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Questions
Describe the following:
Cannizzaro reaction
Write a note on Cannizzaro reaction.
Solution
Aldehydes which do not have an α-hydrogen atom, undergo self-oxidation and reduction (disproportionation) reactions on heating with concentrated alkali. In this reaction, one molecule of the aldehyde is reduced to alcohol while another is oxidised to carboxylic acid salt.
\[\begin{array}{cc}
\phantom{.}\ce{H}\phantom{.......}\ce{H}\phantom{...............................}\ce{H}\phantom{................}\ce{O}\phantom{..}\\
\phantom{.......}\backslash\phantom{........}\backslash\phantom{..............................}|\phantom{...............}//\phantom{.......}\\
\ce{C = O + C = O + Conc.KOH ->[\Delta]H - C - OH + H - C}\\
\phantom{}/\phantom{........}/\phantom{..............................}|\phantom{................}\backslash\\
\phantom{.........}\ce{\underset{Formaldehyde}{H\phantom{........}H}\phantom{............................}\ce{\underset{Methanol}{H}}\phantom{.........}\ce{\underset{Potassium formate}{OK}}}\phantom{...}
\end{array}\]
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\[\begin{array}{cc}
\phantom{...}\ce{CH3} \\
| \\
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\[\begin{array}{cc}
\ce{D}\phantom{........................}\\
|\phantom{.........................}\\
\ce{2D - C = O + OH^- ->[Cannizzaro] X and Y}
\end{array}\]
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