Question

A compound A has a molecular formula \[{C_2}C{l_3}OH\]. It reduces Fehling’s solution and on oxidation, gives a monocarboxylic acid B. A can be obtained by the action of chlorine on ethyl alcohol. A is:

Answer 1

Hint: The compound with molecular formula \[{C_2}C{l_3}OH\]is an aldehydic compound. It is a colorless oily liquid which on dissolving in water forms its hydrate.

Complete Step by Step Solution:
A compound containing aldehyde group (-CHO) reduces the Fehling’s solution to form a red precipitate.
Fehling’s solution is a tartaric acid complex of cupric ions and is blue in colour. When Fehling’s solution is heated with an aldehydic group containing compounds it reduces the cupric ions to cuprous ions forming a red precipitate of cuprous oxide. The chemical formula of cuprous oxide is.
Also, an aldehydic compound on oxidation forms a monocarboxylic acid (-COOH).
It is given that A can be obtained by the action of chlorine on ethyl alcohol.

The reaction of chlorine and ethyl alcohol is shown below.
\[C{H_3}C{H_2}OH + C{l_2} \to C{H_3}CHO\]
First, ethyl alcohol reacting with chlorine gives acetaldehyde.
\[C{H_3}CHO + C{l_2} \to CC{l_3}CHO\]
After that, acetaldehyde on further chlorination gives chloral.
So, the compound A is chloral.

Additional information: Chloral on dissolving in water forms chloral hydrate and alcohol. Chloral hydrate is used as a sedative and hypnotic substance. Chloral reacting with chlorobenzene in presence of sulphuric acid forms DDT. Here, sulphuric acid is used as a catalyst.

Note: It should be noted that chloral is also named as trichloroacetaldehyde or trichloroethanal. Chloral is its common name whereas trichloroethanal or trichloroacetaldehyde is its IUPAC name.