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Cannizzaro Reaction – Definition, Examples, Mechanism

Cannizzaro Reaction

The Cannizzaro reaction is a chemical reaction named after Stanislao Cannizzaro in which two molecules of a non-enolizable aldehyde are disproportionated by a base to generate a carboxylic acid and a primary alcohol. The Cannizzaro Reaction Mechanism explains how two molecules of an aldehyde can be converted into one molecule of alcohol and one molecule of carboxylic acid. Stanislao Cannizzaro succeeded in extracting benzyl alcohol and potassium benzoate from benzaldehyde in 1853. A nucleophilic acyl substitution on an aldehyde is used to carry out the reaction, with the leaving group attacking another aldehyde. The attack of hydroxide on a carbonyl produces a tetrahedral intermediate. When this tetrahedral intermediate collapses, the carbonyl is reformated and a hydride is transferred, which attacks another colony.

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Acid and alkoxide ions are now exchanging a proton. When a high-concentration base is added, the aldehyde forms an anion with a charge of two. A hydride ion is then transferred to a second aldehyde molecule, resulting in carboxylate and alkoxide ions. For the reaction, the alkoxide ion additionally receives a proton from the solvent.

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Cannizzaro Reaction: Definition

The Cannizzaaro Reaction is an aldehyde-caustic alkali reaction in which one molecule of aldehyde is reduced to the corresponding alcohol and another is oxidised to the corresponding acid’s salt. Cannizzaro first achieved this transformation in 1853, when he used potash to extract benzyl alcohol and potassium benzoate from benzaldehyde (potassium carbonate). More commonly, sodium hydroxide or potassium hydroxide would be used in the process, yielding the sodium or potassium carboxylate salt of the carboxylic-acid product:

2 C6H5CHO + KOH → C6H5CH2OH + C6H5COOK

 

Cannizzaro Reaction is given by

The Cannizzaro reaction was discovered by Stanislao Cannizzaro, and it is named after him. Cannizzaro’s chemical interests were in natural products and aromatic compound reactions. He discovered in 1853 that when benzaldehyde is treated with concentrated base, it produces both benzoic acid and benzyl alcohol, a phenomenon known as the Cannizzaro reaction. The Cannizzaro Reaction Mechanism explains how two molecules of an aldehyde can be converted into one molecule of alcohol and one molecule of carboxylic acid.

 

Cannizzaro Reaction: Examples

First Example is of formation of Benzoic Acid from Bezaldehyde

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Another Example is of formation of 2,2 – dimethyl Propanoic Acid from 2,2 – di methyl Propanol

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Cannizzaro Reaction: Mechanism

The carbonyl group of the supplied aldehyde is attacked by a nucleophile, such as a hydroxide ion, resulting in a disproportionation reaction and the formation of an anion with two negative charges. This intermediate can now be used as a hydride reducing agent. The intermediate releases a hydride anion due to its unstable nature.

Another aldehyde molecule is attacked by this hydride anion. The aldehyde is now transformed into an alkoxide anion, and the doubly charged anion is changed into a carboxylate anion. Water provides a proton to the alkoxide anion in this penultimate phase, resulting in the final alcohol product. Because alkoxide is more basic than water, the reaction can continue. When acid workup is utilised, the carboxylate ion now produces the ultimate carboxylic acid product.

The equations steps of mechanism of Cannizzaro Reaction are given below:

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Cannizzaro Reaction: FAQs

Q. What is Cannizzaro reaction give example?

Ans. The Cannizzaro reaction is a disproportionation reaction that produces a primary alcohol and a carboxylic acid by combining two molecules of an aldehyde with a hydroxide base. This is demonstrated by the reaction of benzaldehyde with benzyl alcohol to produce benzoic acid.

Q. What is the reaction of benzaldehyde?

Ans. When benzaldehyde is treated with strong alkali, it undergoes disproportionation (Cannizzaro reaction), in which one molecule of the aldehyde is reduced to benzyl alcohol while another is oxidised to benzoic acid. Benzaldehyde condenses with diols, such as sugars, to create benzylidene acetals.

Q. What is the order of Cannizzaro reaction?

Ans. The reaction is first order in base and second order in aldehyde at lower base concentrations, but second order in both base and aldehyde at larger base concentrations. The hydride transfer occurs directly between aldehydes, without the need for a reaction media.

Q. How benzoin is formed from benzaldehyde?

Ans. The benzoin condensation occurs when two molecules of benzaldehyde react with a cyanide catalyst (e.g., NaCN and KCN) or thiamine to create benzoin (vitamin B). The chemical structure of benzoin is a ketone.

Q. Is benzaldehyde an aldehyde or ketone?

Ans. The Cannizzaro reaction, named after its discoverer Stanislao Cannizzaro, is a chemical process in which two molecules of a non-enolizable aldehyde are disproportionated by a base to produce a primary alcohol and a carboxylic acid.

Q. Why is Cannizzaro reaction important?

Ans. The Cannizzaro Reaction is crucial to industry. Polyols are made from formaldehyde and other aldehydes using a combination of aldol condensation and the crossed-Cannizaro reaction. The synthesis of Pentaerythrit from acetaldehyde is a common use of the process. Polyols are extremely helpful and have a wide range of uses in industry.

 

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