Question

Which reagent will bring about the conversion of carboxylic acids into esters
A. \[{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}}\]
B. Dry \[{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}} + {\rm{HCl}}\]
C. \[{\rm{LiAl}}{{\rm{H}}_{\rm{4}}}\]
D. \[{\rm{Al(O}}{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{{\rm{)}}_{\rm{3}}}\]

Answer 1

Hint: We know that, esters and carboxylic acids both are functional groups. The chemical representation of the ester group is RCOOR and carboxylic acid's chemical formula is RCOOH. Here, R is for any alkyl group.

Complete Step by Step Solution:
Let's understand the esterification reaction in detail. When a carboxylic acid undergoes a reaction with alcohol in an acidic medium, the formation of ester occurs. Another product obtained in the reaction is water. The chemical reaction for the reaction is,
\[{\rm{RCOOH}} + {{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}} + {\rm{HCl}} \to {\rm{R}} - {\rm{COO}} - {{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}} + {{\rm{H}}_{\rm{2}}}{\rm{O}}\]

Therefore, the conversion of a carboxylic into an acid takes place in presence of alcohol in an acidic medium.
In absence of an acidic medium, if the reaction of an alcohol with carboxylic acid occurs, ester will not form. Therefore, option A is incorrect.
The reagent \[{\rm{LiAl}}{{\rm{H}}_{\rm{4}}}\] behaves as a strong oxidizing agent. It gives a product as carboxylic acid when reacts with primary alcohols. And it gives the product of ketones due to oxidation of secondary alcohols. Therefore, \[{\rm{LiAl}}{{\rm{H}}_{\rm{4}}}\] does not forms ester when reacts with carboxylic acid. Therefore, option C is wrong.
All aldehydes when undergo reactions in the presence of reagent named aluminium ethoxide \[{\rm{Al}}{\left( {{\rm{O}}{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}} \right)_{\rm{3}}}\] results in the simultaneous oxidation of aldehydes to carboxylic acids and reduction to alcohols to give esters as product. Therefore, option D is incorrect.

Hence, option B is right.

Note: There are many uses of esterification in our everyday life such as in perfumes, cosmetics and synthetic flavours. The esters of volatile nature are useful in the form of solvents in coating and paints. The role of the ester is to act as an emulsifier.