A carbonyl compound A (C4H8O), which undergoes the haloform reaction, gives compound B on reduction. B on heating with sulphuric acid gives a compound C, which forms a mono-ozonide D. D on hydrolysis in the presence of zinc dust gives only acetaldehyde (E).
Consider the following statements about the preparation and oxidation of aldehydes and ketones.
(A) Ozonolysis of alkenes followed by reaction with zinc dust and water gives aldehydes, ketones or a mixture of both, depending on the substitution pattern of the alkene.
(B) Ketones are generally oxidised under vigorous conditions, that is, by strong oxidising agents and at elevated temperatures, with cleavage of a carbon-carbon bond.
(C) The oxidation of a ketone under vigorous conditions gives a mixture of carboxylic acids having a greater number of carbon atoms than the parent ketone.
(D) The dehydrogenation of alcohols, in which alcohol vapours are passed over heavy metal catalysts (Ag or Cu), is suitable for non-volatile alcohols.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) and (B) only
(A) Ozonolysis of alkenes followed by reaction with zinc dust and water gives aldehydes, ketones or a mixture of both, depending on the substitution pattern of the alkene. — True. Each carbon of the C=C bond becomes a C=O group. A doubly bonded carbon carrying a hydrogen gives an aldehyde; one carrying two carbon groups gives a ketone. For example, 2-methylbut-2-ene gives both:
\( \displaystyle \ce{(CH3)2C=CHCH3} \xrightarrow[\text{(ii) Zn},\ \ce{H2O}]{\text{(i) }\ce{O3}} \ce{(CH3)2C=O + CH3CHO} \)
(B) Ketones are generally oxidised under vigorous conditions, that is, by strong oxidising agents and at elevated temperatures, with cleavage of a carbon-carbon bond. — True. A ketone has no hydrogen on its carbonyl carbon, so it can be oxidised only by breaking a C–C bond, which needs strong oxidising agents and heat.
(C) The oxidation of a ketone under vigorous conditions gives a mixture of carboxylic acids having a greater number of carbon atoms than the parent ketone. — False. The carbon chain is broken at the carbonyl group, so each acid formed has fewer carbon atoms than the ketone.
(D) The dehydrogenation of alcohols, in which alcohol vapours are passed over heavy metal catalysts (Ag or Cu), is suitable for non-volatile alcohols. — False. The alcohol has to be passed over the catalyst as a vapour, so the method suits volatile alcohols.
NCERT (2026-27 edition):
8.2.1 Preparation of Aldehydes and Ketones – “(i) By ozonolysis of alkenes: As we know, ozonolysis of alkenes followed by reaction with zinc dust and water gives aldehydes, ketones or a mixture of both depending on the substitution pattern of the alkene (Unit 9, Class XI).”
“This method is suitable for volatile alcohols and is of industrial application. In this method alcohol vapours are passed over heavy metal catalysts (Ag or Cu).”
8.4 Chemical Reactions – “Ketones are generally oxidised under vigorous conditions, i.e., strong oxidising agents and at elevated temperatures. Their oxidation involves carbon-carbon bond cleavage to afford a mixture of carboxylic acids having lesser number of carbon atoms than the parent ketone.”