Chemistry Multiple Choice Questions on “Preparation of Aldehydes and Ketones”.
1. Which of the following methods cannot produce aldehydes?
a) Oxidation of primary alcohols
b) Dehydrogenation of secondary alcohols
c) Ozonolysis of alkenes
d) Hydration of ethyne with acid
Answer: b
Clarification: The dehydrogenation of secondary alcohols give ketones. Aldehydes are obtained by the dehydrogenation of primary alcohols.
2. Which of the following reactions can produce ketones?
a) Oxidation of primary alcohols
b) Dehydrogenation of primary alcohols
c) Dehydrogenation of tertiary alcohols
d) Oxidation of secondary alcohols
Answer: d
Clarification: Oxidation and dehydrogenation of secondary alcohols results in ketones. The same reactions with primary alcohols give aldehydes.
3. Conversion of propyne to acetone requires three important reagents. Identify which of the following is not one of the three?
a) Water
b) Zinc dust
c) H2SO4
d) HgSO4
Answer: b
Clarification: Addition of water to propyne in the presence of H2SO4 and HgSO4 gives acetone. Zinc dust is an important reagent in the ozonolysis of alkenes.
4. What is the catalyst used in the hydrogenation of acetyl chloride to produce ethanal?
a) Pt over BaSO4
b) Pt over CuSO4
c) Pd over BaSO4
d) Pd over CuSO4
Answer: c
Clarification: Acyl chlorides are hydrogenated in the presence of catalyst palladium over barium sulphate. This is known as Rosenmund reaction.
5. Which of the following carbonyl compounds can be prepared from Rosenmund reaction?
a) Methanal
b) Acetone
c) Butanone
d) Benzaldehyde
Answer: d
Clarification: Rosenmund reaction is exclusively used for the preparation of aldehydes by the substitution of chloride by hydrogen. Given this, methanal cannot be formed from this reaction because its corresponding acyl chloride, i.e., formyl chloride, is unstable at room temperature. Benzaldehyde is formed from benzoyl chloride.
6. Which of the following is required in Stephen reaction?
a) LiCl
b) NiCl2
c) SnCl2
d) TiCl4
Answer: c
Clarification: Nitriles are converted to respective imines with SnCl2 in the presence of HCl, which on hydrolysis gives corresponding aldehyde.
7. Which of the following compounds helps in reducing esters to aldehydes?
a) BINAL-H
b) DIBAL-H
c) DIPT
d) TBAF
Answer: b
Clarification: DIBAL-H or diisobutylaluminium hydride is a reducing agent which are used to reduce nitriles to imines or esters to aldehydes. These are important in the preparation of aldehydes.
8. Identify ‘X’ in the reaction given below.
a) CrO3
b) CrO2Cl2
c) Alkaline KMnO4
d) Anhydrous AlCl3
Answer: b
Clarification: This is known as Etard reaction. The chromyl chloride oxidises the methyl group to a chromium complex in CS2. This complex on hydrolysis gives benzaldehyde.
9. Benzaldehyde can be obtained from the hydrolysis of the product formed during side chain chlorination of toluene.
a) True
b) False
Answer: a
Clarification: Side chain chlorination of toluene in the presence of light (represented by hv) gives benzal chloride which on hydrolysis gives benzaldehyde. This is an important commercial method for the production of benzaldehyde.
10. Identify the reagent(s) for the conversion of chlorobenzene to 3-chlorobenzaldehyde.
a) CrO3 and (CH3CO)2O
b) CrO2Cl2; H2O
c) Cl2/hv; H2O
d) CO, HCl and CuCl