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________ are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved for the preparation.

Last updated date: 20th Jun 2024
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Hint:Compounds formed in the reaction between an alcohol and a carboxylic acid generally have sweet, fruity smells. These compounds can be produced by mildly heating alcohols and acids together so that they react. They can then be identified by smelling the top portion of the vessel.

Complete step by step solution:
The most commonly occurring sweet-smelling substances are esters, and they are widely used to make perfumes, due to the fruity smell they possess.
They can be prepared in a laboratory easily as follows:
Take a clean, dry test tube and add $1mL$ of glacial acetic acid and $1mL$ of ethanol into it. Prepare a water bath on a Bunsen burner. Pour a few drops of concentrated sulphuric acid into the test tube drop by drop. Gently take the test tube and keep it in the water bath for about five minutes. When the water starts to boil, take out the test tube using a pair of tongs. Gently tilt the test tube in such a way that the top portion comes close to your nose. Smell this portion. If prepared correctly, it will have a fruity smell, which confirms the presence of ester.
$C{H_3}COOH + {C_2}{H_5}OH\xrightarrow{{con.{H_2}S{O_4}}}C{H_3}COO{C_2}{H_5} + {H_2}O$

Hence, the correct answer to be filled in the blank is “esters”.

The most common method of producing esters industrially is the Fischer’s process, in which a carboxylic acid is treated with an alcohol in the presence of a dehydrating agent. Esters are the reason for the aroma of most fruits, flowers etc. Note that the esterification reaction is highly reversible. Care must be taken while adding the sulphuric acid. Adding a lot of it will cause the mixture to heat up and splash outwards violently.