Question

What are 'X' and 'Y' respectively in the following reaction sequence? \[ \ce{C6H5CH3→[X] C6H5CO2H →[Y] C6H5CH2OH} \]

• A. X = PCC ; Y = (i) \ce{B2H6} (ii) \ce{H3O^+}
• B. X = (i) \ce{KMnO4 / OH^-} (ii) \ce{H3O^+} ; Y = \ce{NaBH4}
• C. X = (i) \ce{KMnO4 / OH^-, \Delta} (ii) \ce{H3O^+} ; Y = (i) \ce{B2H6} (ii) \ce{H3O^+}
• D. X = PCC ; Y = LAH

Hint:

Oxidation of alkyl benzenes to benzoic acid is done using hot \ce{KMnO4} in basic medium followed by acidification. Reduction of carboxylic acids to alcohols can be done using \ce{B2H6}/\ce{H3O^+} or LAH.

Answer 1

The Correct Option is C

Step-by-step analysis:
(A) The initial compound is \ce{C6H5CH3} (toluene). The goal is to first oxidize the methyl group to a carboxylic acid group (benzoic acid).
(B) Oxidizing agents like hot \ce{KMnO4 / OH^-} followed by acidic work-up (\ce{H3O^+}) are used to achieve this: \[ \ce{C6H5CH3→[KMnO4/OH^-, \Delta][H3O^+] C6H5COOH} \] So, X is correctly identified in Option (3).
(C) Next, \ce{C6H5COOH} is reduced to \ce{C6H5CH2OH}.
(D) This involves reduction of carboxylic acid to primary alcohol. Although this can be done by LAH (LiAlH\textsubscript{4}), in this case the reagent used is diborane (\ce{B2H6}) followed by hydrolysis (\ce{H3O^+}): \[ \ce{C6H5COOH→[B2H6][H3O^+] C6H5CH2OH} \]
(E) This makes Y = (i) \ce{B2H6}, (ii) \ce{H3O^+}, also matching Option (3). Hence: \[ \boxed{\text{Correct Answer: (3)}} \]