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Step-by-Step Solution
Step 1: Formation of the Diazonium Intermediate (P)
• Cyclohexylamine is a primary amine. When it is treated with nitrous acid
(generated from sodium nitrite and a mineral acid at low temperatures),
it forms an unstable diazonium intermediate (P).
• Primary aliphatic diazonium salts are generally unstable and may decompose quickly.
Step 2: Oxidation of (P) to Cyclohexanone (Q) Using PCC
• Pyridinium chlorochromate (PCC) is a mild oxidizing agent commonly used
to oxidize primary alcohols to aldehydes or secondary alcohols to ketones.
However, in this context, it can facilitate the conversion of the diazonium
intermediate to a ketone.
• The product obtained here is cyclohexanone, denoted as (Q).
Step 3: Reaction of Cyclohexanone (Q) with Dilute NaOH
• Cyclohexanone in the presence of dilute sodium hydroxide can undergo
base-catalyzed aldol condensation.
• The enolate ion (formed by deprotonation of cyclohexanone) attacks the carbonyl
carbon of another cyclohexanone molecule, forming a
$\\beta$-hydroxy ketone intermediate.
• On heating, this $\\beta$-hydroxy ketone undergoes dehydration, yielding
an $\\alpha,\\beta$-unsaturated ketone.
Final Product (R)
• The $\\alpha,\\beta$-unsaturated ketone formed is cyclohex-2-enone.
• Hence, the final product (R) is cyclohex-2-enone, which corresponds to:
