Question

How will you convert ethanal into the following compounds?
$But - 2 - enal$

Answer 1

Hint: we know that ethanal is a type of aldehyde. It is also known as acetaldehyde. The molecular formula of ethanal is $C{H_3}CHO$ and the molecular formula of $But - 2 - enal$ is ${H_3}C - CH = CH - CHO$. Ethanal has two carbon in total and $But - 2 - enal$ has four carbons in total.

Complete step by step solution:
We know that ethanol has three alpha hydrogens $(\alpha )$.Ethanal has two carbons and $But - 2 - enal$has four carbon. We can observe that there is an addition of two carbons to get the final product. So the first thing that should strike our mind after seeing aldehyde and addition of carbon atoms is aldol reaction. Ethanal can easily undergo an aldol reaction . In the aldol reaction we use bases like sodium hydroxide. The Aldol reaction of ethanal to produce $But - 2 - enal$ can be written as-
$2C{H_3}CHO\xrightarrow[{NaOH}]{{Oil}}C{H_3} - CH(OH) - C{H_2} - CHO\xrightarrow[{ - {H_2}O}]{\Delta }{H_3}C - CH = CH - CHO$

So it is clear to us that we will use the above reaction to convert ethanal into $But - 2 - enal$ by using the aldol reaction.

Additional information:
Aldol reaction is a type of condensation reaction in organic chemistry in which carbonyl compounds like aldehyde and ketones react to form $\beta - \text{hydroxy aldehyde}$ or $\beta - \text{hydroxy ketone}$. Aldol reaction is followed by a dehydration in which water molecules eliminate the compound when heated. The rate of aldol reaction in aldehyde is more than that of the ketones.

Note: Always remember that ethanal undergoes aldol condensation to produce $But - 2 - enal$. In aldol reaction we use bases like sodium hydroxide and further the obtained compound is hydrated by slightly heating it. Always remember that to undergo aldol reactions the compounds should have alpha hydrogens $(\alpha )$.The examples of some compounds which can undergo aldol reaction are ethanal, cyclohexanone, phenylacetaldehyde and many more.