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Question: Which of the following reactions require an oxidizing agent? A. \(C{H_3} - CH = C{H_2} \to C{H_3} ...

Which of the following reactions require an oxidizing agent?
A. CH3−CH=CH2→CH3−CH2−CH3C{H_3} - CH = C{H_2} \to C{H_3} - C{H_2} - C{H_3}
B. CH3−CH2OH→CH3−CHOC{H_3} - C{H_2}OH \to C{H_3} - CHO
C. CH3−CH2Cl→CH3−CH3C{H_3} - C{H_2}Cl \to C{H_3} - C{H_3}
D. CH3−CH2OH→CH3−CH2ClC{H_3} - C{H_2}OH \to C{H_3} - C{H_2}Cl

Explanation

Solution

A substance which has the capability to oxidize a compound is known as oxidizing agent. In organic chemistry, an oxidising agent converts an alcohol into an aldehyde/ketone, an aldehyde/ketone into a carboxylic acid, etc. Some are strong enough to directly convert the alcohol into a carboxylic acid.

Complete answer:
Let us discuss each reaction in the above given options.
(i) CH3−CH=CH2→CH3−CH2−CH3C{H_3} - CH = C{H_2} \to C{H_3} - C{H_2} - C{H_3}
In this conversion, we can see that there is a breaking of the double bond and the addition of two hydrogen atoms on each of the sp2s{p^2} carbon atoms. In a reaction, when there is an addition of hydrogen, then it is a reduction process and takes place in the presence of a reducing agent.
Thus, this option is incorrect.
(ii) CH3−CH2OH→CH3−CHOC{H_3} - C{H_2}OH \to C{H_3} - CHO
In this conversion, we can see that the primary alcohol gets converted to an aldehyde which occurs in the presence of an oxidising agent. This process can occur in the presence of mild oxidising agents such as alkaline KMnO4KMn{O_4} .
Thus, this option is correct.
(iii) CH3−CH2Cl→CH3−CH3C{H_3} - C{H_2}Cl \to C{H_3} - C{H_3}
This conversion is an example of reduction. There is an addition of a hydrogen atom and removal of a halogen atom. This is also known as the dehalogenation process.
Thus, this option is incorrect.
(iv) CH3−CH2OH→CH3−CH2ClC{H_3} - C{H_2}OH \to C{H_3} - C{H_2}Cl
This process is a substitution reaction and has nothing to do with the oxidation as the oxidation number of carbon still remains unaltered.
Thus, this option is incorrect.

Hence, the correct option is B. CH3−CH2OH→CH3−CHOC{H_3} - C{H_2}OH \to C{H_3} - CHO .

Note:
Alcohol oxidation is considered as one of the important organic reactions. Some of the oxidising agents that help in the oxidation process are alkaline potassium permanganate, potassium dichromate, pyridinium chlorochromate (PCC), etc.