Incomplete oxidation of ethanol yields

Analyze the question: The question asks for the product when ethanol (CH3CH2OH) is only partially (incompletely) oxidized.

Concept: Primary alcohols oxidize in stages:

Primary alcohol → Aldehyde → Carboxylic acid

• Partial (incomplete) oxidation stops at the aldehyde stage.
• Complete oxidation (with excess oxidizing agent, such as acidified K₂Cr₂O₇ or KMnO₄) continues to the carboxylic acid.

Solution:

Step 1: Ethanol is a primary alcohol.

Step 2: Incomplete oxidation removes two hydrogen atoms (one from the -OH, one from the carbon bearing the -OH):

CH3CH2OH + [O] → CH3CHO + H2O

(ethanol → ethanal/acetaldehyde)

Step 3: With further oxidation, ethanal would become ethanoic acid:

CH3CHO + [O] → CH3COOH

Checking the options:

• A. CH3COOH is ethanoic acid, the product of complete oxidation.
• B. CH3COCH3 is propanone, a ketone, formed from oxidizing a secondary alcohol (propan-2-ol), not ethanol.
• C. CH3CH2OCH2CH3 is diethyl ether, formed by dehydration of ethanol (with conc. H2SO4 at about 140°C), not by oxidation.
• D. CH3CHO is ethanal, the aldehyde formed by incomplete oxidation. ✔

Answer: D. CH3CHO

Exam tip: Remember the sequence "Alcohol → Aldehyde → Acid". The word "incomplete" or "partial" means you stop at the aldehyde. Also remember that secondary alcohols give ketones, and tertiary alcohols resist oxidation.