question_answer

The correct sequence of steps involved in the mechanism of Cannizzaros reaction is

A)  nucleophilic attack, transfer of \[{{H}^{-}}\] and transfer of \[{{H}^{+}}\]

B)  transfer of \[{{H}^{-}}\], transfer of \[{{H}^{+}}\] and nucleophiiic attack

C)  transfer of\[{{H}^{+}}\], nucleophilic attack and transfer of\[{{H}^{-}}\]

D)  electrophilic attack by \[O{{H}^{-}}\], transfer of \[{{H}^{+}}\] and transfer of \[{{H}^{-}}\]

Correct Answer: A

Solution :

The Cannizzaro reaction is as                 \[HCHO+HCHO\xrightarrow{KOH\,\,(con)}\underset{methyl\text{ }alcohol}{\mathop{C{{H}_{3}}OH}}\,\]                  \[\underset{acetic\text{ }acid}{\mathop{+HCOO{{K}^{+}}}}\,\] The mechanism of Cannizzaro reaction is as Step I Attack of nudeophile \[O{{H}^{-}}\] to the carbonyl carbon                 Step II The transfer of hydride ion from anion (I) to second molecule of aldehyde and finally rapid transfer of proton takes place. \[H-\overset{\begin{smallmatrix}  O \\  | \end{smallmatrix}}{\mathop{\underset{\begin{smallmatrix}  | \\  H  \\  alcohol \end{smallmatrix}}{\mathop{C}}\,}}\,-H\xleftarrow{Proton\text{ }exchange\text{ }fast}H-\overset{\begin{smallmatrix}  {{O}^{(-)}} \\  | \end{smallmatrix}}{\mathop{\underset{\begin{smallmatrix}  | \\  H  \\  alchol \end{smallmatrix}}{\mathop{C}}\,}}\,-{{H}^{+}}\] \[\underset{acid}{\mathop{+H-\overset{\begin{smallmatrix}  O \\  || \end{smallmatrix}}{\mathop{C}}\,-\overset{-}{\mathop{O}}\,\,{{K}^{+}}}}\,\]