Question

When benzyl alcohol is oxidised with acidified potassium permanganate the product obtained is?
A. Benzaldehyde
B. Benzoic acid
C.\[{\rm{C}}{{\rm{O}}_{\rm{2}}}{\rm{,}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\]
D. Benzidine

Answer 1

Hint: Benzyl alcohol is an uncolored liquid with a soft pleasant fragrant scent. The chemical formula of benzyl alcohol is \[{{\rm{C}}_{\rm{6}}}{{\rm{H}}_{\rm{5}}}{\rm{C}}{{\rm{H}}_{\rm{2}}}{\rm{OH}}\].

Complete Step by Step Solution:
Acetic acid, also recognized as ethanoic acid, is an acidic, uncoloured liquid.
Oxidation of a compound is the addition of oxygen to the compound or removal of hydrogen. Oxidation of organic compounds like benzyl alcohol gives rise to compounds having different functional groups.

Benzyl alcohol possesses an alcohol group attached to the benzyl group.
The benzyl group has a \[{\rm{ - C}}{{\rm{H}}_{\rm{2}}}\]group attached to the benzene group.

Oxidation of alcohols involves the formation of a carbon-oxygen double bond with the cleavage of O-H and C-H bonds. These are also called dehydrogenation reactions as this involves the loss of hydrogen from the alcohol molecule.

The oxidation of the given compound i.e., benzyl alcohol will give benzoic acid.
Oxidation can be carried out with a mixture of reagents such as neutral, acidic or alkaline.
For example, alkaline potassium permanganate acidified potassium dichromate and dilute nitric acid.

Primary alcohols are effortlessly oxidised first to aldehydes and then to carboxylic acids.
The resultant product has the same number of carbon atoms as the parent alcohol.
Benzyl alcohol is a primary alcohol.

The oxidation of this compound in the presence of alkaline potassium permanganate or potassium dichromate gives rise to benzoic acid.
The reaction occurs as follows:

Image: Oxidation of benzyl alcohol
This reaction occurs in two steps.
The first step involves the conversion of benzyl alcohol to benzaldehyde.
Then the next step involves the conversion of benzaldehyde to benzoic acid.
Benzoic acid contains the same number of carbon atoms as benzyl alcohol.

So, option B is correct.

Note: Primary alcohols are oxidised to form the corresponding carboxylic acid. Secondary alcohols are oxidised to corresponding ketones. Ketones do not undergo further oxidation but under harsh conditions get converted to carboxylic acids having fewer carbon atoms than the parent alcohol. Tertiary alcohols are resistant to oxidation in neutral or alkaline potassium permanganate.