What is the final product when butan-1-ol is oxidised with Jones reagent (chromium trioxide in acidic medium)?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Butanoic acid
Jones reagent (\( \ce{CrO3} \) in acidic medium) is a strong oxidising agent. It oxidises a primary alcohol through the aldehyde stage all the way to the carboxylic acid with the same number of carbon atoms.
Butan-1-ol is a primary alcohol, so it gives butanoic acid:
\( \displaystyle \ce{CH3CH2CH2CH2OH + 2[O]} \xrightarrow{\ce{CrO3, H+}} \ce{CH3CH2CH2COOH + H2O} \)
Why the other options are incorrect
Option (1) Butanone — Incorrect. A ketone comes from the oxidation of a secondary alcohol (butan-2-ol), not from a primary alcohol.
Option (2) Butanal — Incorrect. Butanal is only the intermediate stage. It is isolated with \( \ce{CrO3} \) in anhydrous medium or PCC; in acidic medium the oxidation goes on to the acid.
Option (4) Ethoxy ethane — Incorrect. This is an ether with a C–O–C link; oxidation of an alcohol does not give an ether.
NCERT (2026-27 edition):
8.7 Methods of Preparation of Carboxylic Acids – “1. From primary alcohols and aldehydes
Primary alcohols are readily oxidised to carboxylic acids with common oxidising agents such as potassium permanganate (KMnO4) in neutral, acidic or alkaline media or by potassium dichromate (K2Cr2O7) and chromium trioxide (CrO3) in acidic media (Jones reagent).”