Question

The end product in the following sequence of reaction is
$$HC\equiv CH\underset{HgS{O}_4}{\overset{H_{2}S{O}_4}{\to }}A\underset{H_{2}O}{\overset{C{H}_{3}MgX}{\to }}B\stackrel{PCC}{\to }$$

• A.
  Acetic acid
• B.
  Isopropyl alcohol
• C.
  Acetone
• D.
  Ethanol

Answer 1

The correct option is C

Acetone
Step 1: Terminal alkynes react with water in the presence of dilute sulfuric acid and mercuric sulfate at a temperature of 333K. This results in the formation of ketone through a keto-enol tautomerization of the more substituted enol.
Acetylene produces acetaldehyde on acid-catalysed hydration.
Step2: Grignard reagent is a strong nucleophile. It undergoes nucleophilic addition reaction when it reacts with aldehyde, ester and ketone.
Grignard reagent reacts with formaldehyde followed by acid workup to form $1^{\circ }$ alcohol.
Grignard reagent reacts with aldehyde followed by acid workupexcept formaldehyde to form $2^{\circ }$ alcohol.
Step3: PCC(Pyridinium chlorochromate) is a mild oxidising agent. It converts $1^o$ alcohols to aldehydes and $2^o$ alcohols to ketones, but is not strong enough to convert primary alcohols to carboxylic acids.
The reaction is as follows:
$$HC\equiv CH\underset{HgS{O}_4}{\overset{H_{2}S{O}_4}{\to }}C{H}_{3}CHO\underset{H_{2}O}{\overset{C{H}_{3}MgX}{\to }}C{H}_{3}CH\left(OH\right)C{H}_3\stackrel{\left[\text{PCC in}C{H}_{2}C{l}_2\right]}{\to }C{H}_{3}COC{H}_3$$
Hence the correct option is (c).