class 12
canizzaro reaction explain in detail using an example
mechanism too??
don't give useless answers
Answers
Cannizzaro reaction is a chemical reaction named after Stanislao Cannizzaro that involves the base-induced disproportionation of two molecules of a non-enolizable aldehyde to yield a carboxylic acid and a primary alcohol.
Cannizzaro Reaction
Cannizzaro Reaction Mechanism details the method to get one molecule of alcohol and one molecule of carboxylic acid from two molecules of a given aldehyde. Scientist Stanislao Cannizzaro, in 1853 succeeded in obtaining benzyl alcohol and potassium benzoate from benzaldehyde. The reaction is executed by a nucleophilic acyl substitution on an aldehyde where the leaving group attacks another aldehyde. A tetrahedral intermediate results from the attack of hydroxide on a carbonyl. This tetrahedral intermediate collapses, thereby reforming the carbonyl and transferring a hydride which attacks another colony.
Now, a proton is exchanged by acid and alkoxide ions. When a base of high concentration is introduced, the aldehyde forms an anion which has a charge of 2. From this, a hydride ion is transferred to a second molecule of the aldehyde, forming carboxylate and alkoxide ions. The alkoxide ion also obtains a proton from the solvent for the reaction.
Mechanism of Cannizzaro Reaction
Mechanism Step 1
A nucleophile such as a hydroxide ion is used to attack the carbonyl group of the given aldehyde, causing a disproportionation reaction and giving rise to an anion carrying 2 negative charges.
Mechanism Step 2
This resulting intermediate can now function as a hydride reducing agent. Due to its unstable nature, the intermediate releases a hydride anion. This hydride anion proceeds to attack another aldehyde molecule. Now, the doubly charged anion is converted into a carboxylate anion and the aldehyde is converted into an alkoxide anion.
Mechanism Step 3
In this final step, water offers a proton to the alkoxide anion which gives rise to the final alcohol product. The reaction can proceed since the alkoxide is more basic than water. Now, the carboxylate ion gives rise to the final carboxylic acid product when acid workup is used (the acid workup is required since carboxylate is less basic than water and therefore cannot obtain a proton from water).
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Answer:
Explanation:
canizaro mechanism is based on addition of oh
canizaro reaction are of three types
self cross intramolecular
intramolecular canizaro is based on benyl benzylic rearrangement
talking about the self first
add oh on carbonyl
and something of stable will be come out suppose h-,etc
and that h-,etc attacks on carbonyl and o- of this carbonyl gets hydrogen from previously attached oh and these two are canizaro products
talking about the cross secondly
here reactivity of carbonyl decides the game
reactivity is directly proportional to electon deficiency of carbonyl
less reactive gets reduced and highly reactive gets oxidised
gets reduced means gets converted into alcohol and gets oxidised means getting converted into acid
taking about the intramolecular
simply benzyl benzylic rearrangement
when ever there is two carbonyl continously then remove two carbonyl and insert one carbon attached with oh and coo- in place of two carbonyl