Name Reaction - CANIZZARO Reaction and its machanism ~ NEET chemistry

Cannizaro reaction with machanism :---

Only aldehydes gives Cannizaro reaction.
Only those type of aldehydes shows Cannizaro reaction which have Absence of alpha hydrogen.
It occurs in the presence of dil. NaOH(sodium hydroxide)
Dissproportion type reaction.
Order of reaction is three
Rate is depend on molecules of aldehyde and base.
Rate is directly proportional to the [aldehyde ]²[base]1
Rate determing step is tranfer of hydride ion (H-)

Overall reaction :--

Mechanism :--

There are several steps to understand this reaction :--

To understand this reaction we take an example of two molecules of formaldehyde :-

(A) In first step, More electronegative atom present in formaldehyde. molecule, pull the electrons present. in bond and get partial negative.

Charge on it and carbon get partial. positive charge.

Carbone gets partial positive charge, which means carbon became electron deficient species. It attracts the Nucleophillic species(more electron rich species)

(B) In second step, hydroxide ion which is rich in electron (Nu-) attack on partial positive charge carbon of aldehyde and formed hydroxy alkoxide anion.

Hydroxide ion comes from NaOH species. There NaOH is dilute which breaks down in Na+ and OH-

(C) In third step, another formaldehyde molecule comes and take hydride ion from formed hydroxy alkoxide anion species and compound formed are acid and base.

Third step is a slow and rate determing step.

(D) In fourth step, Acid base reaction occur. Base takes H+ ion from acid and formed carboxylate ion (HCOO-) anf alcohol (CH3OH)

(E) In last step, solution contain Na+ ion from NaOH. Carboxylate ion (HCOO-) react with Na+ ion and formed caorboxylic salt.

Overall reaction mechanism :--

Another example of Cannizaro reaction in the form of aromatic compound. :---

Note:-- -M and -I group decrease the hydride donar tendency because the pull the electron density from aromatic ring and ring became electron deficient. So, it cannot donate hydride ion easily.

In another way +M and +I group increase this temdency.

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