Chemistry Aldehydes & Ketones MDCAT 2020
PMDC Verified Question 50 of 94
Which of the following reagent is use to separate and purify carbonyl and non-carbonyl compounds?
A
\( HCN \)
B
\( BrMgCH_2 \)
C
\( NaHSO_3 \)
D
\( H_2O \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: \( NaHSO_3 \)
Concept:

Chemical separation relies on forming a reversible derivative with significantly different physical properties from the impurities.

Solution:

  • Saturated aqueous Sodium Bisulfite (\( NaHSO_3 \)) reacts with aldehydes and small methyl ketones via nucleophilic addition to form crystalline bisulfite adducts.


  • These solid adducts can be easily filtered out, separating them from non-carbonyl impurities (which remain in liquid/solution).


  • Once separated, the pure carbonyl compound can be regenerated by treating the solid adduct with dilute acid or base.


Why other options are incorrect:

HCN and Grignard reagents (like \( BrMgCH_2 \)) form irreversible products (cyanohydrins and alcohols, respectively), meaning you cannot easily recover the original aldehyde or ketone. Water does not react distinctively to separate them.

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