respectively. Both these a colourless alcoholic liquids. Therefore, we cannot identify acetaldehyde and acetone from LiAlH4.



How would you distinguish between acetaldehyde and acetone?

From looking about two compounds, we cannot distinguish acetaldehyde and acetone because both are colorless liquids.

But from a chemcal reaction, we can identify them.

With acidic potassium permanaganate, acetaldehyde is oxidized to acetic acid. Purple colour of acidic potassium permanaganate is changed to colourless.

But acetone is not oxidized by acidic potassium permanaganate.



Difference between acetaldehyde and acetone

Main differences of acetaldehyde and acetone is, acetaldehyde can be oxidized. But acetone is not oxidized. Ketones are not oxidized.



Is acetone an aldehyde

Look thhe structure of acetone. It's CH3-CO-CH3. Around C=O group, there are two alkyl groups. So acetone is a ketone.



What is acetone colour?

Acetone is a colourless, volatile, flammable liquid and is the simplest and smallest ketone.



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