Question

What are x and y in the following reaction sequence?

• A. $\text{H}_2\text{O}/\text{H}_2\text{SO}_4$; $\text{KMnO}_4/\text{H}^+$
• B. $\text{H}_2\text{O}/\text{H}_2\text{SO}_4$; $\text{PCC}$
• C. $\text{H}_2\text{O}/\text{H}_2\text{SO}_4, \text{Hg}^{2+}$; $\text{KMnO}_4/\text{H}^+$
• D. $\text{H}_2\text{O}/\text{H}_2\text{SO}_4, \text{Hg}^{2+}$; $\text{PCC}$

Hint:

Key points: \begin{itemize} \item Acetylene hydration requires Hg$^{2+}$ catalyst \item PCC is selective for alcohol→aldehyde without over-oxidation \item KMnO$_4$ would cleave the double bond \end{itemize}

Answer 1

The Correct Option is D

Step 1: Identify reaction x (C$_2$H$_2$ → CH$_3$CHO)
This is hydration of acetylene requiring Hg$^{2+}$ catalyst: \[\text{C}_2\text{H}_2 \xrightarrow{\text{H}_2\text{O}/\text{H}_2\text{SO}_4, \text{Hg}^{2+}} \text{CH}_3\text{CHO}\] Step 2: Identify reaction y (Aldehyde → α,β-unsaturated aldehyde)
This requires mild oxidation (PCC preserves the C=C bond): \[\text{CH}_3\text{CHO} \xrightarrow{\text{PCC}} \text{CH}_3-\text{CH}=\text{CH}-\text{CHO}\]