Question

Ethanol on complete oxidation gives

• A. carbon dioxide and water
• B. acetaldehyde
• C. acetic acid
• D. acetone

Answer 1

The correct option is C

acetic acid

Explanation for the correct option:

(C) Reaction summary:

• In organic chemistry, the reaction of oxygen with organic molecules is known as the oxidation reaction.
• When organic molecules are oxidized, the number of bonds between carbon and oxygen increases, while the number of bonds between carbon and hydrogen decreases.
• Aldehydes, ketones, and carboxylic acids are formed when alcohols are oxidized.
• By complete oxidation, alcohol is converted to carboxylic acid. Thus, on complete oxidation, ethanol $\left({\mathrm{CH}}_3-{\mathrm{CH}}_2\mathrm{OH}\right)$ is oxidized to acetic acid $\left({\mathrm{CH}}_3-\mathrm{COOH}\right)$. The reaction is as follows:

${\mathrm{CH}}_3-{\mathrm{CH}}_2\mathrm{OH}\underset{\mathrm{or}\mathrm{acidified}{\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7+∆}{\overset{\mathrm{alkaline}{\mathrm{KMnO}}_4+∆}{\to }}{\mathrm{CH}}_3-\mathrm{COOH}$

Explanation for the incorrect options:

(A) Carbon dioxide and water:

• Carbon dioxide $\left({\mathrm{CO}}_2\right)$ and water $\left({\mathrm{H}}_2\mathrm{O}\right)$ are not obtained when complete oxidation of ethanol takes place.
• Carbon dioxide and water are the products of the combustion reaction.

(B) Acetaldehyde:

• Acetaldehyde $\left({\mathrm{CH}}_3\mathrm{CHO}\right)$ is obtained when mild oxidation of ethanol takes place.
• PCC (pyridinium chlorochromate) is a mild oxidizing agent that helps in the conversion of ethanol to acetaldehyde. The reaction is as follows:

${\mathrm{CH}}_3-{\mathrm{CH}}_2\mathrm{OH}\underset{}{\overset{\mathrm{PCC}}{\to }}{\mathrm{CH}}_3-\mathrm{CHO}$

(D) Acetone:

• Ethanol is a primary alcohol. So, it can be oxidized to aldehydes and carboxylic acids only.
• Acetone $\left({\mathrm{CH}}_3{\mathrm{COCH}}_3\right)$ is a ketone which is obtained by the oxidation of secondary alcohols

Hence, option (C) is correct. Ethanol on complete oxidation gives acetic acid.