Chemistry Alcohols & Phenols MDCAT 2017
PMDC Verified Question 76 of 95
\(\text{CH}_3-\text{CH}_2-\text{OH} + \text{PCl}_5 \longrightarrow \text{CH}_3-\text{CH}_2\text{Cl} + \text{POCl}_3 + \text{HCl}\)

Formation of HCl is test for the presence of ___ in a compound
A
Alkyl group
B
Saturated alkyl group
C
Hydroxyl group
D
Acid \(\text{H}^+\) ion
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Hydroxyl group
Concept:

Phosphorus pentachloride is a diagnostic reagent for functional groups containing an oxygen-hydrogen bond.

Formula:

$$ \text{R-OH} + \text{PCl}_5 \longrightarrow \text{R-Cl} + \text{POCl}_3 + \text{HCl}\uparrow $$

Solution:

  • The mechanism involves the nucleophilic oxygen of the hydroxyl group attacking the phosphorus.


  • The subsequent elimination of a proton and a chloride ion generates HCl gas.


  • Thus, this reaction specifically confirms the presence of a hydroxyl (-OH) group.


Why other options are incorrect:

Alkyl and saturated alkyl groups do not react with \(\text{PCl}_5\). An acid \(\text{H}^+\) ion doesn't undergo this substitution pathway.

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