Consider the following statements about the preparation of alcohols.
(A) Aldehydes and ketones treated with sodium borohydride give primary and secondary alcohols, respectively.
(B) Carboxylic acids are reduced to secondary alcohols in excellent yields by lithium aluminium hydride.
(C) The reaction of a Grignard reagent with methanal produces a primary alcohol.
(D) The reaction of a Grignard reagent with a ketone produces a secondary alcohol.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B) and (D) only
The class of alcohol obtained depends on the carbonyl compound used: the carbon of the C=O group becomes the carbon that carries –OH in the product.
(A) Aldehydes and ketones treated with sodium borohydride give primary and secondary alcohols, respectively. — Correct statement. Reduction adds hydrogen to the C=O group: RCHO gives RCH2OH (primary) and R2CO gives R2CHOH (secondary).
(B) Carboxylic acids are reduced to secondary alcohols in excellent yields by lithium aluminium hydride. — Incorrect statement. LiAlH4 reduces RCOOH to RCH2OH, a primary alcohol.
(C) The reaction of a Grignard reagent with methanal produces a primary alcohol. — Correct statement. HCHO + RMgX, followed by hydrolysis, gives RCH2OH, a primary alcohol.
(D) The reaction of a Grignard reagent with a ketone produces a secondary alcohol. — Incorrect statement. With a ketone, R2CO, the carbon that carries –OH ends up bonded to three carbon groups, so a tertiary alcohol is formed. A secondary alcohol comes from aldehydes other than methanal.
NCERT (2026-27 edition):
7.4.1 Preparation of Alcohols – “…It is also prepared by treating aldehydes and ketones with sodium borohydride (NaBH4) or lithium aluminium hydride (LiAlH4). Aldehydes yield primary alcohols whereas ketones give secondary alcohols.”
“(ii) By reduction of carboxylic acids and esters: Carboxylic acids are reduced to primary alcohols in excellent yields by lithium aluminium hydride, a strong reducing agent.”
“You will notice that the reaction produces a primary alcohol with methanal, a secondary alcohol with other aldehydes and tertiary alcohol with ketones.”