Question

$Alcohol\stackrel{P+I_2}{\to }X\stackrel{Mg,dryether}{\to }Y\stackrel{HCHO}{\to }Z\stackrel{H_{2}O/H^{+}}{\to }2-methylpropanol$

In this sequence of reactions, the starting alcohol is

• A. ethanol
• B. propan $-2-$ ol
• C. propanol
• D. butan $-2-$ ol

Answer 1

Answer: (B)

Alcohols on reaction with phosphorous iodide to give alkyl chloride. The product formed has a halogen atom attached to the same carbon which was attached to the hydroxy group.



The alkyl iodide formed reacts with $Mg$ in presence of dry ether to form Grignard reagent, isopropyl magnesium iodide.



The Grignard reagent on reaction with formaldehyde gives $2-$ methylpropoxide ion.



$2-$ methylpropoxide ion on acidic hydrolysis finally gives $2-$ methylpropanol.