Question

Convert the following?
Ethanal into but2-enoic acid

Answer 1

Hint :here we are given ethanal which has a functional group aldehyde. Ethanal needs to be dehydrated followed by aldol condensation to form acrolein. Now acrolein undergoes mild oxidation to form but-2-enoic acid.

Complete Step By Step Answer:
Now in the above question we are being asked about the conversion of Ethanal to but-2-enoic acid.
 $ C{H_3} - CHO \\
  but - 2 - enoic $
First, we need to think of one single reaction which can convert ethanal to but - 2 - enoic acid. There is no single reaction that can do that.
First let’s understand Ethanal, it is a saturated hydrocarbon with an aldehydic group. Now this saturated compound is made to undergo aldol condensation and then dehydration. Now, for this to happen we will take 2 moles of ethanal whose formula is $ C{H_3} - CHO $
Acrolein or $ But - 2 - enal $ formula is $ C{H_3} - CH = CH - CHO $
The reaction for the above conversion is as follows:
 $ 2C{H_3}CHO\xrightarrow[{(ii)dehydration}]{\begin{subarray}{l}
  (i)aldol \\
  condensation
\end{subarray} }C{H_3} - CH = CH - CHO $
Now $ But - 2 - enal $ has one aldehyde functional group and unsaturated hydrocarbons attached to each other.
The above given compound now needs to be converted into the final product which is $ but - 2 - enoic $ acid and has formula $ C{H_3} - CH = CH - COOH $
Now to convert $ But - 2 - enal $ to $ C{H_3} - CH = CH - COOH $ we need mild oxidation but not a strong oxidation because it might break the chain and form two compounds, therefore we will make it react with an oxidising agent but a weaker one.
On reaction of $ But - 2 - enal $ with mild oxidation we get $ C{H_3} - CH = CH - COOH $
 $ C{H_3} - CH = CH - CHO\xrightarrow[\begin{subarray}{l}
  Protecting \\
  Double \\
  Bond
\end{subarray} ]{\begin{subarray}{l}
  Mild \\
  Oxidation
\end{subarray} }C{H_3} - CH = CH - COOH $ .

Note :
An absolute ozonolysis of any unsaturated hydrocarbon gives us two compounds out of the one product. The compound gets broken along its unsaturated hydrocarbon after forming an ozonide intermediate to give two aldehydes or carboxylic acid, depending on the unsaturated compound being alkene or alkyne.