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प्रश्न
Write a note on the self oxidation-reduction reaction of an aldehyde with a suitable example.
उत्तर
Cannizaro’s Reaction:-
(a) This is a characteristic reaction of those aldehydes which do not contain α -hydrogen atom.
(b) When such aldehydes are heated with concentrated alkali solutions like NaOH or KOH then simultaneous oxidation-reduction takes place.
(c) Out of two molecules of aldehyde one molecule, gets oxidised to form sodium or potassium salt of carboxylic acid and the second molecule is reduced to form corresponding primary alcohol.
(d) It is an auto oxidation-reduction reaction under the influence of base
(e) Formaldehyde and benzaldehyde undergo Cannizaro’s reaction as they do not contain α -hydrogen atom.
e.g.
\[\ce{\underset{\text{Formaldehyde(40-50%)}}{2H-CHO +NaOH}->[Redox][Reaction]\underset{\text{Sodium formate}}{HCOONa}+\underset{\text{Methanol}}{CH3}- OH}\]
\[\ce{\underset{\text{Benzaldehyde(50%)}}{2C6H5CHO +NaOH}->[Redox][Reaction]\underset{\text{Benzylalcohol}}{C6H5CH2OH} +\underset{\text{Sodiumbenzoate}}{C6H5COONa}}\]
(f) Acetaldehyde does not give this reaction since it contains α -Hydrogen atoms.
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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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