Question

Choose the incorrect statement.

• A. Propan-2-amine can be obtained by reacting acetoxime with $\text{Na} / \text{C}_2\text{H}_5\text{OH}$
• B. Fluorobenzene cannot be prepared from Benzenediazonium chloride by Sandmeyer's reaction because Fluorination of the Diazonium salt is highly endothermic in nature
• C. The decreasing order of basic strength of amines in aqueous solution is Ethanamine $>$ N,N-Dimethylaniline $>$ Benzenamine
• D. Aniline cannot be prepared by Phthalimide reaction

Hint:

Preparing fluorobenzene from a diazonium salt is always achieved via the Balz-Schiemann Reaction ($\text{HBF}_4$ addition followed by heating). Sandmeyer's chemistry fails here due to the instability of copper(I) fluoride catalysts, making statement (B) incorrect.

Answer 1

The Correct Option is B

Concept: Sandmeyer's reaction utilizes copper(I) salts ($\text{CuCl}$, $\text{CuBr}$, $\text{CuCN}$) as radical catalysts to replace the diazonium group on an aromatic ring. Fluorobenzene cannot be synthesized using a standard Sandmeyer procedure because copper(I) fluoride ($\text{CuF}$) is unstable and difficult to prepare, not due to endothermic constraints. Instead, fluorobenzene is synthesized via the Balz-Schiemann reaction by precipitating benzenediazonium fluoroborate ($\text{ArN}_2^+\text{BF}_4^-$) and thermally decomposing it.

Step 1: Evaluate Statement (B).
Statement (B) correctly notes that fluorobenzene cannot be prepared via a standard Sandmeyer reaction, but its explanation regarding highly endothermic constraints is incorrect. The limitation stems from the lack of a viable copper(I) catalyst pathway. Thus, statement (B) is incorrect, making it the targeted selection choice.

Step 2: Verify why the other options are correct statements.

• Statement (A) is correct: Reducing acetoxime ($\text{(CH}_3)_2\text{C}=\text{NOH}$) with sodium and ethanol ($\text{Na/EtOH}$, Bouveault-Blanc reduction conditions) converts the oxime function into a primary amine, yielding propan-2-amine.
• Statement (C) is correct: In an aqueous medium, aliphatic primary amines are more basic than aromatic tertiary or primary amines because resonance delocalizes the lone pair of the nitrogen atom into the benzene ring.
• Statement (D) is correct: Gabriel Phthalimide synthesis relies on an $\text{S}_{\text{N}}2$ displacement of an alkyl halide by the phthalimide anion. Aryl halides do not undergo nucleophilic substitution under standard conditions, meaning aniline cannot be prepared via this pathway.